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Discussion Starter #1
rebuilt the carb on the 70 Cougar. Edelbrock Performer 1405. runs good. no leaks. replaced the bent metering rod. the exhaust from one side feels hotter than the other. could this be mixture issues? also, one side's compression is good, the other side has three bad cylinders. i guess this could cause that side to run rich and be cooler too? thanks-

billy
 

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what do you mean, bad cylinders? This could cause the difference in temp.
 

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Discussion Starter #3
what do you mean, bad cylinders? This could cause the difference in temp.
three cylinders on the right side, the cool side, only have about 75 psi compression. all four on the left bank have around 120 psi. so until i get the valve job, should i lean out the right side?
 

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There is no way to lean out just one side on non F/I engine, The cylinders pull fuel mixture from the manifold to whichever cyl. is ready to fire. If you lean out the mixture, you lean it out for all the cylinders.
 

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75 psi... Time for a complete rebuild. I don't think just a valve job will fix it. I think it will needs new rings as well.
 

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Discussion Starter #6
75 psi... Time for a complete rebuild. I don't think just a valve job will fix it. I think it will needs new rings as well.
after squirting some oil down the spark plug hole of the offending cylinders, the compression did not come up. do you still think the rings are bad?
 

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Yes, Most likely the rings got carboned up and are stuck in the piston lan, or broken rings. Squirting oil in the cyl won't help that. Are you getting a lot of blow by in the PCV system? This would reflect compression loss past the rings.
 

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Yes, Most likely the rings got carboned up and are stuck in the piston lan, or broken rings. Squirting oil in the cyl won't help that. Are you getting a lot of blow by in the PCV system? This would reflect compression loss past the rings.
good question. how would i know if there was blow by in the PCV system?
 

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In your first post, you said the engine was running good, so don't worry about the compression. If it starts to burn a lot of oil, then you will know it's rings, and then you will have to make a decision.
 

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75 lbs in 3 cylinders, and no increase in compression between a dry, and a wet compression check means a valve sealing problem, not rings. You need a valve job. To check for blow by, pull the pcv out of the valve cover , and remove the oil cap. Run the engine, and look for smoke coming out of the valve covers. Bad cylinders will cause puffing of smoke. Steady flow of smoke usually means all cylinders are blowing by, and pulsing means individual cylinders. Bad valves generally will not cause blow by, unless the exhaust valve guides are seriously worn.
 

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Ok, looks like you got an opinion in every direction on this one..lol With the info provided I can't believe it's running good with three cyl down to 75 psi, and the exhaust temp cold on that side indicate to me all three or at lease one cyl is not firing. Might be running Ok on five or more cylinders, but not all eight. If the exhaust temp is cold on one side the cyl isn't firing and is not going to produce blue smoke if it's not burning the oil going past the rings. If there is already oil going past the rings adding more oil won't help the compression reading. Why I suggested to check for blow by in the PCV system.
Regardless wheither it is a valve seat or ring issue you are going to have to remove the cyl heads. You might have a ahh moment on one the low compression cylinders and find the seat worn or a burnt valve. At that time you can checkout the cyl wall and look for scoring and wear. If you find nothing with the valves then do a full on rebuild. If I were a betting man my money would be on bad rings.
 

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Discussion Starter #12
thanks for all the ideas. i see zero PCV blow by on either side. and since my last oil change 4,000 miles ago, dip stick still shows full. everything points to the heads/valves. once those come off, i will know more-
 

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Ok, looks like you got an opinion in every direction on this one..lol With the info provided I can't believe it's running good with three cyl down to 75 psi, and the exhaust temp cold on that side indicate to me all three or at lease one cyl is not firing. Might be running Ok on five or more cylinders, but not all eight. If the exhaust temp is cold on one side the cyl isn't firing and is not going to produce blue smoke if it's not burning the oil going past the rings. If there is already oil going past the rings adding more oil won't help the compression reading. Why I suggested to check for blow by in the PCV system.
Regardless wheither it is a valve seat or ring issue you are going to have to remove the cyl heads. You might have a ahh moment on one the low compression cylinders and find the seat worn or a burnt valve. At that time you can checkout the cyl wall and look for scoring and wear. If you find nothing with the valves then do a full on rebuild. If I were a betting man my money would be on bad rings.
I will take your bet, any amount. Bad compression rings would show an increase in compression with a wet check. This is what I have done for a living, for over 40 years. The low compression is from a valve problem. Oil burning is caused by issues with the oil control ring, or valve guides. I have seen engines that burn oil with good compression, and not burned oil with bad compression. The oil ring does not control compression, and vice versa.
 

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Discussion Starter #15
those compression numbers were a bit old so I took them again today. it's not a pretty picture-
1-25
2-40
3-155
4-0!
5-165
6-160
7-153
8-155
those were all dry tests. wet tested the three lowest and one and two came up five psi. four was still at zero. so now what do you think? gotta' say the old 351W does pretty damn well on five cylinders!
 

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Hmm maybe bad head gasket
Or valves set too tight hanging the valve(s) just off the seat? Is it a solid cam? Wow zero, man something is way wrong
Kevin
 

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I stand by my diagnosis. 0 lbs, wet or dry, with no blow by tells me this is not a ring or piston problem. A 5 lb increase on a wet check does not worry me. A head gasket blown badly enough to have 0 compression would have to be between 2 cylinders, or you would be able to hear it , or would have blow by, and # 3 has good compression. I do believe you need a valve job, unless you have recently tried to adjust the valves. I cannot speak for the overall condition of the engine, but the current issue is valve related.
 

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How do you define "feels" ?

Is this "feels" in a scientific sense, i.e. measured with a thermometer, or similar device ?
Or is it "feels" judging by holding your hand near it and estimating ?

There's a big difference.

Recently I was running in a cam, and was scratching my head trying to figure out why one header was glowing red hot, and the other wasn't.
After running the gamut of checks, timing, lean mixture etc, and fearing the worst, I later realised it was only hotter than the other because the design meant that on that side, the pipes were touching each other, and heat wasn't being dispersed so easily !! :bloated:

Never overlook the obvious, grasshopper. :wave:

Judging by your compression figures, it certainly seems like you have a head, or valve train related problem.
How is the valve adjustment ? Is there a lot of valve noise ?

There are many possibilities !!
 

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Discussion Starter #19
no valve noise. no cloudy oil on the dipstick. coolant in the radiator is clear green, i can see the top row. no overheating issues. like i say, runs pretty well for as bad as the compression numbers are. heads are coming off. i will know more then-
 

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Discussion Starter #20
p.s. hydraulic valve lifters, so no adjustment available as far as i know-
 
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