Breather on Combat Case

Hi guys, I know that this has been discussed at length, but is there any benefit for the breather on the back of the 72 Combat case to be relocated? I was considering blocking the original breather on the back of the case and moving it to the inside of the timing side case. -Probably ditching the factory breather and using my XS650 reed valve. Would there be any benefit from doing this for a road bike? I've had the valve in line tucked away into my battery box but it's rather unsightly.

I put the XS valve in line with the factory one, works well.

Johnnymac said:

Hi guys, I know that this has been discussed at length, but is there any benefit for the breather on the back of the 72 Combat case to be relocated? I was considering blocking the original breather on the back of the case and moving it to the inside of the timing side case. -Probably ditching the factory breather and using my XS650 reed valve. Would there be any benefit from doing this for a road bike? I've had the valve in line tucked away into my battery box but it's rather unsightly.

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You don't need to ditch the original oil strainer (breather). Put the XS650 reed valve at the other end of the breather hose under the seat then the smaller diameter hose goes from the reed valve to the oil tank. As far as relocating the breather to 850 style, I did this and the sump oil pick relocation mod on my '72 during the rebuild in '98. I would not do it again. Really doesn't improve anything for a road machine.

The Combat breathing issue is really the oil drain up front issue so crank and acceleration froward sweeps oil to rear letting oil volume build up till its returned by low down rear breather hose and a annoying amount oil out every seam > if run into rpms the 2S cam wakes up. If ring blow by is in normal range then I've found only takes a one way valve of about any sort, anywhere in line with the big breather hose keeps oil out the seams, even well into red line the engine becomes an elastic unstable cartoon character. The better the evacuation the better can keep up with increasing wear ring blow by though. On factory stock as can be Trixie Combat just a brake valve in hose up at frame level near tank worked w/o any engine mods - till air boots cracked to let grit in. Nothing clears a wet sump cold start up like the big Combat return hose. Open cap and see for your self, at rather low rpms or stand back to avoid the jet to outside.

Johnnymac said:

Hi guys, I know that this has been discussed at length, but is there any benefit for the breather on the back of the 72 Combat case to be relocated? I was considering blocking the original breather on the back of the case and moving it to the inside of the timing side case. -Probably ditching the factory breather and using my XS650 reed valve. Would there be any benefit from doing this for a road bike? I've had the valve in line tucked away into my battery box but it's rather unsightly.

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No benefit. You are trying to get the crankcase to breathe better, not the timing chest. Best place for the reed valve is on the crankcase or as near as you can get it.

The TS case only has couple small holes to commute with the crank case so not best plan unless new bigger holes made to cut the pumping losses. This is what i did on Peel and even white glove - Q tip test in clear breather hose off back of TS case stayed completely oil free while Peels engine fasteners got dry rusty. Easy enough to put a PCV in the Combat breather hose and see if works well enough, if not there'$ a number of ways to go beyond that. What's best is to add active evacuation but I'm the only one doing that I know of on a Norton.

" You are trying to get the crankcase to breathe better, not the timing chest "

Yea But : the incresed VOLUME of the two combined , reduces pressure fluctuation per revolution .
also with little holes drillede at lower timing chain run , theres a chance it improves lube there . :?

For five million revs , its likely closed breather ( pre 72 system ) increases piston life , in the manner
of the nasty two strokes , whereby the crank case compression cushions the piston about B D C .

This could improve output as well ; as well as increseing external corrosion resistance long term .

CNW has a reed valve replacement for the stock rear breather which just bolts up in the same spot. I got one when I visited out there last month. Really nice work!

Russ

batrider said:

CNW has a reed valve replacement for the stock rear breather which just bolts up in the same spot. I got one when I visited out there last month. Really nice work!

Russ

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+1
Works great on my combat. No leaks

Yes but to put CNW-Comstock's reed kit on a Combat breather baffle location means removing gear box and enough engine vitals to tip engine out the way. Been thinking to try one of these myself.

Engine vacuum pulse diaphragm pump

THe timing side breather works great as long as provisions are made. Remember all 74's on have the breather there. I have used the original location but only to supplement the timing side breather. I truly cannot say whether running both at the same time made a difference.
Here is a good example from Dyno Dave's site of the factory drillings from a later 850 and a 72 from Old Britts.

hobot said:

Yes but to put CNW-Comstock's reed kit on a Combat breather baffle location means removing gear box and enough engine vitals to tip engine out the way. Been thinking to try one of these myself.

Engine vacuum pulse diaphragm pump

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Took me 1.5hrs to install. time well spent, and I dont have to worry........... 8)

hobot said:

Yes but to put CNW-Comstock's reed kit on a Combat breather baffle location means removing gear box and enough engine vitals to tip engine out the way. Been thinking to try one of these myself.

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No

Ok but I wasn't able to access the baffle bolts till engine tilted, so glad to know others can. With Peels moved to the TS back side it allowed trany to slip out with just the primary removed. The state Trixie is in now would make a perfect test case for various breather types and locations as she lost her case, barrel and head sealing from blow by smoking gritting away of rings last year which re-ringing solved the smoking but didn't allow resealing by just re-nipping, so if I got over 70 mph or gave much throttle to accelerate with Combat relish rpms, she'd weap oil enough to drip off excess parked and colors side covers dark oily, and chrome on kicker and rear sets and front of Z plates and rear rim... The Krank PCV in top of breather hose is not able to keep up as it was prior, so might try the XS valve in breather but don't think anything but active evacuation could help her on 2S cam zone upper 5000 grand and beyond, until all the above resealed with Hylomar and silk or cotton thread or dental floss backed up. May try the diaphram pump if I can get a push start or must wait till mood strikes to fix kicker but that half removes engine so might as well keep going to re-seal. In mean time I understand how these ole sweetie pies got set up so long forgotten about - to still find here and there to recover to worry over and shop for again.

hobot said:

Yes but to put CNW-Comstock's reed kit on a Combat breather baffle location means removing gear box and enough engine vitals to tip engine out the way. Been thinking to try one of these myself.

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Steve,
You need to take your mittens off first.

I have installed quite a few of them without moving the engine or gearbox. Jim

Ok so the truth is out I'm just a stranded pilot not a competent mechanic.