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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...
@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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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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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 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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Okay engines stripped again cranks out and I can't find any issues both mains look good and bearing was tight on the crank and needed pressing out of the case
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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
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... -
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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@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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That doesn't sound ideal. If the bearing comes off that easily then even bearing lock is just a temporary fix.
Sounds like the journal needs to be machined and a spigot ring put in its place.
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@calum yeah finding an early crank for cheap probably won't be easy either I'm thinking get a later crank and double up on my base gaskets or cut a base gasket thats thicker to set my squish
