JOHN HARMON 120 c.i. Shovelhead Engine
History & Rebuild
Classic editorials were many through the 1980s covering John Harmon projects. Street Chopper magazine had printed various full page spreads on Harmon engines - the above by Bob Clark. Above images from Street Chopper Magazine 1981 - Hot Bike John Harmon archives
Size does matter - John Harmon flat top 4-300" Venolia pistons were used for 3 years with no issues. Below, a new unused Harmon 120 cubic inch street kit. This one was sitting under a workshop bench in Sweden for over a decade untouched, It was one of two Harmon engines I had managed to purchase in Scandinavia.
Below, an early snap of the Harmon engine with the top end disassembled. Every 12 months or so, the engine received new inlet valve lash caps, head/cylinder viton o-rings and a thorough inspection of internal engine wear and tear. The engine clocked up 1000's of kilometres every summer throughout Scandinavia without any major issues a part from the odd head o-ring letting go. The engine was a cold dragon to kick start for 5+ years until it was finally up-graded with an electric starter. The Harmon's top speed (using a 45 tooth rear sprocket) was clocked @270 kph. Around town, a 58 tooth sprocket was used in junction with an air shift as a teaser blowing off Jap bikes.
Owning two Harmon engines was a bonus. I've also done modifications and fix-it work on other Harmons. The below image was one of my own Harmon 120 engines during a second major rebuild in late 1999. The engine had ran well since its first rebuild in early 1994. As usual, like most Harmon engines, they require more attention and maintenance than other Big Twin engines. When they run - they run good, if slack haphazard short-cuts and cheap parts are avoided.
The first replacement engine part I hunted down in '93 was a Jims machine pinion shaft. Calling directly to Jim for a shaft was positive. He replied " Yeaps, no problem, I'm looking at a shelf full of Harmon shafts". The Harmon ended up using Jims pinion and crankpin, Jims lifter block assemblies, and up-graded Evo block assemblies. All Jims parts survived through the years with almost zero wear and tear - Thats Quality!
The Largest Harmon Engine Of Them All
The largest Harmon ever built and known, which I've personally seen that ran like a rocket was Jims custom 3 litre engine in Denmark. An original Harmon crankcase was used with one-off huge billet CNC machined cylinders and heads. The 3000cc engine displacement was also a kick start only. Image - Harley Davidson Magazine - Denmark.
Below, a quick snap of a Harmon hardtail project by an old friend based in Belgium. His kick-arm lever should have been a taller version, but the bike was mounted with an electric start anyway - a wise move for this engine, unless one enjoys the classic art of kick starting with an odd kickback in the shin.
The Beginning
Firstly I’d like to dedicate this page to the late John Harmon and other bikers out there with Harmon projects. His brake away engine design was the beginning of a new era of big bore engine kits that went ballistic within the biker world after his passing. The John Harmon engine kits weren't flawless. There are several changes needed with the 120 design even before any assembly begins. The cylinder case stud holes were not CNC cantered aligned. Every Harmon case will have varying case stud measurements when replacing original cylinders. Harmon heads were finished without having steel inserts for head bolts. The addition of adding steel threaded inserts into the heads is recommended to keep the heads from blowing head o-rings. The breather case oil hole also requires alignment trimming, and the extended pinion shafts that come with engine kits should be replaced with a Jims pinion shaft. Crankcase bearing inserts on some kits are known to be slightly over machined. Early Harmon heads were designed without squish bands, and came with round top pistons. These early heads lack power flow!
A fastidious construction process is required when rebuilding these engines with several minor changes and modifications to make any Harmon Big Twin reliable.
Checking the pushrod fit on the Harmon 120 Shovel with retro-machined rocker-boxes (designed and made by Rick Hemi). A Vertex magneto and Carls Typhoon carbs were already being used on this engine before it's 2nd major rebuild. Creating and making your own design work is what makes any engine unique.
Replacement Cylinders & Pistons
John Harmon was way ahead of the pack using stronger V8 engine parts in his engine design. Original Harmon pistons are larger in diameter than 454 Chev V8 engines (4.250 versus 4.300). Piston pins are stock Chev V8 (.927). Added bore and stoke to make a 143 square displacement (4.500 x 4.500), or increasing the stroke (4.500 x 4.750 = 151 cubes) are possible options on Harmon engines.
Images showing the size of a Harmon piston compared to stock Big Twin Shovelhead pistons
The first parts that probably require replacing are the original Harmon pistons with other aftermarket brands machined finished with the same weight. Hyperformance pistons are recommended.
Below, Hyperformance billet machined ductile cylinders are good recommended replacements when original Harmon jugs become worn out. New original Harmon cylinders are virtually impossible to find.
Replacing pistons is recommended due to the large cut-out on the original rear piston skirt. Quality made aftermarket suppliers like Hyperformance in the U.S. can reproduce billet CNC ductile iron cylinders and custom CNC machined pistons for John Harmon engines. Hyperformance front and rear pistons are the same weight by keeping a section of the cut-out at the original piston skirt length. This eradicates unbalanced issues, resulting in less vibration and pistons stable under thrust.
