Crankcase Breather

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DaveH,

Are you coming to Donington? I'll show you the one way valve I use....basically just a flapper valve like the G50, but inline! You missed Darley Moor at the weekend......weather was s$%te, paddock was almost like Skerries....you would have felt at home, myself and Cormac certainly did :)
 
John — sadly, I will miss the big Norton meet at Donington because I will be in Spa Francorchamps. I can imagine the quagmire that you had at Darley Moor. I am hoping this summer is not going to be a re-run of last year's, otherwise there will be more muddy paddocks that resemble motocross meetings! I will PM you in the next short while.

Dave
 
I have the Yamaha XS 650 breather valve. Very good results, but the CNW setup looks to be superior. The thing I like about the CNW valve is it's placement. Having the valve at the crankcase does seem superior to having one inline far downstream. I have a 72 Combat so I used the stock crankcase spigot with the XS valve. Right now I have the engine apart and I blanked off the crankcase port and drilled the timing side per old Britts. Having second thoughts now. I'm going to look into placing the XS valve directly to the stock crankcase spigot and plugging the timing side of the crankcase.
 
Hi Jim , so in that way (combat style cases) , would you plug the scavenge oil hole which is in the front of the timing case (as per Old brits mods) ?? I am working on this kind of cases for the son of a freind of mine , and want to do it right first time........my cases were all 850, either in my cdo , or in my cafe racer, and for the moment they've got the XS reed valve in line in the std breather line outing from the timing case, but all theese works make me thinking (specially Jean 's one, and many thanks to CNW/ Jim Comstock , but I am not playing in the same league, unfortunately!!!)........sure there are some people still trying to improve, those old bikes, and I can mention too "Ludwig " who is heading to improve the weight, and the cycle parts (he's quite right , as good brakes are a must when you are thinking about going faster, he said too than saving weight is free horse power.........)," Grand Paul", is heading towards a new style which is amazing and show a lot of work and ingenuity , I love his way of making that new frame/forks............"Jean" is going strong with a lot work but staying in "old style" with drum brakes and featherbed frame though plenty of nice "goodies", another guy which is not on this forum is Jim Schmidt, who works as an independant to make those brilliant lightweight pistons and longer rods, just to save weight and thus reducing dramatically the vibes, he works on his own and never give up still he found the right company to comply with his working plan.............and us , hundred of humble guys , just trying to ride and solve our Norton problems through this wonderfull community with limited budget and /or knowledge, but every day I can go a step further on this particular road , grace to you old chaps .......THANKS !
 
Hi Jim , so in that way (combat style cases) , would you plug the scavenge oil hole which is in the front of the timing case (as per Old brits mods) ??
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I'm going on the assumption oil scavenging and crankcase breathing are mutually exclusive. I have done the Old Britts mod, plug hole and mill off the scraper flange. I really don't know if this will work using the original Combat crankcase breather port. With the Old Britts mod the original crankcase port is blocked off. My concern is that you might get oil evacuation using the crankcase port. If I had not already done the Old Britt mods I would stick with the Comstock/CNW setup.

I do believe Jim Comstock is spot on about a pressurized crankcase robbing horsepower. Not to mention a pressurized crankcase sure creates oil leaks in our Nortons. I changed many a crankshaft seal, even going with a hi dollar teflon seal, all to no avail. Once I put the XS breather in line the leaks stopped.
 
Once I put the XS breather in line the leaks stopped.
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Jim — that's good to hear, and it's good enough for me too, until such time as the cases are apart.

Dave
 
Jim I also have done the Old Britts modification and was also thinking the same thing, Is it going to work if we were to install the breather on the back instead of the timing cover? James Comstock or Matt may be able to help here. I would really like to install that kit as it would be hidden and in my opinion if Comstock developed it and Matt's making it the quality is tops. Reading his post on why it's better to mount it on the cases makes a lot of sense in that all that air could never go back and forth that fast through those holes in the timing cover. I had never really thought of the speed of the pulses. Maybe its time to call Matt and ask if it will still work with our setup? Have a great day guys, Chuck.
 
Chuck,

Keep us posted about the breather mod, i.e. compatibility issues.
 
Im curious as to why the crank case breather mod is placed low on the cases? My thinking would have it placed higher up out of the way of oil . To me it sounds a bit messy but I guess Jim has tried and proven its placement.
Any thoughts?
regards Foxy
 
I am also interested in seeing whether the Old Brits crankcase modification still works with the original breather in place and a PCV valve attached to the breather tube. It strikes me that with the oil pickup further back any wayward engine oil that would previously have jumped over the baffle and out the breather, would now simply be sucked through the new scavenge feed hole and back to the tank. I am sure that I have seen this modification detailed elsewhere without the relocation of the breather.
 
