Timing Chain Adjustment

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olympus

olympus

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Hi Guys. I'm familiar that the timing chain requires 4.8mm of lift... but what the manual doesn't state is that surely the engine needs to be turned backwards to achieve this??... As i don't see how the required lift can be obtained and measured/set with the chain under load being turned forwards....
 
Well you need to check in several places anyway as chains can wear unevenly, 4.8mm on tightest spot, use a spanner to unload the top run of chain if its under tension, sometimes the tension will be on the bottom run depending on engine position.
 
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kommando said:
Well you need to check in several places anyway as chains can wear unevenly, 4.8mm on tightest spot, use a spanner to unload the top run of chain if its under tension, sometimes the tension will be on the bottom run depending on engine position.
Click to expand...
My concern is that some folk may have been looking for the required free play turning the engine in a forward direction.... pity the manual doesn't state this
 
olympus said:
My concern is that some folk may have been looking for the required free play turning the engine in a forward direction.... pity the manual doesn't state this
Click to expand...
It can change as the valves come up on & get past the opening/closing. It's not as simple as turn the engine "forward" or "reverse" rotation.
 
I also now have to ask regarding the chain quality... replaced less than 100 miles ago...
I have a old cover suitably modified to act as idler post support, and yes i can expect a small degree of a tight spot... but no matter which way i rotate the engine i have a "significant" tight spot.
So the lift was set at this tight spot to 5mm and when turned the engine to the slackest point i have 11mm of lift .... in anyone's money this is some tight spot.
Now i will be talking to Andover about this next week, but i have to throw in the possibility of either a Can sprocket or idler sprocket being out of true
Has anyone else had sprocket issues being out of true??
 
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Mart UK said:
Mark the chain and sprockets and rotate to check which is causing it?
Click to expand...
I've checked the run out on the driving sprocket and its barely moving my clock gauge. will attempt to check the driven (cam sprocket) tomorrow
 
Check the sprocket teeth are allowing the chain to drop into the root of all the teeth, check the chain's links are all free and some links have not stiffened up.

RGM's timing chains are in Renolds blue boxes, using chain bought from Renold's and boxed by Velocette.

If the chain ends up being the issue replace it with Jason's Merc big pin simplex timing chain.
 
kommando said:
Check the sprocket teeth are allowing the chain to drop into the root of all the teeth, check the chain's links are all free and some links have not stiffened up.

RGM's timing chains are in Renolds blue boxes, using chain bought from Renold's and boxed by Velocette.

If the chain ends up being the issue replace it with Jason's Merc big pin simplex timing chain.
Click to expand...
That's what I did. Great chain.
 
Hi all,
are there any symptoms of the timing chain requiring adjustment or is it purely on a distance travelled basis?
Does lack of adjustment result in catastrophic failure?
What is the recommended interval.
What stretch to people experience at the recommended interval? That is, does it always need adjustment or is it often ok?
I guess I should just launch into it but it as the bike is going well it seems horrible to pull of apart a perfectly oil tight cover , muck up timing etc.
A pity norton didn’t either have either an externally adjustable or automatic chain tensioner or a gear drive.
I suppose the inspection plug on the Mk3 is better than nothing.
having just rebuilt my 4.6 Range Rover engine I was surprised to see it has no provision for a tensioner and I believe that chain stretch is a problem at very high mileage.
Alan
 
olympus said:
Hi Guys. I'm familiar that the timing chain requires 4.8mm of lift... but what the manual doesn't state is that surely the engine needs to be turned backwards to achieve this??... As i don't see how the required lift can be obtained and measured/set with the chain under load being turned forwards....
Click to expand...
Not sure what you mean by lift but I too I find the cam chain tension frustrating and finally have a method that I think is correct.

73 Riders

The permissible amount of free up and down movement measured in the centre of this run is 3/16 in.

70-73 Workshop

Fit the chain tensioner, and disc washers and nuts moving the tensioner blade to give a maximum 3/16 in (4.8 mm) up and down movement at the tightest point of the chain and ....

Based on those, I take it that when rotating the engine forward, find the tightest point and make sure the chain has 0-3/16" up and down movement at the center of the top run. I suspect that 0 would be best but trying to determine that would be hard so they said max of 3/16". To me, you want no undue strain on the intermediate gear, and you want the motion of the camshaft to be well sync'ed with the crankshaft (1/2 speed of course).

