Jump to content

Excessive Ring Wear Cause

Recommended Posts

I recently bought a CRF70 for my nephew to get him into riding dirt bikes with me and he has really taken to it. He rides daylight to dark every day. The bike needed some TLC, but I got a really good deal and love working on dirt bikes anyway. It was smoking a fair amount, but I let him ride it for the last month while I ordered new top end parts, piston, rings, valve seals, etc. so this weekend I got the bike back and pulled the top end apart. See picture on what I found, the rings were worn out, almost 1/4” ring end gap. The cylinder looks fine and so does the piston, the rings are the only thing that is worn. I have never seen this before, and was wondering what may have caused this excessive ring wear. Again, no ridge in the cylinder at all, and the piston showed minimal signs of wear. Not sure of the history of the bike before I got it, but the air filter was in and looked good. I got it back together and it runs like a top with more compression and power, and no smoke at all. Anyone care to speculate on excessive ring wear?

F8797D07-6DC5-413E-8423-348383D40C02.jpeg

Share this post


Link to post
Share on other sites

In the 70’s one of the guys in the shop tried to “Seat in the Rings” on a fresh rebuild on the customers S90 . 
He ran it at about 3-5 K rpm while sprinkling some BonAmy into the intake of the carb... a little bit more was a little to much.... lost all compression... upon inspection after disassembly, the rings looked similar to the photo above.  Learned what “not to do” that day. 

Edited by adnohguy
  • Like 1
  • Haha 1

Share this post


Link to post
Share on other sites

I’ll take a guess.  They honed it too much with a very coarse hone, didn’t clean it very well, installed new rings, then ran the piss out of it . . . . or perhaps no air filter. 

What’s the gap with the new rings?

You could take it to a shop and have it measured with a bore gauge.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×
×
  • Create New...