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46 cj2a low compression

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heehaw View Drop Down
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    Posted: 23 Jan. 2022 at 7:39am
fighting what i thought  was a carb problem ,  I did a compression test (Cold) 75-65-75-50.  The engine hasn't smoke and plugs weren't oily or black. Oil brought the compression up . Going to do the air compressor test this a.m. but I'm assuming the engine needs a rebuild/ valve/rings .  How would tell if engine original to the jeep. I have a m- 38 engine that went to the machine shop about 10 year ago, got new valves put in. Have new pistons/rings for it.  Was hoping to find a m38  but may have use it unless the cj engine is original.
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Mark W. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark W. Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan. 2022 at 11:38am
If the serial number is within a couple thousand higher of the body serial number very good chance its original. As the engine serial numbers ran higher due to those used in Welders and Generators Pumps etc.

Some one here will know approx. what the number spread was in 46.
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote cpt logger Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan. 2022 at 8:44pm
Mark has the question answered.

With those numbers, I would look hard at installing the M-38 engine now. I doubt that the "Leak-down
test" will be better. It will tell you where the compression is leaking out. The rings are leaking, & the valves probably are as well.

In my world, if the engine in it is indeed the original one, it gets rebuilt right away. If not, it can wait. Either way, I would install the M-38 engine. Yes, it needs reassembled, but you can drive the jeep while this is getting done. This way the M-38 engine goes in when it is convenient for you. Then after the original engine is rebuilt, it is swapped in at your convenience. Thus, the down time is minimal.

After all that, you have a known good M-38 engine that could be pickled and either stored or sold off to generate money for the Willys fund. Pickle it either way. Trust me on this. I can not count how many freshly rebuilt engines I have had to free up when the rings rusted to the cylinder walls after months or years of storage. Not good.

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heehaw View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote heehaw Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan. 2022 at 7:15am
No good news. adjusted valves, no change. Going to pull the head this a.m. and take a look. Calling machine shop about cleaning up the m38. Going thru the parts to see whats short on it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cpt logger Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan. 2022 at 6:39pm
Did you get the "air compressor", or "leak down",  test done? If so what did you find?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan. 2022 at 6:55pm
You said oil brought the compression up. By how much? 

You had initial compression results between 50 and 70, which is low all around. A leak down test is probably going to tell you what you already know. Compression that low, with valves adjusted, and an increase with oil added, means you have worn out rings.

Since you have the other L134 (M38 engine) ready to build the path is clear. 

Were it mine I would go ahead and build that engine, then rebuild the one in the Jeep at my leisure. If you do eventually find a M38 you could then swap them if you wanted to. 
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 heehaw Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan. 2022 at 1:17pm
 Head off. #4 cylinder washed like a small coolant leak. Valves and seats look terrible. No play in pistons. walls aren't scored. Borrowing a mic to see if the holes are outta round. already bored to 30 over.  Head bolts didn't seem tight to to me. 
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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. 2022 at 7:05pm
I would be pleased to find a block that is only bored .030 over. It could be loosing compression from the valves, but that would not explain an increase in compression when you added oil to the cylinders which indicates worn rings.  

  
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 Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan. 2022 at 8:34pm
  It’s almost never “just” the rings or “just” the valves. Both are leaking air. The injected oil will help the rings but not the valves, so compression improves slightly. An engine that is down in all four, as low as this one is, is almost certainly due for an overhaul/ rebuild. Dry/wet low/high better (but not good) readings indicate rings and valves are both in bad shape. 
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!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote wfopete Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jan. 2022 at 9:27pm
If you want the poor mans leakdown test simply bring each cylinder up to TDC and apply compressed air into the sparkplug hole.  A large rubber tipped air nozzle works well here but I've sealed the sparkplug holes) with other things too.  Anyway introduce compressed air into the cylinder and listen.  If air comes out the carb area you have a intake valve leak, if it comes out the tail pipe; exhaust valve leak and if it comes out the oil dip stick tube the air is going past the rings. 

If you have a ring problem as a last resort, you might want to try to put some Marvel Mystery Oil in each cylinder and let it soak in for a week or two.  It may help free up suck rings, if not all your out of is and little MMO and a couple of weeks.

