350 Truck engine to Mercruiser Marine.......

[Fordiesel69]

Often we can get old rotted 2wd chevy pickups & suv's for dirt cheap. I was wondering other than the gaskets and freeze plugs & cam what else I need to look out for & swap over. I don't mind the labor tearing down the truck engine to swap all the parts over.

 

[Fordiesel69]

Re: 350 Truck engine to Mercruiser Marine.......

anyone

 

[Toypirate]

Re: 350 Truck engine to Mercruiser Marine.......

I'm pretty sure the constant load and rpm's generated on a engine in a boat require different bearing tolerances as I have seen 3 small block chevy's out of trucks metallic oil and turn the main bearings blue from heat, poor folks sometimes learn the hard way too. You might be able to check with your local engine builder.

 

[StevNimrod]

Re: 350 Truck engine to Mercruiser Marine.......

Anecdotal evidence can be easily verified (or disproved) by readily available published facts.

According to my service manual for a 1999 Vortec 5.7 (Chevy Truck application) the bearing clearances are:

Crankshaft Bearing Clearance (production):
Journal #1: 0.0007-0.0021 in.
Journals #2, 3, and 4: 0.0012-0.0027 in.
Journal #5: 0.0008-0.0024 in.

Connecting Rod Bearing Clearance (production):
0.0013-0.0031 in.

According to the Mercruiser manual for this vintage engine:

Crankshaft Bearing Clearance (production):
No. 1: 0.0007-0.0022 in.
No. 2, 3, 4: 0.00086-0.0024 in.
No.5 0.00098-0.0027 in.

Connecting Rod Bearing Clearance (production):
0.00129-0.00346 in.

Notice anything?

On a side note, I think there is a fair amount of false economy going around. If the body of the truck wasn't maintained, it doesn't really bode well for the maintenance of the engine. While you're tearing down to swap parts is about as good a time as any to check clearances, and while you're in it that deep you might as well give it a good once over. While there are a few good deals out there, there are also a lot of people unloading junk to people who are too eager to fork over their cash for what they think is a good deal. Often you get what you pay for.

 

[stackz]

Re: 350 Truck engine to Mercruiser Marine.......

finally someone posts rotating assembly clearances for the marine engines.

bookmarking this.

about the only thing I see noticeably different are the middle crank journal tolerances for marine/auto. everything else I would consider approximately close as everything has a "middle" range. auto rod clearances are tighter for range though.

I'd be worried if the auto engine had a couple hundred thousand miles on it but if it were lower miles I'd just use the shortblock as-is.

 

[StevNimrod]

Re: 350 Truck engine to Mercruiser Marine.......

Probably even more useful would be to bookmark THIS.

That's in the sticky "MUST HAVE Technical Information for DIYers," which is at the top of this forum. If the links are ever bad, Google is your friend.

It's interesting to note how many of the auto clearances are included in the "marine" specification (meaning that, for those items, the clearances in an accurate production auto engine will automatically be within the acceptable production range for a marine engine).

As far as the differences go, I'd be interested in doing the math to see if they are statistically significant. Not that it necessarily matters, but for the good and the welfare.

The point I'd still like to stress, however, is that if you do have access to an automotive engine, while it's out is about as good a time as you're ever going to get in terms of double checking specs and setting it up just right. You'd easily waste that much money in gaskets and time (never free) if you're wrong. People buy a lot of snake oils because they are "cheap insurance," but often disregard things that actually are cheap insurance.

 

[Fordiesel69]

Re: 350 Truck engine to Mercruiser Marine.......

This is a 1987 mercruiser. I would still like to get a truck motor if you guys have any more info on what to look for and what I need to swap over.