4 Bolt Vs. 2 Bolt main

[baconbiscut]

Ok, so I posted a while back about our engine in our boat having a knock (Mercruiser 383 Mag MPI) We ordered a replacement long block from US engines. It came in a few days ago, so I went to my shop to go check it out. Our mechanic said it has a two bolt main rather than a 4 bolt. Is this going to be a problem in a marine application?

Thanks, Dan

 

[Don S]

Re: 4 Bolt Vs. 2 Bolt main

No problem at all, 2 bolt mains are all Merc, Volvo, OMC, or anyone else uses.

In addition, I think merc used a 4 bolt mains on the 327, but the last one of those was 1969.

 

[John_S]

Re: 4 Bolt Vs. 2 Bolt main

No problem at all, 2 bolt mains are all Merc, Volvo, OMC, or anyone else uses.

Even their Hi-Perf 6.2L has two bolt mains. The 6.2L do have a forged crank though, where the 305 and 350 have cast.

 

[baconbiscut]

Re: 4 Bolt Vs. 2 Bolt main

My mechanic showed my the 4 bolt main on the other engine. Interesting.

 

[Don S]

Re: 4 Bolt Vs. 2 Bolt main

Does the old 6.2 have a Mercruiser serial number on the block? It would be on the back of the block, just above the starter. It's also a 377 cu in, not a 383.

 

[zbnutcase]

Re: 4 Bolt Vs. 2 Bolt main

Unless you are running nitrous or a blower, I wouldn't lose sleep over it.

 

[baconbiscut]

Re: 4 Bolt Vs. 2 Bolt main

Does the old 6.2 have a Mercruiser serial number on the block? It would be on the back of the block, just above the starter. It's also a 377 cu in, not a 383.

Oh but it is. It's the remanufactured engine from Mercruiser. I believe it's a 350 block bored .030 over and it has the 400 crank in it.

 

[dan t.]

Re: 4 Bolt Vs. 2 Bolt main

Dont worry about it. I used to run 2 bolt blocks in my oval track motors which put out around a hp per cube and turned 6500 rpm,never had a falure that was related to block or crank

 

[TilliamWe]

Re: 4 Bolt Vs. 2 Bolt main

... It's also a 377 cu in, not a 383.

As he posted above, the 383MAG MPI is a replacement engine offered for sale from Mercruiser Remanufactured engines division. They say they take worn out 5.7s, bore them .030, and install a 3.75in crankshaft. Area of a cylinder = Pi Rsquared x Height x 8 = 382.4 cid or a 383.