The best thing rebuilding Harmon engines are the amount of good quality machine shops who can supply all the necessary parts to get them up and running again. Replacement Harmon heads is like finding a needle in a haystack - so take good care them! One can have machine made replica heads if needed, but be prepared to pay a large cash stash - unless you know someone who can programme and use a high-tech CNC milling machine. Some street Harmon cases have enough material to extend bore diameters to 4.500. There is also just enough material on the heads, this would create a square engine @ 4.500 x 4.500 equating to 143 cubic inches.
Hyperformance cylinders, pistons and titan exhaust valves replaced the original Harmon parts. After the 2nd major overhaul, the engine had a run in Denmark and Sweden with positive results.
Original John Harmon cylinders will last for years with the advantage of getting approximately 7 rebores @ 0.10th increments. Those in need of replacement cylinders, hi-tech pistons, valves, and other quality made made products can source it all from one machine shop - Hyperformace USA
Harmon Engine Parts - Cheap Short Cuts
If you're about to rebuild a Harmon engine, don't slap happy assemble the engine with cheap wing bling parts. Avoid any Chinese made engine parts, like bronze bushing and internal bearings. Chinese made bearings have a habit of falling to bits within a very short time period. Using US or European made quality engine parts that already have a history of reliability guarantees satisfaction if engines are assembled properly. I'm not here promoting one particular brand above other brand names. Most aftermarket parts I've used are from well known manufacturers that most bikers are already familiar with. The piston rod set above was pulled from a Harmon engine that had been micky mouse assembled. If the engine had been assembled together properly, it would probably still be running today. The engine required rebuilding because of shoddy workmanship.
Bottom End
A set of reputable aftermarket flywheels, rod and pins is essential to keep Harmon engines together. This engine on its 2nd rebuild received S&S flywheels, Carillo rods, Jims 3 hole crankpin, Jims pinion and sprocket shafts. The previous owner had built the engine with OEM shovel flywheels and rods which were shoddily put together causing engine failure. Some of the inner crankcase sprocket shaft bearings had disintegrated and disappeared somewhere. The left flywheel was also cracked, thus tilting the front rod which seized the piston rings with irreversible damage to the front piston and cylinder. The pistons were also running without any piston pin bushings, and the engine had the wrong oil pump, including no oil filter. This is what usually happens to any engine when taking cheap short-cuts.
Using good quality made parts makes any Harmon 120 engine run properly without issues.
At a certain RPM most Harley engines dish out rhythmic vibrations. Harmon engines are more brutal, they have a habit of slowly ripping and rattling bikes too pieces if parts aren't bolted down properly. I was once on the back of a hardtail Harman on a 300+ kilometre run. The owner had only one thing on his mind - full power with no mercy! During the road trip, the Harmon snapped-off a mirror, and the rear belt pulley bolts became loose. Getting a numb arse is one thing, but the vibration on this Harmon rocket was severe. This was probably symptoms of an un-shimmed engine-tranny-frame. Swing arm or softail frames with Harmon engines are more merciful. Proper flywheel balancing is important on these engines, including a straight frame. The shimming of engine cases before boiling them down in frames will dramatically reduce vibration. Crankcases should be placed into frames to check if the engine mounts are even and parallel with no signs of wobble. Bolting engines down into frames - especially Harmon engines with even the smallest amount of gap between the frame and crankcase supports is asking for trouble. This will add even more vibration through frames causing cracked fenders, broken mirrors, loose bolts, and missing parts. Crankcases can also be slightly uneven on front or rear frame mounting casts. I've shimmed-up several hardtail frames, although in saying that, my own frame had to be shimmed. Transmission mounts are the same. Older frames, including aftermarket frames can have some serious uneven engine mounts and transmission lugs. Avoid using salvaged frames from crashes and accidents unless a proper jig is used to check alignments. Bolting down engines and trannies by shimming run-out - if required, will lesson vibration considerably.
There's no escape - Harmons vibrate! External moving parts should be bolted down using locknuts with an added drop of blue loctite. This will reduce parts becoming loose or falling off on extended road trips. Whatever you do - Don't use yellow loctite - unless you're wanting a permanent bonded weld, and then gas-axing the bolt off later. Stainless hardware bolted into alloy threads should always use a dab of anti-seize paste to prevent galling. I've never had problems or issues over the years with bolts becoming loose on the Harmon. Parts were either bolted down with quality locknuts, a drop of blue loctite, or anti-seize paste. A smooth vibration is a happy vibration - no matter the RPM.
Every workshop biker has their own favourite tools, a partial collection of Swiss and Japanese dial gauges used for various types of machine shop work. I avoid using "chinese wing bling made Junk".
Crankcase Breather
Harmon breather cavities should be trimmed matched with the breather for maximum return oil flow from the crankcase. The breather hole can be square up easily with breathers. Removing the breather screen will also give less restricted flow. Any metal or other bottom end pieces entering through the crankcase vent hole will normally mean the engine has already blown to bits, so removing a screen is relatively safe. Replacing a machined billet scoop fitted inside breathers will ensure maximum oil flow. The only red-flag warning, is not to increase the length of the crankcase breather cavity dimensions beyond breather timing specs. Grinding and filing too much out can't be replaced. This job should be done when the crankcase is disassembled.
