- Joined
- Jan 10, 2005
- Messages
- 1,043
I was using 'Combat style' as a general term for '72 model year bikes with the rear breather and front oil pickup/return. Having a high comp head and hot cam is not likely to be contributing to your problem, not this way.don't think it is a combat, how would you know,being a Dunstall the head is stamped "M" modified where a combat is stamped with a "C". With engine number being 210105 it may be in a series where ther wet sumping may be an issue.
Assuming the cases are being pressurised (the leaks) something is not working properly. Have you tried running the engine and watching the oil tank and breather return outlets? When you start up and with oil cap off there should be a good deal of 'chuffing' for a few seconds until the breather has done it's initial job and evacuated the cases. If you then block the breather inlet at the filler tower with a finger you should only feel pressure and no suction. That should tell you if the breather is at least working. I'm also assuming that your case joints are relatively good and that it's only extra pressure that's causing the problem.
However there might be conflict between both outlets into the Yam valve (not sure of the fluid and pressure dynamics here as I'm not in the Jim Comstock league!). But, if the rear breather is passing a lot of oil during a ride then it's clear it's not being scavenged by the pump. It may also be that this oil flow does not allow the valve to shut properly (floating on a stream of oil ?- just a guess really).
Whatever is going on or not you have to take note of this engine year oil pickup problems. It is documented though not as clearly as it should be even if some owners don't have a problem with the standard setup. But, why would Norton revert to the rear pickup for 1973 and beyond? The fact that you mention 5000rpm rides and have lots of oil going up the rear pipe kind of confirms that.
I know this doesn't really help but until you solve the root cause of all that oil sitting in the cases no one way breather will help that. I use the Norvil valve which is just a spring loaded nylon poppet in a brass housing. I'm told that works with the rear breather OK, well, Norvil sell them with fittings for those engines....doesn't mean to say it works!!
If I were you and don't want to strip the engine during riding weather I'd replace the old breather, block off the timing breather and go back to standard. At least you know there's oil coming up that big pipe. That's unless it was even worse than before you added the Yam valve, I have to guess it wasn't?
Finally, how is the oil tank vented? To a bottle, open pipe or to one of the air filters?