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What is the number printed on the outside of some NOS cylinder bores?

  • amsbstn
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What is the number printed on the outside of some NOS cylinder bores? was created by amsbstn

Hello!  I have noticed a number (like .005) factory printed on the outside of some nos Yamaha 2 stroke cylinders. By outside, I mean the outside of the cylinder skirt.  I'm wondering if anyone knows what this number means?  Is it a factory QA tolerance or something?  Just a mystery (to me) that I thought someone on this forum may have the answer to.

Thanks!
-Adam
04 Feb 2024 09:10 #1

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  • MarkT
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Replied by MarkT on topic What is the number printed on the outside of some NOS cylinder bores?

My opinion is it's the deviation from the standard bore size.  For example if standard bore was 66mm, a "000" cylinder would be 66mm.

A "005" would be 66.005mm.  (I believe I've seen a negative number as well)

Standard pistons were made in incremental sizes such as 65.960 and 65.965.  The correct piston then could easily be chosen to get the clearance correct.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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Last edit: 04 Feb 2024 12:57 by MarkT.
04 Feb 2024 12:28 #2

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Replied by MarkT on topic What is the number printed on the outside of some NOS cylinder bores?

Oh, I based the above opinion on disassembly of engines that still had the ink stamp legible and the original piston installed...  plus I have had a couple of NOS cylinders and was able to measure them.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
The following user(s) Liked this Post: Ht1kid, msavitt, Badrul, cranky_dave
04 Feb 2024 12:40 #3

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