M38A1- Need engine rebuild advice

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Hank Dodge

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I've got a '64 M38A1 that is in pretty darn good shape.... except for the engine. It had low compression and smoked a fair amount, then an issue with the exhaust valve on the #4 cylinder had me take it off the road. At this point, I'm guessing that the engine needs to come out and get torn down. I'm trying to find a shop somewhat local that could handle the job. I just don't have the space right now to be able to yank the engine out and leave a dead vehicle for any length of time.

I'm hoping that I could get some recommendations from folks as to anything special I should be looking for in this process. I'm already planning to have everything balanced as part of the rebuild. Any thoughts on anything that needs to be done to make this vehicle more reliable in the long term? What about clutch & pressure plate replacements that might be better than what came stock? Just trying to think of anything that I'd be into as part of this that could be improved upon over the stock / surplus parts.

Also...I'd be really interested if anyone has a recommendation for a shop that could handle the work within a few hours drive of San Jose, CA.

Thanks
 

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teletech

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Hey neighbor!
There are known solutions to most of the issues.
An electronic ignition module is a big help, www.pertronix.com is one source.
There are a couple clutch mods, not usually so much around the pressure plate and disk as around the linkage. There is a hydraulic setup and also one using a chain that are both said to be far superior to stock. Of course, if you don't appreciate the sudden veer of the steering when braking there is a saginaw conversion...
basically, the better you make your Jeep, the more you wind up modifying it. Finding a balance that works for you is important.
They have a ton of resources and a great knowledge base so I would ask over on EarlyCJ5.com

 

Hank Dodge

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Thanks for the reply. Any thoughts on someone local to do the work? I thought I had a guy up in Santa Rosa who was willing to take on the project, but he never got back to me about it. I've had a couple people recommend Clark's Machine Shop in Cupertino. They sound like a good source for the machining, but they don't really sound like they have the military vehicle experience for the R&R.

Good thought on that CJ5 forum. I keep forgetting that a lot of this vehicle crosses over....
 

teletech

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I've been doing all my own work for so long I can't really say but for the very rare times I don't DIY, the folks at Scotts Valley Transmission have always been knowledgeable and straight shooters.
Once again, they won't specific MV experience but they are well regarded.
If you are in SV anyway, talk to Eric over at 4x4 and more. They will at least recognize the early CJ-5-ness of it and respond accordingly and Eric seemed like a stand-up guy and capable mechanic back when I had a shop in that complex.
If I didn't have my CJ-5 front clip all torn down at the moment I'd offer to help out.

I do recommend spending the time to balance both the big and little ends of the rods, it's not a performance vehicle but it really does make for a nice idle.
A lot of the balancing of pistons, rods, and such doesn't call for much skill, just patience. That means with a scale, Dremel, and some time you can save some real money doing it yourself.
If you aren't cost-averse, I'd also ceramic-coat the exhaust, helps get a little more heat out of the engine compartment. Use Jet-Hot or somebody reputable (I do NOT recommend the guy in Santa Cruz).
Good luck with it.

An M-37 too, nice. I do miss mine from time to time.
 

NDT

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Call Surplus City Jeep Parts and see who they recommend. Nice Jeep! Is it original USMC? Might have that limited slip front axle?
 

Hank Dodge

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Yep....It's a USMC, supposedly off of the base at Barstow. I think that we are the third owner if I'm not mistaken. It does have the limited slip differentials on both ends. Some things have gone missing over the years, but I've been trying to put it back as correct as possible. It's been hard to find some of the late model USMC stuff.

This was a project that I started with my Dad. Unfortunately, he passed away early last year. I haven't been in a position to get back into this before now, but it is something that I want to keep along the path of doing things right as I do them. Time and money never seem to come together at the same moment. Now, I also find myself limited by space to work on certain things. If I can get the engine up and running well, I should be back to a point where I can continue working on the rest of it myself.
 

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Hank Dodge

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Well....The M38A1 is back on the road finally! It's got a few glitches that still need to be ironed out, but I've got it back in hand with a rebuilt engine. I ended up taking it to Clark's in Cupertino....Bad, Bad, Bad choice of places to do the work. I'm hoping that the engine machine work was done to specs. They sure as heck don't understand military vehicles, or bother at all with the details of the installation process. Lots of loose fasteners, oil and vacuum leaks, things out of place etc. I really wish that I would have had the place to R&R the darn engine myself. I would have liked to had the time to clean things up a bit in the process.

