Flywheel Clutch Bolt Circle Dia

Found a flywheel out of a boat, v6 buick, 6 holes in a circle 11 3/4" diameter. Is this the correct pattern? Is the stock clutch pressure plate 10 1/2" dia

 

Though I have never messed with the marine version of the Buick V6, I am quite sure that the flywheel will bolt on to the automotive version of the engine's crankshaft. The marine version could have a different bolt pattern (or none at all) for the clutch pressure plate though. Marine engines often use a triangular flex plate, or bell-shaped coupler on the crankshaft, but not a disc/pressure plate as we are accustomed to.
I just measured the diameter of an aftermarket Buick flywheel I have that takes a 10 1/2" clutch, and the outer diameter is close to 12 7/8". Mine is the LUK brand from RockAuto.
-Donny

 

Thank you for the info! Could you measure the diameter of the bolts for the clutch from the center to center of the hole 180* across (opposite)?
The marine coupler is a hub that bolts to the center near the crank.

 

I just took a quick measure and came up with 3.56" at opposite holes. It looks like this has a symmetric pattern, meaning it will bolt on any way you put it up to the crank.
For what its worth, mine came from RockAuto (#LFW131), listed for A mid'80s Buick Regal.. I think it was less than $55 delivered. I have not had it on an engine yet, but its intended for a 231 even-fire down in the garage.
That coupler bolting on with the crank sounds like a Mercruiser setup.
-Donny

 

I believe the 10-1/2" clutch requires 11-5/8" bolt circle for mounting of the pressure plate.

 

Great! I think this will work!
Thank you for taking the time to get this info

 

Some factory flywheel pics. Hopefully you can make out measurements. That is the dimension of webbing between holes. They are not all equal fyi. Both of these flywheels are factory heavy units.

Old time got you covered on pressure plate bolt pattern.

Edit: apparently I loaded a wrong pic. That first one is useless with tape flopped over.

 

Sorry, I was obviously thinking you were asking the crank bolt pattern. Oldtime has you covered.
The RockAuto flywheel is lighter weight even compared with the passenger car flywheel, but still iron, and made in Mexico by Wohlert. It has 153 teeth on the ring gear.
-Donny