Clutch?

1950 - 1952, M38, questions, discussions, regarding anything related to the M38.
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Re: Clutch?

Post by Adam » Sun Nov 28, 2021 3:50 pm

If it came down to betting on getting more power from running her for a while and power lost due to timing chain on wrong, i would bet on the chain. Just run it and deal with it later. Wile dallying with it, verify what gears are in all her parts. post a pic of your jeep and her tire size.

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Re: Clutch?

Post by dpcd67 » Sun Nov 28, 2021 6:39 pm

Pretty sure it ain't the chain; it's a stock M38, the OP said. No chains.
And the OP said he had stock 700x16 tires.
Last edited by dpcd67 on Mon Nov 29, 2021 8:48 am, edited 2 times in total.
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Re: Clutch?

Post by Adam » Sun Nov 28, 2021 7:07 pm

Lots of people say stock this and stock that, need numbers to verify. and yea, it probably is a gear, which could be 1 tooth off, which affects valve timing and changes hp and torque ratings at a given rpm, with tires that are 10% bigger, therefore lower rpms as compared to a cj2a at side be side comparrison, hp and torque would be lower in the m38. Sweatin the small stuff here,.

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Scott in NM
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Re: Clutch?

Post by Scott in NM » Tue Nov 30, 2021 6:49 am

Believe me, stock. I've had it 45 years and not changed a thing. I know what it did before, I know what it does now, and I doubt the metal has evolved into something different when I was sleeping. :)

The gear has been visually checked and is not one tooth off. NOS M38 crankshaft was also installed, the part number on the tube matched that in the ORD 9 and was dated 12/53.

Tires are 700x16 NDCC from Coker, about four years old.

Going to check if the Auto Hobby Shop on base has a dynamometer. That should tell me a lot. I'm still thinking it needs to run through its breaking-in period.

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Re: Clutch?

Post by W. Winget » Wed Dec 01, 2021 7:18 am

That would be one Helluva Auto Hobby Shop if it has a Dyno.
None I ever used on base had much more than tools/bays and lifts and those had to be empty by the evening. Fort Stewart had a sandblasting cabinet,(guy was blasting his pistons to clean them, skirts too :shock: must not have run long after that treatment) I seem to recall a lathe in Fort Bennings shop.
But a Dyno? doubt it,

EDIT: The below information is incorrect, the valve length can be adjusted for by the tappets...sometimes overthinking hurts. Instead of pulling the mistake I leave it here for clarity of the posts. W. Winget :oops:

I'm still betting on valve duration due to shorter replacement valves (WWII style like Ron sells) without the rotator caps installed (works, but valve ends up being shorter and less air in, less air out = less HP.... :wink:
V/R W. Winget

9-1804A (M38) dtd 1951
https://books.google.com/books?id=-6GrC ... th&f=false
Pg 73-74
Rotator caps
rotator style.PNG
Fig 62
Last edited by W. Winget on Wed Dec 01, 2021 12:48 pm, edited 1 time in total.
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Re: Clutch?

Post by Adam » Wed Dec 01, 2021 12:15 pm

What does the rotator have to do with valve opening? Or shorter valves have to do with valve opening, tappet is in continous contact with the valve stem, with or without the rotator, so why would the valve not open the same amount on both systems, seems like valve lift equals cam lift in a 1:1 setup like this???

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Re: Clutch?

Post by W. Winget » Wed Dec 01, 2021 12:46 pm

You are correct Adam. Lately working on the Wife's 2001 Jaguar head / valve /timing tensioners replacement has driven me mad...
V/R W Winget

So possibly a reshaped cam, but not valve stem length could be the culprit. Now has anyone ever made a lower performance cam? or is his worn down and the tappets merely adjusted for wear, decreasing lift.?
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Re: Clutch?

Post by dpcd67 » Wed Dec 01, 2021 4:37 pm

As for the rotator caps/lash caps; I do not reuse them; I replace them with WW2/CJ type valves. I have never found a source for the components, so I replace the whole setup.
It doesn't pose any issues.
I know of no aftermarket cams having a different profile.
I never saw an Army Post auto shop with a dyno either.
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Re: Clutch?

Post by W. Winget » Wed Dec 01, 2021 5:48 pm

Perhaps an industrial cam inserted along the line. These may have had different profiles depending on application, i.e. pump vs genset vs welder perhaps matching the (sometimes) smaller intakes.
Heck that may be the issue as well if the smaller restrictive manifold ended up on her sometime down the line.
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Re: Clutch?

Post by Scott in NM » Thu Dec 02, 2021 7:30 pm

In response to Winget, my valves have the valve caps. These were checked when the valve adjusting screw was replaced. Now whether this makes a performance difference I don't know but the design engineers had plenty of practice to work out the bugs.

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Re: Clutch?

Post by dpcd67 » Fri Dec 03, 2021 8:36 am

No the lash caps, and rotating keepers (they have ball bearings in them) have zero to do with engine power; their design feature was to make the valves rotate each time they lifted or retracted. In my opinion, the idea did not work and was not worth the extra expense. And of all the M38 engines I see, they wear out at the same rate and the same way that others do.
However, this is not your problem, at all.
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Re: Clutch?

Post by W. Winget » Fri Dec 03, 2021 12:03 pm

I might be onto something about the manifold, unless you looked at the ports compared to the gasket to see exactly if they are significantly smaller than the gasket when installing, it may indeed be the issue. :wink:
V/R W. Winget
From a previous posts (for example)

viewtopic.php?f=129&t=323265&hilit=Genset+Intake
"Lower HP for the PE-95 is due to a different intake manifold. Bolt on an MB/GPW manifold and you'll see all 60 HP that the MB/GPW engine will deliver."
by sjalbert Wed May 05, 2021 11:48 am

Another:
viewtopic.php?f=129&t=189973&hilit=Genset+Intake
"The genset carbs did indeed have a smaller throttle plate bores(as did the intake manifolds) than the jeep carbs, only 3/4 in. on the Models 567S/572S to the 1in. on the 539S and later."
by Ralph » Thu Sep 01, 2011 11:55 pm

And:
viewtopic.php?f=105&t=158296&hilit=Genset+Intake
"Sounds just like my engine. It was pulled straight out of a PE95 Genset. Waterproof 6 volt distributor, front engine plate with both tabs facing the same way, WO carb, 6 blade fan, single-groove pulley on water pump, WWII style air cleaner, King sealy governor, RMCxxx, Cuno oil filter, WWII-style radiator hoses with metal 90 degree elbow, small-diameter intake manifold, Interesting thermostat. So far I believe it to be one of the best purchases yet besides my M38"
by dfield » Fri Mar 05, 2010 12:33 am
Looking for 1918 Standard B 'Liberty' truck parts


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