Below, the Harmon pinion shaft with an oil flow end-cap restricting oil flow to the crankpin. Without doing this - especially on these engines and most stroked engines, oil will over flow crankcases with too much oil. Quite a few Harmon engines including one new un-assembled kit I had sold had considerable amounts of oil spewing out of the breather vent.
Harmon Shovelhead - Inlet Valves
Original Harmon inlet valves are shortened Hemi 426 V8 2.250 inch valves. Replacement Manley valves can be purchased through V8 auto shops, or from reputable aftermarket Big Twin engine builders. The addition of lash caps are necessary on inlet valve-tips from pounding, and flattening the tip edge. For safety, lash caps should be replaced every year!
Harmon Shovelhead Camshafts
Harmon engines work best with cams having early high lift with long durations. I've tried various camshafts, with most of them working well from 3000 RPM up. Some to mention are the Andrews M & C grind, with the Leineweber L5 being the best performer overall. The L5 has a .519 valve lift, the inlet valve opens @42 and closes @72 with a 294 duration. The Leineweber L51 cam is another goody. I was wondering why the previous owner was struggling kickstarting the Harmon when first viewing it. There was plenty of gas and spark, but do you think the engine would fire up. After an hour or so of kick starting, the Harmon finally breathed some life. When the cam cover was removed, I discovered the engine was running with the wrong cam, thus making it difficult to kick-start. The short length kick-arm was also a part of the problem.
The above camshafts mentioned require correct valve spacing. Cam side play can be shimmed at minimum OEM tolerances. The Torrington needle roller should also be replaced when changing cams. Jims Evo blocks and solid lifters never gave issues clocking up road milage.
Harmon Shovelhead - Oil System
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Using good oil systems on Harmon engines will keep them running for years. Most quality brand oil pumps made in the USA will do the job. A larger oil tank with a capacity of 5 litres is recommended. Harmon engines should have an added crankcase vent line for crankcase breathing issues. Tapping a hole into the nose cone with a hose line to the oil tank is sufficient enough.
An added auxiliary oil pump was added on the Harmon to separately feed oil to the top end. The pump has functioned well with no issues from 1994 onwards. The heads were modified allowing oil to return externally back to the crankcase using -6 lines. This avoided the normal route of oil returning through the cylinders. Evo Sportster oil pump gears are used in the auxiliary pump. The pump is driven from a mini slot-hex extension that fits into the Magneto gear drive bolt head.
The most important instruments on a harmon are the RPM readout and oil pressure. A liquid filled PSI gauge and powerful oil warning lamp keeps everything in check - no matter what vibration the engine is dishing out. Many have blown engines to bits because of not having gauges operating where they can be seen.
An integral part of any oil system is the oil filter. The majority of screw on filters require replacing after a few thousand kilometres on air cooled engines. The Oberg filter is one of the best performing aftermarket designs for any engine. The 600 micron screen stops everything right down to invisible dust particles. Changing oil using an Oberg filter is as easy as it gets. Undoing the four bolts will open one side of the filter, The screen can then be removed and cleaned, air blown and used again and again. The bonus of using Oberg filters is how fast it cools the oil down before returning to the tank.
Harley Engine Failure - Oil Change On Time - Or Suffer!
Big Twin HD engines can take a hammering, but those thinking they're indestructible have either been dropping far too much acid or inhaling hi-octane weed. The endless amount of BT engines I've pulled down - like the Shovel shown above are usually the direct cause of irregular oil changes. Some owners I've known haven't bothered to change their engine oil and filters for years. Oil loses it viscosity much quicker in air cooled engines. The result of old oil running through engines end up as pitch black sludge, which slowly clogs oil passages, and oil filters (if any) causing engines to run even hotter. This then turns moving internal parts to eventually peel their harden metal surfaces into fine grinding paste. Sludge oil mixed with metal pumping through engines will slowly destroy an entire engine until crankcase bearings let go. Oil well past its use by date can cause shaft pins and rollers to wear down quicker, thus destroying engines exploding them to bits. Changing oil and oil filters regularly will ensure the lifespan of engines.
One of the best methods to change oil in HD engines, is first by removing the oil filter, draining the oil tank completely, and filling the oil tank with fresh oil. Start the engine, and then wait until signs of fresh oil runs out from the oil filter bypass mount. Once fresh oil appears, stop the engine, and then screw on a new filter. Restart the engine again and top up the oil tank.
