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Compression

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Beach Bum View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Beach Bum Quote  Post ReplyReply Direct Link To This Post Topic: Compression
    Posted: 26 Jan. 2023 at 1:05pm
The motor in my ‘48 has compression in all cylinders between 70 and 75 PSI what I find a bit curious is that although I know that that is no bueno it is so even across all 4 cylinders. Here’s the thing though; it runs very, very well. So well that I question the wisdom of doing anything about it. The motor is quite easily able to push the Jeep way beyond speeds I want to go (I’ve had it up to 50 mph and that’s more than I want to go, 45 is my limit). What might I be missing in power and driveability? I have big hopes of going on the FCT this year, would it be a problem?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan. 2023 at 1:30pm
If it runs "very, very well", "pushes the Jeep way beyond" speed you want to go, and the rods aren't knocking I would say keep driving it. 
If you can't get there in a Jeep you don't need to be there!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joe DeYoung Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan. 2023 at 1:46pm
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Bruce W View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan. 2023 at 1:56pm
  Any deficiencies will be magnified at higher elevations. 
BW 
It is NOT a Jeep Willys! It is a Willys jeep.

Happy Trails! Good-bye, Good Luck, and May the Good Lord Take a Likin' to You!

We Have Miles to Jeep, Before We Sleep.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote IronAge52 Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan. 2023 at 1:04am
If its not broken don,t fix it, you could be opening up a can of worms and years of down time.   I      speak   from wisdom and experience.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Willy Nilly Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan. 2023 at 8:48pm
Try another gauge and make sure there are no leaks.  Or check your gauge on another motor.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ron D Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan. 2023 at 8:57pm
Originally posted by Willy Nilly Willy Nilly wrote:

Try another gauge and make sure there are no leaks.  Or check your gauge on another motor.

And were all the spark plugs out --- and the throttle was wide open?

And after the "dry" test, if you give each cylinder a squirt of oil to take a "wet" compression test, do the readings change much?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 48walker Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan. 2023 at 8:57pm
I agree with WillyNilly, first thing I thought-do you trust your compression tester?
But yeah, if it's running great, I'd just run it
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan. 2023 at 9:57pm
I don't worry much about the accuracy of the reading of a compression gauge if the results of all four are consistent and within acceptable boundaries, but it would be helpful to do the wet test suggested by Ron.

Even an inaccurate gauge will show if there is a significant difference with the wet test. That tells you if the compression loss is from worn rings, or leaking valves.
If you can't get there in a Jeep you don't need to be there!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote athawk11 Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan. 2023 at 11:24pm
Did you test the compression with the engine warm or cold?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Beach Bum Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan. 2023 at 11:53pm
To be honest it’s been 2 years and I don’t recall how I did the test(s) I know the numbers because I wrote them down. I will get a chance next week to do it again following the advice given by you fine gentleman. My concern is that I am fortunate enough to go on the FCT that my engine won’t be up to the task when getting up to 10,000 ft and above. I do not know how compression would affect performance at those altitudes.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2023 at 12:13am
Originally posted by Bruce W Bruce W wrote:

  Any deficiencies will be magnified at higher elevations. 
BW 
BW 
It is NOT a Jeep Willys! It is a Willys jeep.

Happy Trails! Good-bye, Good Luck, and May the Good Lord Take a Likin' to You!

We Have Miles to Jeep, Before We Sleep.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2023 at 9:03am
Originally posted by Bruce W Bruce W wrote:

[QUOTE=Bruce W]  Any deficiencies will be magnified at higher elevations. 
BW 
X2 especially true concerning the compression numbers and ratio 
That’s exactly why Willy designed special F heads for use at high elevation operation above 5000 and 10,000 feet.


Edited by oldtime - 28 Jan. 2023 at 9:09am
Currently building my final F-134 powered 3B .
T98-A Rock Crawler using exclusive factory parts and Approved Special Equipment from the Willys Motors era (1953-1963)
Zero aftermarket parts

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Beach Bum View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Beach Bum Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2023 at 1:24pm
Well, Pappy, that’s what I alway thought. Old time unfortunately an F head isn’t an option on a L134 motor but I do have a NOS head that I could get shaved down. I read somewhere an article about the maximum that should be removed was. Anybody think that I should pursue that. And, I will take a series of new compression tests next week and do will do all the variations suggested here.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2023 at 1:37pm
I don’t know how much a guy can shave an L head without valve clearance issues. 
I’m sure someone on here has qualified experience with that.

I do know that the compression ratio can go “way” up.
Preignition is basically never going to happen on the Willys using 87 octane gasoline.
These were designed to run on 69 octane uncracked gasoline.




Edited by oldtime - 28 Jan. 2023 at 1:44pm
Currently building my final F-134 powered 3B .
T98-A Rock Crawler using exclusive factory parts and Approved Special Equipment from the Willys Motors era (1953-1963)
Zero aftermarket parts

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark W. Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2023 at 2:16pm
Oldtime I don't know the limits but my engine has had the head shaved .035" which gives the combustion chambers the same dimensions and volume as the Kaiser Supersonic head. And my Block has been decked .007" So on an engine without a decked block I know you could shave a head at least .042" and still be OK.

I did some round measurements and I am certain I could have shaved the head another .008" to .010" with no valve problems. I decided to go at this gradually.

With a .015" compressed Fel-Pro head gasket I am getting 7.2-1 Static compression ratio. The copper gaskets I had a could guy measure were much thicker and would have negated some of my head work.

YMMV
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2023 at 2:19pm

I wouldn't even consider shaving a NOS head, or any head that didn't need it.

As you already plan to, do do the compression tests, wet and dry, to find out where you are loosing compression. 

A shaved head is not going to help much anyway if you have leaking valves or worn out rings. 




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Post Options Post Options   Thanks (0) Thanks(0)   Quote Beach Bum Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2023 at 2:24pm
I read that problems (maybe “quench”) would start to cause problems before valve clearance could become an issue, performance would start to go back down again even with the higher compression ratio.

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