INTRODUCTION- Over this last winter and spring, I rebuilt a GPW engine. As I attempted to do with my posts about transmissions, I will try to show how anyone can do this. This engine is a very simple and basic design, and not a bad choice for someone to learn rebuilding. This is the way I rebuild a motor, it is not necessarily the book method.
I think anyone who can turn a wrench, can save a lot of money by doing it yourself.
Machine shop services cost (a lot), but by doing the disassembly/assembly yourself- you will save some money, learn how to maintain, and understand your jeep better. I’m not going into the theory of 4 stroke internal combustion engines. That is available in many places. I won’t quote a lot of tolerances, torque specs, and plast-guage. I don’t try to remember all the figures that are readily found in the manuals (you will need some of them). Again, this is more for people who have not been into a jeep motor. I took many pictures; hopefully they will clarify some things that are not shown in the basic manuals. For those with dial up, it will probably take time to download them all. I tried to keep file size small. If you post a picture 600 pix wide, a lot of scrolling is necessary.
If you need more detail, I can email higher resolution images to you.
HISTORY- this engine came from a GPW that I parted out. Many of you G503’rs have some of its parts. Bill in Albany has the frame, Dino got the f bolts, left coaster got steering wheel, etc… I parted it because the body was pretty shot, and it was before I found the matching number GPW that I sold here recently. Had I known…I would have kept it for GPW parts. The serial number on the boss is just a number without GPW. I was told that this means it was probably a replacement motor while jeep was still in service?
pic of serial number


They were supposed to stamp original number on replacement. I guess instructions didn’t say anything about brand?? I pulled the motor and stripped it. Some cracks on the head surface were visible, so I took it to a welder who specializes in block repair. He baked the block overnight in an oven at 1200 degrees- totally clean! All foreign material is just dust and blows away. He magna-fluxed it. A strong magnet is applied to block, iron particles are sprinkled on …if there is a crack... the particles line up. There were more cracks than I had seen, but nothing that he couldn’t repair.
pic of cracks.


This block must have been severely overheated once. Two cracks went from valve seats to the piston walls, and another was along top of water jacket. He told me that I needed to have those pistons sleeved, so that he would have a good footing for his repairs, welding or pinning.
DIAGNOSIS- this engine was rebuilt because it was broken!. That is not always the case. This engine is getting rare, if we want original jeeps, we need to rebuild them.
There is no readily suitable substitute. Mileage, is usually the primary reason for rebuild. Our jeeps probably don’t get enough mileage. Short runs during a few months of the year are actually more maintenance intensive than everyday usage. They don’t get warmed up, acid and moisture build up…don’t get flushed with normal oil changes, etc. That is bad for motors. I don’t think they get abused with racing and towing. If you’re not rebuilding it because you bought a jeep and are doing a ground up restoration- the most common reasons for rebuild are oil usage and oil pressure. A well-maintained engine can go 300 or 400K. When oil pressure goes south, regardless of the mileage- it is time to rebuild. If oil is going out the tail pipe because of worn rings and valves (no compression)- it is time for a rebuild. Other symptoms are noises from bearings or pistons. But, noises usually result from low oil pressure. This is a low compression, low rpm motor. Idle oil pressure can actually be pretty low…5 lbs or so, if it stays at 20lbs or more while driving, it is OK. If you have better numbers than that…it’s gravy. Noise diagnosis is a lengthy separate discussion. Many are scrapped because of cracks, that is a waste! Again, the basic disassembly and reassembly are not difficult. After you do your first one, you’ll be looking for motors so you can rebuild a spare!
You need the basic books. You should be buying old motor books at flea markets. the Chiltons from the 40’s and 50’s have good sections on rebuilding. The wartime TM’s actually have some mistakes but are necessary. Invest in the early Cj service manual…better pic’s and instructions.
Pics below of TM’s service manuals and the Chilton-one

You can download the necessary TM Manuals off JeepDraw for free.

