Hmmm, you should start a new thread in the engine forum about that front bearing / seal leaking........ how important that actually is, and why that is not affecting the top end as well .... ?

Also, being a true ABC type engine, does your GMS still have a pinch at TDC when cold? Just curious.

Thanks,

Ernie

As I understand it, the front bearing is not intended to be the front seal. The front seal is supposed to be the close tolerance fit between the engine case and the crank. A thin layer of oil is supposed to fill the gap and make the seal. To keep the front bearing lubricated there is a small weep hole between the case and the front bearing that allows crankcase oil to ooze into the bearing. The dimensional tolerances of these features are critical and if they are not correct you have an engine that doesn't transition well and/or doesn't idle well. Certain brands of engines seem to have more variability in their manufacturing, hence more bad samples in the bunch.

I may be totally wrong.

Do I sense a bit of sarcasm here? Not sure I want to open that can of worms. Yes, the engine does have a pretty good pop at TDC when cold. I'll try putting it back on the airframe and futher tweaking the LSN and see if it makes a difference. Thanks again, everyone, for the comments so far.
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No sarcasm there, just thought your question about the front bearing/seal was very interesting and deserved some good attention. However JPGacG summed it up very well and found the words that I couldn't about the front seal function in a ball bearing type 2-stroke. So probably there's no hurry about replacing that front bearing but after run oil will make a mess coming out of it in the mean time.

Keep us posted,

Ernie