Mk3 Primary case oil

MexicoMike said:

Note that Automatic Trannies have clutches - usually two clutch packs that look pretty much the same as a Norton Clutch pack. So from a clutch point of view, I'd think that ATF is a better choice. And since automatic trannies also have gears and need lubrication for rotating/turning parts, it's clear that ATF lubricates adequately in that sort of application. The impact of the chain rollers on teeth and gears hitting gears seems like essentially the same thing...

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I agree with this on pre-MkIII bikes, and Type F if you're using the bronze friction plates. These plates are pretty much identical to the clutch plates used in older Ford automatics.

"Except you didn't read the part about the MkIII chain adjuster."


Actually, I did but don't think it would be an issue - There are numerous hydraulic valves in a car automatic tranny and ATF is considered an alternate fluid for many strictly hydraulic applications if hydraulic oil, such as MIL 5606, is not available. I'm not arguing against using engine oil and frankly, the primary reason (no pun intended...well, maybe a little one) I use ATF in the chaincase is because I like the fact that a drip is easily identifiable as being from the chaincase. In the past 4 years that I have owned this Commando have used both engine oil and ATF in the primary and have never been able to tell any difference in clutch operation regardless which one was in there. But perhaps it's different with the different available clutches. I don't know what's in mine, oem, Barnett, whatever.

MexicoMike said:

Actually, I did but don't think it would be an issue

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From personal experience of using both ATF and engine oil in my MkIII's primary chaincase, I would say that it definitely is an issue,-as far as the hydraulic tensioner is concerned, as it did not work as well with ATF in the case as it did with engine oil. After changing over to engine oil, I immediately noticed less low-speed transmission snatch than there had been previously.

MexicoMike said:

In the past 4 years that I have owned this Commando have used both engine oil and ATF in the primary and have never been able to tell any difference in clutch operation regardless which one was in there.

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I agree. Because as far as overall operation and performance of my MkIII's (bronze plate) clutch was concerned, changing over to engine oil didn't seem to make any difference whatsoever. However I did notice that using engine oil appeared to reduce the build-up of black gunge which is frequently found on the bronze plates.

"From personal experience of using both ATF and engine oil in my MkIII's primary chaincase, I would say that it definitely is an issue,-as far as the hydraulic tensioner is concerned, as it did not work as well with ATF in the case as it did with engine oil. After changing over to engine oil, I immediately noticed less low-speed transmission snatch than there had been previously."

Well, speculation is certainly no substitute for experience so obviously my assumption about ATF's suitability with Norton's hyd tensioner was incorrect and engine oil should be used.

It's not unsuitable per se, it's just thinner and makes for a different rate of damping in the adjuster cylinders. Each has its own spring and a ball-check valve lets lube in when the cylinders move outward and shuts when they return.