Xs650 mount near tank or breather?

rvich said:

pvisseriii said:

acadian said:

hmmmm, how much pressure are we talking about here? Prior to fitting I gave my unit the entirely "unscientific" breath test and found very little was required...

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Being that this is a free flowing (breather) intent, any pressure would be too much. Any more than a very little could cause oil to build up before the reed valve, compounding the problem requiring even more unwanted pressure to operate the valve.

Try this: blow air through the valve, then try to blow 20w50 through it. Or straight 50w. It won't be long before engine oil starts collect in the primary and on the ground.

Keeping air from coming back through is one thing. Keeping it from escaping is another. Any restriction is unwelcome.

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pvisseriii, is your '72 running with a modified or unmodified sump? It might explain the difference in results.

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Now I know this is against the Old Britts theory but I think that the scraper in the sump is there to prevent oil from pooling there and getting blown out the breather. Needless to say, I'll never mod the sump. With a reed valve breather it will work just as intended. Where Norton got it wrong was the uncontrolled breather, just a gauze to catch the emulsified oil.

We know a lot more about the deficiencies of the Norton today, are less willing to accept them and know how to correct those deficiencies."

Totally agree and I am certainly one of the folks trying to correct the deficiencies though clearly, there are varying opinions of the best way to correct some of them and whether they are or are not real problems.

But OTOH, I find it ironic that I feel the need to correct all these things when the bike, as built, still exceeds the capability of most of us to utilize it. Stock Commandos lapped the IOM TT course at over 100 MPH and I probably couldn't do that on a current Ducati 1198! Then again, I love fiddling with classic mechanical things and the Commando is perfect for that!

I suppose some of these things would be just fine if we left them alone, But remember when your Dad told you as a kid "Son if it ain't broke don't fix it" Well I'm grow up now and I want to fix it if it ain't broke, LOL.

Now I know this is against the Old Britts theory but I think that the scraper in the sump is there to prevent oil from pooling there and getting blown out the breather. Needless to say, I'll never mod the sump. With a reed valve breather it will work just as intended. Where Norton got it wrong was the uncontrolled breather, just a gauze to catch the emulsified oil.

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Agree with the first part, oil pooling etc but where does the pooled oil go? With the original pre 72/3 rear pickup out of action on 'Combats' what is to stop the oil going up the breather, whatever kind it is? Folklore or theory, whatever we care to believe, says that the rear breather passed more oil back to the tank than the pump. This is presumably due to the front pickup being exposed at high speed and also why non modified cases with the original breather work OK. It certainly did that on mine emptying the tank in 10 mins at 4k+, with the breather blocked and moved to the timing case. The only 'flaw' ? with this theory is how did the oil get past the foam filter in the 'Combat' breather. So with any kind of breather installed in the LH case how does this persuade the oil to return via the front pickup when it must still be pooling at the rear? Norton after all moved the pickup back to the rear 73 on.

Keith1069 said:

Now I know this is against the Old Britts theory but I think that the scraper in the sump is there to prevent oil from pooling there and getting blown out the breather. Needless to say, I'll never mod the sump. With a reed valve breather it will work just as intended. Where Norton got it wrong was the uncontrolled breather, just a gauze to catch the emulsified oil.

Click to expand...

Agree with the first part, oil pooling etc but where does the pooled oil go? With the original pre 72/3 rear pickup out of action on 'Combats' what is to stop the oil going up the breather, whatever kind it is? Folklore or theory, whatever we care to believe, says that the rear breather passed more oil back to the tank than the pump. This is presumably due to the front pickup being exposed at high speed and also why non modified cases with the original breather work OK. It certainly did that on mine emptying the tank in 10 mins at 4k+, with the breather blocked and moved to the timing case. The only 'flaw' ? with this theory is how did the oil get past the foam filter in the 'Combat' breather. So with any kind of breather installed in the LH case how does this persuade the oil to return via the front pickup when it must still be pooling at the rear? Norton after all moved the pickup back to the rear 73 on.

