I have twin motors that both have crane 1.7 rockers. Each set has a slightly different part number at the end %. What does that mean? One set is -10 the other set is -5. It seems that pushrods are different lengths because of this too. Everything else is identical in each motor (cams, heads, lifters etc). I need a few replacement ones and I don't see any mention of this last part number when looking at the specs, only the ratio.

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Think that is the date they where made .

I sort of thought that until I saw difference in the length of the pushrods of each motor. All other things being equal, why would I have pushrods of different length? 9.250 vs 9.300 for the longer ones. The short ones are the same in both motors at 8.30 in length.

Things like heads being milled, decks being milled, valve stem heights, lifter seat heights, camshaft size, etc can have an effect on what is the optimum pushrod length. Or, simply, whoever built the engines, happened to have a spare set of pushrods to stick in something. Hundred variables here.

I have ones marked -7 and - 10. I'd like to know also.

Dont know if its the same deal but Fords canted valve heads used 1.73 rockers. Until a few years ago when one purchased a set of roller rockers for them you were actually getting BBC rockers they were marked 1.73 -.03. ( at least on Crane rockers) SO NOT ONLY DID you loose lift but valve train geometry was wacked to as valve angles an such were different from a chevy.

Many have different symbols or letters before the - . Even with Part #'s being the same.

Good question for someone who worked/works at Crane.

Mine all say 13-170. Then below that some have the -7 or -10. They were being used on Chevy mark 4 rectangle ports

Are you having engine problem? If i recall your engine were 632 cubic inche right?

No, I've got a pair of 540s with vortec blowers. Motors ran fine, but doing top ends right now (It's amazing what you find out with a leakdown test).