Tower OF Power REbuild, 2 Different Pistons!

[WinnipegBoatMan]

Howdy!
I've got a little bit of a problem that I'm a little worried about! I've recently been working on rebuilding my Mariner 115Hp Inline 6. I've got my whole block machined, all new parts ready to go! BUT! When I was preping everyting to start the assembly I noticed ONE HUGE PROBLEM! As you can see by the pics, I have 6 Pistons for 6 Cyl (I know its CRAZY!) But I had 2 Cyl bored out .015" over, cyl #2 and #4. The piston kits that I baught I had thaught were the original 3 Ring pistons. However they ARE NOT! They are both 2 Ring pistons! Is this going to cause a HUGE problem? I know its alright that I have the cyl oversized, but now to have 2 over sized cyl, and now 2 pistons with different ring configurations?!

If you would like to see the whole scoop on how the rebuild is going here is the link to my other post. Any ideas would help a lot!!
http://forums.iboats.com/showthread.php?t=366059

 

[Faztbullet]

Re: Tower OF Power REbuild, 2 Different Pistons!

Wont make a bit of difference The 2 ring is in all the later model engines, just make sure it has the power port in side of new piston. If you measure the "eyebrow" on top of piston it may be shorter which is a "low dome" piston. You can run high dome and low dome together but the low dome will be about 10psi lower on compression.

 

[emckelvy]

Re: Tower OF Power REbuild, 2 Different Pistons!

2 or 3 ring doesn't matter. I'm assuming the 2-ring pistons have a keystone ring on top and a 'straight' cut ring in the 2nd groove. This is actually better than the old design; the keystone ring is tapered such that combustion pressure pushes the ring against the cylinder wall for better sealing.

This also promotes a slight movement in the ring which makes it more resistant to sticking from carbon-buildup.

Just be sure you get the correct ring profile in the correct groove. The tapered side of the keystone ring points to the top of the piston, BTW.

Nor should you have any concern about balance, replacement pistons have the same weight as the old ones or they're so close as to be insignificant.

More important is that the replacement pistons have the "power port" hole machined into their sides, as can be seen in the old piston. The new one is turned and can't see the hole, but I'm assuming it's there.

If not, that would be a problem!

Also I'm assuming the dome height of the new pistons matches that of the old, i.e. you're not mixing hi-dome with lo-dome and vice-versa. That wouldn't be so good either!

HTH & G'luck with the reassembly..........ed

 

[WinnipegBoatMan]

Re: Tower OF Power REbuild, 2 Different Pistons!

Thanks Guys! The new pistons do have the power port in the side. The pic only showed the rings. They are as well the same dome design! Phew! That makes me a little more happier! THANKS!

 

[arsenalpsu]

Re: Tower OF Power REbuild, 2 Different Pistons!

When i did my rebuild I used 6 new pistons that all were semi-keystone 2 ring. I was told that the old pistons can have bad piston ring pins (that little pin that stops the rings from moving around the piston) which will either push into the piston or come out. In either case you'll loose that ring. 2 of my pistons had that problem (and a ring gone on each), and a few others the pin looked short so it was soon to fail.

I'd use all new pistons since you have here apart but if you are going to use the old ones check very carefully that all the pins are good. I did keep 2 good 3 ring pistons if you need them.