There are a number of modifications to the clutch pushrod mechanism to prevent oil coming from the gearbox into the clutch basket. As my commando is standard, the clutch runs in oil anyway.
so my questions are.
1. Does gearbox oil affect clutch plates in some magic way that primary drive oil does not?
2. For those that have a belt drive and thus run the chaincase dry (obviously not 850 MkIII's) do you get a problem with oil contamination coming along the pushrod?
your thoughts...
I'd be interested in answers…
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Hi Stan, I had the same…
Hi Stan,
I had the same problem with clutch slip. Solved by modifying the plates in the same way as the RGM hi torque ones, reduces the contact area by about half, plus using ATF in the primary.
hopefully we will get a good number of responses from those running belt drives.
Tony
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The subject has been covered…
The subject has been covered extensively over many years:
https://www.nortonownersclub.org/support/technical-support-commando/clutch
and, of course, Mr Leadbeter's exposition on the shortcomings of the clutch itself:
https://www.nortonownersclub.org/comment/16032#comment-16032
But, having read these articles, I'm still trying to understand why I never, ever suffered from clutch slip when using my Commando regularly in the 70s. And the several Commando owners I knew never complained about their clutches either. Yet now, using the exact same parts, it can be truly awful. Yes, the parts are half a century old but they've just been in a box on the shelf for 40 years.
Things that are different are: oils and time spent parked. Is that it?
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Hi, Thanks for details about…
Hi,
Thanks for details about slipping clutches. But PLEASE could responders read what the question actually asks.
I am interested if those who run a dry primary, have issues with oil coming down the pushrod tube and contaminating the clutch plates.
If not, then why are there methods suggested to prevent this happening?
If so, then I will know that it does happen, and then try to decide if it is actually a problem.
Tony
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As noted, I never saw any…
As noted, I never saw any oil on the plates running a dry clutch and belt drive on a race bike so I'm as mystified as you to whether clutch pushrods seals are a panacea or snake oil.
The link to the NOC compendium on the clutch does offer suggestions on how oil might get onto and down the pushrod but also how this can't happen. There was a trace of oil on my bronze plates before I swapped them out this year, but the usual smell test didn't identify gear oil. I suppose one could add a dye to the gearbox oil and look for it in the clutch.
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To answer the question on…
To answer the question on the Gearbox oil, it usually contains extreme pressure additives that could affect the clutch plates more than other oils.
I don't use the side stand and don't get gearbox oil in the in the clutch.
My clutch used to slip but on the first aggressive overtake of the day, after that it would be fine all day.
If you fit Barnett plates then they should work fine in oil as they are designed to run in oil but will also run dry.
Most race bikes with belt drives most probably don't experience this much as they are usually on paddock stands and thus upright.
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Gearbox Oil
For gearbox oil to get sucked along the box mainshaft and into the Commando primary case, there has to be a partial vacuum in that case. The main culprit for this/that would be rising pistons sucking air through a worn crankshaft seal.
Plus probably pushing engine oil the other way and overloading the primary case with vapour. Which in turn will keep the Triplex chain or belt nicely lubricated but also get in between the clutch plates.
Of possible interest.........my RGM belt drive conversion has now carried me over 22,000 miles. Due to the open primary cover, it get water cooled in the rain, oil from the now worn crankshaft oil seal and dirt, dust and anything else the front tyre can throw at it.
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Gearbox Breather
When the gearbox it hot it will be pressurised unless it has a breather. Later Commandos have a small brass breather next to the cable entry - check that it is clear, earlier Commandos don't have this. I'm working on a 750 and I've made a filler cover with a small hole drilled in it. Might work?? Just looked, I thought this was my idea! Andover sell them 04.1104
The other trick is to cut the pushrod in half, find a ball bearing that just fits in the mainshaft bore, reduce the overall length of the pushrod by the diameter of the ball and refit it with the ball in-between the pushrod halves and the hardened ends where they were originally.
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Pre-Mk3 Commandos have a…
750s and pre-Mk3 850 Commandos have a little hole drilled in the inspection cover, Mk3s have the little brass tube screwed into the inner cover.
The clutch cable entry doesn't present any significant obstacle to air flow either - unless you apply sealant.
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OK, lets try again. Before…
OK, lets try again.
Before anyone adds to this thread, could they PLEASE look at what the original question is.
I am not asking why oil migrates from the gearbox, or methods to prevent it.
I am ONLY asking if anyone who runs their primary 'dry' has issues with oil coming from the gearbox.
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I'd be interested in answers to those questions too.
The standard bronze clutch on my Mk3 slipped badly at about 5,000 rpm - dangerous if passing a line of cars in 3rd. Cleaning helped for a few miles but it kept coming back. I've fitted the RGM pushrod seal and changed to Surflex fibre plates and changed from a semi-synth car oil to a 20/50 4T specified for wet clutches. Seems to have worked. But having changed three things I don't know which has had most effect.
I would note:
So is it that modern oils are much "slippier" or infrequent use, with the bike parked on the side-stand for days/weeks, allows the oil (primary or gearbox) to permeate the clutch where previously it was flung off? Or something else?