Help! Newly rebuilt engine/engine timing question!

rb6874 · Post by **rb6874** » Sat Sep 06, 2014 9:36 pm

I have a question for which I believe I know the answer, unfortunately...

Forgive me for my lack of mechanical knowledge, but I'll explain it the best I can.

I just received my M38A1 back from my mechanic's shop with a freshly rebuilt engine. The jeep will start up usually only after several engine rotations. Then, when I first take off the she runs fairly smoothly. After it gets warmed up, the engine seems to jump or stutter, and it losses power. It feels almost as though it losses as much power as it gains when I give it gas past 40 mph. Also, the start up is significantly more difficult when the engine is hot.

I took it back to the shop and spoke with an assistant mechanic and asked if he would check that the timing was correct. He put a timing light on it, after working around the shielded cables. The notch in the pulley was lit counter-clockwise from the mark on the cover by approximately 7/8 inch. I am unsure how far that is in degrees. He told me that running the engine timed in advance that far is appropriate, and that it would help the engine run better. He explained the engine issues as the engine just needing broken in.

I felt uneasy questioning his logic, as I have a clear lack of mechanical knowledge.

Does the engine timing/break-in period explanation sound reasonable? Do the symptoms sound related to timing, or anything else specific. Any thoughts or advice would be greatly appreciated.

Post by **wesk** » Sat Sep 06, 2014 10:36 pm

Sounds like a snow job by your shop. Excessive timing advance is not helping your engine break-in. It will make starting hard when hot, can result in excessive pinging and shortens the life of your starter.

Find a shop that works with older engines and take it there.

Your symptoms seem to point to a vacuum leak, or a weak coil that gets worse as it heats up. Worse case would be poorly fitted pistons/rings which will find it harder in the cylinders as they get hotter.

It would help you to put your location in your post. There me a member close to you that can visit and help. You can make a permanent display of your location by entering it in your profile.

rb6874 · Post by **rb6874** » Sun Sep 07, 2014 7:39 am

Thanks for the advice. I live in Lakeland, FL. The coil was replaced while the distributer (and just about everything else) was being rebuilt. I suppose a brand new one could still be bad?

4x4M38 · Post by **4x4M38** » Sun Sep 07, 2014 7:40 am

Wes,
Would a stuck valve in the exhaust manifold cause this kind of problem?

Forgot what it's called. Heat riser valve?

Xamon · Post by **Xamon** » Sun Sep 07, 2014 7:41 am

is the jeep 24 or 12 volt, if they used the wrong coil, or other parts, for the voltage it could be an issue.

rb6874 · Post by **rb6874** » Sun Sep 07, 2014 8:12 am

The jeep is 24v. The distributer rebuild kit was 24v, from the KaiserWillys site.

I believe I am going to do a little more studying and do the timing myself, by the manual, starting with the break point, and going from there. I've never done it before, but I'm hoping if I follow the manual, I'll have success.

Also, if I am wanting to check the valve clearances, should the engine be hot or cold?

wilfreeman · Post by **wilfreeman** » Sun Sep 07, 2014 8:19 am

4x4M38 wrote:Wes,
Would a stuck valve in the exhaust manifold cause this kind of problem?

Forgot what it's called. Heat riser valve?

The m38a1 doesn't have one. Could cause problems in an m38 though.

wilfreeman · Post by **wilfreeman** » Sun Sep 07, 2014 8:25 am

rb6874 wrote:The jeep is 24v. The distributer rebuild kit was 24v, from the KaiserWillys site.

I believe I am going to do a little more studying and do the timing myself, by the manual, starting with the break point, and going from there. I've never done it before, but I'm hoping if I follow the manual, I'll have success.

That's the best way to learn - do it yourself, BY THE BOOK! Always helps to have someone familiar with old engines to help answer questions though. Adjust your valves cold. After you are done, go back and check them again before you button everything back up.

Post by **wesk** » Sun Sep 07, 2014 8:40 am

The offshore coils are problematic right out of the box. It's simple to check. Disconnect the coil and check it's ohms across both the primary and secondary. Then Run her till she gets hot and acts up then make the ohm check again. If it is significantly higher then you need a coil.

