G'day

The GP series of engines are like the FP and LA series from OS. They are bushed or plain bearing engines. They do not have ball bearing races and so the bearings cannot wear out. There are none. the "bearings" are replaced by a bronze bush.

These engines like fuel with plenty of castor oil in the mix. The more the better. They do not need a lot of nitro either and will run fine on FAI fuel (20% castor oil and 80% methanol). If you run the engine on fuel with a large proportion of synthetic, oil you can damage the bush and if the bush wears, the engine is effectively worn out and cannot be replaced.

So .....

I'd suggest you find some fuel with 5 or 10% nitro and as much castor oil as you can find. At least use a fuel with some castor in it. This will really help the bush to last.

If you are getting black oil from the engine, this is either wearing alumimium and or wearing bronze. Check the tightness of the muffler as this is often the cause of black oil.

Hope this helps a bit. The GP engines are great sport engines and with the standard, are very quiet and work well in trainers and small scale models.

Cheers

Mike in Oz