1984 Merc 150 Pistons

[Doug57]

I'm rebuilding the power head on my V150 Blk Max. The Selco book says that the bumps/marks on the crank end ou the rod must be turned up. The 4 pistions I am reusing have the rods turned the other way. Will this matter? I have inserted the pistions and when I turn the crank I can see the round hole in the side of the four existing pistons and can't see that hole in the 2 new pistions. Help!

 

[arsenalpsu]

Re: 1984 Merc 150 Pistons

YES- but not so much for the rod, the piston direction matters. That hole in the side of the piston is for fuel flow. All the pistons should be facing the same direction and that hole should be facing the intake side. If somehow the original RODS were put in the wrong direction I don't think that should make a difference (as long as the pistons are good), I'd keep them the way they are as all the bearings are worn in and use to how it's together now. I'd put your two "new" ones the same way as the old ones. It lasted 25 years that way, couldn't have been too bad for her! (This is assuming you put her back together correctly if you remove the 4 good old pistons from the crank?)

The two new pistons, I'm asuming you're using the original rods? If you're using the old ones you can reuse the bearings but if you're using new or different rods than you need new bearings. They tend to wear to how an engine likes to run and old ones from a different engine aren't the best to use.

 

[Dukedog]

Re: 1984 Merc 150 Pistons

I have inserted the pistions and when I turn the crank I can see the round hole in the side of the four existing pistons and can't see that hole in the 2 new pistions. Help!

Are you sayin' you can see tha ports in tha piston through tha exhaust holes of tha block?

 

[*EdC*]

Re: 1984 Merc 150 Pistons

Do yourself a favor, Get a factory manual.
I just rebuilt my motor and had 3 manuals, Clymer, Seloc and a Merc manual
I couldn't believe how different they were on some of the same procedures.
The factory Manual assumes you already know alot. The others, I found, were more of a guide to get to a certain point. A good example would be,, the Merc manual said "remove starter". Were the others would explain how to remove it. I always used the factory manual for specs and assembly. Hope that helps

 

[B4Istart]

Re: 1984 Merc 150 Pistons

Thanks everyone. I can see the ports thru the exaust holes in tha block on the 4 original pistons with the rods turned the way the book said, so I'll have to turn them back around. I'm replacing all the rod berrings and installing new rings on all the pistions.

Thanks again

 

[Faztbullet]

Re: 1984 Merc 150 Pistons

When I rebuild a engine I turn all my rods casting number up, but all that really matters is:
A) Rod caps is aligned properly(bump to bump) and not mismatched
B) Pistons are in their correct holes, they will be marked on their tops with UP and a S for starboard and P for port.

 

[arsenalpsu]

Re: 1984 Merc 150 Pistons

Good thinking on the rings, might as well as she's all apart and you'll get even compression then. For the piston direction just make sure you double check your book, should be the same way they came out- regardless of how the rod should be facing. The last post is right, the bumps on the caps must meet the bump on the rod. I believe those rods are not machined parts, they are one piece then broken so they're a 100% exact fit.