Scooterotica

As the title says, I've holed another Imola piston. Went for a ride yesterday and was cruising at at 60-65 MPH and bang it went.
Is there a possible air leak on the exhaust side of the cylinder head?

The piston seems to have melted at the top exhaust port side. Is this due to a possible air leak?


A photo of the top of the piston.

The top end was professionally rebuilt roughly 200 miles ago and was carefully run in. I know there could be several factors as to why this has happened but I'm after a few thoughts to point me in the right direction. I think I've been lucky with the cylinder and crank and they are re useable. I'll post some pics of those later. Any comments very welcome cheers Pete.

That definitely looks as though the head has been blowing, did you re-torque the head after the first 100 miles? the damage to the bottom edge of the piston was probably caused by the debris from the hole in the piston when it finally blew. I have holed a few myself and all mine have displayed similar damage.

Looks like my TS1 did.

I think the marks are just the debris being spat out of the exhaust together with the gas.

Looks like you head was blowing

Obviously coaster types quicker than me......

what "gue" are you using on the head to seal it?...not knocking it,i always use a locktite retainer,just looks like its failed...you using a gasket or not?..were the mating surfaces lapped?

The top end was built by a top tuner after I built the 1st version myself. As that failed I thought I'd let a pro do this one. To be honest I used a base gasket when I built it and assumed he'd done the same so not sure which sealant he used. The head was re torqued at 100 miles at his recommendation. He also set it up on his dyno but if I'm honest I think he didn't bother and just printed off an old reading of the version I built which was suffering from bad clutch slip. The reading was exactly the same which was strange as I'd sorted the clutch by the time he rebuilt it. I obviously can't prove that so I won't be naming him. I've taken the crank out and luckily I got him to tig the pin so that's fine. The cylinder has some of the piston "smeared' along the bore but it's not scored at all. I'm hoping this will clean up with some wet and dry. So the general census of opinion is air leak. I'm going to get a new head and piston and take it to another guy in Littlehampton who comes highly recommended.

youll probably save that head too if thats just ally built up from your piston with a bit of wet/dry treatment,just express youd like the mating surfaces lapped if you have concerns that its not flat.

Would an air pressure test help identify a potential leak ? (not sure if there'd be enough pressure)

I think the head is gone. The photo is'nt very clear but theres a section missing at the top and i doubt it would seal properly now.

The cylinder only has this build up of piston on it but I'm sure this will clean up ok.


Other than that I think I've been lucky (again)


Ok so what sealant are people using on the head / cylinder joint? Also base gasket or not? Thanks for your comments thus far Pete.

Bugger thats definitely your head gasket blown and then the air leak will have holed her