my sherpa 350 (159) runs ok but the motor feels and sounds a little bit 'gratey' to me, its been like that since i got it which isnt that long. my question is are the motors usually silent and normally smooth or are do they feel little bit gratey ? I sense a strip down coming on :-(

probably the main bearings sorry mate

+1 on main bearings, good news is that theyre not expensive if a little long-winded to change,

check the flywheel and crank pinion for "play"

Dom

Generally smooth motors, but some Sherpas can make some strange noises when you drop the revs right down to nothing and ride at near stall speed, nothing untoward but possibly the grating noise you describe. I've heard it even on a fully rebuilt motor. No idea what it is but it's only at that point where the engine is almost stalling.

There could be other causes, ignition flywheel catching the inside of the timing case if it has previously been damaged by the chain coming off. Clutch crankshaft weight loose, even the mesh between the bottom frame tubes touching the engine through being dented from rocks can cause vibration noises you may think come from the engine - same for the alloy bashplate on the later bikes.

If it's anything more than that then you're going to have to look at the possibility you may have the onset of main bearing wear, or just a worn piston that is noisy but doesn't cause any loss in performance.

thanks for the help and advice guys, I'm going to pull the casings off and have a good look this morning. I will let you know what I find.....fingers crossed

well unfortunately it's not looking good. I took off the magneto and if you hold the end of the crank there is a bit of play. The engine is now sat on the bench :-(.

any recommendations about what else I should change while I have the casings apart...crank seals as a matter of course but advice very welcome.

I have a Haynes manual which apparantly covers my model (159) but the images look to be older models, is there a better manual that I should be buying ? Oh and best place to buy all the bits ?

Thanks in advance

If you have to spilt the motorcases, I would in your situation replace everything that is weard out, beside this every oil seal, as they get stiffed as older they are. Then I would take a look at the bearings if they still roll smooth, especially main bearings and lower con rod bearing, piston, cylinder and piston rings should be looked at. Often the mushroom like bearing for the clutch rod is behind wear, clutch plates?. I would also replace primary chain and chain tensioner. Some shims between the gears of the gearbox of my 199b where weard down too so I had to replace them too, (custom made).

Points and capacitator come in my mind too.

I don't know where you live so I can't give you a good hint for parts beside Bultaco UK.