The CJ3A Engine

This page highlights efforts to fire up an untested Jeep Willys L134 four cylinder flathead engine.

To skip ahead to the 2020 full engine rebuild, Click Here

February 6th, 2015

Jeep L134 Flathead Engine Testing

Willys L134 Jeep engineIn 2009, I found an ad for a good candidate replacement Go Devil L134 that was pretty local to me. I went for a visit and found the seller to be a young fellow with a serious Willys Jeep affliction. He had Jeeps, engines and parts all over the woods in his backyard. 

He used a pine tree as his engine hoist and the engine I was interested was hanging in the tree. I was a little hesitant about buying an engine hanging in a tree, but then the dad meandered over and started throwing in extra parts in order to make the sale. I think he mostly wanted to clean up his backyard. So, with an exhaust, generators, and springs thrown into the deal, I bought it.

Willys L134 Jeep engine 641087 The engine has a casting number of 641087, but curiously the last 4 digits were ground off and then stamped with the "1087" And the stamps look old. The engine was promptly put away in a corner while I worked on other projects, and years have passed.

But recently, the Jeep whisperings have been bubbling to the surface of my brain, and a window of time has opened up at Squids Fab Shop. It was time to get busy on the Jeep. I had never test run the engine, and I wanted to hear it run, so the engine was pulled out from it's dusty corner to begin work.

Willys L134 engine standA crude engine stand was my first mission. A cart was fashioned with some lumber and casters. Old scrap steel was employed to adapt the motor mounts and bellhousing to the cart. More scrap steel was used to position the CJ radiator and shroud in front of the engine to take advantage of the cooling fan. A small panel was made to hold water and oil gauges, as well as switches for the ignition and charging system (not shown yet.) Note how previous owner did some custom stenciling on the side of the block. Also note the head is not the same....keep reading below....

Bypass Oil Filter System

External Fram bypass oil filter for Willys L134 engineWith the "stand" ready, the engine systems were next: The old Jeep flathead engines (like many engines in those days) used externally mounted oil filters, and I was missing many parts. I sourced the external oil lines from, but saved some dough by getting the hard-to-find flare fittings at a local hydraulic supply company. (It pays to search around...there can be huge variations in costs across suppliers, both local and online.

Broken head stud Willys Flathead 134 on 1950 CJ3AInstalling a new oil filter mount disturbed a few of the head studs/nuts, necessatating a re-torquing. Unfortunately one of the head studs broke while approaching the torque value. So off came the head in order to drill out the offending stud. While certainly a bummer, it did allow an inspection of the pistons, cylinder walls and valves. The good news is that it's in pretty decent shape and in fact still has standard bore pistons. 

Industrial Willys L134 head before sandblastingIt seems that a crack in the head gasket allowed gases to erode the stud which weakened it. I managed to drill out and remove the stud without damaging the original threads in the block. I sourced some Dorman head studs p/n 675-013 from Amazon (sometimes you can get Dorman stuff on Amazon for extremely good prices...woot) and switched to my blasted and cleaned "INDUSTRIAL" head from the seized engine that came in the Jeep. (The head I removed was riddled with cracks). I also inspected the tappets, and removed the intake exhaust manifold which in turn required me to source new manifold studs. I got those, shockingly enough, on a twirly rack at a Pepboys.

Charging System

The original CJ Willys charging system was a 6 volt generator with an external regulator. The components on the Jeep have long been dormant and likely corroded beyond usefulness so I decided to "upgrade" to a modern (well, 80's vintage) Delco 12si 3 wire alternator. 

Jeep Willys Alternator swap CJ3a flatfenderThe Delco alternator has internally regulated 12V output, it's cheap, super reliable, and easy to use. The 12si is probably the ultimate unit to look for (better internal cooling according to my research), but the 10si's are fine as well. The P/N I sourced is for a 1980 Camaro application.

A minor glitch when using a modern alternator is the relatively narrow pulley that does not work well with the very wide "V" belt the L134 crank and waterpump use. There are suppliers that sell wide "tractor" type pulleys, or you can chuck the narrow pulley in a lathe and machine the "V" groove wider.

