RMA Automatic Cam Chain Tensioner?

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With one of my old bike cronies, we got the timing cover off and removed the automatic chain tensioner and replaced it with the stock unit. The studs had been removed at some point and socket head screws substituted so we just reused them rather than delay the project while new studs were found.

There was quite a difference between the tight & loose spots when adjusting the chain so it is easy to see why the automatic unit is such a good idea. I had thought there was some sort of ratchet built in to it, but on examination, none could be found. The sole fault really was just an overly strong spring. It might even be worthwhile to find a better spring and try this again when the timing cover is next off.

I think the real solution would be a set of sprockets with good centers that would run true and not cause the issue in the first place.

Vintage Paul, another step closer to riding this Norton again
 
hudson29 said:
With one of my old bike cronies, we got the timing cover off and removed the automatic chain tensioner and replaced it with the stock unit. The studs had been removed at some point and socket head screws substituted so we just reused them rather than delay the project while new studs were found.

There was quite a difference between the tight & loose spots when adjusting the chain so it is easy to see why the automatic unit is such a good idea. I had thought there was some sort of ratchet built in to it, but on examination, none could be found. The sole fault really was just an overly strong spring. It might even be worthwhile to find a better spring and try this again when the timing cover is next off.

I think the real solution would be a set of sprockets with good centers that would run true and not cause the issue in the first place.

Vintage Paul, another step closer to riding this Norton again
Click to expand...

No, the answer is gears. :mrgreen:
 
It occurs to me that a variable-tension chain is like a cam with loose/floppy lobes, I don't see that as a plus.

Short of gear drive, a properly tightened chain allows the cam to most closely follow the crank's relative position. Allowing the cam chain's tension to be "adjusted" while running seems to me would allow the valve spring tension to work against it with negative consequences.
 
swooshdave said:
No, the answer is gears. :mrgreen:
Click to expand...

Is there an affordable reliable gear drive set up available for the Commandos? I too like that idea, but would have to believe some well made sprockets might work pretty well, at least better than the stock setup.

Vintage Paul
 
grandpaul said:
It occurs to me that a variable-tension chain is like a cam with loose/floppy lobes, I don't see that as a plus.

Short of gear drive, a properly tightened chain allows the cam to most closely follow the crank's relative position. Allowing the cam chain's tension to be "adjusted" while running seems to me would allow the valve spring tension to work against it with negative consequences.
Click to expand...

I have a Yamaha SR500 single that has a very long cam chain with a tension part way along its length. This seems to operate well without any drama at all. When running with the cover off, you can see the tensioner mechanism riding slightly in and out as it controls the chain tightness. Adjusting the tensioner is part of the tune up drill. The Norton would certainly be happier with something like that!

Vintage Paul
 
I have used the RMA chain tensioner in all my bikes(commando) for a long time...since the late 80's. However I am aware of recent problems with new ones. I am wondering if through the years any engineering details or manufacture or material change of new batches at a new job shop has caused a technical detail to change with disasterous results.... :oops:
The failure to provide a satisfactory customer service about this situation has it's own separate downside...
I still have some new ones in the bag but they are from the old days when they were $70...and before the "detail change".
 
RMA Automatic Cam Chain Tensioner?
 
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