dean51267

here is the story:

Nearly new 454 mags, new dart heads, new roller cam, elderbrock intake/carb, motor is on dyno now.

#8 shows no compression, NO leak down, distributor is firing, other cylinders strong, 200 lbs compression plus, no vacuum leaks detected, valve springs compress as normal, rockers act as intended.............

Here is my thinking:
No leak down means no failure in rings or valves
No vacuum leak = no vacuum leak
Cam IS timed accurately
Valve train moving means no failed lifters or bad lobe on cam

Only thing I can think of is not enough lobe separation on that particular lobe?

Am I missing something? Cam is new comp cams kit.

Thanks...

TC

Dean, Has the engine run any yet?

dean51267

yes, it fires and runs, but #8 shows no power, or heat at the header tube...

TC

Do you think it has run long enough to get all of the lifters pumped up? It took me a long time of priming to get oil through all of my valvetrain. No heat in the header tube?? No compression?? No leak down?? I must be missing something here.... Will be watching this thread a while longer this a.m. for responses. What else can you tell us about it??

dean51267

I had thought about a lifter not pumping up to, it has run for 5 to 7 minutes, long enough....

The tech guy said the rocker arms were loose when they pulled the valve covers after the motor say for a couple of days (this has been going on for a couple of days).

The guys running the dyno are my clients (I do all their tax/accounting work) and build lots and lots of wicked motors, so plenty of experience there (pulling trucks)

They pulled front end off motor and checked if cam was degreed today, it was.

We looked for a vacume leak, did not find anything. The heads came from another shop (client) they build lots and lots of motors.

Cam has 540 lift, not a wild set up, dual plane air gap intake (new).

Builder is long time small block racer, 40 plus years experience.

I keep thinking either the distributor is screwed or cam is, or I am missing something really, really simple, like lifter not pumpong up all the way.

dean51267

added info - #8 has 80 lbs compression, no leak down, not even 1/2 #

TC

Does not make much sense....but Im sure you have been saying that for a few days now. If you decide its a distributor issue I have an extra Thunderbolt IV complete set up you are welcome to use. Let me know if you are in need of any parts. Ill bet you will get more ideas from the from the OSO members than you will know what to do with before long. Good luck and give me a call if I can be of any help. 270-559-tony

stevesxm

makes no sense really... zero leak down and no compression are mutually exclusive from a mechanical sense if the valves open at all...and i mean AT all.

am wondering/ suggest that instead of leak down w/ leak down tester which puts air in cylinder at VERY slow rate that you put full bore unrestricted 100 psi into cyl at TDC w/ rockers removed. i believe you will hear immediatly where compression going... which sounds suspiciously like a broken second ring or huge end gaps lined up or similar or cracked piston crown or somebody milled a valve eyebrow too deep...

can not see any way on planet timing or camshaft issue... lifter will open valves enough to open valves for compression test w/ zero oil pressure and timing irrelevant and lobe sep same on cyls that DO have comp....

has to be sealing issue in piston/ring/cyl / valve/ package that you aren't seeing because not enough cyl pressure during your leak down to make it evident.

pressurize it full w/ no restriction and it will be immediatly evident. at least thats what i would do.

GOODT

sounds like a bad valve,

when you do a leak down where do you hear air leaking from, That will answer all your questions.........

Lmarth

I agree with the last two posts. I must have said it 3-4 times here in the last few years--Leak it and use your mechanics stethoscope. With the valve covers off and the exhaust manifold off, it should be easy. Best to compare a known good cylinder to the suspect one. Normally, you'll get a good 'whoosh' sound past the rings if you drop the stethoscope probe down into the crankcase via the big oil drain back holes above the cam. Normally, just a little noise in the exhaust port and virtually nothing from the intake if you drop the probe into the intake. This being a NA motor makes that easy. Again, compare a good to a suspect cylinder to calibrate yourself. Let us know what you find.