Oil in primary case - belt conversion...

Hi Paul,

If you don't regularly use the bike and it wet sumps, (oil drains down from the tank to the crankcases) when you start it up, even the best scavenge pump will not remove the oil before some of it has been squeezed through the seal into the chaincase. (particularly if the oil level in the crankcase is above the edge of the seal) Maybe consider starting the bike a bit more frequently and fit a pressure control valve in the breather pipe to create a partial vacuum.

Whilst reams have been written about PCVs, and pretty recently on this forum, I use a Yamaha XS650 item available from XS650shop.de via the web costs about 20 euros. You can spend a lot more, (the Bunn breather is about £80) but the Yamaha item is a quality piece of kit and hasn't got Yamaha written on it.

Your model was famous for passing more oil up the breather than the scavenge/return pipe on initial start up.

You could always fit a drain pipe on the chaincase - there's no need for the chaincase to be oiltight now. Or how about a nicely distorted pressed steel one from a Dominator - that wouldn't let oil build up...

'I've had this issue since I bought the bike, over two years ago - I get a build up of oil in the primary case which I have to drain down every six months or so.'

Does it do this whilst in use? Or are youreferringto when it's been standing a while? I've always 'managed' the wet sumping on my bike, rather than attempt to cure it, by draining the sump every 2-3 weeks during the winter layoff and tipping it back into the oil tank. No big deal. This way it doesn't get to a high enough level to seep past the crankseal. The problem is not an issue during the warmer months because it is used regularly. Perhaps not the best solution, but the cheapest!

Hi Paul, my personal belief with the Combat engine is that the problems were not down to the state of tune at all (had nobody ever fitted high compression pistons to a 750 Norton before 1972? There wasn't a rash of wrecked main bearings when racers tuned thier Atlas's or Commandos before '72).

So what was different on the Combat? The scavenge was moved to the front of the crankcase and the breather to the lower back of the crankcase. The theory being that the scavenge would return the oil from the lowest (front) part of the crankcase and the large bore breather pipe at the backwould handle breathing problems. What happened was the crank throws the oil to the back of the case and the scavenge sucks air. The oil meantime builds up in large amounts in front of the rear mounted breather, reducing the crankcase capacityincreasing crankcase pressure and it's only means of escape is by being blasted up the breather (the breatherwas even fitted witha foam "separator"in it to further frustrate the oil's passage) and socreating extra load on the bearings and making the engine work extra hard. If you are at all a sporty rider, as well as increased oil leaks you will also find the bike runs a lot hotter. In my humble opinion wet sumping due to oil pump bypass while it is standing is not the issue but the fact that your engine will be permanently wet sumped when running due to the fact that the oil can't get away.

Is it not strange that Nortonran with this system of scavenge and breathing for one year only?They movedthe scavenge back to it's original position for 73 onwards and moved the breather high up in the rear of the timing case.

The problem can be resolved but it is a total engine strip down I'm afraid. If you would like to email me iltrail@gmail.com">oiltrail@gmail.com I'll give youthe details of how to do it and some photos, otherwise if you would prefer someone to do it for you I can recommend Pete Lovell Developments on 0121 558 2110, again in my humble opinion he is the best engineer in the UK still working on Nortons and he also manufactures parts for them.

There you go, the theory and the fix.

http://www.oldbritts.com/n_c_case.html

You could try a Yamaha dealer. One of my branch members has changed his to a Bunn breather, I'll ask him if he's finished with the Yam one.

I paid â?35.50 from Heiden tuning in March but I cannot find them on their website anymore. It looks like they are getting hard to get, they are out of stock at XS650 direct aswell.

Previously wrote:

Wow - lots of info - thanks.

Its a lot worse the last few months, with the bike standing and not riding - great summer we have had!

An engine strip, while fixing the root cause, would be very expensive, for what is an small job to empty the primary case every few months.

I spent a happy hour on the Dutch web site (XS650shop.de) looking for the PCV and then sent the guy an email - out of stock and no outlook - I did find one on a US web site for $20, but add $37 postage.. (http://www.xs650direct.com/products-40.html).

Anyone know of any otherEuropean supply?

Thanks - Paul.

Due to what I imagine to be some unique American emissions legislation they have some very useful one way valves for use as crankcase breathers on cars- Positive Crankcase Ventilation (PCV) valves and also Power Brake Check valves, these are an inexpensive answer to crankcase breathing problems on our parallel twin engines. They are a one way valve that keeps a decompression in the crankcase and allows the small amount of blow-by that occurs past the piston rings to be vented. My experience was that when touring the USA these little devices were readily available in car accessory shops in racks of bubble packs in much the same way & quantities as we would find bulbs presented in Halfords.

I have asked local motor factors but they don't list any such valves and are unaware of them. However internet searches do find these items in American shops, they are inexpensive (as little as $4) so I guess that the cost of postage may well exceed the cost of the part â unless of course you are lucky enough to know someone who is travelling back from the States.

I'll give the hose inlet and outlet dimensions because they are easily inserted in the hose line and remember because such a small amount of air moves you really don't need large bore pipes.

Listed below are some of the examples that I spotted while there and have used myself;

The first one is a Power brake check valve, it has a very useful 90 degree which can be used as a neat way of routing the breather pipe around a tight bend. The inlet will suit 1/2â breather pipe and the outlet 3/8â.

http://www.summitracing.com/parts/rnb-80190

You can search on the U.S. Fram website for all PCV valves by entering *FV*

Others that I bought back are

http://www.framcatalog.com/PartDetail.aspx?b=F&pn=FV275 â probably more suitable size wise â straight valve 1/2â in, 3/8â out, plastic valve. Unfortunately the one I bought passed air in both directions.

http://www.framcatalog.com/PartDetail.aspx?b=F&pn=FV277

http://www.framcatalog.com/PartDetail.aspx?b=F&pn=FV263 â FV 277 & 263 both more robust metal valve but 5/8â in and ?â out