Large engine displacements require larger oil tanks. You don't see V8 engines running with micro mini sumps, and they're water-cooled. Older generation Big twin engines over 100 cubic inches should have at least 4 litres of oil capacity. This allows oil volume to constantly flow through the engine and cool down before being recycled through the oil pump. I've never seen a Big twin engine blow to bits because of too much oil. For instance, the Harmon engine pinion, crankpin, sprocket shaft and crankcase roller bearings after 6 years of run-time were still within tight tolerances. Even the camshaft lobes, and lifters had no signs of wear, including the camshaft cone bushing and Torrington needle roller. The only parts replaced (at an earlier inspection during the first year) were the Crane rocker arm needle rollers. Galling was apparent on all four rocker shafts - which has nothing to do with oil, and were replaced, including a fresh set of bronze bushings. The needle rollers were the weak link not withstanding the rotation weight of the pushrods and valve springs. Inlet valve lash caps were also replaced every second year - a safety precaution for these particular engines. The Harmon oil tank was designed to take approximately 4.5 litres plus whatever oil is left through the lines, crankcase and filter. Neglecting oil changes on Big Twin engines can result in major repairs costing an arm and a leg that can be avoided - Screaming won't help if your engine implodes because of neglect.
Have you checked lately where your one-time throw away oil filter is made? Cheap wing-bling imported oil filters can destroy air-cooled engines from clogging or failure from stuck internal bypass valves. Obreg Kits
John Harmon Shovelhead Modifications
One of many modifications were the replacement of the OEM Shovelhead rocker boxes. I had begun first by chopping up a pair of 1966 early Shovelhead rocker boxes that came off an engine from Baghdad. I had a constant flow of early and late Shovelhead engines, including Evo engines coming out of Iraq during and after the invasion. Some early Shovelhead engines were discarded for decades because of no apparent reason. Pulling down an early shovelhead engine that's never been touched since its assembly from the 1960s is a rear event. I even had one Evo engine from Iraq that had been found laying on its side inside a chicken pen with chicken shit all over it. The only thing wrong with the engine were the spark plugs and a botched homemade ignition module.
Chopping a pair of 1966 military cast OEM rocker boxes in half was the easy part, but cleaning them up to match together is another story. Crane roller rockers with Jims rocker shafts were used on this Harmon for many years. I found in the early stages while replacing head o-rings the Crane needle roller bearings had caused galling to the rocker shafts, and were removed and replaced with bronze bushings.
The first build was a mix and match of all sorts. The Harmon ran with Del-Orto carbs, Venolia pistons, Andrews cam, Vertex single fire magneto, tapperlite adjustable xxl pushrods, Jims solid lifters, triple valve springs, inlet valve lash caps, S&S oil pump etc. The Harmon was a kick start only. Through 7 years of kick-starting this monster, it had bent 5 kick starter shafts - it even bent a Jims machine shaft, which Jim himself couldn't believe, and wanted the shaft returned to see for himself with his own eyes. Kickback on this engine was aggressive, it gave pain if the kick-arm had the chance to strike the lower leg. On various violent kickbacks, kick pedal replacements that had rubber and chrome inserts would actually fly-off and disintegrate into pieces. Most of my biker friends who were game to kick start this Hamon only did it once.
I ended up retiring the OEM chopped rocker-boxes and designed making my own. They were made from hi-grade billet alloy, with removable lids for easy inspection. This made it quick and easy when the inlet valve lash caps needed replacing. Larger diameter rocker shafts were also made.
Using weak el-cheapo aftermarket wing-bling valve springs made in the "far east" on big cube engines is a no brainer! Top brands made in USA guarantees engine valve train reliability. Harmon engines use high lift cams requiring strong springs. Any of the above mentioned manufacturers make quality valve sets complete with retainers and keepers. Triple or double valve springs kits is optional. Harmon cam lift usually doesn't pass the .600 mark, so a strong set of double valve springs and titan retainers and keepers will do the job.
Pushrods vary with one or two designs way ahead of the pack. Taperlite pushrods are probably one of the best designed constructed pushrods - if they're still available. Taperlites are made from chrome moly, the top ball ends fit snug, right up inside the rocker arm sockets. The lower adjusting ends have super fine threads, which completely removes all up and down play. Locking up the pushrod adjuster nut tight with a good nip ensures freedom from a rattling valve train. Harmon engines require the XXL set. This keeps more than half of the lower adjuster inside the pushrod. Sumax pushrod covers have plenty of inner clearance - they don't leak either when using their upper & lower silicon seals. Lower pushrod covers on both exhausts should be checked for clearance if using other brands. pushrod rubbing may occur.
The most difficult task completing the boxes were the underside centre locations and angles for pushrod covers to seal properly. A centring tool was made that fitted into the lifter blocks. The tool had a 12mm slide rod with a pin point tip that gave the accurate centring location. I'm still waiting for the return of this tool from someone who wanted to make a copy whom I trusted - He knows who he is!
