k5.9 airleak

[liquidcool]

I'm a newbie to nitro RC so forgive my terminology. I have a HPI K5.9 and can't keep a tune on it. So I pulled the engine and found that the front(? the clutch side.) bearing to be leaking air. I found this with a soap test. Is this normal or should it be air tight? The engine also has a kinda catch at TDC is this normal thats with the plug out so its not the compression I'm feeling.

 

[2revo1maxx]

Your engine should be tight at the top, it has a tapered sleeve. That tightness is the key to a good running engine.

As for the bearing, they will always show some leakage. How much is another question that you have to figure out....I'm betting that a tight engine will not have bad bearings. One way to tell is by how much crud builds up on your chassis underneath the crank bearing. A small line of crud is normal, slinging lots of fuel around is not.

 

[liquidcool]

thanks for the tip. there is a bunch of crud under the engine. i got a bearing on order.