Mk3 Shakedown Gremlins

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Boxerfan

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Hello all.

Back in the mists of time (well, 8 years ago), I bought a Mk3 Commando in need of refreshment. I sorted out the brakes, electrics, carburation, exhaust and primary drive, then, inexplicably, didn’t get round to riding it this year. I have now done about 130 miles on a few shakedown runs, the last being about 50 miles.

Two slightly odd problems reared their head. I became aware of a strange clanking noise from the primary drive side, plus a strange kind of misfire seemingly on the left cylinder.

Primary first - I started to suspect that the primary chain tension wasn’t properly tensioned. It’s been a while since I was in there, so I pulled the cover off to be reminded of the hydraulic tensioner. There is nothing obviously out of order in there, but I was surprised at how little oil came out - about a shot glass full.

I’m not sure what’s going on here. Does the primary share it’s oil with the engine (like a late unit Triumph), or is it separate? Where does the oil pressure for the tensioner come from? Is there any way to check Jain tension? Any explanation on how the system is supposed to work would be most welcome. It’s always possible that I forgot to put any oil in & the shot glass full has leaked past the tensioner pistons…

The misfire is an odd one. It showed up at idle after a run back. I wonder if it’s something to do with the new ignition setup I’m running - Pazon and a Harley double ended cool - that means that there’s a spark on the exhaust stroke. My priority is to sort the primary drive, then monitor the misfire, as the engine runs strongly otherwise.

Cheers, Jon
 
Boxerfan said:
Primary first - I started to suspect that the primary chain tension wasn’t properly tensioned. It’s been a while since I was in there, so I pulled the cover off to be reminded of the hydraulic tensioner. There is nothing obviously out of order in there, but I was surprised at how little oil came out - about a shot glass full.
Click to expand...

There should have been at least 200cc (of 20W/50 for the 850 Mk3).

Boxerfan said:
I’m not sure what’s going on here. Does the primary share it’s oil with the engine (like a late unit Triumph), or is it separate?
Click to expand...

It is separate.

Boxerfan said:
Where does the oil pressure for the tensioner come from?
Click to expand...

The tensioner mechanism doesn't have a pressure feed, it relies on oil dripping from the upper run of the primary chain into the tensioner reservoir for its oil supply (a gravity feed through a one-way ball valve to the chamber between the plungers) so the tensioner oil is the primary case oil.

If there is insufficient oil in the primary case then the tensioner won't function correctly.
 
Last edited:
Bernhard said:
Oh dear!
Have you also forgot to put oil in the engine? :cool:
Click to expand...

And gearbox?;)

The 'book' refill quantity for the primary case is 200cc, however, if the level plug is used for the refill then the quantity will be somewhat more than 200cc not that I've found it to cause any problems but could potentially cause clutch slip.

ATF is often preferred for the pre-Mk3 primary but is too thin for the Mk3 tensioner.
 
Yes the MK 111 primary uses regular 20/50 , not A.T.F. fluid as previous models benefit from. Enjoy your MK 111 !
 
My mk3 was very little used before I bought it in March, having done only 3,100 miles following a rebuild nearly 10 years ago. Nothing in the last 2 years.

I had a few problems in the primary, caused by incorrect hydraulic tensioners. If the case is off, it's easy to check the spacers inside the plunger mechanism. Make sure they are the factory versions and are in the correct way round and the plungers move freely. The wide part of the plastic spacer, inside the cylinder needs to be facing the spring.

There was also a lot of alloy swarf in my case, which needed everything thoroughly cleaned and a new starter sprag.

My clutch was adjusted nicely first time I put it back together, but became stiff after a few hundred miles. I adjusted it again and it's been fine since (over 1,000 miles). Maybe lack of use needed it to find its happy place, before it was finally adjusted?

Other things I've needed to do is regularly retighten, particularly the rocker covers and exhaust headers. They are now tight and staying put. I also stood the fuel tank full of distilled white vinegar for 24 hours and then thoroughly flushed it out. A lot of muck came out including long dead insects! Cleaned the taps and filters and fuel lines and the carb and rebuilt it with the Amal maintenance kit.

I've now done 1500 miles and am still working through minor niggles, but am so happy I chose a Commando.
 
Thanks for your replies. All looked good in the primary, so I popped it back together, put some oil in and took it out for an enjoyable 40
Mile evening ride down into the very north of Oxfordshire. The clatter has gone (unsurprisingly) and so has the odd misfire. The LH silencer was a bit loose on the pipe - maybe the resulting air leak was causing the odd noise?

Good to see it now marks its territory too, another side effect of oil in the primary case
 
A thin layer of grease each side of the primary gasket has solved my primary case weep, for now at least.
 
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