CJ3a alternator conversion bracket Willys L134Adapting a modern alternator to the little flathead requires a custom bracket which can be had from some Jeep specialists online, but it's easy to fabricate your own. My little box of scrap metal yielded enough bits and pieces to weld one up. It's fairly thick steel so I used a propane torch to preheat the metal for better penetration.

Last thing to do was to replace the cap, rotor and ignition wires. I figured the rest should be okay since it was advertised as running when I bought it. At the first start attempt, cranking speed was normal, but there was no sign of a pop. A test for spark (with a removed spark plug) was positive, but there was no ignition when installed. I put in a new coil, and still nothing. I replaced the points, and bingo! Instant ignition. A few leaks were attended to, and a few minutes of run time indicated a dirty carburetor. The solex carb has a bunch of plugs and caps that can be removed to access internal passages. I removed all of them and blasted everything I could with carb spray cleaner. A dramatic improvement to idle quality was observed and after a little warmup, it revved nicely too. There is a bit of blue smoke I think from leaky valve guides, but this little flathead is a decent runner.

I made up a low quality phone video of the running engine:

2019: Project Oil Jet

The Jeep was pretty much restored by winter 2018/2019, and the engine served well. Sure, it was a little stinky, and it had various ticking noises, but it was super reliable and consistent......but also with consistent low oil pressure: on the order of 2 or 3 psi at idle when hot. The engine didn't seem to care, but one day I was a little bored so I took off the oil pan and timing cover in order to inspect the timing gear oil jet to see if that was a culprit in my low oil pressure issue.

At the start of my quest, I spent a week of head scratching to get the front pulley nut off. I tried 3/4 inch air impact guns. 7 foot bars. It escalated into cutting the nut off....the job went well after that.

pulley nut

The timing gear oil jet is a small fitting installed onto the end of one of the oil galleries with a hole drilled into it that directs oil onto the timing gears. "Word" at the scuttlebutt is that the jet size on early flathead engines is overly large, at about 0.070" in diameter. In the mid 50's Willly advised that this jet size be reduced to 0.040" which would help increase oil pressure, particularly at the #1 rod bearing. Here it is right in the center of this picture:

oil jet between gears

This is the large 0.070" hole.

oil jet with 0.070" hole

To shrink this "jet" to 0.040 or so, I plugged the hole by drilling it oversize, tapped it with an 8-32 tap, and installed short set screw plug. I staked the plug and then drilled a 0.035" jet hole. The jet was reinstalled, I cleaned up the pan, oil pickup and painted up all the parts so things look a little better under there.

The result of this work yielded about 3 to 4 psi oil pressure at hot idle speed. A rather small gain but it was worth a try.

2020: Engine Rebuild

A year passed. Early summer 2020. I noticed some ticking noises were getting a bit louder. This, along with a little boredom, compelled me to drop the pan again to check the bearings.

Off came the rod and main caps for inspection. The bearing shells had date codes of 1965, and it appears the crank is "10/10" indicating it was "gone through" to some extent back in the 60's. I plasti-gaged the mains and rods and found clearances were worn to just about the limits.

rod bearing wornrod bearing at 0.003"

I thought I'd just replace the bearings and maybe the rings too. I pulled the motor, started disassembly, and found that all the top rings in each piston were shattered.

broken rings

Some were in broken in a dozen pieces or more. I believe that was the source of my light tapping. I planned to replace the rings, but then I found one piston had wedged two pieces of ring, one on top of another, in the top ring land. The ring land was destroyed, so I need new pistons.  (Note that the narrow top groove in L134 pistons is not for a's for combustion gases.)

top land with a stack of broken rings

So the plan was revised to include new standard bore pistons...still not terrible, but...


Despite my good clean living, my luck finally ran out. Whilst inspecting the block, I beheld a fine crack in cylinder 4 going from the bore, over the top edge onto the deck. Ugh. On the plus side, it's nice to know why I experienced the occasional mystery coolant fog out the tailpipe. If you click the picture below you can see the crack....