No, there should be enough oil coming back from the head which will be flung around by the timing chain and gear train.

Jean
 
ludwig said:
Just wondering : a reed valve in that location ( bottom of crankcase ) will become filled up with oil . I would think this oil will prevent the membranes to work as designed .
Why not putting it on ( top of ) the oil tank , well above the oil level ?
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It'll be interesting to see what happens to the first wetsumped engine with the reed valve and someone tried to kick it over. Wouldn't it just blow past the reed valve and up into the tubing to get stuck there?

The reed valve needs to be as close to the crankcase as possible. Further away and the pressure pulses and vacuum won't be as effective because of the volume of air in the tubing.
 
ludwig said:
when blocking all these holes , aren't you concerned about the lubrication of your timing gear , chain and camshaft bushing ?
i asked the same question a couple posts back,and got same answer.it seems like if cnw do it like that its godspel.as i see it the feed hole into the timing chest from the head and the new lower drain hole are the same size,so in theory there will be as much oil going out as there is coming in,leaving nothing for the crank pinion to pick up on and splash about, i would leave the original drain just above the pump on the left,
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Moving the drainback holes lower is done to reduce the amount of oil hanging out and being whipped by the timing gears that on a stock Commando are completely imersed in oil. This tends to heat the oil and cause foam, neither being desireable. I have run my engine with a clear cover over the points cavity which has had the bottom removed so I could watch the gears. There is still plenty of oil being thrown off by the timing gear to lube everything very well. Drilling the hole lower on a Commando engine brings the oil level in the chaincase down to about the same level that stays in an Atlas motor with its vertical engine. It also drops the oil temp considerably. [ Jean, it looks like you did a fine job modifying your cases and building a valve assy. I don't have a problem with people with the tools and knowledge copying my design. It ain't rocket science and I am never going to get rich doing this. I just hope to be able to keep my head above water so I can keep doing what I enjoy.] James Comstock
 
James, I was wondering if the mods by Old Britts have been done to my 72 cases can I still use the CNW breather with the same results? He did the extra holes in the timing side and also milled off the scraper part at the rear. Are you familiar with his work? Thanks for your time and keep up the good work, Chuck.
 
The Old Britts job of milling away the scraper and adding extra holes for the oil scavenge pump pickup are good. I have found best results with the reed valve breather if the holes into the timing chest are blocked off. The smaller crankcase volume that results makes the reed valve work better.
 
Thanks James for your willingness to share this information with us - it is very much appreciated.

As I am yet to modify my Combat cases, I just want to be clear I have it right (sorry I'm a little slow).
- remove oil scraper as per Old Brits and add extra scavenge holes
- block timing chest holes and reposition oil drain hole lower
- fit CNW style crankcase breather

Cheers, Ben
 
I ride a Norton 750 72 breather at the back of the crankcases I have not any problems with breather or oil leaks ,I build my own engines rather than let a shop do the work.
yes cnw does make some fine parts but the breather is over doing it.the engine design is over 40years old take it for what is .
ride it.

if it ain't broke don't fix it
 
comnoz said:
Moving the drainback holes lower is done to reduce the amount of oil hanging out and being whipped by the timing gears that on a stock Commando are completely imersed in oil. This tends to heat the oil and cause foam, neither being desireable. I have run my engine with a clear cover over the points cavity which has had the bottom removed so I could watch the gears. There is still plenty of oil being thrown off by the timing gear to lube everything very well. Drilling the hole lower on a Commando engine brings the oil level in the chaincase down to about the same level that stays in an Atlas motor with its vertical engine. It also drops the oil temp considerably. [ Jean, it looks like you did a fine job modifying your cases and building a valve assy. I don't have a problem with people with the tools and knowledge copying my design. It ain't rocket science and I am never going to get rich doing this. I just hope to be able to keep my head above water so I can keep doing what I enjoy.] James Comstock
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Thanks, but I am just applying a receipe you wrote. All this talk is probably going to bring more customers though so be prepared to make some more of those kits :D :D :D

Jean
 
I may have missed something but I didn't see any instructions for drilling additional scavenge pick up holes in the Old Brits description, the milling away of the oil scraper uncovers a drilling hole for the scavenge system further back from the original hole which then has to be blocked up. Am I reading this correctly?

Norton in Japan, you are my nearest Norton neighbour, assuming of course that your chosen soubriquet actually indicates a geographical location rather than something more obscure or whimsical. I know a chap at the Tokyo Peninsula Hotel who has a Commando. I have to go there from time to time to fix a vintage Rolls Royce.
 
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