C    D   E      E1  

It would take too much G space to do a detailed disassembly- just follow the TM’s and start taking every nut and bolt apart! Spray and soak with penetrating oil for a week or more before you begin! The only special tool needed is a valve spring compressor. I’ll show other tools you may need, as they are required. You must have a good torque wrench. I have tools and machines accumulated over 30 years. It would cost a lot to buy them for just one rebuild. You can rent, etc., but, join a local chapter! You can borrow!
I took the block to a machine shop. I asked him to sleeve (per welder’s requirements) two front cylinders. This involves boring out cylinder walls, inserting a sleeve, and boring that out to either the original standard bore, or another size depending on pistons that you want to use. New cylinder wall is also honed (final wall surface prep for rings). When you take a block to a machine shop, you need to take the valves and one of the pistons. A good machine shop will:
Completely clean block, (again in this case) this shop uses a media tumbler.
Check valve guides for wear- replace, knurl, or insert.
Grind the valve seats and valves- (I have a valve grinder for seats and valves, but in this case there was welding on seats, and I asked him to do it) to fit old or new valves.
I also took the crankshaft in to have it turned- grind and polish journals for new bearings.
pics from machine shop- one

 F    G    H    I 
After sleeves were inserted, block went back to the welder for repairs.
   M   N 

During his work, I went to find the old pistons to determine the old bore (he could have measured), so that I could decide what size for new pistons, or if to reuse the old ones. The old pistons were .060 oversize.
pic of old pistons.
I could have used them. This would mean boring the new sleeves to .060, and hoping the other two cylinders were good enough to not need re-boring. These pistons are actually ok, you clean grooves, de-carbon, new wrist pins. Pistons only go up and down!.. they don’t really get worn. The wear on the side is because pistons are eccentric- they change shape as they heat up. Pistons and rings are available up to .080 oversize. I decided to sleeve all 4 cylinders, and have them re-bored .020 oversize. I have never used .080 oversize, but I just didn’t like the idea. New pistons are available for around $30 apiece and up. I called around to dealers (including Ron) etc, but found some NOS .020 oversize for less from a friend. Saved on shipping etc. Local NAPA got .020 oversize rings overnight.I am going to post pictures of stripped bare block. I want to show and label every bolt hole, oil galley, plug, stud hole, etc, etc. I’m going to discuss them and as I assemble, I’ll try to show the parts that fit and give their sizes, etc. This is pretty basic, but again I’m hoping some will see how it is not too complicated, and that they should try it.
pics of bare block.
Throughout all this work, I clean all holes, galleys, etc…I use compressed air, bore brushes, thread chasers, taps, etc. I do it repeatedly.
Pic of chasers.

This is because as I move the block around, new debris, especially from the water jacket is falling around. When I actually get to install a bolt or stud or part…I clean that specific hole again. This block had two broken studs, that is not uncommon. I have found the back manifold stud broken many times. With motor in jeep, that nut is very difficult to reach, bubba probably torques it off with off center ratcheting etc. For that broken stud, I bolted up a manifold and used it for a centering jig to drill out stud. I have a pretty good extractor set. For the other broken bolt in the generator mounting, I just used a mounting bracket as a jig. Drill out broken piece, inset extractor, turn out.
pic of broken studs1    2  MISSING PHOTO

Pic of extractor set-one

It includes sleeves for all size holes to use for drill centering
Pict of chasers, extractor-one

Block is now ready for assembly. This block has been baked and blasted. It was very clean and porous, it would readily accept any paint. As a GPW, it will wind up grey. The problem with grey is that you can miss a spot and not see it. So, to protect, and to better see the finish coat, I primed it. It will get oily, etc. But, in the end, a good wipe down with lacquer thinner will prep it for final color.






The valve train goes in quickly. I have a rotating engine stand, but I prefer a wooden bench with carpet. Small parts don’t bounce or roll away, sometimes I want to put the engine on end, and in the beginning…it is easier just to manhandle the block.

The valve train consists of the camshaft, the tappets, the locks, the retainers, the springs, the guides, and the valves. 

 You can buy every piece brand new. I don’t replace unless it is necessary. The camshaft turns at half engine RPM’s which is really slow by engine standards. I have replaced some, but I’ve never seen one that probably couldn’t be used…just lucky I guess. Part of it depends on how the oil pressure was. On some engines, replacing the main and rods bearings will cure low pressure. On some it doesn’t help at all…a lot of pressure can be lost at the cam. The cam has four journals with corresponding bearings in block…the front one is replaceable; the back three are machined in the block. The back three can be sleeved and re-bored. Ask your machinist to check the iron ones…the replaceable one is usually around $12. Replace it! The cam journals can be polished if they are pitted. The lobes for the tappets are actually pretty sharp. You need to see a good one to compare. If you don’t get a good feeling from the machinist…NOS camshafts are still available. They usually need to be polished anyway from storage surface rust. The bottom surface of the tappets can be worn. If there is a depression there, replace. If they just have a light circle pattern on them… they are ok and turning properly. The top of the tappet is more likely to be worn.