Crack in Go Devil cylinder 4

For this situation I would need a professional. The first person I thought of was "MetalShaper" of Youtube fame. I recently realized he was fairly local to me, so I contacted him. He had me bring it to his shop to take a look. He said he could fix it, and he did. He made some videos of the process which I'm linking to below. In the first video, at about a minute in, he starts on fixing cracks in the center of the large coolant passage on the deck, and at about 8 minutes in, he starts fixing the crack you see above...

He has more video of the boring job.

It ultimately required an overbore of 0.040" as there was excessive wear near the tops of some of the cylinders. A honing machine finished the job.

I purchased a set of 0.040" Keith Black pistons, which were easy to find, but it was difficult to find some of the other parts (unless they were exorbitantly priced at some online "marketplaces"). I ended up finding "King" brand main bearings, Crown rod bearings, Crown valves and no-name valve guides. I purchased a Neway valve cutting kit to re-do the seats too.

I picked up the engine from Brian in mid-August and it looked great. Here's a shot of the lock and stitch repair on cylinder 4. The top ring does not come up to the location of the pins.

lock and stitch in cylinder

Here you can see lock and stitch pins were also required between the central coolant slot and adjoining stud holes. Threaded inserts were fit to restore the stud holes.

coolant slot repair

Valve Guides

The first task after getting the block back was to remove the old vavle guildes. I used a press for some of them, but ended up using a 3/8-16 x 6 inch grade 8 bolt to pull most of them out. An inspection of the new no-name guides indicated the surface finishes of the I.D.'s didn't look great, so I mounted a more rigorous search for Sealed Power guides. I managed to scrounge some but not a complete set. They were definitely superior, so I used the ones I found along with a couple of the best looking no-names. I used the same bolt to pull the new guides into place. Below, note the bore of the Sealed Power on the left, and the no-name on the right.

sealed power and crown valve guide comparison

After installation, a couple of guides needed a tiny bit of reaming for sufficient valve stem clearance. I think I used a 0.375" reamer.

With fresh guides in place, it was time to re-face the valve seats. I purchased Neway P/N CU208 which will cut both 31 and 46 degree angles, and P/N CU205 will do the 60 degrees. These cutters work on pilots that fit into the guides. I got two pilots, P/N PF14038-STD and PF10438-.001 to cover the range of sizes likely for the I.D. of the guides. A handle, P/N TW505 allows you to rotate the cutters. Here's the CU208 sitting next to the seat just cut. The pilot is wedged into the guide.

neway cutter on willys engine

I cut with the 46 degree until the seat surface was clean, then used the 31 degree to just chamfer the top edge, and then the 60 degree to break the inside inner edge. The 60 degree cutter did not cut very smoothly, but with some finesse, the job came out fine. I fit each valve and checked the contact patch as I went. The Universal Service Manual explains specifications. After the cutting was finished, I did a few spins with the valves installed with some manual valve grinding compound to just dress them a bit and clean them up.

The dirty work was done, so it was time to scrub the block with engine cleaner, then soap and water. I dried it quick and oiled the cylinders.

clean block

The crank surfaces looked pretty darn good with just a little staining here and there from, I presume, sitting for long stretches. It measured out good.

older machined crank

The rear main seal surface was corroded, but I think a rope seal will do nicely here.

rear main seal surface corrosion

I test fit the new bearing shells, and found the front upper did not fit with the dowel. I had to file the hole in the shell oversized to get it to fit. Not a big deal. Here it is before the filing.

Bearing won't fit dowel needs trimming

The caps were test fit and torqued down.

bearing mains test fit

I then installed the crank and checked clearances with plastigage. I was very happy to see the mains came in a bit under 0.002".


The rod bearing clearances were checked at this time also with the crank on the bench. They all came in at about 0.0015".

plasti gage rod bearings


Before I got too far installing the crank, I thought it best to install the cam while it was easy to get my hands in there to slip it past the cam bores. First, I had to replace the front cam bearing. Using a home made aluminum puck with a bolt, nut and bar, I pulled out the old bearing, and reinstalled a new one with the same rig. Be sure to line up the oil feed hole with the oil hole in the block! The image below is all I've got of the new bearing.

cam bearing

The front engine plate was installed next, then the cam. I was able to remove and install the cam without ever having to remove the cam gear, so it can be done.

