Compression Problem
 

Here we go... 502 mag, Wiped out cam on mothers day, had motor rebuilt w/ minor upgrades, head work, cam (Reputible local machine shop) He knows the difference between auto and marine application after inital cam break in, lanched boat for initial run, felt fine but noticed a squeek after about ten minutes of run time. Could not pick up location but with mechanic on with me it did not sound serious. 40 min later making different random rpm changes squeek changed pitch (high to low) then quit. Had decided that it had to be a alternator bearing or something of that nature. Then it hit! running around 34 to 3600 Rpms the motor developed a miss I mean the damn thing developed a shudder, pulled wires of dist foud that 1 and 7 had no change. checked compression on the two suspects, barely moved needle on gage. Called motor builder, he said he would pull heads and fix whatever it was (covering his ass) well to help end this thread. What else should I be worried about? He really seems concerned and willing to fix his screw up but........ am I the one screwed here or what???

Sounds to me like a valve problem of some sort. As long at the sqeek never turned to a knock or a kaboom... should be ok. Anything on the oil pressure showing before hand? How was blow-by? Did you get new valve springs in the deal? New guides?

BT :cool:

I would not shoot from the hip on this one. Make sure where the problem is BEFORE you take the motor apart. Run a leakdown test on all the cylinders. That is the only way to make sure where the problem is, be it valves, pistons, or whatever.

Yes new springs, guides, rockers total rebuild, salvaged block crank rods and heads all the rest new. Will do on the leak down. Am I just asking to much for a littlle satisfaction and the motor to be right? I guessI just wished to hard for it all to work out the first time around.

compression problem
 

jrocket,

Did you run the motor on the ground before you installed it?
It is always a good idea to start them up in the ground, prime the oil system with an electric drill on the oil pump and run them for thirty minutes or so to inspect for leaks, roughly set timing.
Something always shows up water leaks or oil leaks, whatever.
Did you find any evidence of water when you pulled the plugs to check compression?
Typically I would leave all plugs out and crank the motor over and watch each cylinder to see if any water shoots out of any cylinder.
A Basic compression test will tell you what cylinder is acting up.
Keep us posted with your findings we are all curious!

Yes we did initial start and cam break in on stand, primed all the lines, filter and motor w/external pressure gage. everything was perfect no leaks so we installed motor. Not until up on plane and running did I notice the squeek, then the miss. But the motor was very smooth before hand. I did notice that the RPMs didnt come up as they had been, can't really tell till I get it back, it was so short of a time. Prior to rebuild it turned 4900 now it looks like 42 to 43 I thought it shoud have been higher, i really was expecting to reprop

Also the plugs looked well no water or oil. That was promising. Ishould no more thrugh the weekend as the machinist is clearing his shop to support 27ft of boat and trailer. That is another thing this shop is in a very industrial area. He cant just park it outside the folks around this area would love to getup and play with my VHF and new XM stereo

For anyone who wondered new lifter gave up the show! Mercury has agreed to replace all (seeing how they had 30min on them) and broke push rod and rocker so fingerpointing is over and outa be wet by Sat:D
Rocket

good to hear it was nothing major!

jrocket,
Glad to hear you have a resolution!! I hope you didnt loose too much sleep.. Let us know how it all turns out. And hopefully you see some big numbers over the old setup..

Good luck.

Dick