1975 atc90 standard piston size? [Archive]

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RawnLouver

03-01-2021, 10:13 AM

Rebuilding my atc90 engine. Put new valve guides in, reamed to 5.50mm and new valves are on the way. Went to check piston and cylinder and measured 52.2mm.. I saw online they were suppose to be 50mm bore. The cylinder is stamped 89cc. Maybe a aftermarket piston?

Will post photos below. https://uploads.tapatalk-cdn.com/20210301/c0d4e272d36da5d55317967d066de2a0.jpghttps://uploads.tapatalk-cdn.com/20210301/1339ad44b65b40203dee5c5014fb16a1.jpghttps://uploads.tapatalk-cdn.com/20210301/83c43567a9c03b77e71170e12e9c7c10.jpghttps://uploads.tapatalk-cdn.com/20210301/c362439d7df826ffbd4f6f5fe07fe046.jpg

DAM shop

03-01-2021, 11:05 AM

Yep, someone bored it 2mm over and uses a factory Honda piston it looks like. Not uncommon at all for these motors

Jim mac

03-01-2021, 09:04 PM

so that's a stock 110 piston? jim

RawnLouver

03-02-2021, 01:53 AM

so that's a stock 110 piston? jim

From the research ive done, it looks to be a piston out of a CB175/CL175 etc. They are the only pistons i see with a tall dome and 52mm. This piston has been modified for spark plug clearance as well by the looks of it.