Commando Crankcase breather Mod. as late Triumphs by removing crankshaft oil seal.

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TopgunPeter

TopgunPeter

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I use the standard chain primary drive and suffer the usual oil contamination of the clutch plates giving drag. I am considering converting to the Triumph breather technique as described in https://www.classicbritishspares.com/blogs/news/triumph-crankcase-breather-mod.

This might reduce the oil level in the Primary Chaincase to avoid contamination of the clutch plates if the return drain holes were at the optimum level.

Anyone tried this or have any thoughts ?
 
TopgunPeter said:
have any thoughts ?
Click to expand...
The link shows a UNIT constuction engine where the primary and engine are attached.
For a laundry list of complications this mod seems unlikely to be implememted to interconnect the commando primary to the seperate engine.
The over oiling controls of the commando clutch are long and well known and effective if one is intelligent enough to implement them.
 
It would seem to me that this is not a good way to go, for two reasons.

Commando primary chains and clutch plates work very well with ATF. If the problem is engine oil contaminating the plates, it would not seem an improvement to set up a system where engine oil is introduced into the primary case on purpose.
If the Commando crankcase is so poorly ventilated that it's blowing oil past the crank seal, then there's a problem. It would seem that a system using a high-capacity crankcase vent like James Comstock's with vapors being drawn from the oil tank into the intake cross-over tubes would solve two issues -- providing a useful engine breathing system, and preventing engine oil from contaminating the most effective oil in the primary.

Also, if the engine breathes so poorly that such a mod would be helpful, it seem to me that you'd, in turn, also be pressurizing the gearbox -- and there is precious little sealing of the clutch bearing-to-mainshaft area as it is. This would introduce contaminating oil into the gearbox, and this would also be a drawback in my opinion.
 
The unit engine breather arrangement shown in the link is actually NOT very efficient. But passable for a road bike. Many instead opt to to use either the crank indexing plug aft of the barrels (Triumph), or drill/tap an outlet at the engine mount flange at the front of the engine (Triumph & BSA). The point being, locating the breather outlet as close to the crank as possible. On a Commando you're best bet is the rear case outlet (requires machining on non-combat cases), the sump plug breather designed by Comnoz, or off the back of the timing chest with a reed valve (less efficient unless you open additional holes in the inner timing case).
 
The slipping clutch is from gearbox oil contamination, the fix is the oil seal on the gearbox mainshaft on the clutch end to stop the oil getting into the primary. Using the primary as an engine breather does nothing for the gearbox oil issue.
 
Generally agree:)

kommando said:
The slipping clutch is from gearbox oil contamination, the fix is the oil seal on the gearbox mainshaft on the clutch end to stop the oil getting into the primary. Using the primary as an engine breather does nothing for the gearbox oil issue.
Click to expand...
Expanded as
The slipping and/or dragging clutch is primarily from gearbox oil contamination, the fix is the oil seal on the gearbox mainshaft on the clutch end to stop the oil getting into the primary. Using the primary as an engine breather does nothing for the gearbox oil issue. As arguementative as BDM was, I fully agreed that the too high primary engine type oil level is a strong second source of clutch plate contamination that adversely affects proper clutch function.
 
As above, the slipping clutch can be cured by a mainshaft seal to keep the gearbox oil from entering the chaincase.

Or, use a gearbox oil that is suitable for a wet clutch.

The breather idea is not a good one...

1. The Commando chaincase hardly has a reputation of being easy to keep oil tight. Doing this will put it under positive pressure.

2. Its not the best crankcase breather method either. Better is to limit the volume in the case area (rather than add to it) and deploy a reed valve breather that allows gas out, but not in, thus preventing pressure build up and oil leaks.
 
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So far I appear to have solved my dragging clutch issues (a lurch when engaging 1st gear),by fitting Dynodaves clutchrod seal and reducing the primary oil volume to 170cc. Also switched to tqf oil (fibre plates)......
Seems a lot easier than changing the Near perfect design of the commando;)
 
Fast Eddie said:
use a gearbox oil that is suitable for a wet clutch.
Click to expand...
Even an insignificant motorcycle company such as Ducati uses a clutch rod seal (on my 3 Ducati), and BDM chided me mercilessly in public and in his writings about the clutch being a "DRY" clutch. My retort was Norton knew it would be used in a wet environment. So after 20 commando years I started offering a seal that Norton tried to fix with machined circles on fiber plates and switching to thin clutch /more plate interfaces and using sintered bronze.

Even at the 2015 INOA Ashville NC rally I was asked to impromptu tech session speak because John Favill had not shown up yet...When John did show up (transportation delay) the rally chairman unceremoniously yanked the mic out of my hand and passed it to John.
So I sat around for a little while to hear the later commando evolution story John was telling.
Two noteworthy items, to me, was the indepth analysis of the commando clutch problems and bronze plate upgrade with an added tidbit that "some fellow" came up with a proper clutchrod seal fix.
Another topic he went into was the weak prestolite starter and that "some fellow" had come out with a new better replacement.
Once the story evolved to harley, I left to go back to my camp site for a good Canadian beer.
I pondered the feeling of being "some fellow".
So now "some fellows" clutch rod seal and starter design must be good enough ... to be copied (design stolen) while both have never been dropped always been available direct or through acknowledged vendors.
 
TopgunPeter said:
I use the standard chain primary drive and suffer the usual oil contamination of the clutch plates giving drag. I am considering converting to the Triumph breather technique as described in https://www.classicbritishspares.com/blogs/news/triumph-crankcase-breather-mod.

This might reduce the oil level in the Primary Chaincase to avoid contamination of the clutch plates if the return drain holes were at the optimum level.

Anyone tried this or have any thoughts ?
Click to expand...
Another possible issue has not yet been mentioned. By sharing engine and primary oil, you might select an engine oil which is not compatible for use with a multi-plate wet clutch. Refer to Jim Comstock's article on best oil for a Commando. See

https://www.accessnorton.com/Oil-Tests/NortonOil.php

Your proposed mod would limit the oils that you could use.

Charlie K
 
I used dyno daves seal .It works well.I also drilled and tapped the inner primary just ahead of the clutch basket just above halfway up and used one of those 90 deg barbed fittings on the back. I put a 1/4" hose on it and ran it up into the battery box area.It was a test to seal the primary by venting any pressure build up at all and it has worked. Just like a vent tube on a jeep axle.My 2 cents worth.
 
Wouldn't such a propsal, running crankcase oil to flow into primary and back into crankcase, also carry contaminants from clutch plate wear back into engine? How do modern bikes cope with sharing oil laden with clutch wear particles?
 
bchessell2 said:
It was a test to seal the primary by venting any pressure build up at all and it has worked.
Click to expand...

Obviously this works, only because there will never be a pressure build-up in the primary chaincase. Look at the mainshaft going through the sliding disc center. How can this wide tolerance "washer" ever keep overpressure in?
Rest assured it doesn't.

-Knut
 
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