Notice the left one has a bowl shape from the valve stem hitting it. The one onthe right has been put on the valve grinder. It makes a new squaresurface.

The hole in the block where the tappets ride are usually not a problem…tappet is constantly splashed in oil, and there is a drain hole in the valve chamber that feeds them also. The groove around the tappet is for oiling the hole sides. Tappets that are .002 oversize are available…I have never used them. I don’t know if the hole needs to be reamed or if that is the wear.

The only problem with the locks and retainers is that you loose one!! If you only need one, let me know. If you ever do a valve job with motor in jeep…You will learn to put a rag in the valve chamber after the first key falls into the crankcase!!..I have never done that!!

For the springs I just line them up.. all the same height.. no leaners.. ok. I do check with a square, and look for pitting, breaks etc.

Once in your jeep's life, you will have to buy a new valve (two actually since that’s the only way they come). You need it to check the guides. If you take it to machine shop, he has pilots and can check for you. He will do that if you are having seats ground. All the manuals have pages about replacing valve guides. If the guides have been rusting in the block for 60 years.. it is not so easy! But, it is also not necessary. You put the new valve in the guide. If it rattles, you need to fix. If it barely moves side to side.. it is ok.
I’m sure there are specs and you can measure deflection with dial gauge.….??
You can buy new guides. Pulling them out the top as instructed is not easy, the machinist will probably just drive them out the bottom. Then you have to set the new ones to correct heights…they are different for exhaust and intake. Too much trouble and money.
The first alternative is to have them knurled. A special tap is put through them raising metal. Then they are reamed back to original size. Some machine shops believe knurling is better since there are now grooves that help oil. I have done that. The machinist I used for this engine prefers putting in bronze inserts…he claims it is just as fast as replacing or knurling. The guides are drilled, the insert is put in, and it is reamed. In this engine the guides where good, and I had enough valves around to grind some good ones. I wire wheel them to remove any carbon on top or on stem. I also chuck them up in my lathe and polish the stems with 1200 grit emory paper if necessary.


I have a valve grinding machine. If you are nearby and want to grind some valves, come on over! The valve surface is ground at 45% (not exactly) to match the seat in block.

The bottom of valve stem is ground square

Then the bottom of the stem where it contacts top of tappet is chamfered. It takes about two minutes per valve.




When you grind valve face, it now sits down further in block. When you square the stem, you are supposed to take off the same corresponding amount that the valve moved down. In the old days…machinists would measure valve height difference with run out dial, then use micrometer on stem grinder (you can see it in picture- to take off same amount). But I have also faced tappet!! they are even further apart. Fortunately these tappets have more than enough adjustment to make up the differences- so it is not that much of a concern. Besides, you only take the smallest cut.
I have seen a lot of discussion on the G about hardened valve seats, satellite valves, leaded gas, etc…I don’t know…? It is probably a good discussion. If you have the money.. it can’t hurt. I don’t think it is necessary with this motor. I do use lead substitute in my gas when I drive a lot. I have a valve seat grinder. It is a big drill with pilots and stones to grind the seats. You dress the stones, then put them on pilots and spin them in seat with pilot inserted in guide. Check the picture in part one. I asked the machinist to do it because of the repairs. He told me I could have done it as usual, but he did have a special stone to grind the hard pins. He also did not think this engine needs any special valve seats. There are two cuts- one is 30 degree angle for relief…and then the 45 degree to actually contact valve face. The amount of contact has to be pretty precise.

Too little and valve will break or distort from pounding. It can overheat because there  is not enough contact to transfer heat away. Too wide and it will leak because there is too much surface area. The spring can’t hold it down enough. Just a hair over 1/16th is what I use.
When I have all the parts like I want…I lay them out. It makes assembly go very quickly. ½ hour or less.


