Fitting a Bob Newby belt drive

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When I was at P&M a couple of years ago I was chatting with Dave about a TR7 motor he had built for a bloke. He used a Matchless type breather in the end of the crank. The drive side shaft is drilled to 1/4" dia & the valve fitted to the end & used to hold the alternator rotor on as per AMC twins. Dave reckoned that no oil came out. By coincidence, I have been working on my AJS CSR 650 today which is fitted with the very same setup, & the primary case oil did not appear to have been contaminated by any engine oil.
I did toy with the Manx style breather slot in the front chamber of my TR7 cases when I tried the Hemmings belt drive, but didn't want a breather pipe running up the front of the engine. With hindsight I should have done this.
 

Fast Eddie

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If the rocker box breather works, that’s interesting.

It’s an easy way to plumb a breather in.

So TT... you didn’t sound too convinced about this rocker box breather idea if I may say so.

Well, in the interest of adding to the body of knowledge...

With breathers fitted to inlet and exhaust rocker boxes, and the timing cover breather blanked off, after a 50 mile fast ish road test, the main bearing seal passed oil into my dry primary, not a lot, but more than none.

With the timing cover breather fitted, tested on the same route, it does not, the primary remains bone dry.

So, I can absolutely confirm that NO, the rocker box breather idea does not work !
 

acadian

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So TT... you didn’t sound too convinced about this rocker box breather idea if I may say so.

Well, in the interest of adding to the body of knowledge...

With breathers fitted to inlet and exhaust rocker boxes, and the timing cover breather blanked off, after a 50 mile fast ish road test, the main bearing seal passed oil into my dry primary, not a lot, but more than none.

With the timing cover breather fitted, tested on the same route, it does not, the primary remains bone dry.

So, I can absolutely confirm that NO, the rocker box breather idea does not work !

I was under the impression that Triumph fitted the exhaust rocker box breather to mitigate pressure within that rocker box in particular, not for engine breathing purposes (which was still facilitated via the primary vent).
 

Fast Eddie

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I was under the impression that Triumph fitted the exhaust rocker box breather to mitigate pressure within that rocker box in particular, not for engine breathing purposes (which was still facilitated via the primary vent).

Not sure. As mine was originally connected to the frame I had assumed it was to allow the frame / oil tank to breath?

My thinking was that if I fitted another to the inlet, then took them both to the reed valve, the combined breathing capacity would be enough for engine breathing.

I was wrong !
 
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