factory engine bore markings

[Kdancy]

I gave a friend a 1957 289 for rebuilding to put into his Hawk. He pulled the heads and at the bottom of each cylinder are stamped markings == the front two look like 45 and the rest are 35. Is that factory markings for over size pistons? The motor looks like it has never been into.

[Tom Bredehoft]

It is very possible that the two numbers represent .0045 and .0035 inches over standard dimension. Yes, they would have been supplied with oversized pistons. Unless taper or bore is out of tolerance (IIRC .005 all he needs is a hone and new rings. Somebody correct me on the acceptable tolerance.

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Tom Bredehoft
'53 Commander Coupe (since 1959)
'55 President (6H Y6) State Sedan
(Under Construction 617 hrs.)
'05 Legacy Ltd Wagon
All Indiana built cars

[Dwain G.]

Those numbers can be confusing because they don't mean exactly what you would think.
Finish bore size could be as much as .002" oversize, but no one block would vary more than .001" between cylinders.
The decimal size of the original 3 9/16" bore of a 289 is 3.5625. So if it was finished to that size it would be stamped '25'. If it finished .001" over to 3.5635, it would be stamped '35'. And if it was .002" over it would be stamped '45'. Different numbers were used for the 232 engine.
This was done to allow assemblers to pick pistons that matched the bore size, because they were also marked. I always wondered why they didn't just write those numbers with a permanent marker instead, because they didn't mean a thing after a few thousand miles of running.


HEY, you're not Wilbur!

[Tom Bredehoft]

Thank you Dwain, while it makes sense, it isn't logical, 'cause we don't know that 25 is standard.

[img=left]http://www.alink.com/personal/tbredehoft/Avatar1.jpg[/img=left]
Tom Bredehoft
'53 Commander Coupe (since 1959)
'55 President (6H Y6) State Sedan
(Under Construction 617 hrs.)
'05 Legacy Ltd Wagon
All Indiana built cars