First, I de-burr the bearing. It is bored straight through. I just chamfer the front edge, it won’t catch when I install the cam.

Next, I install it. I put a layout line from cam bearing oil feed hole to the front of the block.


Then, gently smack it in with bearing insert tool. You don’t absolutely need this tool; a flat plate will work if you line it up correctly.
Put some compressed air to galley on front main bearing, and you’ll know if you lined them up correctly. I do not stake the bearing. 
I grease the tappets. I use STP mixed with assembly lube…very sticky! I have the block upright on it's back end. This way you don’t have to clip or tie them in up position to install the

With tappets all in up position, lube the  cam and gently drop it in. Guide it through with other hand to avoid hitting or scratching the bearing surfaces. After it is in, I just lay block down in normal position. I put cam gear on front with a couple of the bolts so I can turn cam to raise and lower tappets. They are now riding on the camshaft lobes.

Now, put a retainer in bottom of spring. Close coils on spring go up against block. Put spring over part of guide that sticks down. You can usually just use your hands to snap spring over tappet. If not, just pry it over with screwdriver. You need to turn camshaft so tappet is in lowest position.


When all the springs are in, install valves from the top. The intake and exhaust valve are different. They are usually marked.


If not the intake has the larger head. 4 intakes, and 4 exhausts. If you’re not familiar with the layout, get manifold. Check picture on first post for labelling of intake and exhaust ports. But look at the manifold, and you can figure it out.
Ex-In-In-Ex-Ex-In-In-Ex front to rear (same either way) 2 per cylinder, one of each.
cylinders are number 1 2 3 4- from front to rear.

Next, the spring compressor

This is one from sears that I have had since …?

It ratchets the spring up. I put the greased keepers in place. Then let it down!
You need to turn cam again as you go, to do each set, to lower tappet. There is a place on the cam where both valves are closed. Pretty slick!

Valve train is now in place. I have been cleaning, lubing, etc as I go. Now I want to close up the oil galleys. The main galley runs along bottom in crankcase. Several passages are drilled to it and through it, to feed oil pump and bearings. The outside holes don’t serve any function, but are the result of the machining to make the passages. Here is one concession to modern parts. The two 3/8 pipe plugs at front and rear of block originally had recessed square drive…it is not a standard size. I replace with a hex head. You must learn the difference between standard threads and pipe threads. Don’t chase or clean these galley plug holes with standard taps. There are pipe taps…but a good bore brush is fine.
I bore brush all the galleys one last time, compressed air, then plug with Teflon sealant on threads.





I also install the cam bore back plug now. It is a cupped disc. Put a little sealant on edges, insert it in place, and smack center to expand edges. You are supposed to use a smooth rounded surface like a ball pien hammer. I don’t like striking the face of one hammer with another, so I use a large brass drift with smooth face.
The original plugs for the passages inside the crankcase were a square socket drive. See picture. I replace those with modern hex drive, because one easier, two…there are mentions of interference with the counterweights in some manuals.

The old style plug could get hit by crank. I do use the original ones on outside of block to keep original appearance. These passages go up to two center cam bearings.

The two other outlets are for oil pressure gauge and to oil filter. The get brass fittings, but they are also pipe thread.

I put on the front plate now. It needs to be in place for crankshaft and cam gear. I have labelled the bolts and studs. The stud dimensions mean that it is threaded course on one end and fine on the other. The middle number is overall length. The course end goes in the block, the fine threads are for plate and timing cover.

The main and connecting rod bearings used in the jeep engine are two semi circular halves called inserts. When installing these in the block and connecting rods, some care must be observed. If there is good clean oil, and the engine is not abused, they can last a long time. As long as there is an oil film, the rate of wear is slow. Grit or dust getting into the oil, either through the carb, or from installation, can ruin a bearing. In my pictures, you can see that I use a lot of assembly oil. But, by having everything ready…I get it closed up quickly. I wipe up excess- no oil should get on threads or bolts…to get proper torque, they need to be clean and dry. Wipe down all bearing surfaces, there should be nothing behind an insert.

This is how the crankshaft comes from the machinist. Leave it in the bag until ready to install. The journals are precisely ground and polished. Scratches, etc are no good, and they will rust in a minute. The tag indicates that this crank was cut .040 undersize on mains and rod journals. From old inserts, you can see what old size was. This crank was .030/.030. So it was cut the minimum, increments are usually .010.