Stock Shovehead lifters blocks were replaced with later model Evo blocks. The above image shows the severity of the front exhaust pushrod angle. Tapperlite adjustable pushrods with solid Jims lifters were used after the engine's first rebuild which clocked up over 5+ years of non-hassle running. There was also no cam or pushrod clatter, rocker-box noise or piston slap before the engine was pulled down for new modifications. The original Harmon head-cylinder viton o-ring seals were replaced with custom-made copper gaskets. These engines can actually run without head gaskets if heads and cylinders are perfectly machined matched. S&S one inch wide carb spigots were added as exhausts spigots instead of using the original one bolt exhaust hole. On the 2nd rebuild, the Del-Orto carbs and flanges were replaced with custom made spigots to mount Typhoon carbs. The original Harmon cylinders were replaced with Hyperformance jugs and pistons. The original cylinders were already at their maximum bore diameter @0.70 th., due the previous owner's sloppy engine short-cuts that caused the engine to internally destroy itself. This wasted 0.60 th of reboring to the original cylinders. A damaged piston with seized rings created deep scars down the front cylinder. This is what happens when bottom end assemblies are put together with mixed unmatched wing bling parts with sloppy tolerances. A set of 10mm compression release plugs were added, including titanium exhaust valves, a fresh set of 2-1/4" inch thin stem inlet valves and lash caps.
John Harmon 120 Project - Stainless Hardware
Chrome Versus Stainless
Hardware is an integral part of any Big Twin project, but what's the difference of choosing between chrome and stainless steel bolts, nuts and washers? If you live near or ride along coastlines, chrome hardware will eventually peel-off with rustic looking finishes - great for rat bikes. Quality grade Stainless hardware will keep on keeping-on! 12 Point grade 12 stainless bolts are normally used on tanks and other military vehicles. Knowing a direct US supplier will keep the costs down. The above image shows various sizes of 12 PT grade 12 polished hardware that was typically used on the Harmon project.
American made stainless Allen and hex bolt hardware is normally produced at grade 6 or 8. The quality isn't as good as grade 12, but it still beats imported Chinese chrome hardware that's normally seen through most aftermarket Harley part catalogs. Purchasing ready polished stainless hardware also isn't cheap, but saves the time and energy of manually polishing each bolt, nut and washer. I had my own industrial polisher that was used to finish-off billet alloy designs direct from my trusty 1961 FP1 Deckel miller. To stop galling, Anti-Seize paste must be used on stainless threads - If not, the next time any stainless bolt is removed, it will rip out the alloy thread it's attached too. The above image shows a treasure chest of US polished grade 6 and 8 hardware collected over the years.
Counterbore tooling sets are a must have for certain custom made parts requiring clean flush finishes for Allen-head bolts and other work. I personally use Granlund counterbore tool sets from Sweden. Even though all sets are metric, the finished diameters are within US imperial tolerances.
John Harmon 120 Shovelhead Drive-side
The John Harmon street Shovelhead drive side received a makeover from its former construction. I designed and made-up a newer heavy-duty adjustable plate that could hold everything in place. The two inch wide billet two section alloy plate is adjustable with a centre rod bolted to both half sections. It could easily adjust the drive belt up in a few seconds. Re-tightening the plate is with four 12 point bolts. The plate is used to hold the starter motor, the belt guard rail, the stone catcher, air shift pump, timing pointer, and left carb extension rod. Vibration issues on these engines can rattle items to bits, a solid thick plate keeps parts intact.
Getting oil out quickly from the heads is via external lines to the crankcase. The original Harmon cylinder oil drain holes were sealed and blocked when they were being used. Both front & rear external lines join together on the drive side beside the crankcase. This was one of the first engine modifications done in 1994. The engine had clocked up thousands of kilometres through the years with zero issues to all oil modifications.
Street Harmon Shovel Air Shift
In the early 90s, street air shifters weren't so common as they are today. Making air shift systems for Big Twins requires a mini air pump with enough air pressure to push the gearbox linkage arm super fast. A micro mini electronic switch valve unit is easily hidden out of sight under the frame. A homemade handlebar unit constructed from billet alloy is needed to hold a thumb push activation switch, a refill air valve, and a mini pneumatic gauge. The air line is connected directly opposite to the air refill valve using an air line push-in fitting. Air supply can be from any mini tank. The Harmon since mid-1994, had used a NOS slimline bottle mounted to the swing-arm drive side. There was plenty of air for several 1st-4th gear changes. Did it work? You can bet on it! Air lines have to be totally sealed and secured properly for the system to work. There were times at traffic lights when rice-burners got a shock of their life with the Harmon roaring up the street using air shift. Changing front and rear sprockets gearing the Harmon down gave quick power take-offs through the streets of Copenhagen.
The angle of the air pump to release, engage, and return to its neutral position is important. The air pump arm should be adjusted to move backward just past the engagement of gears. A much larger bronze bushing or needle roller can be used on the double arm lower support shaft. An STD 4 speed case with a full house of Andrews gears and shafts worked well with this engine. The less gears to change - the better.
Street Harmon Shovel - Air Shift
The SSC Wiwo swing-arm had plenty of space on the chain side to mount a slimline NOS bottle for the air shift system. Two alloy machined ring mounts with stainless support lugs held the bottle in place without issues from early '95 onwards. The snap above was taken in 2000 after a quick clean-up.
John Harmon 120 Shovelhead - Carburators
The Harmon engine's single carb per head is what make the this classic engine different to all other HD engines. The design had probably originated from the Vincent. The concept of using the same cast head for front and rear cylinders by just reversing the heads around was genius. Del-Orto and non-pump S&S carbs work well with the engine. The Carls Speed Shop Typhoon carbs also operate on this engine with minor adjustments. Zipper Thunderjets will also add a 3rd fuel circuit supply eliminating flat-spots on CV carbs.
