PR ENGINE BREATHER

Jubilee · Jul 24, 2018

A 1972 production racer is on display in a local shop here in Invercargill. It has an engine breather like the original fitting ones that were mounted low down at the rear of the motor, but this one is mounted on the rear of the primary chaincase. Is this a factory fitting? Is it an owners/tuners modification? Does it work? Is it something I should be doing to my '73 combat?. I've never seen this or read about, or even heard of it before. Does anyone know anything about this modification?

Mr. Rick · Jul 24, 2018

We took a vote while you were out, Jubilee, and reasoning that the machine is local to you, have decided that you yourself will be the best person to ask these questions, write down the answers, take pictures, and report back with your findings.

lcrken · Jul 24, 2018

Jubilee said:
A 1972 production racer is on display in a local shop here in Invercargill. It has an engine breather like the original fitting ones that were mounted low down at the rear of the motor, but this one is mounted on the rear of the primary chaincase. Is this a factory fitting? Is it an owners/tuners modification? Does it work? Is it something I should be doing to my '73 combat?. I've never seen this or read about, or even heard of it before. Does anyone know anything about this modification?

I think that is correct for the '72 model. Read this spec for them from the factory brochure. It specifically mentions the chaincase breather setup.

Ken

rvich · Jul 25, 2018

It also mentions modified scavenge pick up to allow high RPM operation. I'd be curious as to what they did for the pick up as well as the breather.

Holmeslice · Jul 25, 2018

I remember poring over Mick Hemmings' Commando PR Racer many years ago and noticing all kinds of breathers on it, including one from the primary. When I asked him about it he said, "Some of these breathers are very useful, and others not so much" and gave me a nod and a wink. He certainly put that bike through its paces.

kommando · Jul 25, 2018

rvich said:
It also mentions modified scavenge pick up to allow high RPM operation.

Likely to be moving it to the back as 72's lost the sump filter and had the forward pickup point so at high revs all the oil was in the back of the crankcases and nowhere near the pickup. Moving the breather to the primary would have made it worse than the road bikes as at least the rear crankcase breather on the 72's allowed oil an alternative route back to the tank.

rvich · Jul 25, 2018

kommando said:
Likely to be moving it to the back as 72's lost the sump filter and had the forward pickup point so at high revs all the oil was in the back of the crankcases and nowhere near the pickup. Moving the breather to the primary would have made it worse than the road bikes as at least the rear crankcase breather on the 72's allowed oil an alternative route back to the tank.

I was sort of wondering if they machined out the weir and redrilled the pick-up or if they did something a little more elegant. I suppose an email to Mick Hemmings might sort it out, as most of us will never see the inside of one of these.

lcrken · Jul 25, 2018

FWIW, my '71 PR came from the factory with only the timed breather at the end of the cam, with no other extra breathers added. I've seen a couple of other similar PRs with the same setup. It looks like there was a significant change for '72.

Ken

xbacksideslider · Jul 25, 2018

Neat brochure, thanks Ken.

PR ENGINE BREATHER

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