So, without looking I turn the engine forward feeling the cam chain and stop when I think I'm at the tightest. Mark with chalk and do the same a couple more times. If the chalk marks agree, I set the tension there to no more than 3/16" and try again. I everything still agrees, I'm done.
 
marshg246 said:
Not sure what you mean by lift but I too I find the cam chain tension frustrating and finally have a method that I think is correct.

73 Riders

The permissible amount of free up and down movement measured in the centre of this run is 3/16 in.

70-73 Workshop

Fit the chain tensioner, and disc washers and nuts moving the tensioner blade to give a maximum 3/16 in (4.8 mm) up and down movement at the tightest point of the chain and ....

Based on those, I take it that when rotating the engine forward, find the tightest point and make sure the chain has 0-3/16" up and down movement at the center of the top run. I suspect that 0 would be best but trying to determine that would be hard so they said max of 3/16". To me, you want no undue strain on the intermediate gear, and you want the motion of the camshaft to be well sync'ed with the crankshaft (1/2 speed of course).

So, without looking I turn the engine forward feeling the cam chain and stop when I think I'm at the tightest. Mark with chalk and do the same a couple more times. If the chalk marks agree, I set the tension there to no more than 3/16" and try again. I everything still agrees, I'm done.
Click to expand...
I don't see how the chain movement, free play or lift can be check when turning the engine forward as the top chain run is under tension?? this is why I'm asking about turning the engine backwards as now the loading is on the lower chain run and giving the free play into the top chain run.
I do think its a chain issue (despite it being less that 100mls old) as neither sprocket has run out or sprocket teeth that catch on the chain.
Is their a site address for Jason's big pin simplex chains

Some while ago i recall reading a post about automatic chain adjusters, does anyone know if there still in production or available??
 
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olympus said:
I don't see how the chain movement, free play or lift can be check when turning the engine forward as the top chain run is under tension?? this is why I'm asking about turning the engine backwards as now the loading is on the lower chain run and giving the free play into the top chain run
Click to expand...
The chain needs to be under tension to check it and there's no place to check up and down on the bottom run anyway. Sounds to me like you've misread the instructions since you call it lift and not up and down movement.

Fit the chain tensioner, and disc washers and nuts moving the tensioner blade to give a maximum 3/16 in (4.8 mm) up and down movement at the tightest point of the chain and ....
 
The cam followers can put the camshaft under a forward or reverse load as they rise and fall over the cam lobes. So at some crank positions the top run will be loose and other times under tension. So move the crank so the top run is loose and do your chain slack measurement then.

Jason

the-chain-man.co.uk

The Chain Man

Specialising in providing high quality chains and accessories for motorbikes. The Chain Man in Stourport-on-Severn
the-chain-man.co.uk the-chain-man.co.uk
 
not wishing to hijack your thread (but not worth starting a new 1 )
just to put it out there there ... are apparently 2 types of reynolds camchains for commando ... those that fit & those that almost fit (ask me how i know).
i bought a reynolds camchain from rgm (building new engine from parts) while the chain fitted, there was NO slack whatsoever .... last thing that occurred to me was the chain was too fekin short.
after MANY wasted hours a knowledgeable friend pointed out there are imperial reynolds chains (pins fixed in plate with centre punch) & metric reynolds chains (pin being peened on 2 edges - like a drive chain)
 
Imperial 05B has a pitch of 5/16 or 7.94mm, there is 05B advertised with a pitch of 8mm (don't know if it is 8mm or just 7.94mm sold as 8mm because most people measure in metric outside of US). So metric 05b would be slacker than imperial 05b. So your tight chain is tight for another reason than imperial vs metric.
 
olympus said:
I don't see how the chain movement, free play or lift can be check when turning the engine forward as the top chain run is under tension?? this is why I'm asking about turning the engine backwards as now the loading is on the lower chain run and giving the free play into the top chain run.
I do think its a chain issue (despite it being less that 100mls old) as neither sprocket has run out or sprocket teeth that catch on the chain.
Is their a site address for Jason's big pin simplex chains

Some while ago i recall reading a post about automatic chain adjusters, does anyone know if there still in production or available??
Click to expand...
At one point in time Jim Comstock had a hydraulic cam chain tensioner. I have no idea if he still markets them.
 
kommando said:
Imperial 05B has a pitch of 5/16 or 7.94mm, there is 05B advertised with a pitch of 8mm (don't know if it is 8mm or just 7.94mm sold as 8mm because most people measure in metric outside of US). So metric 05b would be slacker than imperial 05b. So your tight chain is tight for another reason than imperial vs metric.
Click to expand...

The cam chain is 3/8", 0.375"/9.525mm (06B) pitch.
Timing Chain Adjustment
 
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