Mercruiser serial numbers

[pschauss]

My boat is a 1978 B31 SF. Engine serial numbers are 4890nnn. Is it likely that these are the original engines?

Thanks,
Peter Schauss
Water-Lou
B31 SF

[Tony Meola]

Are they MercCruisers and what size?

I would think that Bruce might have some idea if they are or not based on the serial number since he is more familiar with the different engines.

I found that even Mercruiser has issues Identifying their own engines. My 75 came through with 454 Mercs with Thuderbolt ignition. We needed a special size hose one time that we had to go back to Merc for. They told us no such engine, so we had to jury rig a replacement. Go figure.

[Pete Fallon]

Peter S
The big block 454 CID engines should have a few more number than just 4 and a couple of letters. There is usually a metal tag that is either in the front of the block just below the manifolds or near the bell housing aft near exhaust manifold. The newer engines(1996 and newer) have the numbers on the plastic cowling over the carbs they begin with OK 41#### or try looking in the front of your engine manual if you have them or on an old survey of the boat. Most of the late 70's were 350 Blocks and the metal tag number could be painted over or completely missing.
Pete Fallon

[Bruce]

4623115-6083144 are the common engine serial numbers for a 454, 330 model in the year range 77 to 81.

[pschauss]

Full serial numbers are 4890408 (port) and 4890233 (starboard), read directly from the plate on the bell housing. The port engine had remnants of the original label on the right side valve cover which had traces of a serial number which looked like it would have matched the number on the plate. Along with the papers I got which the boat there was a survey from 1984 which showed the same serial numbers.

thanks,