At any rate, it's been great driving it again. It runs well, but has what seems like a miss under load. As the RPM spools up, it starts backfiring out the exhaust. Running with the choke pulled out seems to help things a bit. Timing is set at 5 deg base, with it climbing to about 20 deg total advance. Does that sound right? Any thoughts?

Thanks
 

exhogflyer

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With modern fuels I'd bump that to at least 10 deg BTDC. Backfiring could be several things, but make certain the points are gapped correctly . Vertronix makes an electronic replacement for the points plate that works very nicely ( I put one in mine)
 

snowtrac nome

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sounds like a lean mixture in the carb. and yes bump the timing I remember my m37 said it would burn 68 octain gas even the 87 is usually closer to 90.
 

JEB

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Of you're thinking about better deliveability and more power, I've stumbled across two classified ads for M38A1s re-engined with Buick V-6s...The same engine offered as an option in pre-AMC CJ-5s.

Just put of curiosity I looked online and couldn't find any correct 4s for sale.
 

cucvmule

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Yep....It's a USMC, supposedly off of the base at Barstow. I think that we are the third owner if I'm not mistaken. It does have the limited slip differentials on both ends. Some things have gone missing over the years, but I've been trying to put it back as correct as possible. It's been hard to find some of the late model USMC stuff.

This was a project that I started with my Dad. Unfortunately, he passed away early last year. I haven't been in a position to get back into this before now, but it is something that I want to keep along the path of doing things right as I do them. Time and money never seem to come together at the same moment. Now, I also find myself limited by space to work on certain things. If I can get the engine up and running well, I should be back to a point where I can continue working on the rest of it myself.
The Bronco looks to be in Great shape also, yours?
 

cucvmule

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Congrats on getting the M38 back and running. Now you can pick one problem at a time and fix, adjust.

I agree that an off idle carb problem may be the problem. Try spraying some gumout in the carb while it is running and spray some in the vent tube to get inside the float bowl. You may get lucky and it helps. An air bleed may be clogged.

Or one of the exhaust valves need adjustment. Points may need adjustment, a bad fouling spark plug, or is the timing really at 5 degrees advanced. The timing could be less, may need to advance distributer more. Retarded time will cause the backfire also. So many different things that can have the same symptoms. But I am going with the off idle air bleed because choking the carb richens the mixture, but then after that it should not backfire, but may stutter.

Look around and find a person that can work on pre pollution control vehicles. Remember one change at a time as to see if you are chasing the same problem or you may make a new one. Very simple mechanics going on you just need to understand what is happening.

I am not going to say find an old guy.:whistle:
 

Hank Dodge

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Thanks for the thoughts. Timing was checked with a light against the marks on the front cover. It's set at the 5 deg mark at idle. How much total advance should I see and at what RPM? I'm wondering if my advance is working as it should. I do have a NOS distributor on hand that I think I'll try swapping in.

I did find a decent vacuum leak where they had neglected to tighten the line fittings by the pcv valve. That made it idle nicer, but it didn't seem to have any effect on the back firing under load. Maybe it is still just a partially clogged jet. I did run a couple cans of SeaFoam fuel system cleaner into the fuel tank and am running it through the system. Do these carbs have any adjustment to make them richer them under higher throttle?

cucvmule..... Yes, the Bronco is mine. It's a 1973 with the 302 and the automatic transmission. I've had it about 15 years I guess. It's a great utility vehicle and a really comfortable little rig.
 

jnissen

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Under load popping is indicating weak spark. Verify all your plugs and wires are in good shape. A faulty cap and rotor can cause this as well.

Once you fixed the vacuum leak did you readjust the idle mixture screw? It will pop primarily when you let off throttle if mixture is off.


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Hank Dodge

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So....I swapped in an NOS distributor with a Pertronix kit installed. Set the base timing at 10 degrees. The advance seems to spin up smoother than it did, and it runs well up until the point it starts popping. Pulling the choke out a bit seems to allow it to get past that point. Is there a way to adjust the mixture at the upper end?
 

TGP (IL)

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NO, I don't think so,
other than re-jetting to a bigger jet, I guess that could be a altitude issue.
Are you high up in the hills?

Otherwise could be a fuel restriction issue.
Tom
 

jnissen

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So timing is OK and did you adjust idle mixture screw. I typically adjust in till RPM just starts to fall then back out about 1/8.

I bet you have fuel delivery issues. At higher RPM the pump needs to deliver a lot more fuel. Your needle, carb bowl , and of course the main jet need to be clear of gunk. If it sputters at RPM but then you let off and it recovers sounds like fuel.

Ignition cutting out is also normally under load but it’s much more abrupt when it kicks out. Fuel tends to be a softer hit. Make sense?


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