I have acquired a spare engine( not for sale). I have taking the clutch and alternator covers off and it all looks good just black oit. I was thinking of giving it a flush out. What should I use
You might try and find flushing oil. I think that only works if you use the engine, get it through a heat cycle and through the gears with load on it. Don't take my word on that though.
Otherwise, if you were trying to clean it, I'd think flushing it on the bench with diesel may help.
If you suspect it's filled with old oil that is sludge, I reckon it's a matter of splitting the cases. I wonder if draining it and measuring how much oil is required until it comes to the full level? That may give you an indication of the volume of sludge in it?
Have fun.
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In the Riverina.
'73 RD250, '80 XS1100, '81 RD373LC, '96 Tiger 900/sidecar, '02 TTR250, and another XS11 - this time a chain drive Period 5 race bike that may be ready to race eventually.