Are breather mods necessary

I'm still in the tear-down phase for my '72 Combat Interstate. I've decided to restore it to as nearly stock as possible save for electronic ignition. My question is whether relocating the breather from the back of the crank case to the timing cover is necessary for a daily rider. I don't ride very hard and rarely see the angry side of 5,000 rpm on my other bikes ( 71 BMW 750/5 and 78 Yamaha SR 500). I am going to check and if necessary replace the crank bearings and will install an anti sump valve. Thanks, Ben

Scout63 said:

I'm still in the tear-down phase for my '72 Combat Interstate. I've decided to restore it to as nearly stock as possible save for electronic ignition. My question is whether relocating the breather from the back of the crank case to the timing cover is necessary for a daily rider. I don't ride very hard and rarely see the angry side of 5,000 rpm on my other bikes ( 71 BMW 750/5 and 78 Yamaha SR 500). I am going to check and if necessary replace the crank bearings and will install an anti sump valve. Thanks, Ben

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OMG! You are going to tear your engine down to "check" if it needs new crank bearings? If you go that far then by all means do this engine right. Unless a low mileage Combat, it is most likely that the crank bearings were changed out long ago. Shit can the stock breather and install a proper reed valve as sourced from Colorado Norton Works or others. Yes, daily riders benefit from not leaking oil from a pressurized crank case. Send the timing cover to Alternative Motorcycle Repair in Arizona to modify it so your bike will stop wet sumping. Yes, an anti wet-sump valve will also stop wet sumping, but at the risk of diminished oil supply as a best case scenario, and catastrophic engine failure as a worse case should total loss of oil to the engine occur. Do some more research on this forum before proceeding. Nothing worse than to strip and rebuild an engine without having a full picture of what could have been done when it was apart. Lots of discussions on these topics.. Good luck! You will love your Commando.

There is no need to move it. Mine has been as it was built since the day I bought it new 44 years ago. Only change I made was to fit a one way valve in the line. Mine was from a VW car and is fitted close to the oil tank.

Ian

Hello Scout63

Definitely agree that the one-way valve on the breather helps reduce oil leaks.
I have the XS650 type valve on my '72 Roadster (non-Combat).

I don't know how much you know about the main bearing types but if you are unsure it would be worth posting some photos on this site for identification. See LABs sticky thread for how to do this http://www.accessnorton.com/technical-information-how-post-photos-t2357.html

Good luck with the rebuild.

Andy

IMHO, nothing is 'necessary'... But many things are 'desirable'...

It must be considered to be proven beyond reasonable doubt that a one way reed valve breather is a good idea on Norton's by now?

The 'inline' versions are a great fix for those not wanting to delve into the engine.

However, if you are intending to strip the motor anyway, then plugging the timing chest and fitting a reed valve to the cases is definitely a good idea. It's very little extra work on top of a good rebuild and then you know you've 'done it right'. Buy 'right' I mean it is theoretically better to have the reed valve closer to the 'pulses' created in the cases. Comnoz did a thread on here where he tested the various types showing that they all work, but the case fitted versions do work best.

Matt at cNw sell one that bolts to the back of the cases. Comnoz sells one that screws into the sump plug hole on most Commandos (Comnoz actually makes both).

I use the sump plug version and a plugged case and it seems to work great.

On my 920 build I'm going to use the version that bolts to the back of the case, mainly because it's already machined for it, so it seems an easy thing to try.

I am definitely going to install a check valve. Also going to check the bearings, lay shaft bearing, etc. The bike has 12000 miles. I am also seriously thinking of machining the cases ala Old Britts for better oil pickup and various mods to control leaks. At this point I like the idea of it appearing showroom but for ikon shocks which I have always used and shouldered alloy wheels. I know I'm tiptoeing on the edge of a slippery slope and there are as many looks as owners. But motorcycle rebuilds are one of the few things where we can do exactly what we want. Probably a different post but I'm not sure which is better - fixing a bike and dreaming of riding it, or riding a bike and remembering fixing it.

pieas dont butcher your cases like this. as you are in mass contact dyno dave as he can do a far nicer job with out the butcher work.

Scout63 said:

I am also seriously thinking of machining the cases ala Old Britts for better oil pickup and various mods

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If you have combat cases, you already have the option to bolt on a more effective reed breather than a timing chest modification would give you.

I have a '70 commando. It doesn't have the bolt on reed breather option because it doesn't have the rear crankcase breather port that a combat case has. It also has a frame crossmember which precludes using Jim's sump plug crankcase breather SO,.... I have an "oldbritts" style timing case breather modification. It works, but If I had the option to bolt on a reed breather directly to the crankcase like you do, I would have done that.

As far as a rebuild goes, I think a lot of experienced norton owners might inspect the bottom end, (look to see if the bearings are superblends, and have a tug on the connecting rods to establish if they are worn) but there's certainly a chance that your bottom end could be good as is, which saves time and money.

