I think I already know the answer to this, but before I ruin an unused seal, I thought I'd get a ruling from the judges about whether you can get a good end play reading with the seal in place.

Thirty years ago I rebuilt the bottom end on my 2L engine and checked the end play with a feeler gauge. Then the project was put into deep sleep for decades before I finished the rebuild. Now I'm finally doing it and would like to recheck my work with a dial indicator just to be sure. So I set up my indicator on the flywheel and pulled the flywheel away from the case followed by a few very gentle taps on the impeller end of the crank shaft with a plastic mallet until it stopped moving. Zero the gauge and then squeeze the flywheel into the case with my hands. When I squeeze hard, the gauge reads about .0035" and when I let go, it moves back to about .002". I'm assuming the spring back is the seal pushing the crank back out a little. Would it be stupid to think I'm okay here?

I actually have a spare NOS seal I bought back when I started the rebuild. All I can find stamped on it is the size and FPM/ACM which I believe tells the inner and outer rubber material.

TIA

I hate to say it, but a seal that has been sitting dry for thirty years is probably just going to split and leak as soon as you start running the car. You might as well replace it and do so with a new one.

FWIW, I was recently checking flywheel endplay on my rebuild, without a seal, a month or two ago and saw similar results: end play at around .04 and would "spring" back to like .02 when I removed pressure.

So, I'm also interested in hearing what the sages have to say.

I've built VW AC engines for 30 years, I never use a dial indicator for end play.
In the 90's my tool and die, machinist buddy bet me a round that his dial indicator was more accurate than my feeler gauge. It was a draw, we bought each other rounds.
I use the simple $10 feeler gauge fixture and a good set of feeler gauges.
Put the engine at TDC, clean a spot, bolt on fixture, pull on the fly, set screw, push in, feeler gauge. Done.

If it's "popping back" it has a load on it. is the fan belt off? I set it at TDC when I do endplay.
Or is it gorilla grip syndrome? A guy with gorilla grip could bend a flywheel .002...which would be seen on the dial indicator.

Use a new RM seal AND flywheel O-ring, but leave the O-ring out till you have set the endplay.
I'd do the pilot bearing, lock washer and felt seal as well.

I just pulled the flywheel to get a better look. Only thing I could see that would cause the bounce back was the o-ring which I had forgotten about until Mark mentioned it. I pulled it, and sure enough, I now get .004" consistently with no rebound even with the RMS in place. The RMS obviously makes it impossible to swap shims but doesn't seem like it should interfere with the measurement.

All the seals still have a thick coat of assembly oil on them so I doubt any air has gotten to them over the years but maybe I should replace just to be safe? Pilot bearing and felt were also replaced back then. Can't imagine they'd go bad just sitting unused in grease.

For the RMS, I've read that some suck. Is Sabo the brand to get? What's in there now is a Kaco and is white. Like I said, it still has a thick film of oil from when I first assembled.

Saboseal or enjoy the leaks!

Ordered - and a new lock plate/washer. Thanks!