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Thanks for your comments.
History - I built the engine using a bottom end - no heads - from eBay.
It had been cut out of the frame, mounts still attached!
I won't bore you with all the details but examination of the tensioner and chain surprised me as no signs of wear, looked new and when adjusted all the gap was above the tensioner locking bolt.
There was gouging damage to the case that suggests it had suffered a broken chain/tensioner previously - so the new parts made some sense.
I've run it for 600 miles since the rebuild and adjusted the cam chain 3 times as per Haynes manual.

As for the design aspect, I think the amount of space on this community devoted to the subject tells a story - it's not one of the cx's strengths.
Don't get me wrong, I'm very impressed with it, 50 bhp out of a 500cc, my bsa Firebird 650 was tuned and made less.
And when I stripped the cx the difference in technology blew me away - the BSA's were positively agricultural compared to the cx!
But one thing the pushroded BSA won on was the gear driven camshaft.
Cam chains and pushrods each have their own problems, the cx has both!
I apologize if I've committed heresy, I know the people in this community love their bikes and I don't want to offend anyone.
I shall press on with the additional tensioner adjuster bolt mod and post results - good or bad.
Cheers all and take care.
Don’t worry, no heresy committed. I was just trying to tell you that the inertia forces you think the camshaft has don’t really exist. Remember, the camshaft has the forces of the valve springs against it when a valve is open. Another thing to keep in mind is the camshaft is spinning at half the speed the crank shaft is. The chain isn’t really a weak point, just a maintenance item as said earlier.
 

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Cx500 1978 engine probably later
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13 Posts
Discussion Starter · #23 ·
Many thanks again for your comments.
Ok job done.
Before -
Automotive tire Light Motor vehicle Bicycle part Rim

This is with the chain adjusted on the spring - plenty of life in it 😀
With the new adjuster -

Automotive tire Motor vehicle Bicycle part Rim Alloy wheel


Automotive tire Bicycle part Wood Rim Metalworking


Automotive tire Automotive design Rim Bicycle part Auto part

I've positioned the new adjuster over the tensioner arm locking bolt.
All buttoned up now, expect to have the lump back in the frame next week sometime to check it out.

On close inspection the adjustable tensioner blade has two slots in either end.
Wood Bicycle part Metal Auto part Composite material

Along with the thick lug in the centre it seems to me there is something missing - a piece of spring steel tensioned against the slots and pushing against the lug in the centre.
Seems to be designed and made to take a spring in the back.
Any thoughts on this?
Cheers
 

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On close inspection the adjustable tensioner blade has two slots in either end.
View attachment 211717
Along with the thick lug in the centre it seems to me there is something missing - a piece of spring steel tensioned against the slots and pushing against the lug in the centre.
Seems to be designed and made to take a spring in the back.
Any thoughts on this?
Cheers
I've never seen a spring used there. I wonder if that lug in the center is from casting the blade? I suspect that the mold would have cast several pieces at the same time and the lug is where the channel was connected. Not sure about the two slots in either end.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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The two slots are just the ends of the wrapped metal spine of the tensioner. Nothing connects there.
The center lug was added, or maybe beefed up, during the redesign in 1978. I believe it's intended to stiffen the middle of the tensioner.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Not sure what you've gained with your addition, other than a redundant lock bolt on the tension adjuster. Slippage of the stock lock bolt has never been an issue. What performance change do you expect to see?
 

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The chain guides also have that thicker centre bit.....tho these are less likely to fail.
Is it reinforcement or a manufacturing artifact .. dunno.....
BUT....having said that my earlier NOS blades without the thick centre bit have been assigned to the emergency parts bin.....(i.e. not the preferred choice.....)
 

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Cx500 1978 engine probably later
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Discussion Starter · #28 ·
Not sure what you've gained with your addition, other than a redundant lock bolt on the tension adjuster. Slippage of the stock lock bolt has never been an issue. What performance change do you expect to see?
When adjusting the cam chain as per manual it seems it's still a little slack on the spring tension alone - with this mod I can move the tensioner arm manually, it's not an additional locking bolt - only an adjustment aid.
Trial and error - I'll start with spring tension plus 1/2 turn.
The screw is only for use when making the adjustment, it will be backed off away from the tensioner arm the rest of the time.
 

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Cx500 1978 engine probably later
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Discussion Starter · #29 ·
Okies, lump back in the frame and firing up. I've adjusted out the noise with my adjustment mod - took about 2 turns to quieten it down - 6mm screw with pitch 1mm, so that's just over 2mm of additional moment flexing the tensioner blade.
I'll post as soon as it blows up - or later if it doesn't 👍
Cheers all.
 

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Cx500 1978 engine probably later
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Discussion Starter · #30 ·
Well that was a mistake - now the noise from the rear case has gone I can hear the noise from the front!
Goes when clutch is operated - first motion shaft bearing methinks - wonder if I can leave the engine in the frame for that - or should I put wing-nuts on the engine mounts to make it easier 😉
Happy spannering.
 

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Commonly, what you describe is caused by notching in the fingers of the clutch basket preventing the clutch plates moving smoothly.
 

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Cx500 1978 engine probably later
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Discussion Starter · #32 ·
Thanks for that, I'll double check the basket though my recollections are the slots are good.
I think I got luck with the scrap engine on eBay, £46 and the crank was factory spec - not just within service limits. I'd guess it was low mileage. It had been sitting a while with no heads on and the inside was full of mayonnaise - should have changed all the bearings - only did the ones at the back
 
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