M38a1 questions/ build thread

1952 - 1968, M38A1, M170, questions, discussions, regarding anything related to the M38a1 series.
Post Reply
JM101
G-Private First Class
G-Private First Class
Posts: 10
Joined: Thu Dec 28, 2023 8:28 pm
Location: Central Sierra Nevada Foothills of California

M38a1 questions/ build thread

Post by JM101 » Fri Dec 29, 2023 9:48 pm

Hello all,
Family heirloom jeep I am finally getting around to.
I will update this thread more in time, but for now I am looking for general advice on a backfire. This jeep has been mostly sitting in my grandparent's garage since 1970. I dragged it home a couple years ago and parked it up alongside my shop.

It is finally getting a little time. Did the usual, fresh oil/filter, added coolant, replaced coil, points, condenser, plugs, rebuilt the carb, boat tank-fresh fuel, filled the carb bowl with sthil fuel and fired it. Also soaked pistons/valve train with motor oil several times over the years, but the motor has always spun freely. Checked that the valve train moved freely. I also pre-lubed the engine with air pressurized oil before firing, so it started well lubed and oil was getting up to the rockers.

It ran good on initial startup. As I ran it a little longer it started backfiring after 8-10 minutes of running.
I figured somebody here might have some off the top of the head ideas of things to look out for and/or check.

Initial running: https://youtu.be/Lp7YqmjNB8Y
Video of backfire: https://youtube.com/shorts/cQ-qV3NEhfA?feature=share

I shut it down and haven't fussed with it anymore. I broke the clutch cable, so I am waiting on a new one to come in to see if the jeep will move. I will work on it more then. Hoisted the back end and started it in gear, tires moved forward and back, no weird drivetrain noise. Tires have been holding air all these years.

Couple thoughts I had.
I haven't verified if the valves still open/close properly or re-verified that the top end is getting lube. I only verified top-end lubrication using outside pressure, so I should probably check that the oil pump is lubricating the top end. Perhaps pull the distributor and run the oil pump that way.

The dipstick still shows just oil, doesn't even smell much like fuel.
Plugs are dry, they smell like fuel but that probably doesn't mean much here, though it might.
A bit of steam was coming out of the radiator, I assumed it was the engine warming up. Probably smart to give a quick check for combustion gas, but as I mentioned oil appears to be just oil. I checked it about three days after running it, still just oil.

Anything else that comes to mind for you folks? Most of the time problems are right in front of me, I often find myself thinking "I sure am glad that wasn't a snake," once I figure out what the problem was.

The few bits I know.
Original drivetrain, 4-banger Hurricane motor/ T-90/ ect.
The jeep has been very civilianized.
YF carb
Unknown civilian distributor, mechanical advance. No slot to set timing by rotating the distributor, just one hold down bolt.
12v wiring that fried as soon as I did the 'ol smoke test connecting a battery. Not a single fuse in the system, probably rodents or rotten insulation.
Full set of '60s stuwart warner gauges. MPH, Tach, Water temp, oil temp, oil pressure, vacuum
Heater and radio
The previous owner was my uncle Ben, he had a college education in automotive engineering. He was a B52 navigator that never made it home from the Linebacker II bombing campaign, Christmas 1972 bombing of Hanoi. The M38a1 was one of a collection of classic cars he left behind.

Thanks all for reading and helping out as we get this old jeep going and hopefully back out on the red dirt roads it used to run.


User avatar
Bill H.
G Moderator
G Moderator
Posts: 6228
Joined: Sun May 31, 1998 8:00 pm
Location: Yonna Valley, Oregon

Re: M38a1 questions/ build thread

Post by Bill H. » Sat Dec 30, 2023 9:20 am

Welcome aboard! The second video sounds as if you have a valve starting to stick. You might want to pull the valve covers and check adjustments and inspect the springs for breakage. Do you have a good gas tank?
Bill H.

"Each shall seek his own kind, in other words, a bird may love a fish but where would they build a home together?" Tevye, Fiddler on the Roof

1952 Dunbar Kapple M100
1953 Willys M38A1
1962 AMC M422A1
1965 Stevens M416B1 X 2
1967 Kaiser M715

2 Timothy 3:1-5

JM101
G-Private First Class
G-Private First Class
Posts: 10
Joined: Thu Dec 28, 2023 8:28 pm
Location: Central Sierra Nevada Foothills of California

Re: M38a1 questions/ build thread

Post by JM101 » Sun Dec 31, 2023 6:06 pm

Bill H. wrote:
Sat Dec 30, 2023 9:20 am
Welcome aboard! The second video sounds as if you have a valve starting to stick. You might want to pull the valve covers and check adjustments and inspect the springs for breakage. Do you have a good gas tank?
Thanks for the response Bill.
Valve sticking was my initial thought as well, I will investigate next time I get to working on the jeep.