For years, the Harmon engine had run with two 40mm Del-Orto carbs. It ran well, the carbs were easily accessible to fine tune or be removed from the engine within a few minutes. New parts for 40mm Del-Orto carbs are still available through various suppliers around the planet. The only minus for this particular model is the rubber mounting from the carb spigot to the head. A solid mount carb to head mount flange is superior for this engine due to vibration.
Carls Speed Shop Typhoon carbs were used on the 2nd build. The engine response from these billet machined carbs was instant with no delays. I also used a Carls Typhoon carb on a 132 Knuckshovster which also had an amazing fast full throttle response with zero lag-time.
Another 120 cubic inch Harmon Shovelhead engine kit I had owned, It was sold to a friend who decided to use 2 Qwiksilver carbs. The engine response was quick, but both carbs had horrible clattering sounds at idle. The carb slides would constantly rattle and could be easily heard a street block away. This engine was bolted into a hardtail frame. Within one year, the Harmon engine ended up vibrating almost everything that was bolted on the bike. Mirrors would snap off, bolts would come loose, and the vibration was extreme. The engine also left pools of oil wherever it was parked. This was caused by the pinion shaft not having a restricted end cap to stop excessive amounts of oil filling up the crankcase, which then ends up all over road pavements and footpaths from the breather vent.
Using one Carls Speed Shop Typhoon carb on a bike is something, but having two of these cnc billet machined carbs running on one engine is insane. The John Harmon Shovelhead 120 ci engine had two Typhoon carbs pumping out street gas with a blend of leaded aviation fuel. The mounting system was tricky, but anything's possible. Extra 12mm adjustable rods were added underneath each carb. This keeps the weight of both carbs from cracking the inlet spigots when vibration occurs - which happens on Harmon engines.
Harmon Flat Top Piston
Early Harmon engine kits came with round top pistons. The heads were without squish-bands. These engine kits were lacking in horsepower until the heads were re-designed at later stages. Anyone having early head designs are out of luck to replace early heads for later models - there are none! One can either machine make new billet heads identical to the later John Harmon heads to keep the 2 carb design, or use a set of blank STD heads using one carb. Images shows an original late model flat-top Harmon piston.
If there was ever an image worth remembering - this is it. A snap shot of a Harmon piston within the first week of purchasing the 1st Harmon engine. Notice the monster inlet valve cut-out clearance, which is the same size as a stock Hemi 426 V8 ci valve. John Harmon was certainly well ahead of other aftermarket engine designers in the early 80's. The smaller piston is from a worn out mid 70s HD 1340 shovelhead. Below, a set of original Harmon 120 Arias pistons that had run with OEM 1200 shovelhead rods - a no brainer!
Harmon Ignition
All quality made ignition systems work on John Harmon engines. The Vertex, a single fire magneto has had an excellent reputation in the V8 world for decades. The Big Twin models are made with their own nose cone by Karata Enterprises- USA. The Vertex comes with a high voltage transformer that produces a constant flow of hot spark to the plugs. The more more rev - the more spark the magneto produces. The Vertex was used on the Harmon since 94 without any problems of malfunction for over a decade. The Vertex mag is heavy if for those who are weight conscious. The cam cone housing is well made, it's thick and strong made to last. Timing the Harmon with a Vertex is straight forward - like any other engine. Once TDC has been established, the magneto needs to be turned approximately 10mm anti-clockwise with the points ready to open - Ignition setup can't get easier than that - that's it.
An early 1994 garage snap of a Vertex magneto mounted to the Harmon 120 engine. The first rebuild also included 0.50th Venolia pistons, S&S flywheels, carillon rods, Jims pins, Andrews cam, black diamond exhaust valves, replacement inlet lash caps, crankcase bearings, Del- Orto carbs, Sumax pushrod covers, Crane roller rockers and Tapperlite pushrods, including an OEM set of Iraqi military early shovel rocker boxes chopped in half. The engine ran and performed well every year until the bike was pulled down in 99 for upgraded cylinders and other modifications.
Harmon Shovelhead - Scandinavia
An image of the Harmon Shovelhead during a 2nd road trip in Sweden. As usual, the short Scandinavian summer months are unpredictable. The Harmon had done a run along the southern coast to Goteborg some years before with zero issues. The large ugly Danish number plate was removed for the above snap.
Drive side Snap of the Harmon Shovelhead during the autumn - Denmark
Harmon Shovelhead 120 Big Twin - Custom Exhaust
Stock OEM HD frames require modification clearances for the Harmon engine exhaust ports. It's easier to use aftermarket frames with more front and rear tube space, rather than chopping-up and altering stock frames. Designing your own exhaust system on Harmon engines is straight forward with whatever finished concept one desires. Thick 2mm stainless piping with an outer 54mm diameter was used on this project. A supply of 90 and 45 degree bends made it simple creating the necessary angles.
