relief valve friction

[mcjweller]

Building a 1776 motor, new case. pre-assembled to check fit of everything. I noticed that both the front and rear oil relief valve pistons slide nicely in their bores, but when fully seated in the bore they sort of "stick" almost as if the oil film held them in place. I kind of expected that they would fall out when the case is vertical.

I dressed the pistons with some crocus cloth just to ensure there were no burrs, etc, this freed things up to the point where they would fall out again with gravity, but still snug all the way up the bore.

Now fully assembled for real and glued together, I find that they now "stick" again only at the top of the bore.

I used a piece of rubber fuel line that fit inside the bottom of the piston just tight enough that the piston won't fall off. I can use that to insert the piston and pull it back out...so the "stickiness" is not enough to pull it off the light contact of the fuel line. In other words, it sticks enough to overcome gravity, but nothing else.

I realize under operation these will see downward force from above (trying to push them out of the bore) from oil pressure. So...should I be concerned with this light stickiness or perhaps it doesn't matter at all because natural forces will be pushing against that sticking? Hard to understand what is "normal", although in other non-VW motors I'm used to similar mechanisms having zero "stick". Thoughts?

[Dougy Dee]

Oil pressure easily overcomes that stickiness.

[Bobs67vwagen]

What I have done in the past is take some fine wet or dry sandpaper like 400 grit and put it around something round like a dowel and work it up to the area of sticking with some oil on it and work it around. Do it for a while and try the piston. If it still sticks do a little more. When satisfied flush the area well with wd 40 or similar and reinstall. Good luck-Bob

[slalombuggy]

Nothing to worry about. It it required some effort to get it to slide out, I'd do something about it, but oil pressure will push it down easily.