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Does anyone have a clearer picture of a 72 crankcase that what's on the Old Britts site? Ideally an empty crankcase photographed together and then of each side.

What I was trying to see is how the oil escapes from the pocket in an unmodified case. There must be some way, I assume the other side of the case allows it to escape?

Am I correct in assuming that if you modify the case of an early 72, you HAVE to move the breather because you are now allowing the oil to pass to the breather outlet unobstructed where as before the oil had to slosh up over the barrier(the area milled out in the modification) to be expelled and also causing pressure from oil trying to pass through the gauze of the breather and pushing it out the crank seal whether you have a check valve in place or not?

Or, if I may add, does the modification allow pooled oil in this pocket to escape to the oil pickup in which case the breather could remain, a check valve added and perform more effiecently?

Or, Is there an other answer all toghether?

In conclusion, depending on the answers given to the question stated above, a check valve mounted on the breather of an unmodified 72 is mute. And finally trying to push 50w oil past the gauze/screening much less a check valve is going to cause crank some pressure(60 pumps per second @ 3600 rpm). (It took me a little while to wrap my head around that one.) With the xs650 unit in place which in my opinion functions too good for our own good and you got puddles. Mounting it as far as possible from the casing is your best bet for relief of pressure giving air a chance to push the oil through to the tank.

Again, much of this depends on the answers to the questions stated above. :roll:

OK I'm ready, let it fly!

The breather is closed on the back of the case, And then added to the timing side of the case. It mounts like the 850 models, I would think and have been told that the closer the valve is to the case the better. On the issue of pickup for the oil it is moved back to the rear of the case like the older cases and a pocket is created so the oil has a place to pool. You can read about it on the Old Britt's page. http://www.oldbritts.com/ob_start.html Look in the tech articles under oil pressure loss.

I have read the article on OldBrits and moving the breather to the timing case is not manditory but prefered by some. The real question they leave me with is about pluging the forward located oil pickup. They never say to drill another hole to the rear of that tunnel for oil pickup. Im I missing something?

Sorry if this gets off topic, but its related. I've seen much worse that goes unrepremanded. :?

No new holes are needed, Just plug the one in the front. The ones that lead from the back will do fine.

If you look closely at the pictures Fred has on his site you can see the timing side has holes drilled in it for oil pick up, They are in the mating surfaces of the case. Also there is a channel that also runs along the mating surface that brings oil to one of these holes.

So what the heck does the inside of an 850 case look like. I can find multiple photos showing 750 cases with and without modification but after searching I can't find any photos of an 850! CNW/Jim Comstock are moving their breathers on 850s to the 750 location. I have faith that they didn't guess it was a good idea.

I posted shots of my 850's cases showing both sides open, side by side in the "test mule" build thread.

Note: I modded the left half.

test-mule-850-monoshock-build-t4774-60.html

Thanx Paul,
Sometimes it is hard to figure out what to use as a search!

grandpaul said:

I posted shots of my 850's cases showing both sides open, side by side in the "test mule" build thread.

Note: I modded the left half.

test-mule-850-monoshock-build-t4774-60.html

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That would help but I'm trying to figure out what a 72 looks like (same pose tho').

Little slow finding the disk, LOL LOL

Sorry for asking such a noobish question, but what are these breathers connected to? Is it in the line that is already coming from the crankcase and going to the oil tank? I thought that was pumping oil up into the tank. Is there a vent line that I don't know about or are you all drilling a new line into the crank case? I have a 75 and would like to do this mod to cure some leaks. I need the details that you would assume everyone already knows. :|

Thanks

If you have a 75 Mk3 you have the breather off the back of the timing case, it runs upto the oil tank which itself is further vented to the air filter, on a 75 there is a oil seperator in the routing somewhere as well but I don't have a Mk3 to know exactly where. If you have oil leaks you need to add a one way valve in the breather pipe running from the timing side to the oil tank, this reduces the crankcase internal pressure and reduces oil leaks, it lets air out on the down strokes but does not allow it back in on the up strokes.