Power loss, clattering and seizure - EXPENSIVE OUTCOME!
Posted: 18 May 2007 18:04
Okay. Following much anguish, NLM have put me out of my misery by providing a report on the engine within 24 hours of it being deposited in their workshop. They'd never seen a crank and big-end so chewed up. apparently, it's worthy of putting on a plaque!
One big end was oval and the crank journal was much reduced and blue. The white metal bearings had gone completely, and the piston had lost much of its skirt while crashing around. The piston had also been hitting the head, but they think I've got away with it. I expect a diagnosis on the valves and guides quite soon. Amazingly, the other con-rod and piston were okay.
Outcome is a new crank, con-rod and piston inc new shells. The bores were okay (slightly oval) but as I need new parts I've decided to go down the 375cc route with a rebore and new pistons. I can also get various other improvements such as roller bearings and gas flowing made to the engine at the same time.
An expensive lesson learned i.e don't expect too much from a cheap ebay purchase without a full service and MOT history. It'll cost you more in the long run.
The cause would appear to be normal wear and tear (the oil pump is fine), but lack of use by previous ownership may have played a big part through moisture retention in the sump corroding bearing surfaces.
Keep your bikes on the road to keep your money in your wallet is my advice! See you at Cadwell in the autumn with my 3 3/4
Martin
One big end was oval and the crank journal was much reduced and blue. The white metal bearings had gone completely, and the piston had lost much of its skirt while crashing around. The piston had also been hitting the head, but they think I've got away with it. I expect a diagnosis on the valves and guides quite soon. Amazingly, the other con-rod and piston were okay.
Outcome is a new crank, con-rod and piston inc new shells. The bores were okay (slightly oval) but as I need new parts I've decided to go down the 375cc route with a rebore and new pistons. I can also get various other improvements such as roller bearings and gas flowing made to the engine at the same time.
An expensive lesson learned i.e don't expect too much from a cheap ebay purchase without a full service and MOT history. It'll cost you more in the long run.
The cause would appear to be normal wear and tear (the oil pump is fine), but lack of use by previous ownership may have played a big part through moisture retention in the sump corroding bearing surfaces.
Keep your bikes on the road to keep your money in your wallet is my advice! See you at Cadwell in the autumn with my 3 3/4

Martin