Correct cylinder head to use on a RBLT 3.0L short block

[rmyauck]

Old engine is an 87 Mecruiser 3.0L which suffered an oil pump failure (will rebuild), but found a RBLT shortblock with the same manufacture in 87 and it has flattop .060 over pistons. The old engine however has dished pistons maybe 3/16 deep in a D shape.

I assume the resulting compression would be too high using old , but good head, but maybe premium fuel would solve the problem.

The fellow with the short block says it originally had flat top pistons and it is a 2 piece rear seal block like ours. Our old flywheel will bolt up (12 3/4 in) , but strangely it doesn't have a harmonic balancer , but instead has a hub for a crankshaft pulley like on a 2.5L. The seller says the machine shop must have put that on , and there is no identification plate. Could it be a 2.5L block bored that much?

Is balance critical on these engines if you change the pistons? The old one needs new pistons as #2 & #3 pistons have the rod pin seizing from the oil pump failure.. #1 is not as tight in that area and #4 is normal. Synthetic oil saved the cyl. walls cam bearings and crank.

I see the 1990 and up heads have a different part #

Thanks for any info!

Randy

 

[rmyauck]

To make it short , can I use the older 1987 head (from a block with D shaped dished pistons) on a block with flattop pistons, both 3.0L of course? Premium fuel will be used for sure!

 

[Bondo]

can I use the older 1987 head (from a block with D shaped dished pistons) on a block with flattop pistons, both 3.0L of course?

Ayuh,.... Welcome Aboard,..... The Only way to get that answer is to Measure the motor, 'n calculate it's displacement, 'n compression ratio,....

but strangely it doesn't have a harmonic balancer , but instead has a hub for a crankshaft pulley like on a 2.5L. The seller says the machine shop must have put that on ,

I ain't buyin' that crap,..... a 2.5l uses only a pulley,...
A 3.0l will shake itself to tiny bits in no time without it's harmonic balancer,...
Any reputable machine shop wouldn't let such a thing outa their door,....

Is balance critical on these engines

Balance is Critical to Every motor,....
As well as cylinder diameter, 'n roundness, 'n bearin' clearance, 'n everything else involved with buildin' a Reliable motor,....

Send it to a machine shop, 'n punch all 4 holes .030" over, 'n use 4 new pistons that actually fit the cleaned up bores,....

 

[rmyauck]

Thanks much Bondo!

I found a guy that says it will run, but for sure use HI Octane! I can get some AV gas to cut with premium unleaded. When I can find the the proper head affordably (I'm in Canada) I will put it on. I will of course use the proper balancer off the old 3.0L..

Will let you know how it works. I think an Accusump or Canton etc. oil pressure reserve cylinder will probably be added with low oil pressure shutdown.

Thanks!

Randy

 

[alldodge]

Can reduce the compression some with a thicker head gasket