As with the valve train parts, I lay out everything. I assemble pistons first.

The pistons must be assembled with T-slot and squirt hole in correct relationship. They must also be installed in cylinders with offset in correct relationship to main bearings. The connecting rods may be numbered, check during disassembly. The numbers, letters, dots, etc. can be on either side. You can’t always use them as a reference. Cylinders are numbered 1-4- front to rear. Often one rod has been replaced. So, you must use correct assembly and offset to install. As shown in part one, pistons often have an arrow on top pointing to front. Use the arrow, slot, squirt hole, and offset to check that pistons are assembled and assigned correctly.

Scan from CJ manual that shows correct piston assembly.

These new pistons came with wrist pins. Place connecting rod in vise leaning away with lock bolt on top side. Slide wrist pin into piston, lining up slot with bolt. Place piston on connecting rod and finish pushing wrist pin through. The torque setting for the lock bolt is 35 lbs. I don’t have a torque wrench that will fit up there. I snug it tight. You can use a crow’s foot on a torque wrench and do the math etc. I also lube each pin in the piston.


I leave piston in vise to install rings (straighten it up). Rings come in different styles, but are generally same shape. There is usually an instruction sheet, or the packages are labeled to show which ring goes in which groove. The widest is the oil ring, it can be one piece or three pieces, and it goes on first in bottom groove. Two different compression rings go on next, see picture and explanation from scan. Most rings have a dot or TOP, but you can figure it out from shape. The ring expander tool is cheap. Rings are brittle and will snap if twisted or opened too much, Open only enough to fit over piston. No ring goes in top groove. If using old pistons, clean all grooves. Use an old ring, break it, or buy a groove cleaning tool. Most manuals show measuring the ring gap, and the play in the groove. I check a few of the rings by installing a piston head half way down a cylinder, inserting a ring on top and seeing that they are close to specs. I’m using new pistons, new rings, and a machine shop I trust. I do not measure every single ring.


The gaps in the rings must be staggered around the piston- 120 degrees from each other- do not line them up as in picture.

Picture of new rod insert in a rod cap. There is a notch that must be lined up. Inserts come with a spread, so it will stay in place. To set it in place, gently tap it on a flat surface. As mentioned above, it must be clean behind insert. Most modern inserts have two holes in both halves, one of them lines up with squirt hole in connecting rod top, not necessary in cap. The old insert show the worn bearing material flaking away and scorched.

Install upper shell (interchangeable) in connecting rod. Notch and squirt hole have to line up. Connecting rods should have been cleaned, but check that squirt hole is clear. Cover the bolt heads with cut off piece of 3/8’s rubber hose. The fit down the cylinder is tight, big fat pieces of hose will not work; these are part of an old air line.

I lay out the crank with inserts. I’m pretty liberal with the assembly lube. Buy the time I close up the crank case, every galley in block and crank will have been squirted a couple of times. Wipe up excess when installing caps and bolts etc. Clean threads for torque!

Put the upper shells in the block, some brands are labeled with a U or L. The front bearing has a flange- to control thrust. The rear has two grooves. So you can figure out which goes where by lining up oil galley holes and dowel pins. In earlier pictures, the dowel pins where in place. They usually don’t fall out. Clean around them; make sure bearing surface is clean and dry.

Here is a picture of rear main cap with dowel pin out. The front cap does not have a dowel pin, the flange prevents the bearing from spinning, and there should be five dowel pins.

Picture of old insert. Again, you can see the flaking metal.

Spread some assembly lube evenly on the inserts in the block and the caps. Put the rear main seal in place (pictures below), lay the crankshaft gently in the block. Put the flywheel bolts in crank rear flange. One you put the rear cap on…you won’t be able to get them in! Just before I put the caps in place, I squirt more lube down the crankshaft oil galleys. The assembly lube, with STP will stick and stay until engine start-up.