Rear Main Seal

I thought I'd try the fiberglass rope rear main seal that came in my Felpro gasket kit. Right away I had a dubious feeling about it as it seemed hard and unyielding. But I wrestled with it, and forced it into the grooves, used many razors to trim the ends (gad that fiberglass is murder on blades). I then installed the crank, all the while suspecting this wasn't going to work.

fiberglass rope seal fail

And it didn't. With the caps torqued down, the crank wouldn't turn. It was waaaay too tight. After reading all the complaints about this seal on the forums, I decided to just get a "Best Gasket" brand PTFE rope seal kit.

Best Gasket teflon rope seal

The kit comes with a roll pin, two pieces of rope, a shim, and a cutting blade to trim the ends. You drill a hole in the bottom of the groove of the cap and install the roll pin. It serves to lock the rope in place to keep it from rotating.

roll pin in best gasket rear main seal rope kit

I flattened the rope into a wedge profile to more easliy force each piece into the grooves, carefully mashed them in, and here's what I got:

frayed ends of PTFE rope seal

To trim the frayed excess rope, you place the shim onto the mating surface, and use the cutter to trim off the ends.

trim ends of rope seal

After cutting, the rope obviously stands proud of the mating surfaces of the block and cap by the thickness of the shim. This extra height allows the ends to mash into each other when assembled. But, it's important to prevent any strands from folding over onto the mating surfaces, so you should use a tool (I used a small dull screwdriver) to carefully push any loose strands hanging over the mating surfaces up and onto the rope endfaces. Here's the "dressed" rope ends:

dressed end of rear main seal rope

The crank was finally installed for the last time and everything torqued down. I checked endplay and it was in spec. I measured about 5 ft/lbs running torque to turn the crank.

crank endplay check

Next was installation of the valves, springs and keepers. Lash was set to 0.016".

installing valves

I measured about 8 to 10 ft/lbs to rotate the crank with the valvetrain installed.

testing torque to turn valvetrain


The rod/piston/ring assemblies were assembled. The pistons were numbered by Brian (metalshaper) so I of course fit them to the corresponding rods. I fit Sealed Power Kromex rings which have a chromed top ring and chromed oil rings...(the box is old...I don't think these are made anymore). I measured the end gaps of the rings and they were in spec. However, I couldn't leave well enough alone, since I learned that the latest practice in engine building is to gap the second rings a little on the bigger side; this allows the top ring to seal better. Yes, it's absurd to care about this for a Go Devil, but I filed the second rings anyway to achieve 0.017" gaps (from the as-supplied gap of 0.011"). The top ring gaps are about 0.014". So I'll bet I'll gain a good half a horsepower...haha.

piston assembly

The pistons installed easily and I got the caps torqued down. I did not bother with new "pal nuts" on the rod nuts.

pistons installed

I measure about 10-11 ft/lbs to about 30 ft/lbs to rotate the crank/valvetrain/pistons. The 10-11 ft/lbs is when the pistons are all at the top/bottom of travel (no piston movement) and about 30 ft/lbs when the pistons are in the middle of the cylinders (maximum piston speed as a function of crank rotation). I'm thinking while this seems to be a lot of torque, I think it should loosen up with break in.

Oil Pickup Mod

I thought I'd try to put an o-ring in the oil pickup joint. There is not supposed to be anything there, but it seems like a decent idea. I could not find a conventional "english" size Buna o-ring size that would fit. In metric sizes, a 14mm x 16mm would be ideal, but I couldn't find anything locally. I then remembered I have some A/C HNBR o-rings laying around in my A/C stuff and it so happens one seems to fit okay. I'm thinking this might just keep some tiny bit of extra sealing when the engine is out of level.....maybe. Eh, I don't think it could hurt.

o ring in oil pickup tube Willys Jeep
o ring installed in tube

I installed and bolted down the oil pan, which felt good after all these months of engine parts laying around!