As to the gas tank question, I sort of have one.
The tank the jeep came with is in fine shape. It was removed, drained and cleaned before the jeep was stored. The tank is out of a '51 mercury, it fits under the seat, has increased capacity, and has the appropriate outlet/ inlet brazed onto it. However, it takes up much needed leg room and I am on the hunt for a new tank at some point, not a top priority though.

User avatar
Bill H.
G Moderator
G Moderator
Posts: 6228
Joined: Sun May 31, 1998 8:00 pm
Location: Yonna Valley, Oregon

Re: M38a1 questions/ build thread

Post by Bill H. » Sun Dec 31, 2023 7:50 pm

Keep us posted on your findings please.

How original are you wanting your A1?
Bill H.

"Each shall seek his own kind, in other words, a bird may love a fish but where would they build a home together?" Tevye, Fiddler on the Roof

1952 Dunbar Kapple M100
1953 Willys M38A1
1962 AMC M422A1
1965 Stevens M416B1 X 2
1967 Kaiser M715

2 Timothy 3:1-5

JM101
G-Private First Class
G-Private First Class
Posts: 10
Joined: Thu Dec 28, 2023 8:28 pm
Location: Central Sierra Nevada Foothills of California

Re: M38a1 questions/ build thread

Post by JM101 » Sun Dec 31, 2023 8:00 pm

Bill H. wrote:
Sun Dec 31, 2023 7:50 pm
Keep us posted on your findings please.

How original are you wanting your A1?
Not worried about originality. This jeep is very civilianized and I have no problem with that. In time, I would like to make it a reliable driver.
Your build is top notch work, I am not looking for anything like that. My mom drove this daily drove this jeep back in high school, I would like her to be able to putter around it in a bit.

parker007
G-Lieutenant Colonel
G-Lieutenant Colonel
Posts: 1195
Joined: Fri Oct 18, 2019 4:35 pm
Location: california

Re: M38a1 questions/ build thread

Post by parker007 » Sun Dec 31, 2023 8:22 pm

does puling choke stop backfiring?

JM101
G-Private First Class
G-Private First Class
Posts: 10
Joined: Thu Dec 28, 2023 8:28 pm
Location: Central Sierra Nevada Foothills of California

Re: M38a1 questions/ build thread

Post by JM101 » Thu Jan 04, 2024 7:07 pm

Fussed with the jeep today, it runs without a backfire.

Replaced the clutch cable, but it won't move under it's own power. I am guessing the pressure plate is toast.

https://midwestjeepwillys.com/917181.html Pressure Plate
https://midwestjeepwillys.com/930731.html Clutch disc


Video if current running condition.
https://youtu.be/Vc_QYFvHcrY

JM101
G-Private First Class
G-Private First Class
Posts: 10
Joined: Thu Dec 28, 2023 8:28 pm
Location: Central Sierra Nevada Foothills of California

Re: M38a1 questions/ build thread

Post by JM101 » Sat Feb 10, 2024 9:46 am

Headed up to clear out a spot in the garage for the M38a1, Clutch kit came in yesterday.
Hopefully will manage to get the jeep cleaned out and parked in the garage today. Not sure how much actual progress I will make dropping the trans, gotta keep up with the honey do list too.

If anyone has sage advice or things to watch out for when changing the clutch I am all ears.

JM101
G-Private First Class
G-Private First Class
Posts: 10
Joined: Thu Dec 28, 2023 8:28 pm
Location: Central Sierra Nevada Foothills of California

Re: M38a1 questions/ build thread

Post by JM101 » Sat Feb 10, 2024 9:59 am

I realized I never actually mentioned much about the solved backfire.

I went through and checked all the valve adjustments and ran the motor with the valve cover/ side cover off. I also went through and smacked all the valves -that I could get to- before hand to make sure they were free. Lubrication was visible with engine running, valve lash was correct.

After all that, no change. I started moving plug wires around the distributor, kept the firing order the same, just moved location of #1... if that makes any sense. Sure enough, that did the trick. Runs like a sewing machine.

Doesn't make much sense to me, because it ran well at first and then began to backfire. I would have thought firing order issue would be always present. Might have been a combination of issues. Either way I have run the engine several times and it fires easy, quickly and runs smooth. I suppose after sitting for 50years the engine is entitled to be a little cantankerous.

