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hey guys so it was test fire fast today and after a ton of kicking it ran twice for a few secs it was very weak I've narrowed it down to a weak spark the spark is blue but even if I hold the plug it doesent shock me nor if I put my finger in the ht cap the stator was tested as good not too long ago I will have to re check that I can't see anything obvious on the cdi side of things, but my wiring loom is bad a lot of connectors that just don't have anything connected mostly bullet connectors behind the headlight besides the kill switch which I also don't have is there any wires not including the key switch that can ground and weaken spark
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The bike runs decent but I still have play in the stator side crank even though it has brand new koyo mains is it possible the crank has worn down somehow over the years, it was all tight when I fitted them and it's only ran for around 3 minutes and I have a top end rattle I can't find any cause for this piston fits good no compression change powervalve seems fine it didn't have this sound before the only thing that's channged are new mains new piston and v force reeds it doesent sound like the crank I'm also using a thinner base gasket but surely that's not enough to cause issues?
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The play in the flywheel feels the same as it's always been I rode it for years with the same play so I'm assuming the crank surface might have worn down, when it's running and I put my finger on the plastic pv pulley there's a deep sounding impact noise as far as I'm aware it's always done that is that normal?
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Is the piston over 57mm? Sometimes the power valve needs grinding to profile so it doesn’t hit the piston. The same with the head and the head gasket.
Have you adjusted the power valve position and/or gotten a rebore very recently?The new bearings should eliminate any play. Are you sure the flywheel is tight on the crank? Do you have the thick washer fitted under the nut?
If you undo the nut and the flywheel is anything other than on there tight and needing a puller to remove, there’s something wrong...I use a large flathead screwdriver to check for main bearing play on the flywheel side. Very gentle up and down pressure shows any real wear. Anything else is just flex in the shaft...
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@spookdog thick washer is not installed since ive lost it but there's enough thread that its not needed flywheel is tight and fitted correctly, removed the cylinder earlier no damage or marks on piston or rings no sign of detonation i fitted an oem thickness base gasket while i was there nothing wrong with the rod or bearings wrist pin is good
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The power valves knock, when the bushes wear. But the valves also seem to wear aswell. Also the right hand power valve cap isn't a great design, having only one fixing point. Probably why Yamaha changed the design of the power valve on the 4fu cylinders.
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The only potential issue I can see is the clutch side crank bearing is a slip fit to the crank it can be dropped on and pulled off the crank without any force what so ever does anyone remember if that's normal for the clutch side to be a slip fit
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Nether of them should be that easy. See if that bearing slides easy onto the other side of the crank. If it doesn’t then the clutch side bearing journal is worn...
If so you could try using fully hardening bearing lock. Like the Lockheed thread lock stuff... -
@spookdog I tried one of the old bearings that I removed and that was the same, the bearing locker probably won't work it's only meant to stop spinning bearings this has lateral load so I'd imagine it would last a few seconds and then fail I'm gonna grab a used crank I just don't know what one to get some say the stroke used to be shorter but I don't know
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