barfy Posted January 25, 2015 Report Share Posted January 25, 2015 I went out practicing today and after a couple of hours I occasionally felt a rumble our unbalance in the engine. It wasn't constant and only at low revs. I'll have a look during the week, but in the mean time any ideas where to look? Quote Link to comment Share on other sites More sharing options...
tlrmark Posted January 25, 2015 Report Share Posted January 25, 2015 Classic symptom of worn main bearings in a two stroke. Quote Link to comment Share on other sites More sharing options...
ruffmutt Posted January 25, 2015 Report Share Posted January 25, 2015 Hi barfy, almost certainly magneto side crank bearing. Quote Link to comment Share on other sites More sharing options...
barfy Posted January 25, 2015 Author Report Share Posted January 25, 2015 Thanks guys. Is it a main bearing even if it isn't happening all the time and just (sometimes) just about 1/8 turn off tick Over? Quote Link to comment Share on other sites More sharing options...
lbhbul Posted January 25, 2015 Report Share Posted January 25, 2015 Barfy. Check motor mounts. You can pull the mag cover & check for movement. Those engines have very robust bottom end. Larry Quote Link to comment Share on other sites More sharing options...
lineaway Posted January 25, 2015 Report Share Posted January 25, 2015 I would agree that it could be mains on that old bike. But mains are constant. Check the rear hub bearing as it can be going bad and feel like the motor. 1 Quote Link to comment Share on other sites More sharing options...
feetupfun Posted January 26, 2015 Report Share Posted January 26, 2015 also check the exhaust system for loose or broken mounts or touching something where it should not 1 Quote Link to comment Share on other sites More sharing options...
barfy Posted January 26, 2015 Author Report Share Posted January 26, 2015 Thanks for the ideas. I'm going to start looking for the problem tonight. I'm favourite on something loose. Just before this outing I took the clutch off and washed it out so I hope that I didn't tighten something properly. There again it's probably wishful thinking. 1 Quote Link to comment Share on other sites More sharing options...
barfy Posted February 1, 2015 Author Report Share Posted February 1, 2015 The bolts at the rear of the bash plate were loose because the thread had stripped. Also one of the engine mounts was loose. Seems to have lost the rumble (around the garden anyway). Give a proper go in anger next weekend. 1 Quote Link to comment Share on other sites More sharing options...
woody Posted February 1, 2015 Report Share Posted February 1, 2015 That should hopefully account for it. I had an engine bolt come loose on my Sherpa once on the road and the rumble was bad enough for me to think the clutch flywheel weight had come loose - or worse. Rumble disappeared when we tightened the bolt.... Also had the same affect on another Sherpa when a badly mis-shaped bashplate was touching the underneath of the engine. The rumble disappeared when the bashplate was removed Quote Link to comment Share on other sites More sharing options...
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