Sluggys' L188 - Piston Broke

[Diesel Dave]

So riding home from the MOT test yesterday and Sluggy grinds to a halt a mere half mile from home. pushing the bike in gear reveals there is no compression to speak of. Great, just in time for the good weather then!

Head off doesn't reveal any issues, both valves are holding up with no leakage and the cylinder head gasket looks ok too. Piston isn't rocking so the skirt is intact.

Time to dig deeper, Primary off, clutch off, side cover off (How many bolts! jeez).

Nothing lurking at the bottom of the casings



Time to scape away the carbon from the top of the bore and pop the piston out, conrod cap bolts are f'kin tight.

Rings pop out all springy and intact and the piston looks fine........oh wait....



Time for a new piston then...

[Tetronator]

I thought you were going to weld it?

[mark_in_manchester]

Glad you found it Dave, and thanks for the cup of tea the other afternoon.

Given the rings were intact, which I guess means the bore is intact, that all seems like a bit of a result. Are pistons available?

[Diesel Dave]

Well welding didn't work, at lest not with my old MIG anyways.

So it was a case of new piston and rings and I threw in some big end shells at the same time, there is some evidence of cavitation on the old ones (bubbles of oil that collapse leaving a distinctive circular pattern).



Still, all good now and 100 miles in rather questionable weather followed by re-torque of the head and a fluids check - ready for the summer.

[Diesel Dave]

I don’t care of the alloy side cover gasket was bent in half by the postman; I don’t need no damn sealant......

Famous last words....



On the plus side I now have automatic chain lubrication and the rear rim will never rust....

[Diesel Dave]

In the past few days I've managed to put about 350 miles on the new piston and it's holding together.

Even the oil leak is getting better (or it could be running out of oil...)

A good run today to Norfolk for the Beer, Bikes and Bands bash



Some nice old school chops to look at too

[arnaud]

This is the 13HP 456cc yanclone? Damn, i have a similar engine..
Did you do something special? like pulling away in a high gear at slow speed/low RPMs?

[Diesel Dave]

Nope, nothing changed about the way I rode the bike.

The new piston appears to be fine so far and survived thenEuro tour this year and that was 2500 miles of hard slog.