I have a good spread of ignition timing photos here:
http://www.willysmjeeps.com/v2/modules. ... _album.php

We have helpful articles here:
http://www.willysmjeeps.com/v2/modules. ... tit&lid=17

http://www.willysmjeeps.com/v2/modules. ... tit&lid=15

http://www.willysmjeeps.com/v2/modules. ... tit&lid=28

http://www.willysmjeeps.com/v2/modules. ... tit&lid=29

rb6874 · Post by **rb6874** » Sun Sep 07, 2014 9:56 am

Thanks guys! You're a wealth of information. I just spoke with my mechanic. He says he'll help walk me through timing it for the first time later this week.

I really appreciate the detailed responses, and all the illustrations, Wesk.

wilfreeman, I clicked the link under your name. I've actually been checking in on your blog for sometime now. I first run across your blog while you were rebuilding your distributor, actually. I've enjoyed the updates. Finding little problems with my rebuild is a little frustrating, but I really am enjoying being able to work on my jeep, now that I do have it back!

wilfreeman · Post by **wilfreeman** » Sun Sep 07, 2014 12:24 pm

rb6874 wrote:Thanks guys! You're a wealth of information. I just spoke with my mechanic. He says he'll help walk me through timing it for the first time later this week.

I really appreciate the detailed responses, and all the illustrations, Wesk.

wilfreeman, I clicked the link under your name. I've actually been checking in on your blog for sometime now. I first run across your blog while you were rebuilding your distributor, actually. I've enjoyed the updates. Finding little problems with my rebuild is a little frustrating, but I really am enjoying being able to work on my jeep, now that I do have it back!

Thanks for following my blog! I try to detail everything I do with my Jeep for the benefit of myself (future reference), and anyone that is working on one of these old things. As you have seen on the blog, I am working on my m100 now. I hope to rebuild the spare engine before the Denton, NC rally in April. I will not be taking the Jeep to the GA rally next month. Keep checking back (or you can subscribe to get a notice when I post an update to the blog).

I hate to say it, but these Jeeps are ~60 years old - there will almost always be something wrong or something that needs fixing. That is half of the fun of the hobby, and the main reason for jumping in with both feet and learning to work on it yourself! The beauty of it is that most of the mechanical stuff can be done with simple hand tools and the manual. These things were designed for the average farm boy to operate and work on.

G740 · Post by **G740** » Mon Sep 08, 2014 5:51 am

If you need help, call me. You would do yourself a favor by purchasing the timing adapter for this job as well. Will make doing the job a snap. You can also statically time the engine with it not running.
John
MWM

Post by **wesk** » Mon Sep 08, 2014 7:43 am

The adapter John mentions is part of a military harness adapter kit and you should keep your eye open for one of these kits. They have several different adapters in them.
http://www.willysmjeeps.com/v2/modules. ... _album.php

Also the links I posted for you in my last post include the directions for static timing. It can be just as accurate as using a timing light. The timing light is useful for checking the amount of centrifugal advance but you can also check the centrifugal advance mechanically by twisting the rotor with your fingers. It should not rotate in one direction and it should rotate about 10 degrees in the other direction and snap back on it's own.

4x4M38 · Post by **4x4M38** » Mon Sep 08, 2014 8:07 pm

This site and its members continue to amaze me.

It is the equivalent of a PHD course in the subject.

BullRun · Post by **BullRun** » Mon Sep 08, 2014 11:07 pm

Don't forget the diagram error on the spark plug wiring in the TM.

The adapter kits are worth the money though not as inexpensive as they used to be.

I came across a NOS Prestolight distributer for the M38A1 and could never get it to work correctly. After extensive checking and frustration I realized parts of it were installed backwards. The reason it was NOS was because it was a reject. There are probably more floating around out there.

It is also good to check the fuel lines for over heating that can create vapor lock.

Once you get the methods down on timing you can go anywhere knowing you can repair it yourself.

Help! Newly rebuilt engine/engine timing question!

Help! Newly rebuilt engine/engine timing question!

Timing