timing side crank seal

I am working on an early Atlas and have run into a problem. I cannot get a crank seal for a commando to press into the timing cover. By some chance was there a change in oil seal O.D. perhaps from fractions to metric? I've ruined two new commando oil seals and even the circlip is a bad fit. I have a bearing driver set and this is usually a 5 minute job.

If the seals are the same then I have a possible answer to my problem. The timing cover has been chromed...much chrome on the whole bike. This includes the INSIDE of the timing cover. I lightly sanded off some of the rubber on the O.D. of the seal and it went in easier though I could have sanded off a bit more. I barely got the circlip in place and I could have taken off some of the rubber on the closed end of the seal. What a battle.

Thanks for the post giving us a "heads up" on the consequences of chrome plating a Norton timing cover.

I have often contemplated chroming mine (every time I polish it, I suppose), and i have to confess that i never considered the seal pocket would close up a few thou.

For those who would chrome the timing cover, be sure to have the plater mask off the seal pocket, the half time gear shaft pocket, as well as the area around the oil pump conical washer. The latter precaution is to avoid a non flat porous surface, rather than a clearance reduction.

Slick

It looks like the previous owner had a fight putting the cover back on. I noticed that the numbers on the seal (what was left of them) gave a dimension in fractions hence my question about a possible difference in seals. This little incident cost me two extra seals and much aggravation until I figured it out. Had I known I would have left the seal alone. I only removed the timing cover to replace a leaky paper gasket. I also replaced the oil manifold gasket and discovered the feed hole was partially blocked with silicone seal.
Another thing to be careful of is the conical oil pump washer. Since I replaced the original paper gasket with a new thicker Commando gasket, it gave very little crush on the conical washer. Fortunately I have a supply of oil pump shims..very small, thin washers...yes there is actually a Norton part # for this....and got past the problem.