Compression |
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Beach Bum
Member Joined: 21 Sep. 2019 Location: Seattle Status: Offline Points: 936 |
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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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Oldpappy
Member Joined: 09 Apr. 2018 Location: Tennessee Status: Offline Points: 4908 |
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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.
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If you can't get there in a Jeep you don't need to be there!
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Joe DeYoung
Member Sponsor Member x 2 Joined: 20 July 2005 Location: Madison WI Status: Offline Points: 3362 |
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2X... Enjoy it!!
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Joe DeYoung
to many jeeps, parts, and accessories to list here, but apparently enough to keep me in trouble with my wife. |
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Bruce W
Member Joined: 29 July 2005 Location: Northeast Colorado Status: Offline Points: 9651 |
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Any deficiencies will be magnified at higher elevations.
BW
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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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IronAge52
Member Joined: 22 Aug. 2016 Location: San Diego Status: Offline Points: 257 |
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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. Jerry San Diego.
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gearwrencher
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Willy Nilly
Member Joined: 23 Aug. 2022 Location: San Diego Status: Offline Points: 106 |
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Try another gauge and make sure there are no leaks. Or check your gauge on another motor.
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1946 Willys CJ2A military clone
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Ron D
Member Joined: 27 Oct. 2019 Location: South Carolina Status: Offline Points: 1441 |
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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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1951 M38
1951 M100 |
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48walker
Member Joined: 17 Mar. 2017 Location: Wisconsin Status: Offline Points: 366 |
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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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Oldpappy
Member Joined: 09 Apr. 2018 Location: Tennessee Status: Offline Points: 4908 |
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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.
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If you can't get there in a Jeep you don't need to be there!
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athawk11
Member Joined: 18 Jan. 2012 Location: Arvada,Colorado Status: Offline Points: 4151 |
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Did you test the compression with the engine warm or cold?
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1- 1946 CJ2A
2- 1949 CJ3A |
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Beach Bum
Member Joined: 21 Sep. 2019 Location: Seattle Status: Offline Points: 936 |
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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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Bruce W
Member Joined: 29 July 2005 Location: Northeast Colorado Status: Offline Points: 9651 |
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BW
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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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oldtime
Member Joined: 12 Sep. 2009 Location: Missouri Status: Offline Points: 4184 |
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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 |
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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
Member Joined: 21 Sep. 2019 Location: Seattle Status: Offline Points: 936 |
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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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oldtime
Member Joined: 12 Sep. 2009 Location: Missouri Status: Offline Points: 4184 |
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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 |
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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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Mark W.
Member Sponsor Member Joined: 09 Nov. 2014 Location: Silverton, OR Status: Offline Points: 7986 |
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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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Chug A Lug
1948 2A Body Customized 1949 3A W/S 1957 CJ5 Frame Modified Late 50's 134L 9.25"clutch T90A D18 (1.25") D44/30 flanged E-Locker D25 5.38 Since 1962 |
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Oldpappy
Member Joined: 09 Apr. 2018 Location: Tennessee Status: Offline Points: 4908 |
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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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If you can't get there in a Jeep you don't need to be there!
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Beach Bum
Member Joined: 21 Sep. 2019 Location: Seattle Status: Offline Points: 936 |
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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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