Layshaft bearing wise, I ran my original inner layshaft bearing for the first 20,000 miles. Then when I wanted to rebuild my gearbox because it was leaky, I decided to replace the layshaft bearing too. (the original I removed was still good, but it did give me peace of mind to swap it out)

I can't speak to the validity of the scavenging modification because I don't have a combat crankcase, but it makes sense. It's more a matter of whether it's an essential modification or an optional one... You should use the search function to look for the concensus of opinions on that.

The relocation is obsolete with the CNW breather. It is now the preferred location.
http://coloradonortonworks.com/part-categories/engine/

I'm unclear on the necessity of the pick up mods on the case. Dyno Dave is an excellent source.

Since I'm currently going through a Combat, I would like to know the consensus on this.
Is any pickup modfication necessary for a Hard ridden road bike? If so,what?

pieas dont butcher your cases like this. as you are in mass contact dyno dave as he can do a far nicer job with out the butcher work.

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Plus 1, the Old Brits version is a cure to the high rev wet sumping but leaves the oil pump exposed with no filtering at all, by leaving the weir in place and drilling lots of 1mm holes you get the high rev wet sumping cure plus a crude filter, I also plan to fit a sump bolt with magnet to improve this further.

The cNw breather mod definitely looks like the right option and will keep the stock look I want. I'll keep pondering the pickup mod. I don't know the vendors yet - I've purchased specialty tools from Old Britt's and am very satisfied. Everyone here is knowledgeable and gracious - I need to get the lay of the land about who provides what services. My hubs are definitely going to Buchanans for rims and lacing. Thanks all.

I use a one-way valve in my breather because I think it tends to cause a vacuum in the crankcases which sucks the gaskets. The only motors I have ever built which did not leak oil were Japanese two strokes. Nothing looks worse to me, than an oil leak on an old bike.

acotrel said:

Nothing looks worse to me, than an oil leak on an old bike.

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You'd better not look at old bikes then.

the CNW/comnoz breather is the best route to take. if you do the old britts butcher job it will remove the weir which IMHO is the wrong thing to do. dyno dave can do an oil pickup mod that is a LOT less intrusive and gives you a crude strainer instead of a 1/4 open hole for the pickup. you can PM him from here and he is a very nice guy to talk to.

Scout63 said:

The cNw breather mod definitely looks like the right option and will keep the stock look I want. I'll keep pondering the pickup mod. I don't know the vendors yet - I've purchased specialty tools from Old Britt's and am very satisfied. Everyone here is knowledgeable and gracious - I need to get the lay of the land about who provides what services. My hubs are definitely going to Buchanans for rims and lacing. Thanks all.

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Triton Thrasher said:

acotrel said:

Nothing looks worse to me, than an oil leak on an old bike.

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You'd better not look at old bikes then.

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A friend has a '69 BSA Lightning in his living room that has been drained of all fluids. And it STILL leaks.

If you have oil leaks from the engine, like i did with my 750 Commando 40 years ago, then pull the engine apart and refit he crank cases together again with a decent sealer. My bike had done about 6,000 miles when i did this 40 years ago and I used Pliobond to glue/seal the crank cases together just like i did when working on chainsaws. It never leaked after that. If I had known then about super-blend bearings, i would have replaced them as well. This is a good chance to check the bearings and I suspect they may be ok at that mileages, but if the timing side main bearing is still a ball bearing then replace both mains with the super-blends. It would not hurt to check and fit new big end bearings as well although I suspect they may be ok at that mileage, [ if you can believe the speedo ],. Buy new crank and BE bolts and strip the crank shaft to get rid if the solid crud inside the journals. Check the pistons to make sure you dont have the cut skirt type and renew them if so.[ that type are know the break up ]. If it is a 72 combat, fit a Comstock breather which will enable you not to be concerned about wet sumping. [ Jim's demo of the oil being shoved back into the tank after only a couple of turns of the engine is an eye opener ] I dont recommend you ever just fit new rings to old pistons. Better to buy new piston kits and fit them. Saves time and worth the effort. Dont hone or degalze the bores,. Just ride it hard when you get it back together. that will bed the rings in. see otheter writeups on this forum from those who know what theey are doing. I am an "A" grade mechanic as per NZ qualifications. [ retired of course ]
Dereck

I wouldn't fit an anti wet sump valve as they can un-prime themselves and run your crank dry. I learnt the hard way on this. All the other advice on here is sound.

Two things that don't leak are my forks. I just removed them and there was zero oil in them.

I'm going to go with the cNw breather and send them my oil tank for refurbishment/ strengthening. Maybe no internal crankcase mods are really necessary other then superblends. I am not a hard rider. Most of my riding is 60mph or less and I usually shift around 4K. HD would be a perfect bike for my riding style but i really like old standards much more.

I hate to read how you would abuse an HD by shifting at redline all the time :lol: you will find that the commando is happy between 3000-4500

Scout63 said:

Most of my riding is 60mph or less and I usually shift around 4K. HD would be a perfect bike for my riding style but i really like old standards much more.

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Thanks to all for the notes. Special thanks to kerinorton for the succinct but comprehensive notes.

Ben