I'm no expert but how does the primary pressurise?
We've been here before about sealing dynamos. The primary chaincase needs to breathe so if you seal the end face of the dynamo it can't. Ask Hugo Myatt about the consequences! I'm surprised that a newly built engine has a problem of oil transfer through the drive-side mains. Taken as read bores and pistons are new, is the breather timing correct?
Hi Len,
Many thanks for your reply - I'm finding your responses very helpful - I've said it before, it is such a shame that you aren't closer for me to bring the bike in and let an expert do it for me.
I'm an interested amateur - with an inquisitive mind. I haven't managed to get a copy of FYO yet as they are out of print with Russ (I'm on backorder). I plan to do some ATY, KYB and other reading before the weekend but have found the Forum rapid, helpful and convenient.
As the interested amateur, I can't fathom out why the primary will pressurise and need to breathe: my logic is telling me:
1 - There are no reciprocating parts to create pressure
2 - A properly machined dynamo face would lead to an effective (relative) seal
3 - Actually, wouldn't an effective seal help to stop oil finding it's way through the main bearings from a pressurised environment to a non-pressurised environment.
What am I missing - I have managed to get all MPH's from 1969 until today - is anybody able to point be to some reference points in there to read about the problem?
I've e-mailed Terry Prince who did the engine to ask his thoughts on the primary filling up. You are right that everything from the big end upwards was replaced in the engine, but he told me that the big end was fine and so was left - not sure what that exactly means in terms of it not allowing oil through though.
I've PM'd Hugo to ask him what his experience was that you mention so I can learn from that - have offered him the opportunity to post it on here so we all see it.
It seems to me I have two issues:
1 - Why is the primary "filling" up?
and
2 - Why is the oil coming out of the primary?
I think these are actually two seperate issues to deal with though although back to my amateur (puts tin hat on) logic viewpoint that a sealed primary might actually resist oil finding it's way in through the bearings from a pressurised environment.
The "gunk" on the dymnamo face plate and the back of the primary suggests that whoever did it, did not know about possible issues of preventing the primary cases from breathing.
Thoughts?
Stuart