My 2 cents and worth every penny.


Edited by wfopete - 28 Jan. 2022 at 5:38am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote heehaw Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan. 2022 at 6:25am
I'm assuming the oil help seal the valves better. buddy couldn't get a inside mic. Picked up one from harbor freight( not the best) but came up with fore to aft 1 / 3.157 , 2 / 3.155 ,3 /3.160 and  3.162 . port to stern 3.16 ,3.157 , 3.16 and 3.155. Pretty much top of  the spec for outta round . Gonna to find a better inside mic. 1st inclination  is to clean it up, dress up the valves  and throw a set of rings in it. Have the 10 year old gasket set that I don't want to use on the m-38. Wasn't  smoking before, just didn't have vacuum . Numbers on block were milled off at some point. Would buy some time till I get the m-38 engine put together .
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan. 2022 at 12:52pm
  You’re assuming against basic common knowledge that’s been handed down from veteran mechanics to every beginning mechanic for a hundred years. 
  Yep, you’re pretty much at the limit for out-of-round and taper both. A bit over, in fact. But you might “hone the hell out of it” as Pop would say, throw some rings and a valve grind at it, and get by for a while. If you don’t drive it a lot, you may be surprised at how long it lasts. 
BW 
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Happy Trails! Good-bye, Good Luck, and May the Good Lord Take a Likin' to You!

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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. 2022 at 1:07pm
Bruce is, of course right. Squirting oil into the cylinder temporarily creates a better seal on the rings, it does nothing for leaking valves. 

In my youth, when I couldn't afford to do better, I have done as just as Bruce's Pop said to put a worn out engine back into service. 

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 cpt logger Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2022 at 4:03am
No, the increased compression comes from the oil temporally sealing the rings. Why would you assume it affected the valves?

Bruce's Pop might have used oversized rings. Back in his time one could buy 0.003" oversized rings for just this application. Machine shops could also knurl the pistons to fit the oversized bore better. The valve guides could also be knurled to close up the clearances there. Today this is not an option for most folks.

Even without the oversized rings & the knurling this can work for a very short time. While I enjoy rebuilding engines, I would not go to this work without a re-bore & new pistons, valves & guides. For this engine I might reassemble it as is with a new head gasket & run it until the M-38 engine is ready.

I am unsure why no vacuum is an issue. Unless it is needed for the wipers? I do not recall which, but some rigs had electric vacuum pumps to run the valves in the climate controls. Some folks have used these electric vacuum pumps to power their vacuum wipers.

IHTH, Cpt Logger.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote heehaw Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2022 at 8:22am
Your probably right. Really only know what I see #4 had coolant leak as it was washed. valves looked terrible and I  don't know how they were sealing. It would cold start with no smoke , run a little while then act like it ran out of gas. Would start again with hand over carb but die soon as it came off.. A couple buddy's came by yesterday and were of the same opinion.  Clean up the valves, new head gasket and put it back together.  Going put a pint or so of mm oil in the cylinders to see if any drains out faster than others.
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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. 2022 at 8:56am
Marvel Mystery oil is thinner than most engine oil so I am unsure what you expect by whether it drains out faster. It will sometimes free up stuck rings, but you have to give it a couple of weeks to work. Certainly would not hurt anything, but I don't think there is any magic potion in a bottle that is going to fix your engine.

I remember using oversized rings years ago, but don't know if you can get them nowadays. 
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 heehaw Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2022 at 9:04am
Your probably right. Really only know what I see #4 had coolant leak as it was washed. valves looked terrible and I  don't know how they were sealing. It would cold start with no smoke , run a little while then act like it ran out of gas. Would start again with hand over carb but die soon as it came off.. A couple buddy's came by yesterday and were of the same opinion.  Clean up the valves, new head gasket and put it back together.  Going put a pint or so of mm oil in the cylinders to see if any drains out faster than others. mainly #4
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Post Options Post Options   Thanks (0) Thanks(0)   Quote heehaw Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2022 at 9:07am
I would just see if #4 drained out a lot quicker ( broke ring?)
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