Engine heat seize

[warniep]

I'm running in my bog standard GP 150 after a complete engine rebuild, I've done just over 100 miles. I was recently out for a run, I was keeping speed down about 30mph when the engine nipped up. The rear wheel didn't lock up, I immediately pulled the clutch and stopped. I kicked it over and started straight away. I continued home with no other problems. I wonder if I will have to check in bore and piston, or will it be ok ? Any information would be greatly appreciated. Cheers.

[Warkton Tornado No.1]

I think you have two issues to consider:


Figuring why it seized is one issue & that may be down to the ‘running in head’ that many seem to adopt. IMO there can be a tendency to feather the throttle as if it in some way helps the process of bedding in an engine. It doesn’t as there is less gas as the result, whereas, if anything, you need to stay on the gas.

It’s a compromise between caning & labouring the engine, too. Revs won’t kill the engine, whereas short-shifting will. You should keep going up & down the gearbox for no particular reason….other than running in. Remember that more revs means more cooling air from the fan.

Keep on the gas going downhill, when there is a natural tendency to back off. Doing so will mean that the engine is fed little more than what’s available @ tick-over.


The other issue is whether to strip down or not.

If you can analyse your own influence honestly from the above, & consider you may have been responsible, then it might mean a seizure is less likely in the rest of the running in period as you change your riding style.

If so, you really should consider checking the bore, piston & rings for peace of mind sooner rather than later, confident that it is unlikely to re-occur.


I hope that makes sense.

[coaster]

It sounds like it was a bit of a 'soft seize' as it kicked over immediately afterwards so you might be ok without stripping it. Re the running in technique, I would differ slightly from Walton's view in that I think it is never a good idea to hold the throttle in a fixed position for too long and just easing back on the throttle to the point where the engine begins to 4 stroke (stutter like a machine gun) will cool the piston with excess fuel. If it doesn't 4 stroke when you back off slightly then you know you have a weak mixture situation.

[warniep]

Warkton and Coaster. Thanks very much for your reply, I think It sound like my fault for the problems, all though I haven't over revved it through the gears I may have travelled at the same speed and revs for too long. I will probably have a look inside the engine for piece of mind. Thanks again for the info, great help. Paul.