Boy, didn't know there would be a fight over a simple question. To answer a couple questions, yes the car runs better cold. I have driven it on the street but only put about 150 miles on it. As far as ring break in, there are half a million opinions on how to break in molly rings. I did the 20 - 30 minute cam break in and have done various driving from just cruising to full on wot. Maybe the rings haven't seated yet, but it seemed odd that compression would drop when hot. It seems to go against the law of physics. As far as the cylinders go, it was bored .040 over, brought home from the machine shop and assembled. The heads were milled .006 to true up a .005 variance found from end to end. The valves were checked by the machinist and reground accordingly. Valve guides were also checked and reconditioned or replaced accordingly. Anyway, I will perform a leakdown test as soon as the tester gets here. Thanks for trying to help.
Low compression when hot
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Started by adjusting the valves to zero lash and then 1/2 turn. I had the same thought about too much preload and readjusted them to zero lash and tested again. Same problem. That's when I put in a set of antipump up lifters to eliminate that possibility.
Things were exactly the same with the previous lifters, which were not antipump up lifters.
You seem to be clumping anti pump up lifters into the same class as Rhoads variable duration lifters. 'Taint the same thing. Anti pump lifters are designed to allow the engine to rev much higher than a standard lifter. That is their ONLY function. PERIOD. Over and out. Roger Wilco.
Anti pump up lifters also MUST have an adjustable valve train, because their adjustment varies from almost NO preload to .002" LASH. Yup. You read that right. Anti pump up lifters are NOT supposed to have any preload at all to speak of and they run best with about .002" lash. So if you're running anti pump lifters with preload, that ain't right.
Anti pump up lifters also MUST have an adjustable valve train, because their adjustment varies from almost NO preload to .002" LASH. Yup. You read that right. Anti pump up lifters are NOT supposed to have any preload at all to speak of and they run best with about .002" lash. So if you're running anti pump lifters with preload, that ain't right.
Darthomas
Ashamed to be seen in foreign cars
Then I agree with those who are suggesting valve lash and stem length growing from heat, or rings not really seated yet.
Yes. Existed before. That was the reason for swapping then.
DARTH V8R
It's a TRAP!
Lol. Did you check the compression in other cylinders as well? Put oil in the low cylinder and check again? You seem to be wasting a lot of
money when the basic checks will tell you the whole story.
money when the basic checks will tell you the whole story.
How many times did I beat on the air test? After awhile, this becomes cheap entertainment.
MOPAROFFICIAL
Oogliboogli
In my experience if the valves are hung open with some decent camshaft you'd be lucky to see any reading at all on a compression gauge when testing, especially with an exhaust valve hung open.
Things that could potentially cause the problem you are encountering could be wrong size rings, major bore taper, as well as fuel washed cylinders. That along with some of the others mentions. best of luck and don't let old buzzards bother you too much.
Things that could potentially cause the problem you are encountering could be wrong size rings, major bore taper, as well as fuel washed cylinders. That along with some of the others mentions. best of luck and don't let old buzzards bother you too much.
T56MaxTorq
Well-Known Member
Sounds like a leak down test is in order to truly find the issue. I'd suspect the exhaust valve is slightly hung open when hot. Hopefully it's just an adjustment problem.
magnummopar
Well-Known Member
I asked about oil because if you put synthetic in it too soon, rings will never seal but you dont seem to want to answer that question . BTW moly rings will take more than 150 miles to break in
I'd hate to think that you thought I was ignoring you. 20w50 valvolive racing oil.
Natural oil.
magnummopar
Well-Known Member
no worries, regular oil is great! There seems to be some difference between what you said and what popl are thinking, did you do comp on all cylinders or just one?
All cylinders across the board. I really didn't think this would end up being this big of a discussion. I just found it odd that it would be lower when hot. Seems it should be higher when hot. Most of what had been said here I've either done, thought of, or am in the process if doing. My original question was posted out of curiosity and to see if anyone has seen this before. I appreciate all the advice, though.
Rings usually are fully expanded at around 170 degrees, so it shouldn't "loose" compression.
yellow rose
Overnight Sensation
If the bores were finished correctly, and the rings weren't dunked in oil then the rings should have been 90% broke in BEFORE it fired. If it takes more that a heat cycle, maybe 2 you didn't finish the bores correctly.
I see very little ring seal gains from miles and miles and miles of run time.
yellow rose
Overnight Sensation
No offense but if your moly rings take more than 150 miles to break in you need to correct your procedure.
Moly rings were developed because they have almost ZERO break in requirements. Dealerships used them because they didn't even have to hone the bores on a warranty job and the rings would seat.
Moly is pretty much outdated tech for anything but a dead stocker. NOS and forced induction pretty much kill moly rings.
To the OP, if your rings are not yet seated, pull the engine and get it to a shop that can hone a cylinder.
I suspect RRR is correct. You are not using the anti pump up lifters correctly. Most of the time, the APU lifters clatter on start up when adjusted properly.
In solid tappet applications, I have never seen lash close up with heat.
Roger wilco...that's a good one.
yellow rose
Overnight Sensation
You do realize that static ring tension has little effect on ring seal right?
Rings function from compression pressure. The better the engine, the less radial tension rings have.
I used chrome molly rings in a 340, sealed from the start up. I didn't have it bored, but it was honed by a great machinist
nm9stheham
Well-Known Member
I was gonna say, if the hone finish is right, Moly rings will break in fast and the OP sounds like he has loaded them reasonably. Hone finish is still a question.
And thanks to RRR and others on the anti-pump-up lifter information .....I never have distinguished them from Rhoads lifters. I have some remedial reading to do.
OP, you brought in an interesting problem and everyone is excited....that is the way it works here. Ain't the internet great?!?....LOL
And thanks to RRR and others on the anti-pump-up lifter information .....I never have distinguished them from Rhoads lifters. I have some remedial reading to do.
OP, you brought in an interesting problem and everyone is excited....that is the way it works here. Ain't the internet great?!?....LOL
Not to nitpick, but there is no such ring as "chrome moly". You either have regular cast rings, moly rings or chrome rings.
Yellow rose, if you don't mind........you say moly rings are outdated. What do you recommend for a good performance street build?
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