My Sherpa has run well for a couple of trials but last weekend decided to 'eat' another piston thrust washer. On stripping down it looks as if I will get away with the bore which is +1.00mm (which I think is the limit) but the piston crown has been damaged and needs to be replaced.

I am not clear why it has destroyed the thrust washer.

Secondly, the conrod has no up or down play but some sideways play and on one side it looks as if it has been scuffed by the flywheels.

Is it worth taking the engine down and having the crank rebuilt and could this be why the thrust washers have been failing.

Any advice gratefully received from experienced Bultaco owners.

Edited March 13, 201115 yr by penno350

Hi I would check the conrod is not bent and i think you can bore out by 2mm not 1mm check with dave at inmotion bultaco

Check your parts manual because some 159's did use different conrods. Some may utilize the thrust washers some don't. I'm sure Bultaco uk could tell you what is what. It seems to me that I had this problem when I built up my 159 some years back. But yes it may be related to the rod.

Steve

Check your parts manual because some 159's did use different conrods. Some may utilize the thrust washers some don't. I'm sure Bultaco uk could tell you what is what. It seems to me that I had this problem when I built up my 159 some years back. But yes it may be related to the rod.

Steve

Thanks chaps, I can't tell with the naked eye if the rod is bent but at the lowest point of the stroke you can rub it on the flywheel (clutch side) which is where the scuff marks are. There doesn't seem to be any up/down play but I assume the excessive side play has put strain on the piston washer (same side).

Penno -

You don't say on which side the small-end spacer was "eaten", nor how/why the piston crown was damaged.

I think some con-rod side play is intentional and necessary because of the design and nothing to worry about.

However, "excessive" side play could indicate wear (or collapse) of a big-end thrust washer (if fitted), maybe as a result of, as already suggested, a bent rod...............

Edited March 15, 201115 yr by Lorenzo

Penno -

You don't say on which side the small-end spacer was "eaten", nor how/why the piston crown was damaged.

I think some con-rod side play is intentional and necessary because of the design and nothing to worry about.

However, "excessive" side play could indicate wear (or collapse) of a big-end thrust washer (if fitted), maybe as a result of, as already suggested, a bent rod...............

Hi Lorenzo, the thrust washer was the same side as the scufing and the piston crown was damaged by a couple of big chunks of debris which made their way into the combustion chamber.