Spirolox Fit Issue

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nm9stheham

nm9stheham

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Not Mopar, but I figure I'd get some decent thoughts here. I have some oddball 4-banger Arias forged pistons here, and the pin bores are at .912". Got some JE 2 layer spirolox that fit the .042 width of the pin lock grooves just fine. And the .927" diameter sizing of these spirolox should be OK for the pin bore size.

But when I fit one in, the ends of the spirolox just barely overlap the step in the middle of the spirolox... I mean just barely. So of course, it won't quite settle into the groove there. I think what is going on is that the groove depth is on the shallow side. It is only maybe .020-.025" deep, and that makes the groove outer diameter smaller than maybe normal.

I can't find a .912" spirolox in a .042" width anywhere. And the next size down in diameter looks to be too small for a .912" pin bore.

So:
  1. Anyone got a performance type of piston to measure the pin lock groove depth? I just never pave paid attention to what is typical. I am gonna root around to see what I have here.
  2. I am thinking of just trimming these spirolox maybe .100-.150" at each end. Comments?
 
The pistons probably aren't made for spirolox, but rather a wire lock, aka Cosworth lock. If the bottom of the groove is radiused, it won't accept a spiral type lock.
 
B3RE said:
The pistons probably aren't made for spirolox, but rather a wire lock, aka Cosworth lock. If the bottom of the groove is radiused, it won't accept a spiral type lock.
Click to expand...
Tnx B3; however the lock grooves are indeed squared; checked that out a long time ago. Being old Arias they were probably thinking of using Tru-arcs.

The Spirolox fit nicely in the groove about 90% of the way around. It is just where the ends lap ever so slightly on the step in the middle of the spirolox; if the groove diameter was just a tad bigger, it would all expand a bit and the ends would not bump onto the step, and would drop into the groove nicely. I may try to take a pix here shortly... you know, worth a 1000 words LOL

And tnx, b6p.... I'll look at those.
 
FWIW.... here is a pix of the issue. The spirolox is being squeezed just a bit too much and the ends are overlapping each other and the 'step' in the middle.

I trimmed the ends off of each end by about .150-.200", re-shaped like original, fine filed the burrs off. They all went in and seemd to seat in fine. Probably a tad smaller diameter pin lock groove than these are designed for but the next smaller ones seemed too small.
IMG_20200316_132554918~2.jpg
 
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