Crankcase breather question

BERT

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This 72 has the breather at the rear DS crankcase half. Is that piece of foam filter material ( called a separator on the parts list) between the 2 screens important? It was missing when I took it apart, so I got a new one, and looking at it, wonder if it could eventually disintegrate and clog oilways. Any thoughts or advice would be appreciated. Thanks.
 
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This 72 has the breather at the rear DS crankcase half. Is that piece of foam filter material ( called a separator on the parts list) between the 2 screens important? It was missing when I took it apart, so I got a new one, and looking at it, wonder if it could eventually disintegrate and clog oilways. Any thoughts or advice would be appreciated. Thanks.
I would install one of these breathers instead. Pricy but worth it
 

maylar

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I would install one of these breathers instead. Pricy but worth it
where does it go?
 

robs ss

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I did this mod on my 650 and goes well.
Bought a peewee 50 reed valve on ebay plus extra for carbon fibre reed (expensive - $26 in all)
Decided where to mount (LHS lower rear crank half - your's will be dictated by your existing port) and drilled and smoothly ported to suit.
The hard part, unless you have a machinist friend, is to make the clam aluminium housing - but can be done with hand tools - I did.
I have no guilt is using Jim Comstock's original idea for this - kudos to him. @comnoz
400% better breathing than any stock Norton crank ventilation.
Will replicate on my 500 when time allows.
Cheers
Rob
 
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where does it go?
Its only for 72's and the 73's 750's, it replaces the breather body on the back of the crankcases which was a 72 750 onwards feature dropped for the 850's. A cheaper alternative is to keep the breather body and fit an inline reed valve in the pipe above the breather body using a ebay motorcycle EGR valve which is a reed valve of similar function.
 

Carl H

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This 72 has the breather at the rear DS crankcase half. Is that piece of foam filter material ( called a separator on the parts list) between the 2 screens important? It was missing when I took it apart, so I got a new one, and looking at it, wonder if it could eventually disintegrate and clog oilways. Any thoughts or advice would be appreciated. Thanks.
When I took my Combat breather apart, it did not have the separator in it, I might have not have assembled it with one years ago when parts were not so readily available ? When I rebuilt the engine. So I did put a new foam in.

To prevent wet sumping .

I put in a shut off valve in the oil feed line from the Oil tank to the engine. Also I did install an oil pressure gauge , so I would know if I forgot to turn the valve on. So that is not a worry. And the Combat will no longer wet sump.



AS for the foam.. it could have been pushed into the oil tank ( in small pieces) when the sumped oil was forced through it. But it would be in small pieces over a period of time. Or some of it went into the oil in the base and returned to the oil tank. In very small pieces over a period of time.

For years I have used these as my vent valve. Because the Combat will pump sumped oil through the breather, I think I'll be OK as the shut off valve will not let my bike sump. , I know this type of vent valve works in my other bikes , 1973 -75 models , so I'll be testing the results as weather permits on the Combat.

I was lucky the valves I brought , recently, were NOS and made in the USA and very inexpensive. So I hope the testing goes OK, but I will keep my eye on it. I just installed it on the weekend , so the new "plumbing" is new to me. But so far so good.

  • thumbnail 1 - GM Power Brake Booster Vacuum Check Valve - Chevrolet Ford Buick Olds
  • thumbnail 2 - GM Power Brake Booster Vacuum Check Valve - Chevrolet Ford Buick Olds
  • thumbnail 3 - GM Power Brake Booster Vacuum Check Valve - Chevrolet Ford Buick Olds
  • thumbnail 4 - GM Power Brake Booster Vacuum Check Valve - Chevrolet Ford Buick Olds
 

robs ss

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Its only for 72's and the 73's 750's, it replaces the breather body on the back of the crankcases which was a 72 750 onwards feature dropped for the 850's. A cheaper alternative is to keep the breather body and fit an inline reed valve in the pipe above the breather body using a ebay motorcycle EGR valve which is a reed valve of similar function.
Agreed, but given @BERT already has the porting on the rear of his crankcases, he may as well use it.
 
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When I took my Combat breather apart, it did not have the separator in it, I might have not have assembled it with one years ago when parts were not so readily available ? When I rebuilt the engine. So I did put a new foam in.

To prevent wet sumping .

I put in a shut off valve in the oil feed line from the Oil tank to the engine. Also I did install an oil pressure gauge , so I would know if I forgot to turn the valve on. So that is not a worry. And the Combat will no longer wet sump.



AS for the foam.. it could have been pushed into the oil tank ( in small pieces) when the sumped oil was forced through it. But it would be in small pieces over a period of time. Or some of it went into the oil in the base and returned to the oil tank. In very small pieces over a period of time.

For years I have used these as my vent valve. Because the Combat will pump sumped oil through the breather, I think I'll be OK as the shut off valve will not let my bike sump. , I know this type of vent valve works in my other bikes , 1973 -75 models , so I'll be testing the results as weather permits on the Combat.

I was lucky the valves I brought , recently, were NOS and made in the USA and very inexpensive. So I hope the testing goes OK, but I will keep my eye on it. I just installed it on the weekend , so the new "plumbing" is new to me. But so far so good.

  • thumbnail 1 - GM Power Brake Booster Vacuum Check Valve - Chevrolet Ford Buick Olds
  • thumbnail 2 - GM Power Brake Booster Vacuum Check Valve - Chevrolet Ford Buick Olds
  • thumbnail 3 - GM Power Brake Booster Vacuum Check Valve - Chevrolet Ford Buick Olds
  • thumbnail 4 - GM Power Brake Booster Vacuum Check Valve - Chevrolet Ford Buick Olds
I used those plastic brake booster valves for years as well, they don’t last in the Combat configuration because a lot of oil can be forced through them on start up. This isn’t a problem on pre-Comeat and 850’s. I fitted the Madass140 version, which is similar to the CNW one Show above.
 

Carl H

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I used those plastic brake booster valves for years as well, they don’t last in the Combat configuration because a lot of oil can be forced through them on start up. This isn’t a problem on pre-Comeat and 850’s. I fitted the Madass140 version, which is similar to the CNW one Show above.
But, I have a shut on valve in the oil tank feed to engine , so I will not wet sump. And I will be looking it over carefully as I get more time on the new plumbing. I'll know more as time goes along.
 
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Agreed, but given @BERT already has the porting on the rear of his crankcases, her may as well use it.
His choice, the air goes the same way for both types of reed valve, the one in the pipe above the current breather body is slightly less efficient than the CNW one which is in the body, but you either pay $220 for CNW or typically £10 for an EGR valve off ebay in the UK.
 

Tornado

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The better alternative to the brake booster type is the Yamaha XS 650 reed valve from Mike's XS site:

 

Carl H

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I have one, But is is large and because I have the AC backing plate on space is limited, But iIfigured I'd try the Brake booster type first. It was a tight fit even with the booster valve.
 
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The Yamaha XS650 breather is a repurposed EGR valve, the 90 degree bend inlet to outlet limits where it can go, I use one where the inlet and outlet are at opposite ends eg 180 degrees making it easy to fit in a straight pipe. The internals are the same in both valves.

2011 Yamaha YBR 125 - EGR / Air Valve with Pipes

s-l1600.jpg


The brake booster valves are not designed for opening and shutting at 7000 rpm, so if you do a high speed run then it will not clear the pressure build up in the cases and your leaks will come back.
 
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