Extended 1" inch spacers were welded to the heads. This gave enough inner lip with the addition of a 2 bolt 5/16 UNC hook-up securing the pipes. A set of carbon custom mufflers were chopped up keeping only the front sections for inner baffles to keep the noise down.
Workshops
The last few workshops were made with the same design. A long workshop bench with racks of quality tools mounted on the wall(s). My crappy tools, even though most of them were US-European made had their home inside toolboxes. No Chinese wing-bling tools made it through the door!
Having enough room to create a mess without having to worry about anyone screaming about the mess is always a bonus. Workshops were many, mainly because of constantly moving or shifting off-shore. Some were poky little garages, while others had enough room to construct 12+ metre workshop benches.
Having enough workshop table space makes engine construction simpler. The top right image was taken in Asia showing how some machinists don't worry about their floor space or safety. Below, a 3rd replica of the same designed workshop in New Zealand.
Workshop Tools - Storage - Moving Off Shore
Quality workshop tools are addictive! Those who are shifting house, on the move, or spending considerable time off-shore - like myself, can always place their workshop tooling securely in lock-up container storage. Accumulating good tools can take years. The selling of workshop-gear can be done in a day, but there's no reason to sell-off workshop equipment - unless retiring. Think before you sell, or maybe you'll regret it further down the road. Image - 20 ft secure storage container N.Z.
John Harmon - Kick-start Only
The below quick snap was taken in 1994 somewhere at a bike meet in Denmark. The rough homemade exhaust was thrown together using scraps of 2" inch piping and gas welded and coated with a few cans of matt black heat resistant paint. The kick-arm was the tallest strongest solid model available on the market. The Vertex magneto gave unlimited amounts of voltage to the plugs via a transformer through the years with 100% reliability. Karata enterprises were the USA supplier for Vertex magnetos and parts.
The Harmon had it's off-days over the years, but when it was on the open road, it roared like a 70's Mack truck on steroids. At times, it was ridden and treated without mercy, the Harmon liked a quick twist of throttle through the gears all day non-stop. It didn't matter if it was snowing @ minus 5C or during the warm summer months - the engine ran! The only part I ever regret removing off the bike was the kick-starter. I used to enjoy watching others trying to kick start this "cold dragon" without warning them how painful it was to have the kick-arm pedal returning up faster than lightning bruising legs. Once, in the early years, the kick-arm pedal on the Harmon had actually hit my leg so hard, it shoved my leg up over the handlebars. I would normally kick start the engine with one knee bent up on the seat to get maximum height leverage. Below snap - the Harmon at a biker meet during the 3rd year of its 1st rebuild in Scandinavia.
Today, kick-starting engines is a bygone era with only those having nostalgia classics from the 1970s and before who are left. The art and technique of kick-starting Big Twins certainly varies from engine to engine. The Harmon, when cold, would normally give a series of violent kick-backs to begin with. The single fire Vertex magneto was one probable cause for kickbacks. The engine didn't like to much gas pumped down the spigots either. Removing the front spark plug, and turning the engine over a few times evaporating gasoline was ritualistic with this engine. When the Harmon was hot, it would normally fire up on the first or second kick using no gas. Two metre tall bikers with plenty of muscle power struggled kick-starting this old Harmon up -including a few patched gang members who suffered some serious kick arm bruises. Being only 70 Kilos, I used technique instead. I would kick the engine over until the front inlet valve shut on the compression stroke and then give the engine an almighty whack - which worked most of the time.
The tallest offset kick-arm made it easier to boot the Harmon up - powerful kickbacks were common.
Above, a rebuild done in 1999, below, a snap during a road trip to a Swedish bike meet in Goteborg-Sweden
John Harmon 120 Shovelhead
John Harmon's legacy still continues today even after 4 decades since his engine was first designed. Harmon engines hold their own special nostalgia because of its unique design. The 120 cube Shovelhead engines - even though the rarity of how many have survived through the decades are owned by biker enthusiasts around the planet. Data shows Harmon's are still blasting on highways through Scandinavia, Holland, France, UK, Japan, Australia, NZ and the USA.
The John Harmon 120 Shovelhead engine is classified as an old timer these days, but you'll be hard scratched to find any plastic, or any cheap wing bling bolt-on parts on these engines. Most Harmon Shovelhead owners take pride keeping John Harmon engines for what they were designed for - A 1980s muscle engine.
John Harmon 120 Shovelhead Rebuild
Most John Harmon Shovelhead engines through the decades have been modified in some form or another. Some have blown-up, or have suffered engine failure due to maintenance issues. A few owners even change the engine to run with one carb - Why? it beats the purpose of what the Harmon engine design was known for - a two carb engine. One thing I can personally vouch for, a Harmon engine does run if quality parts are used, and maintenance is kept up to scratch. The engine on this page clocked up thousands of kilometres from 1994 onwards. The quick spec sheet lists some of the main parts that have been used since it's first rebuild.
