Over this last winter and spring, I rebuilt a GPW engine. 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 disas-

sembly/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 man-

uals (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.

HISTORY

-

this engine came from a GPW that I broke up.

I broke it up, because the body was pretty shot, and it was

before I found the matching number GPW that I sold recent-

ly. Had I known…It would have been a different story. 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 the jeep was still in service.

They were supposed to stamp the original number on

replacement. I guess instructions didn’t say anything about

brand. I pulled the motor out and stripped it. Some cracks

on the head surface were visible, so I took it to a welder who

specializes in block repairs. 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

and if there is a crack... the particles line up. There were

more cracks than I had seen, but nothing that he couldn’t

repair.

This block must have been severely overheated once. Two

cracks went from valve seats to the piston walls, and anoth-

er 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 bro-

ken!. That is not always the case. This engine is getting

rare, if we want original jeep engines, 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 mois-

ture 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 pres-

sure. 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

By

John Barton, USA

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