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Cylinder markings

  • srsnow
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Cylinder markings was created by srsnow

Doing the top end on my 125 and I am pretty sure it is a standard bore, I don't have a proper dial bore gauge but my calipers read just under 56mm. What is throwing me off is there is .013 on the base of the cylinder. At first I thought it might be and over bore size but since .25mm is just under .010" that didn't really make too much sense. Any ideas, I attached a pic.
04 Jul 2022 18:51 #1

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Replied by MarkT on topic Cylinder markings

Factory ink stamp used when new.  Probably was 56.013 mm.  Then piston would have been selected to give proper clearance...  new standard pistons were available at factory in incremental sizes for this purpose. 

In any case those numbers mean NOTHING at this point in time.  Cylinder could be 4th over and the same marks would be there. 

What are the markings stamped into the top of the piston?  They are the best clue...  as well as the fit in the bore. 

Nothing can replace proper measurement tools and the skills to use them though...  calipers always seem to read small... sometimes by a bore size or two. 
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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04 Jul 2022 20:09 #2

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Replied by srsnow on topic Cylinder markings

Here is a pic of the top of the piston
04 Jul 2022 21:33 #3

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Replied by MarkT on topic Cylinder markings

Looks like a standard piston...  should have been 55.970mm when new.  If you subtract from 56.013 you get a clearance of 0.043 mm which is the correct clearance. 

My guess is you're trying to just replace the piston without boring?  Might be possible. Always best to measure properly.  If that piston is fairly tight still you could be okay.  If it's a rattler, probably best to have it measured per the manual.

 
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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04 Jul 2022 21:45 #4

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Replied by srsnow on topic Cylinder markings

Was planning on going up a size, may usable but engine has 6600 miles on it and was all original, the clutch was toast. First over pistons for the 125 are cheap on ebay. Thank you for the info
04 Jul 2022 22:14 #5

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Replied by MarkT on topic Cylinder markings

If it were mine, I'd send to someplace like Bill Bune and have it measured/inspected.  You could also send a new piston with it and hope it cleans up.

Really hard to find a good shop these days that knows what they are doing and will follow Yamaha clearance specs. 
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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05 Jul 2022 02:44 #6

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Replied by RT325 on topic Cylinder markings

Could "realy" go up a size & bolt on a 175 top end. Straight swap & need more weight to hold the front wheel down. Trying to guess what it is, but AT2 or 3 i'm guessing. Pretty lucky to find a 125 on Std bore after 50 years but 125's never got hammered by kids compared to 175's.
05 Jul 2022 05:38 #7

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