Looper Pistons!

[Laker]

THese are early loopers pistons. Circa 1985
What is the funny little holes in the bottom exhaust port section of the piston?

[Laker]

Early piston on the left.. 1985..
Later 1992 model on the right.
Notice the different cutouts?
which is better?

[Laker]

Boost port window
Early model on the left
Later on the right...
Why the design change?
It seems the Later block castings got rougher and rougher...
my 1.8 IS much cleaner than the 2.0 inside and the mis match of the ports is Half that of the later model block.

[MattGreen]

The little holes bleed oil onto the bridge; the piston was also relieved in this area. Merc did the same thing on their BP pistons I beleive.
I don't think the window opening for the main transfer ducts makes much of a difference in stock form - I think the bigger windows allowed more "slop" in tolerances so the piston won't block the lower port window no matter where it ends up. I'm sure Al and Nosub will jump in and corect me if I'm wrong.
Also, there are more piston differences than just what you've outlined.......
QC?! Yes, QC went downhill as the model years progressed; early to mid 90's are the worst, and it's not just casting garbage in scavenge ducts and sleeve misalignment. Line boring problems, junk in fuel manifolds and carbs, electronics, aluminum bits in assembled powerheads and trim systems, bad VRO's, the list goes on.
I still like 'em though !

Merry Xmas,
Matt Green

[Laker]

yep
Matt im just staring with the obvious ones... LOL
The holes one this pistoneee dont line up with the bridge... the wear marks are above lower exhaust port.
It does look like it could lube the bridge however. Any Ideas on how to drill on new pistons? 2mm drill perhaps?
THANKS!!
Chris

[chris_lacey]

Chris, I'm glad you're building a new engine. I can just read your posts and get a good idea of what to do and buy without the pit falls.
Thanks,

[Instigator]

On mine those holes oiled the bridge as Matt said.
Mine weren't relieved from the factory though.
I drilled my own lube holes and filed a small relief on the piston as well.
The sacry part of the lube holes is you can see it coking the piston.
If it cokes/glues the ring in the groove, you're done!
That is why I also relieved mine.

[Laker]

You can see the scoring from the bridge on this one.
THe holes dont line up well with oiling the bridge...
Gator, did you line the holes up ?
These also were not relieved..

[Instigator]

Yes
Are you sure yours don't line up??
Just checked an old OEM piston on a spare block and they do line up too.
That scoring could be from something else, a damaged exhaust port window for instance??

[racer]

Laker, That score is not from the bridge if it was in the correct bank and the rod is good.

[Instigator]

did'nt want you think I was making fun of you;)

[Laker]

Yep they do line up,
On the looper the exhaust ports aim down some unlike the Xflow which shoot straight across. LOL
The Later pistons dont have this feature.. Why did they go away from it? It seems to be a good Idea to protect the bridge... Unless the bridge can be removed?

[racer]

The later piston does have the cam in it for the bridge, this is why the oem 4&8 cyl piston have a different # than the 6 as the 6 is an oval port.

[BRENT GILL]

v-4 & v-6 & v-8 differance between v4 , v-8 & v-6
the late model v-6 has a different part # because the piston is finger ported where the 4 & the 8 are not . Brent

[racer]

Brent, I was talking about the 88-92 non finger port v-6. the finger port version is also lighter.