Head Gasket Leak

[BrianH]

So I just finished re-building the top end on my bike. I've got the head on with all the nuts torqued to spec(29ft/lbs) which secure the head to the barrels.

When I crank the engine over slowly I hear a hiss, as if air is escaping from somewhere. The sounds is coming out of the engine, in the middle of the engine where the cam chain travels.

I don't have any of the cams in so the cylinders are completely sealed while I crank it so it cant be escaping from the valves.

Could pressure be escaping through the rings? Or is it probably the head gasket?

Thanks
Brian

[rapidray]

Are the spark plugs in or out? If they are in, it is either air going by the rings or the valves. You need to do a "leak down" test to be sure which it is. Ray.

[BrianH]

Its got to be the rings. I leaked down tested it and it passed with flying colors. I just had the valves re cut and the head re-decked too.

Is it natural for it to leak like that with the plugs in?