1972 Crankcase Breather Mod

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I know his is a well covered topic, but a lot of the posts are from a good few years ago.

I have a small but annoying leak from the top crankcase joint immediately behind the barrel on my 1972 Commando. It only leaks when running. I don’t have any other leaks and since she is running well I don’t want to do any major tear down work at this point.
Compression is OK so I don’t think that is the cause of the crankcase pressure.
I like the look of the CNW breather mod and it makes sense to me to have the valve attached to the crankcase so it gets hot and condensation issues are avoided.
But.. it ain’t cheap - especially when you factor in 66USD to get it to the UK!

Please can I have feedback from anyone who has fitted this mod. Has it fixed these types of weeps/leaks?

Also are there any other alternatives that attach directly to the crankcase that I should consider?
 
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It fixed my leak behind the cylinders (1972 also). It will still leak there one time when I start it after a winter of sitting but that is because of wet-sumping. Perfectly dry otherwise.
 

olympus

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Hi Steve, I opted for the crankcase valve from HNW, this isn't a bolt onto the crankcase valve, but the way I have located mine means I only have a 75mm hose form the OE breather, now only there to mount on the hose and just retaining the metal disc with holes.
When you look at the installed valve on HNW website it above the carbs and my worry with this location is the same as yours....condensation
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Go to Ebay UK, search in Motorcycle parts for EGR valve, there will be a selection of valves which will be exactly the same as the XS650 reed valve and variations, new and second hand. For the 72 I use that route and select a 180 degree version so it fits in a straight run of the breather hose close to the outlet.

This is the XS650 version ie 90 degree turn.


And a 180 version I use.

 

Fast Eddie

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I know his is a well covered topic, but a lot of the posts are from a good few years ago.

I have a small but annoying leak from the top crankcase joint immediately behind the barrel on my 1972 Commando. It only leaks when running. I don’t have any other leaks and since she is running well I don’t want to do any major tear down work at this point.
Compression is OK so I don’t think that is the cause of the crankcase pressure.
I like the look of the CNW breather mod and it makes sense to me to have the valve attached to the crankcase so it gets hot and condensation issues are avoided.
But.. it ain’t cheap - especially when you factor in 66USD to get it to the UK!

Please can I have feedback from anyone who has fitted this mod. Has it fixed these types of weeps/leaks?

Also are there any other alternatives that attach directly to the crankcase that I should consider?
Steve I’ve got an unused one you can have at cost, free postage (in U.K.) and no import duty!

They‘re a great unit, but I didn’t have clearance for it with my none standard set up, so I used the sump plug type instead. The bolt on unit is therefore unused. PM me if you’re interested.
 
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Hi Steve, I opted for the crankcase valve from HNW, this isn't a bolt onto the crankcase valve, but the way I have located mine means I only have a 75mm hose form the OE breather, now only there to mount on the hose and just retaining the metal disc with holes.
When you look at the installed valve on HNW website it above the carbs and my worry with this location is the same as yours....condensationView attachment 17927View attachment 17928
I didn't bolt mine down, just let it float on the hose. If you use a stiff enough hose coming off the stock breather it can't really go anywhere.
 
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I used the MIkes XS breather on my 72. Hardley any leaks. He does seem to be out of them for quite some period of time.
 

olympus

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I didn't bolt mine down, just let it float on the hose. If you use a stiff enough hose coming off the stock breather it can't really go anywhere.
Not that is true...it's just Me being me with it... :rolleyes:
I also used two long legged pre formed elbow hoses joined together just for good measure...
I have to say they do what they say on the can.... after initial start up to check oil flow I took off the rocker covers and you could feel the vacuum physically pull the covers back on
 
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Not that is true...it's just Me being me with it... :rolleyes:
I also used two long legged pre formed elbow hoses joined together just for good measure...
I have to say they do what they say on the can.... after initial start up to check oil flow I took off the rocker covers and you could feel the vacuum physically pull the covers back on
I mean it’s a lovely bracket and all but I couldn’t have brought myself to drill the holes in the cradle.:p
 

trevorpacker

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I used the MIkes XS breather on my 72. Hardley any leaks. He does seem to be out of them for quite some period of time.
Mapcycle.com have them
 
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Thanks Trevor for the link. That's actually 10 dollars cheaper than Mikes XS has them listed for.
 

xbacksideslider

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I used that one, the one depicted at MAPS, but made a plate to go between it and the crankcase, tossing the barb on that side.

Clamped to crankcase by two bolts and a steel straddle strap. Wish I had a pic


Not elegant, just gets the reed as close as possible to the crankcase.
 
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Translucent hose. I wish it was a little clearer but you can see the oil if you look hard enough.


Short hose just and the EGR sits just above the cradle so it doesn't bang on it. Whomever I bought this from many moons ago had put the barbed fitting on it. Made my life a lot easier.
 

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