Engine vibration

Engine is finally in the boat--BUT has a bad vibration--trying to save a buck, I installed a barley used 496 flywheel on this new 502!!!! Is this flywheel an OK fit or could that be the vibration-----engine is a brand new marinized 502/502!!! Thanks---Mike Tampa Bay !

Sounds like an issue of balancing that changed with the flywheel.

Thanks----I have been doing some re-search and am learning some engines are balanced internally and some externally and the 496 flywheel will not be balanced the same as a 502---Soo I need to pull the engine and buy a 502 flywheel!!!!! Thanks again--Mike---Tampa Bay

You can get ahold of BAM or Eickert etc and tell them the year and serial number of your engine and they should be able to get you setup with the correct flywheel. However, make sure you know that the engine has not been rebalanced by some shop after it was new. They could easily balance an engine with the entire rotating assembly internally or externally.

Internal or External
With "internally balanced" engines, the counterweights themselves handle the job of offsetting the reciprocating mass of the pistons and rods. "Externally balanced" engines, on the other hand, have additional counterweights on the flywheel and/or harmonic damper to assist the crankshaft in maintaining balance. Some engines have to be externally balanced because there isn’t enough clearance inside the crankcase to handle counterweights of sufficient size to balance the engine. This is true of engines with longer strokes and/or large displacements.

If you’re rebuilding an engine that is internally balanced, the flywheel and damper have no effect on engine balance and can be balanced separately. But with externally balanced engines, the flywheel and damper must be mounted on the crank prior to balancing.

You should find out what type of engine balance you have (internal or external), and be cautious about indexing the position of the flywheel if you have to remove it later for resurfacing. Owners of externally balanced engines should also learn about installing different flywheels or harmonic dampers and how it can upset balance.

Thanks Ratickle----I will talk to the engine company and ask about the balancing and go from there!!!

It only took a second to see a 496 flywheel only works on a 496.

A 502 flywheel is the same one these models.

This Mercury Marine part number 6540 FLYWHEEL is used on the below models
330 GM 454 V-8 1977-1981
330 MIE GM 454 V-8 1977-1980
454 MAG. ALPHA GM 454 V-8 1986-1988
454 MAG. BRAVO GM 454 V-8 1988-1992
465 (GEN. V) GM 502 V-8 1992-1994
465 GM 502 V-8 1990-1992
500 Bulldog
500 Bulldog GM 540 V-8 1990-1996
502 MAG. BRAVO GM 502 V-8 1990-1992
525 SC GM 454 V-8 1991-1992
525 SC (GEN. V) GM 454 V-8 1992-1995
7.4L BRAVO GM 454 V-8 1988-1991

This Mercury Marine part number 881640T01 FLYWHEEL is used on the below models
496 MAG (Base Model)
496 MAG (H.O. Model)

I don't know what 502 you have but take the time to figure it out. The wrong one for free is worth nothing to you.

MOBILMERCMAN---Thanks soooo much for that info----I have learned to save a buck--cost me more bucks---I have to pull out the engine again----AND I have learned to be aware what U wish for!!!!!! Thanks-so much-----Mike--Tampa Bay !!!

Don't feel bad. There are much more expensive lessons.
And you seem to have caught it quickly.
Good luck.

I can't remember where, but the Merc flywheel also had a GM part number on it and that saved me a bunch one time...