This is how I turn crankshaft. Hand tighten the main caps, turn crank one complete revolution. From now on, every time you tighten a main cap bolt, turn the crankshaft one complete revolution. I start with middle cap, torque to 50 lbs- turn! Either one of the other caps-turn! Last cap-turn! The first time you do not turn for each tightening, if there is a problem-it will bind, and then you need to start backtracking to find the problem. Now torque to 65 lbs, again, turning between every bolt. You can put the front crank nut on and use a ratchet and socket to turn crankshaft. Either way is fine. When all the caps are torqued, and all have a lot of assembly lube, you should be able to spin the crankshaft with one or two fingers on a regular ½ inch drive ratchet on the front nut. Note the rubber dowels that fit in the drilled hole between cap and block. Just before putting pan on, I coat these in indian head shellac and insert, the pan compresses then to seal. I also use a little on rear cap mating surfaces.


Picture of lube on journals, spread it out. Picture of diagonal oil galleys in rod journals. I always squirt more oil down because of turning, plus as I said a few times now…I want all the parts covered with assembly lube when I start it for the first time.

Picture of the three types of rear main seals. The rear main cap has a large groove that the oil slinger on the back of crankshaft fits into. There is a drain hole there for oil to flow back to sump, make sure it is clear. The smaller groove toward the back is for the seal.

Picture of the asbestos rope type seal. Still works, I have used them, they need a little care and attention when installing.

Picture of the rubber seal that was used for most of the service life of jeeps.

Picture of the modern, metal supported, wider rubber/neoprene seal that comes in most new gasket sets. I have seen or used them all. They work equally well, the newest one is more forgiving of a rough or worn surface on the crankshaft.

Main caps installed and torqued down with first piston coming in. For crankshafts, many manuals show checking clearances with plasti-guage, etc. I use it, but more to check working engines to see why or where oil pressure is going? Again, This is new bearings, new crank, and a machinist that I trust. The front gear sprocket stayed on this when it was ground, so I did check the endplay per the books. It was ok. The rubber on the bolts keeps them from scratching journals, but you still need to guide them by hand.

The ring compressor is a ratcheting sleeve that pushes rings into grooves so that assembled piston can be inserted. Use a wooden hammer handle to knock them down.
Wipe cylinder walls clean, use assembly lube on rings and compressor before tightening it down. I still have the block on a wooden bench, but you might find the engine stand easier. I put all pistons in from top just so rings are in. Then with block on side, I can reach and pull rods into place or control them while I knock from top. Do 1 and 4 together, 2 and 3…so the journals are up or down together. Just before putting connecting rod on journal, more lube. Squirt in galleys and rod cap, then snug it in place. The torque for connect rod nuts is 50 -55 lbs. I do it in 35, then 50 lbs steps. Again, rotate crankshaft a complete revolution between each step, and between each cap. As you connect more pistons, and with the added resistance from the rings, the crankshaft should still spin.
You should not need to push hard. If, on one of your tightening sequences, it does bind,
you have problems. I once got a set of rod bearing with one odd size out of the eight!. I wasn’t turning between every nut or bolt….darn! There are other things that can happen.
A bent crankshaft is usually picked up by the machinist. But, bore mis-alignment on the main bearings has happened. Old engines take a set, fatigue, over heating!!

Two scans from manuals, the first one is from 1803A, and is wrong! Every other picture and description is fat side away from nearest main bearing. It took me a while to reconcile this the first time I rebuilt an engine. I didn’t have all the other books, and this didn’t make sense with T-slot, squirt hole, etc. Also you will find some assembled wrong, the engine runs, just has more piston side play wear I guess?

Rods 2 and 3 with correct offset. Fat side away from nearest main bearing.
MISSING PHOTOS 28 Substituted 


These connecting rod bolt nuts are the split locking kind. If you have a plain hex nut, you should use the PAL nuts.
I put this picture of using the torque wrench in to show that the engine must be secure whether on a bench or on a stand…it will tip over.

Clean the float well, install gasket and tighten it down, and check that it doesn’t hit crank in any position.

Put the pan on.

I appreciate the nice comments on earlier posts, but I can’t be the only G503’r that rebuilds engines? Others must have tricks or short cuts or better ways? I put this out to learn as well as show new people. Is this the way you do it? I will post the costs later, but what do others do- send it out? I’m sure others besides myself would like to know. It is a forum.

