Siezed but Plug looks OK?

[Granty]

Was out on my red & white S2 last week after dropping the main jet down to 124 from 125 to loose a boggy spot just after 3/4 throttle -- when out doing a plug chop I noticed the engine was racing slightly but settled down. Off on a motorway run on Friday and seized, back wheel didn't lock up, I got the clutch in but it's seized solid, checked the plug and it's a good brown, choccy colour as usual. Is it always a wee air leak that races the engine or could there be another reason.

Lesson for the day is I should have double checked after the engine raced a bit I guess -- G

[Toddy]

Agree always best to pick up the warning signs early they are usually telling you something , let us know the outcome when you get it stripped to investigate

[MickYork]

An air leak is certainly the favourite. Do the leak test before you strip it down.

[holty]

Fuel starvage can also give similar symptoms as an air leak and will cause seizures, a flow test will rule this out, a fast flow tap should do a pint in about a minute.

[Granty]

OK -- good news & bad news, got the head of it and piston still stuck in barrel, gave it a tap and all was free, got the barrel off and no sign of air leak or gasket failure anywhere, some small bits of "swarf" but no scoring. Piston looked OK with the top ring stuck but will emery cloth up I'm sure or new piston to be safe.

Head scratcher until I checked out the conrod & crank -- real clunky with 1/4" play at least back to front, looks like a big end failure of some description with bit of "jaggy metal" sicking out from crank. Also drained the gear box oil ready to split it in the morning and not a lot left in there, I've not been burning it for sure so I guess one of the seals must be away.

Going to split the case tomorrow and see what I can find, flywheel, stator off already preparing for the inevitable open heart surgery -- Braw