Seizure on a cast barrel

[mick1]

I didn't put it together. The top end was purchased of a friend who had bought it from Rayspeed. As part of the deal it was fitted on my engine by a 3rd party, consequently the piston holed which was attributed to a dodgy jetex. Another piston was purchased by myself (I think it was the Ron Moss Mitaka ?) and fitted by the 3rd party. This was 3/4 years ago. The engine had been run in but hasn't been used much and the C2C was probably it's longest haul.

[Strummer10]

Mick 1......we stripped the engine this morning and the piston scoring is very similar to yours in the post above. There are 3 distinct score marks to the bottom skirt areas of the piston and 2 at the top. Where the piston is scored to the bottom areas the two rings (like yours in the photo) are closed into the piston ring grooves from the seize.

As a hunch I just checked my mates ignition timing again to ensure it was still at 19 degrees, whereupon we discovered it is at 19 degrees on tickover and say quarter throttle, thereafter the timing jumps and the arrow on the flywheel completely disappears from view whilst using the strobe gun ?

Guys would this therefore be the seize problem (ie; timing may have jumped to advance up the rev range ?) and WHY would it now deviate, when after the build it was static when thrashing up through the rev range ?

Mythed ?? is it poor stator or poor flywheel or pick up box or ALL (all parts are brand new ?)

[mick1]

My plug looked quite good......in fact very good which wouldn't suggest I was running lean, if your timing was out I would have expected a silver plug and a holed piston , not a seize. I'm tempted by Rich T's suggestion of a "foreign" body being sucked into the engine........but I suspect it's one of those when the answer will never really be known.

[Strummer10]

Its on a bike that runs a filter conventionally through the airbox so a foreign object could be ruled out I guess ...........yes I would have thought hole or start of a hole on the piston crown, but that's all good. Spoke to a lambretta guru just now and he said the variable timing experienced would cause the heat seize.

Must confess when I had the problems of a similar nature on the very lightweight AF flywheel the engine was misfiring and spurting, so it was obvious. But on me mates bike it starts and revs like normal. I did wonder if the timing gun might be faulty as well so could try another

[eden]

As a hunch I just checked my mates ignition timing again to ensure it was still at 19 degrees, whereupon we discovered it is at 19 degrees on tickover and say quarter throttle, thereafter the timing jumps and the arrow on the flywheel completely disappears from view whilst using the strobe gun ?

That will be due to a dodgy pickup, change it and the timing will ok. if you had aimed the gun at 180 degrees from where it should have been you would have seen the arrow.

[Strummer10]

Thanks Eden. If the timing had jumped to the 180 degrees would this possibly be the reason for the heat seize ?

[eden]

could be but the usual symptoms on the ones that jump 180 degrees is that the engine just wont rev past that rpm point, but if the pickup is breaking down anything is possible.

[Strummer10]

Its hard enough to build an engine, then have the issue of new parts being faulty ? Any ideas on good UK suppliers that perhaps check out stators being they are posted out ? Mind you that said it was defo static previously but the wandering seems to have happened recently .........