In a previous part, I mentioned that it was not necessary to know the 4-cycle engine theory to rebuild this engine. It does, however, help a little to understand some of it when dealing with setting up the timing. In a 4 cycle (also called 4 stroke) engine, the usual description of this cycle starts with: the intake, then compression, then power, then exhaust stroke. During these 4 strokes the crankshaft rotates twice.

Turn the crankshaft clockwise, looking from front, (nut on front/or with flywheel bolts) until the front- #1 piston is at the top. #4 (back) is also at the top.

Both are at the position called TDC- top dead center. You don’t need to worry which stroke is involved at this point. Until the crankshaft and camshaft are in time, just realize that the crankshaft turns twice during the four stroke cycle, and that the camshaft turns once- (half speed).

When the cam gear is installed- temporarily as in one of the pictures below, you can see the relationship. Cam gear is twice as large as crank sprocket. When connected by chain, the crankshaft must turn twice to each cam revolution. This is because while the pistons must go up and down twice (2 crankshaft revolutions) to complete the 4 stroke cycle, the valves must only work once for each cylinder (1 camshaft revolution) during the 4 stroke cycle. I have all the camshaft parts laid out.

Both types, rope and the newer modern timing cover seal are shown. When the old steel retainer is removed, the asbestos rope seal must be removed. Clean up the surfaces and install new type with seal driver…a large ½ drive socket that fits diameter of seal, also works.




Note the dots on crankshaft sprocket and on camshaft gear, turn cam gear until they are lined up. Take camshaft gear off, lube camshaft spacer/thrust washer, and put in place behind gear. The holes in front of camshaft are offset- the gear will only fit one way. Slip chain over sprocket, then place chain over cam gear- keeping it in the same position…watch dots and camshaft holes, and wiggle gear until bolt holes line up.

When in time, the timing marks on both gears will be in line.

Place special washers- have a curved surface that fits in cam gear- and bolts, and torque them to 35lbs. Bend the tab on the washers over.

Place spring in camshaft hole, then thrust plunger. These provide thrust when cover is installed to hold camshaft in place. Put oil slinger on crankshaft in front of sprocket. Install timing chain cover. This probably wont be coming off, so I do use some sealant.

I labeled the bolts sizes. 3 are 3/8-24x3/4, the last is 1”- doesn’t specify where the longer one goes, but- two of the top bolts also get a clip- one holds the oil line that feeds the filter, the other holds the steel fuel line going to fuel pump. It may also be for the different front (reinforced) mounting plate? While the other bolts for oil pan are 5/16-18 x11/16, the four across the front are only x1/2”. The parts books are a little confusing concerning oil pan bolts. They list 4 different sizes, but they add up to more than required, and only two sizes have descriptions of where they fit. The short ones in front are so they don’t pierce the timing chain cover. You need to use a little care here with gaskets. The oil pan gasket is already in place, when you put timing chain cover on- make sure you don’t push pan gasket out of place. No pulley guard for now

I put the flywheel on now because it helps visualize timing with the markings. Put back engine plate in place. Two bolts thru the flanges will hold the plate temporarily. Bolt up flywheel. Two of the bolts are dowels or shouldered. Make sure timing marks are visible in timing hole. It will go on in two positions-correct and 180 degrees out. Torque to 40lbs.

Now that everything is hooked up, you can see the valve timing relationship. Turn the engine clockwise (viewed from front again). As #1 travels down, notice that the intake valve opens. #1 is on the intake stroke. Watches #4, as it travels down, both valves are closed. #4 is on the power stroke. Ignition has just fired in #4. It actually occurs just before TDC- takes a few milliseconds for explosion of fuel-air mixture, and for the power to develop that pushes piston down.

This may be a little confusing, because most manuals, etc. deal with #1 when setting ignition timing and installing oil pump. However, we have just set the crank-cam timing and #4 is on ignition? Easy to fix…!

