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Automatic camshaft drive tensioner

Submitted by kevin_feltoe on Wed, 29/03/2017
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Commando

I have heard one or two horror stories aboutautomatic camshaftdrive tensioners. For instance they tighten up to the slackest part of the chain and can't then slacken off when the tight bit comes around. Does anyone have first hand experience of these things? I'd be most interested to hear if anyone has.

Kev

Submitted by david_evans on Wed, 29/03/2017

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Jim Comstock makes a hydraulic cam chain tensioner I believe, probably sold through Colorado Norton Works. There is a fair bit on accessnorton about these. Some are not so good.

Submitted by bennie_hulshof on Wed, 29/03/2017

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I have a "Nissan" type on a Mk3. It has a ratchet. It is not hydraulic. The difference between tight and slack was limited, so no issues with the tensioner. More on Jim's hydraulic one here. Better to sort out the root cause (other than caused by valve spring forces) of any tight and slack spots first.

Submitted by john_holmes on Wed, 29/03/2017

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Andy the Chainman does an Iwis heavy duty pre stretched camchain, so no need to re tension the chain after 1000 miles plus very low maintenance after due to the large pin size. So I now have 2 auto tenstioners spare and have another use lined up.

Submitted by keith_glassborow on Thu, 30/03/2017

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My RMA wrecked itself after a few thousand miles. I never did get to the bottom of it but it seems it was the usual failure....the tiny circlip got rattled off, the pin got dislodged and the shoe came off its track. Here's a pic.......

Attachments failed-rma-tensioner-jpg

Submitted by gordon_johnston on Thu, 30/03/2017

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Can't help thinking automatic cam chain tensioners are out to solve a non-existent problem and end up adding complexity.

The original cam chain very rarely needs adjusting. I have had no problems there in not far off 50 years of Norton twin ownership so I'll stick to the factory setup.

Submitted by kevin_feltoe on Thu, 30/03/2017

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Previously Gordon Johnston wrote:

Can't help thinking automatic cam chain tensioners are out to solve a non-existent problem and end up adding complexity.

The original cam chain very rarely needs adjusting. I have had no problems there in not far off 50 years of Norton twin ownership so I'll stick to the factory setup.

Hi Gordon.

You have what would seem to bea wise head. It does seem that a lot of people try to improve a system where a problem doesn't exist. I can't say that I've had a problem with the original system, but one can't help wondering if an automatictensionermight be better or not. In this instance and having done my homework,I think I'll pass.

Thanks for all the opinions.

Kev

Submitted by david_comeau on Fri, 31/03/2017

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Interesting thoughts, though I don't necessarily agree.

First, I think something happened during the production life of the RMA tensioner. My RMA was installed in the late 80's in my combat and has run fine for the whole time...and has yet to disintegrate.

The slap happy norton cam chain does have a reputation for destroying the AA units, which seems to be one of the problems that is being addressed. Therefore if there is no problem you would then keep the points and not benefit from a tensioner.

On the manual tensioner the electronic ignition jumps around like crazy...if you have ever looked at it with a timing light. This is the problem I was going to fix, especially later on for my MKIII with a starter, since I like my sprag and was trying not to kill it.t

I have noted the RMA's current production design problem does exist but have not studied it for the cure, or the cause beyond the circlip problem.

 


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