Mercruiser 120 153cid engine rebuild

[stevicroberts]

Hi, I have a mercruiser 120 153cid engine which had water in the sump, took the sump of and the pistions would not turn easily so removed one of the piston end caps and checked the bearings. These need to be replaced, howwever do not know whether they are standard or not.
I have found the following numbers on the shells.
18001796
A 00
19 Degree sign H
Could anyone shed some light on whether they are standard or not.
Regards Steve.

 

[Fishermark]

Re: Mercruiser 120 153cid engine rebuild

I don't know specifically, but since you have the caps off - how does the crank look? Rusty? You may need to have it either ground or polished... in which case you would need undersized bearings anyway.

If you end up having to rebuild this engine, I would suggest moving up to the 3 liter engine. Pretty big difference in "seat of the pants" performance between the two engines.

 

[stevicroberts]

Re: Mercruiser 120 153cid engine rebuild

Hi the crank looks to be ok. This is why I need to find out whether they are std or undersized.
Regards Steve

 

[Eric 3.7LX Alpha 1]

Re: Mercruiser 120 153cid engine rebuild

Don't know on your engine but any engine work I've had done, the machine shop has stamped the size on the crank if it has been turned to a different size.

 

[stevicroberts]

Re: Mercruiser 120 153cid engine rebuild

Thanks for that but I am doing the work myself so need to find out whether they are std or otherwise before ordering them.
Regards steve

 

[Eric 3.7LX Alpha 1]

Re: Mercruiser 120 153cid engine rebuild

Thanks for that but I am doing the work myself so need to find out whether they are std or otherwise before ordering them.
Regards steve

If the crank is virgin from the factory and has never been to a machine shop in it's life except when new then it is always std.

If it has previously been rebuilt either by you or a previous owner then you have to check it and see if it has been turned down and by how much either by a stamping mark the machinist left on it or by measuring it with a micrometer or dial indicator. I would not assume it is standard if you do not know the history of the engine. Either measure it or have it done.

And use plastigauge when you reinstall it.
http://www.plastigaugeusa.com/how.html

BTW: rods and main bearings might be turned a different amount on a crank (THATS if it is) so do not assume that they are the same.

 

[bigskiohio]

Re: Mercruiser 120 153cid engine rebuild

go to harbor freight or borrow some micrometers and mic them.

 

[Adirondack]

Re: Mercruiser 120 153cid engine rebuild

go to harbor freight or borrow some micrometers and mic them.

That's the ONLY way to be sure. Also the only way to know if it needs to be turned.