I thought of re-using the original oil pump, so I took it apart to clean it up. The rotors measured to spec, but the bypass system spring was broken and I lost confidence in replacing that spring with an equivalent. Note the broken spring end to the right, and to the right of that is a goofy slotted set screw that someone must have installed in the past to increase bypass pressure...

old oil pump

I bit the bullet and ordered a new (pricey) pump from Rockauto, and was surprised to see it had a date code of 2001 on it. I hoped this unit was from the "good old days" before the faulty batches of pumps hit the market in the late 2000's. It turns pretty stiff, so I worry a little bit...but I bolted it on. Incidentally, the new oil pump has a cast iron housing whereas the original was aluminum.

new cast iron sealed power oil pump bolted on

I installed new Dorman head studs and sealed them with Permatex 51813 sealant as recommended by metalshaper.

new Dorman head studs and felpro gasket

Distributor Rebuild

I took some time to "rebuild" the distributor also. I knocked out the lower retaining ring pin and then installed new bushings (correct sized bushings can still be found at the hardware store). Make sure to add an oil hole to top bushing for oil flow.

Distributor rebushing

The distributor as installed in the block sits on a precision washer (just to the left of the centrifugal weights on the shaft in the picture above) and this sets the height of the distributor body so that the shaft will float between the thrust surfaces between the body and shaft. Mine showed signs of rubbing the top thrust washer, so I made a thinner washer, which set the body down lower in block, and this introduced equal gaps between the shaft features and thrust surfaces.

I installed the distributor into the engine and timed it statically, using a multimeter to check when the points open. I wasn't sure where the distributor body orientation is to be, so I set it so that the oil drip fitting was at the 10 o'clock postion. I may re-do this as I think I'd prefer the oil drip fitting in the 2 o'clock position.

The Remaining Stuff

I proceeded to install the head, (which was resurfaced by Metalshaper), waterpump, the oil filler tube, freshly blasted and painted manifolds, thermostat housing, flywheel, new clutch and spark plugs.

Completed assembly of refreshed L134

To install the engine with a bit more ease, I made up a bracket to tie the top bellhousing bolts together which allows one hand installatoin of the nuts. It makes for a much easier installation of that hardware. Click to see it installed.

Bellhousing upper bolt retainer bracket

Finally, shockingly, I was able to loosen the exhaust flap counterweight and adjust the bimetallic spring/flap for cold starts. I was even able to reuse the sheet metal tab used as a stop at the end of the spring. It's odd what survives and doesn't in these old Jeeps.

flapper weight, bimetallic spring and spring stop

I installed the engine, hooked everything up, pushed it out into the driveway and fired it up. There were a couple glitches: gas leak, coolant leaks, but I sorted it all out. I made a video of the experience:

The manifold stud coolant leak was quite persistent, and after a couple tries I installed a new stud and used Permatex 56521 to seal it up.

56521 Permatex on manifold stud to seal

I switched to Motorcraft Diesel 10W-30 oil. This has enough zinc and phosphorous for flat tappet engines, and the viscosity is good for this type of engine. I measure about 40 psi oil pressure at idle when cold, and about 18-20 psi at idle speed when hot. When at cruising speed, it's about 45 psi.

The aluminum radiator (an ebay no-name special) is fantastic and keeps temps at 180-185F. I was stuck in traffic (before the rebuild) for a half hour once in 90+ degree weather (at the Simsbury CT Airport Fly-in/Car show 2019) [I just realized my Jeep is in one of the gallery pictures from the Hartford Courant haha! Can you spot it in that link?], and the engine crept up to 200 degrees F, but I used the throttle control to bump up the idle speed to about 1000 rpm, and the temp came down to 190F. I'm happy with that.

The Finished Compartment

Having the engine out allowed me to touch up paint and some doo-dads, and it looks great. It's definitely not a stock Jeep, but I like the look of the black flathead engine with all the clean details. I drive it every chance I get, whether it's 20 degrees or 90 degrees out, as long as the roads are mostly dry. I have gotten caught in a shower or two, but no deluge yet!

Restored engine driver sideshiny engine go devilshiny engine go devil

So until the next fun project, Keep on Jeepin'.

CJ3a cruise windshield down

To see Willys Jeep CJ3A drivetrain rebuild, click here!

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Willys Jeep CJ3A Forum

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