1986 Mercruiser 5.7 Engine Rebuild Crankshaft Questions

[jws123]

1986 Mercruiser serial 6793665 5.7 1 Piece rear seal with roller lifters I picked it up to put in my 19ft speed boat It has 2 spun road bearings. It looks like it was built not to long ago and in really nice shape so not sure what happened. I am going to rebuild it myself my problem is I have no machine shops left in my area and that's if the crank is fixable. My question is what is the difference between a crank from a Automotive 350 and marine? Could I get away with ordering a new crank from like summit racing or something or a auto store? I tried looking up new merc cranks saw one site they wanted like $1500 for it that's more then I paid for the whole boat ahaha any suggestions much appreciated.

 

[flashback]

No different as far as I know. Some great engine guys here so just hang tight

 

[Scott06]

1986 Mercruiser serial 6793665 5.7 1 Piece rear seal with roller lifters I picked it up to put in my 19ft speed boat It has 2 spun road bearings. It looks like it was built not to long ago and in really nice shape so not sure what happened. I am going to rebuild it myself my problem is I have no machine shops left in my area and that's if the crank is fixable. My question is what is the difference between a crank from a Automotive 350 and marine? Could I get away with ordering a new crank from like summit racing or something or a auto store? I tried looking up new merc cranks saw one site they wanted like $1500 for it that's more then I paid for the whole boat ahaha any suggestions much appreciated.

Marine and truck engines use same parts on same assy line. Yes if you cant acess a machine shop buy a rotating assebly from summit or like often good aftermarket parts like this arent much more than maching your old parts.
you still have to verify bores etc are ok as it sounds like someone messed up a previous rebuild

 

[jws123]

OK thanks will probably order one from summit then saw a few kits that come with the correct size bearings for the crank ect.

 

[Scott06]

OK thanks will probably order one from summit then saw a few kits that come with the correct size bearings for the crank ect.

Make sure you get the correct rods. Maybe they didnt redo the rod big ends correctly.
or if you cant correctly measure etc might be better spending more and get a new base or complete reman. You could update to vortec head engine and pick up 30 hp https://www.michiganmotorz.com/

i got a new base six years ago, was more money but has been completely trouble free

 

[Bondo]

1986 Mercruiser serial 6793665 5.7 1 Piece rear seal with roller lifters I picked it up to put in my 19ft speed boat It has 2 spun road bearings. It looks like it was built not to long ago and in really nice shape so not sure what happened. I am going to rebuild it myself my problem is I have no machine shops left in my area and that's if the crank is fixable. My question is what is the difference between a crank from a Automotive 350 and marine? Could I get away with ordering a new crank from like summit racing or something or a auto store? I tried looking up new merc cranks saw one site they wanted like $1500 for it that's more then I paid for the whole boat ahaha any suggestions much appreciated.

Ayuh,.... There's more to rebuildin' a trashed motor, than just throwin' new parts at it,.....
You really need a machine shop's services to get it right,.....

The block needs to be boiled out, to get rid of all the metal from the failure,....
With a new crank, the block should be line bored, 'n squared up,....

In yer case, I suggest you buy a crate long block, either new or rebuilt,....

 

[Scott Danforth]

Marine engines =truck engines with regards to rotating assembly, block and heads.

A 1986 motor would not have a roller cam unless it was a retrofit roller assembly. First SBC roller cams were 1988 and for boats/trucks 1996

Roller lifters would have been added as aftermarket

So you need to look up block and head casting numbers to see what you have

While you can just get a crank. I wouldn't for the reasons stated in the above responses and because you need to determine what caused the bearing failure in the first place

 

[jws123]

Marine engines =truck engines with regards to rotating assembly, block and heads.

A 1986 motor would not have a roller cam unless it was a retrofit roller assembly. First SBC roller cams were 1988 and for boats/trucks 1996

Roller lifters would have been added as aftermarket

So you need to look up block and head casting numbers to see what you have

While you can just get a crank. I wouldn't for the reasons stated in the above responses and because you need to determine what caused the bearing failure in the first place

Yea it for sure has roller cam will get some casting numbers later. I found a machine shop 1 hour from me going to give them a call on Monday. I just looked at the website posted above while it would be nice I don't have the budget for that. I even looked around for used motors normally plenty of cheap ones around but people right now are insane with their prices they are asking almost the same price as a new one. I have rebuilt a few motors myself with success but with this one I kind of agree now things need to be measured/see why it blew up hopefully the machine shop can do it.