i just measured it.i was thinking maybe .025 but it was .045 narrower.this is a55 272 CEBY ENGINE so a canadian engine.i had these blocks before but never run into this.but i have so many parts laying around i may have used a newer one.

I personally have not run across a rear seal retainer that had the side grooves not tight enough for the vertical side seals. And I’ve dealt with all years, and they all fit the same.

Lorena, Texas (South of Waco)

under just when you think you seen it all.working on a 55 272 and putting on the rear seal holder using the side rubber and nail i noticed how easy the sideseals went in their usually a pain to get down.the nail went in like nothing.i knew something was wrong.it would have leaked like a sieve.got another holder from a newer engine perfect.the 55 holder was to narrow.it still had its original rope and side seals.is this common with the early engines and i just never seen it before.