Before that, set the valve clearance. If you turn crankshaft another half turn again, when #1 starts up, it is on compression. When it reaches TDC again, both valves are closed. This is when valves for that piston are adjusted (when each piston is TDC for ignition). The tappet is not on a cam lobe, and valve is held closed by a spring. Adjust clearance using two ½ inch open-end wrenches. Special thin tappet wrenches are available, but not absolutely required. The clearance on chain drive engines is adjusted to .014 or 14 thousandths. You need a set of feeler gauges that has a .014 piece. Since the tappets and stems have been ground, you may need to play with adjustment to get them close. Hold the tappet with one wrench on the flats. The adjuster is like a regular bolt. Turn right (clockwise /in) to turn it down into tappet, which opens/increases clearance. Turn left (counterclockwise/out) to close/decrease clearance. Valve clearance is important. Too much and engine will clatter as tappet hits bottom of valve stem. Too little and valves will open too soon.
It usually takes a few times to get exact adjustment. You adjust, try feeler, adjust, try feeler again, etc. The clearance is ok when gauge slides with a little resistance.

In the picture, you can see that I hold two wrenches in one hand, hold feeler with other. After major adjustments get the clearance close, by changing which wrench is on top, I can increase or decrease clearance by squeezing wrenches together. I adjust to a loose .014, then make final closing while sliding feeler gauge between tappet and valve.

The firing order is 1 3 4 2. Turn crank half turn again until #3 is coming up to TDC, both valves closed, … adjust them. Same for 4 and 2- half turn, adjust. Try to get clearance exact now. Normally, you will need to adjust again after engine is run in a few hundred miles. But, sometimes it is not necessary.

After #2 is adjusted, another half turn should put you back at TDC for #1 with ignition. This is where you need to be for final steps. If not sure, turn crankshaft until you have seen all the strokes:
Piston going down with intake open- INTAKE
Piston coming up with both closed-COMPRESSION
Piston going down with both closed- POWER
Piston coming up with exhaust open- EXHAUST

You want #1 at TDC, both valves closed, at ignition. This is important because oil pump and distributor must be installed in time to crankshaft and camshaft. You can actually install oil pump in any position, install distributor, and wire from wherever the rotor points, to spark plugs, in firing order. But, for the sake of future jeepers and our kids…. lets try to make all jeeps match the books!


Note how in TM9-803, the #1 spark plug wire is always at 5 to 5:30 clock position, looking down on distributor. OK, for the second photo- you have to turn it upside down and imagine looking at the distributor on the right
side of the block! Strange- manuals refer to engine sides as if you are sitting in jeep- but describe rotation as your looking at front of engine!

This question has come up on G503 many times. When the oil pump is removed, it must be re-installed in time! If you have seen these discussions, there is always a question about finding TDC for #1 at ignition. You can’t trust the flywheel, whistle devices, thumb in #1 spark hole, etc. With head or valve cover off, you should be able to see and establish #1 TDC exactly.

When oil pump is installed, the drive gear engages with the gear on cam. When the gears engage, oil pump turns- The top of gear has an offset slot.

So, you need to turn it back, engage gears, with slot winding up in correct timing position. The bottom of distributor shaft has corresponding key, with offset, that fits into slot. The oil pump drives the distributor. Look down through distributor shaft, slide oil pump part way onto mounting studs. With long screwdriver turn oil pump gear so slot points to 9:30 clock position with fat part on top. When oil pump is pushed to final position, the gears engage, and it should turn to 11/11:30 with fat part still on top.

Put one nut on to hold oil pump in position. Install distributor, you need to wiggle it to get key into slot (remove anti rattle spring for this part). If oil pump timing is correct, the rotor on distributor, will point to 5/5:30. Because of offset, it will only engage in one position. If not correct…drop oil pump and adjust gear position accordingly. Try distributor again until rotor winds up pointing to 5/5:30.

Crank, cam, oil pump, and distributor are now all in time! You can wire spark plugs just as shown. As I mentioned above, you can install oil pump and distributor in any position and wire spark plugs from wherever rotor points. Just go around distributor cap counterclockwise in firing order. But all manuals show #1 firing position as 5/5:30, so we should do it for uniformity.

I’m not making final distributor installation now because of painting etc. When you do install distributor, turn body so coil-wiring terminal is near 11 o’clock. If you haven’t turned engine…rotor will still be pointing to #1. With ignition mark on flywheel lined up with marks on cover,turn body clockwise until points just open. Tighten distributor clamp- should be close enough to get engine started…!

In the final post, I’m going to show all rest of the bolts and plugs, etc. As I mentioned, this engine is replacing a MB motor in a GPW. For this post. this will essentially be a short block with remaining parts coming from other motor.



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