John Harmon 120 Shovelhead Achievements
Wrinkle Finish - Respraying HD Engines
Masking and respraying engines is certainly an art in itself. Over the decades, I've seen some real shoddy resprays because of the lack of not putting some real effort to complete a paint-job with a clean finish, and won't peel-off in a matter of months. For instance, the Harmon engine only received one VHT black matt can spray job that lasted for 6 years without peeling off. The cylinders and heads were thoroughly cleaned, and then sprayed over a few days with several coats. The heads and cylinders were then baked in an oven for an hour or two which hardens the paint.
Wrinkle finish resprays are easier to apply, but the trick to have an even finished look is by applying even light coats of VHT. Spraying heavy coats will cause the paint to run and sag. Spraying wrinkle paint on engine parts outside in sunlight also helps the drying process. A final very light coat should be sprayed when the previous coat has nearly dried. This will give an even wrinkle effect almost immediately in front of your eyes. Rotating the parts around in direct sunlight will ensure a 100% even wrinkle finish.
The images above of a plain Jane Evo showing the finished result gives any engine a clean and spotless look. Fresh wrinkle finish paint jobs should be untouched for at least a week, with engine parts placed and rotated in direct sunlight during this period. This allows the paint to harden properly before grinding head and cylinder fins. Baking wrinkle finish parts in ovens can be done, but the slow method of drying parts in direct sunlight for 5-7 days is recommended.
Grinding fins is a pain in the arse, but needs to be done to finish any resprayed engine The cylinders should already be rebored or honed before spraying and grinding work begins. A small hand held variable belt sander is required, including a stack of replacement sand bands. Staring off with 40/60 grit, this will clean off wrinkle paint from fin edges. After cleaning off paint, the art of moving the sander evenly around cylinder and head fin edges is with 100/150 grit. Placing each part inside a half-ripped up cardboard box helps angle and stability while grinding away. Shaping the width and getting even bends on fins is done on the final stages. Heads should be placed on cylinders to check that they have the same matching curves and widths. Air blowing, and thoroughly washing down parts in kerosene, or other cleansing liquid until all alloy specks and grit sand is removed.
An S&S 113 Evo engine that had blown apart received a full rebuild with a wrinkle finish makeover. The following items are required to paint engines properly. Super sharp razor to fine trim masking tape along edges, quality grade masking tape, a hand-held variable belt sander, VHT wrinkle, matt, gloss heat resistant paint, sunlight, an oven for gloss and matt spray jobs, and most of all - some patience.
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Old School '70s Snap Rant
During the late 70s I was a V8 rev-head Down Under before I began my solo overland travel adventures around the planet. It was a time when there was plenty of work, good pay and prosperity. It was a time without internet, wifi, smart phones, selfies, and trolls. The cries and screams of wanting Socialism within the western world was non-existent - except for Sweden (that now has a failed Socialist program). In the 70s, if one wanted to debate on any particular subject with others - you'd do it face-to-face without spitting or triggering on each other, and walk away in a non-hostile atmosphere. Universities back then had just begun their campaign agendas to dumb their students down as useful idiots - look where it is now - it's now officially the 3rd generation of totally dumbed down people.
For those with high regard to Socialist values - Just try living in Cuba, Nicaragua, Russia, China or in Venezuela as a peasant to see how long you last - maybe a month? maybe not? Experience all those Socialist promises that were actually "made up lies" by using deceptive tactics. It certainly doesn't hurt Socialist regimes ruling over their populations, until cash flow handouts die out from Elite Globalists. Slave labour wages controlled and exploited by Elites is nothing new - just look at Hitler and Stalin! Who believed in their lies and doctrine? Is this what's now coming to overthrow western capitalism? What a plan - yes? A global controlled Socialist/Marxist system with promises of free benefits - that actually don't even exist? - Hello wake up!
Socialism has in fact a 100% failure rate. Excellence is achieved by productive competition. When competition is removed, the population relies on Government to be the dictator of your mind. They end up controlling and manipulating peoples minds to their advantage. Historical facts don't lie. Under Socialism, social justice disappears - freedom of speech disappears, the right to bear arms disappears, including freedom of religion - all down the toilet. Marxist Socialism leads directly to hardcore Communism - It never delivers what it promises ...the latest terminology "Democratic Socialism" uses the exact promises as other drained Socialist Marxist countries have used through history, but glossy sugarcoated to dumb people down! Are you dumbed down? Maybe you don't even know you're being dumbed down?
There is no such thing as free benefit handouts - The cash has to be extracted from somewhere. Employed working populations end-up paying - How's your gasoline tax? cigarette and alcohol tax? income and import tax? One look at the Scandinavian tax system shows where all the cash is being squeezed out from. I was paying 55% tax from my monthly salary in Denmark. 25% tax on anything bought, and employers preferred hiring those who had a mountain of debt! Be a good slave now, and work your bone piece off! Decriminalising cannabis sounds great, another ploy dumbing down youth populations. Most who have stoned brains don't even know what's happening around them - Smoke that Gunja man, and collect your free monthly benefit handout without worrying who's paying for it!
Meanwhile, during the 70s in Aussie, classic cars and motorbikes during this time period were cheap. The weekends were free, the beaches packed out, and the sound and roar of V8s, hot rods and Harleys were heard up and down streets. Rent was cheap, food was cheap, and Aussie beer tasted great.
