russelld Posted March 22, 2009 Report Share Posted March 22, 2009 Hi Everyone, Ive got this nice looking TY125, it has always been really hard to start, and takes awhile to get itself together, it would die on me whenever you put it next to a hill and was as if it was drawing in too much air, so changed the crank seals put it all together again and it ran better but has a really bad knocking noise (worse than the norm) and then the bike locked up, and when stripping it back I noticed the primary gear shaft nut had came loose and that had jammed the engine (luckily no damage) , it does have an aftermarket piston kit in it which are not the best so got a 2nd hand genuine head and piston to try it (Good Condition) and the bike still took ages to start but when it did, it ran good but the knocking noise was still there - any ideas? Big end was ok aswell Quote Link to comment Share on other sites More sharing options...
feetupfun Posted March 22, 2009 Report Share Posted March 22, 2009 You may have bent the crankshaft while changing the crank seals in which case the knocking is the primary gear mesh running out of clearance and then when the nut jammed in the primary drive its possible that you may have bent the gearbox shaft. You should be able to tell if the crankshaft is bent by taking the spark plug out and turning the motor over by hand, feeling for tight spots. If there are tight spots then the primary drive mesh is running out of clearance. If the tight spot is once per revolution, the crank is bent. If it is once per clutch revolution, then it is the gearbox shaft that is bent and you may even have a combination. Having the nut jam in there may also have deformed some of the teeth on the clutch or on the pinion, which can also make a knock. Quote Link to comment Share on other sites More sharing options...
russelld Posted April 5, 2009 Author Report Share Posted April 5, 2009 Thanks for the info. I tried taking the plug out and turning the flywheel over, there was a slight tight spot but would this just be as the piston changes from top dead centre, as I checked on another of my bikes that has just been rebuilt and it had the same slight tight spot, I then stripped the clutch off and checked in there and there didnt seem to be any damage on the gear mesh and it seemed to be running true, also with the clutch off i turned the flywheel as quick as I could by hand and the slight knocking noise was coming from the top end, do you think it might just be a new piston and re-bore that is needed, or am I just putting off the inevitable? Cheers Russell Quote Link to comment Share on other sites More sharing options...
alan_nc Posted April 5, 2009 Report Share Posted April 5, 2009 I think you have two seperate problems. You mention changing seals - did you replace the bearings at the same time? If not, did you check the clearance on the big end and small end bearings when you had it apart? You can narrow down the location of the knock with a stethoscope - take the side covers off, start the bike, put probe on different areas (there will be no question when you find the spot). If you don't have a scope a wooden dowel about a foot long held against different areas with the other end pressed to your ear will work. 1st guess on the starting problem is: Carb needs a complete cleanout. 2nd guess: Points are burned or not set correctly. If the seals were not installed correctly you could be leaking enough air around them so that you are not pulling fuel through the carb. Good luck Alan Quote Link to comment Share on other sites More sharing options...
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