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Discussion Starter · #1 ·
So, in weak moment, I won a 71 CL175K5 on ebay. I hadn't run in quite some time, so it had the normal issues that I worked my way through to get it running. Carb kits, new coils and wires, seafoam soak, etc. Runs, but weak. So I decided that it was time for exploratory surgery to find the low compression problem. 100psi LH and 90 RH, more or less depending on the day. I didn't find much, rings were free, valve passed the leak test, very little carbon. There were some rust marks from moisture at some time, which pretty much went away with light honing. Standard pistons and cylinders measure +/- 52mm.

My question is, I ordered OEM rings from Thailand, p/n 13012-235-000 arrived. I found on Bikebandit that these are superseded by 13011-439-005, cool, should work, right? When I went to check my ring gap, the old rings were .28mm and the new rings are .91mm! The manual says .80mm is max. Wouldn't this be a recipe for disaster? Low compression, excess blowby, and the chance of the ring ends hanging up?

I appreciate any comments or ideas from you all. This site has gotten me this far and the little bit I've ridden it, is so fun! I just love the exhaust note.

Ideas?

Regards, Brian

struggling to attach pics, will add later.
 

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Clean the piston tops and look for oversize markings. First oversize will read .025, 2nd oversize will be .050, etc. The rings should have similar markings on the top side.
 

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Discussion Starter · #3 ·
thanks Mike. I think that has to be the issue. I got focused on the new rings being for a 1968 C175A model, but research shows all 175s had the same bore. One piston was pretty clean and easy to see if there were OS markings. I can't see any marks on the rings.
Guess it is time to buy oversize rings and check, 2nd over would get it back in spec?
Thanks again.
 

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More like 1st over. .25 x 3.14(pi)= .785 mm end gap reduction. Best to have someone accurately measure your cylinder to be sure.
 

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What Mike said. You need to have your cylinders and pistons measured to verify what you have before you can fix it.
 

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Discussion Starter · #6 ·
Yep, will take to the shop today. All I can figure is he PO bored the cylinder and put on oversize rings on std piston (?).

Things that make you go "hmmmm?".

thanks all, will report my findings.

P3112760.jpg P3112761.jpg P3172763.jpg
 

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You can measure it yourself by sticking a feeler gauge into the cylinder, and then slideing the piston in. Start with 0.002" If you go past 0.0035" and the piston still has slop, you need a bore job.
Also, the top of the piston is smaller then the bottom. You measure them at the skirt.
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