JM101
G-Private First Class
G-Private First Class
Posts: 10
Joined: Thu Dec 28, 2023 8:28 pm
Location: Central Sierra Nevada Foothills of California

Re: M38a1 questions/ build thread

Post by JM101 » Sat Feb 10, 2024 1:39 pm

After a little more fussing with the clutch cable and what I could get to through the inspection over. I got the jeep to move under it's own power w/o changing the clutch.
Drove it up and down my long driveway a couple times without brakes, using low range. First time it has moved under it's own power since 1970's.

Backed it into it's home in the garage, it was steaming out the rad cap and overflow pretty good. Did a quick combustion gas check and the blue fluid changed to clear/yellowish. My test fluid is several years old, so I don't fully trust it. Overall, I am pretty sure there is a head gasket issue. I didn't drive it nearly hard/ far enough to get hot enough to boil over otherwise.

The engine also backfired under load. Not too bad, but I am back to the stuck valve theory.
Figuring on ordering a head gasket and water pump for now, probably end up doing more once the head is off.
Going to start looking into brakes as well and figure out what I need there.

User avatar
Bill H.
G Moderator
G Moderator
Posts: 6228
Joined: Sun May 31, 1998 8:00 pm
Location: Yonna Valley, Oregon

Re: M38a1 questions/ build thread

Post by Bill H. » Mon Feb 12, 2024 5:06 am

JM101 wrote:
Sat Feb 10, 2024 9:59 am
I realized I never actually mentioned much about the solved backfire.

I went through and checked all the valve adjustments and ran the motor with the valve cover/ side cover off. I also went through and smacked all the valves -that I could get to- before hand to make sure they were free. Lubrication was visible with engine running, valve lash was correct.

After all that, no change. I started moving plug wires around the distributor, kept the firing order the same, just moved location of #1... if that makes any sense. Sure enough, that did the trick. Runs like a sewing machine.

Doesn't make much sense to me, because it ran well at first and then began to backfire. I would have thought firing order issue would be always present. Might have been a combination of issues. Either way I have run the engine several times and it fires easy, quickly and runs smooth. I suppose after sitting for 50years the engine is entitled to be a little cantankerous.
Great news!!!
Bill H.

"Each shall seek his own kind, in other words, a bird may love a fish but where would they build a home together?" Tevye, Fiddler on the Roof

1952 Dunbar Kapple M100
1953 Willys M38A1
1962 AMC M422A1
1965 Stevens M416B1 X 2
1967 Kaiser M715

2 Timothy 3:1-5

mcj115
G-Sergeant
G-Sergeant
Posts: 48
Joined: Mon Nov 22, 2004 6:15 pm
Location:

Re: M38a1 questions/ build thread

Post by mcj115 » Mon Feb 12, 2024 8:36 am

I got my M38A1 running after sitting ~25+ years and had cooling issues.....before you pull the head I would suggest draining all the coolant from the engine and radiator, remove the thermostat/housing and heavily flush the system with water; I was amazed how much crap came out of the engine/radiator which was plugging the thermostat. I ran with no thermostat and some baking soda for a while to further clean the system. I then drilled a small bypass hole in the thermostat and not it runs in range and well.

Remember that these cooling systems don't have an overflow tank. So if you fill them cold, once they warm up they will purge some coolant. After the fist couple of times getting to to operating temperature the radiator will find it's full point and not purge further.

After the initial revival start and running for 5 minuets of my jeep, I also proactively pulled the pan and removed the layer of sludge and replaced the rear main seal. I did this so when I add a semi modern detergent oil it didn't dislodge sludge and clog the oil circulation.


[quote=JM101 post_id=1965221 time=1707604762 user_id=174419]

Backed it into it's home in the garage, it was steaming out the rad cap and overflow pretty good. Did a quick combustion gas check and the blue fluid changed to clear/yellowish. My test fluid is several years old, so I don't fully trust it. Overall, I am pretty sure there is a head gasket issue. I didn't drive it nearly hard/ far enough to get hot enough to boil over otherwise.

[/quote]

JM101
G-Private First Class
G-Private First Class
Posts: 10
Joined: Thu Dec 28, 2023 8:28 pm
Location: Central Sierra Nevada Foothills of California

Re: M38a1 questions/ build thread

Post by JM101 » Wed Feb 14, 2024 8:54 pm

Setup a hosting account and figured out posting images here, so I can update this thread a little easier.

Pulled the cooling system open, pretty corroded. I have the gaskets in hand, so I will be opening this engine up a little further soon.

Before I started tearing it down, I was able to get the fuel system working. A couple new lines and a filter, primed the pump both directions, and it started pumping. I was gravity feeding it from a boat tank till now.

Image

Image


Post Reply

Return to “M38a1 Technical Knowledge Base”

Who is online

Users browsing this forum: wc56daveyboy and 5 guests