alan_nc Posted January 6, 2009 Report Share Posted January 6, 2009 So I'm riding through a section this past Saturday and hear a light rattle sound from the front of the engine ('74 TY250). Shut her down and just turning it over with the kick starter could hear metal parts moving around loose. I have pulled the engine apart and found a broken ring, small end bearing with a lot of slop and a cir clip missing. The ring caught in a port and broke the ring land so the piston is trash. Found no metal parts inside the engine - don't know if they went out the exhaust or down into the case. I have washed the cases out several times with kerosene (then turned the engine over to drain it out). Nothing has come out - pieces wise. Bore wasn't scored. Crank and rod look O.K., from what I can see. I have pulled both side cases and see no problems in either. Drained oil from trans and it was clear. I have been riding the bike for a couple of months but prior to that it sat for several years. May have had some rust build up in the bearings during that time. Have located and ordered all of the replacement parts needed. Would appreciate any comments or suggestions from the group. Thanks Alan Quote Link to comment Share on other sites More sharing options...
andy m Posted January 6, 2009 Report Share Posted January 6, 2009 You won't see anything by draining the oil. Have you shaken the silencer (muffler) to see if anything got out the exhaust port. Does it all turn over clean and free (not lodged in bearings ) Quote Link to comment Share on other sites More sharing options...
alan_nc Posted January 7, 2009 Author Report Share Posted January 7, 2009 Bo, Yes I did turn the muffler up-side-down and tap (could be stuck to all the gunk inside). Crank turns over easily with no noise, no hard spots. I will "burn" the muffler prior to reassembly. Don't you sometimes wish you had the answer to why something happened? Thanks for the ideas. Alan Quote Link to comment Share on other sites More sharing options...
feetupfun Posted January 7, 2009 Report Share Posted January 7, 2009 Breaking a ring is relatively common in YZ and IT Yamahas but that's the first I have heard in a TY250A. I am interested in the failure mechanism in your bike. Here are some things to check that might help work out what happened: Was there much gum in the ring grooves? Which ring land failed? What side of the ring groove broke away? What port did it catch in? Was it the original piston and rings? Is there evidence on the rings of uneven ring wear? (uneven radial thickness) Does the port that broke the ring have chamfers around the edges? Is there evidence of ring blowby on the bore (uneven ring sealing?) How rattly is the piston in the bore without any rings? Is there a lip near the top of the bore? (if the little end develops play, the rings can hit a previously generated lip) Quote Link to comment Share on other sites More sharing options...
max1956bikes Posted January 7, 2009 Report Share Posted January 7, 2009 sounds like circlip has failed gone up piston and broke the ring.i would say small end bearing probably been going for a long time,you have got used to more noise over time. Quote Link to comment Share on other sites More sharing options...
alan_nc Posted January 7, 2009 Author Report Share Posted January 7, 2009 Feetup/Max, I think Max probably is correct. The piston is standard, no overbore - so it's been in the bike for a long time. Both rings were broken into several pieces. Ring grooves surprisingly clean. There is a mark on the exhaust port - nothing else. All ports have the stock (factory) chamfer. Broken land on the piston is directly at the front. Bore not sloppy or out-of-round so have decided to just put a stock piston and rings back in. Have new piston/rings/cir clips/piston pin and bearing on order. I don't think this is a normal flaw. I think this poor bike had a history of being rode hard and put up wet. It has scars all over the cases and the gas tank looks like it's been through a demolition derby. P.O. had been using pre-mix (pump disconnected) so the gas tank was rust free. Fenders look original but both have several cracks. I just patched them as the bike will be used weekly in Vintage Trials so there is no use making it pretty. I rode a Model 92 Sherpa T last year but have really enjoyed riding the TY - it just seems to fit my riding style. OH, yea I rode the T in the Sunday event. Alan Quote Link to comment Share on other sites More sharing options...
alan_nc Posted January 14, 2009 Author Report Share Posted January 14, 2009 Well she is back together and running. Got all the parts off Ebay (all shipped in less than a week). The surprise was that the baby is quite a bit harder to kick over than it was before - guess it had been going for some time. Alan Quote Link to comment Share on other sites More sharing options...
feetupfun Posted January 15, 2009 Report Share Posted January 15, 2009 Thanks Alan. Thats great to hear. Quote Link to comment Share on other sites More sharing options...
Tillerman6 Posted August 23, 2018 Report Share Posted August 23, 2018 Alan_nc, I have a bike with something similar going on. When I took it apart one of the needles in the upper needle bearing was not there. Can't find it. bought a cheap borescope and looked under the con rod and as far along under it as I could. Not on the floor either. Still looking and have the pipes off for clean out. Silencer is clean. Maybe the front pipe in the goo, but I hate to split the cases for no reason. This bike is from a previous owner and he may have put it together that way. Don't know. Tried magnets no luck. Turned bike upside down no luck. Have not tried compressed air or any liquids under the crank. Any suggestions are much appreciated Quote Link to comment Share on other sites More sharing options...
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