If a manual timing chain adjustment is out of travel, does it indicate the timing chain needs to be replaced?

Question

I have a 1981 Yamaha XT250H.

This motorcycle uses a single cylinder engine with a single overhead cam and two valves. The timing chain has two guides, one on both sides of the timing chain. The adjuster threads into the cylinder block on the right hand side. It uses a piston and a spring to adjust the timing chain. To get the tension anywhere near correct I have to turn the adjuster all the way in. There is no way to get the cover back on after that.

Does this indicate my timing chain needs to be replaced?

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Answer 1

Your cam chain has reached the end of it's service life

Your cam chain is stretched beyond service limits it appears. If you have no more adjustment available to push your cam chain guide against your cam chain then you can no longer take up the slack that is created as the chain continues to stretch and lengthen due to normal use.

• You should not have to split your cases to access the crank sprocket for the cam chain.

• Ensure you put the crank at TDC and mark your camshaft if you choose to remove the cam chain to replace it with a new one

• Check your cam chain guides for cracking and splitting while you have the covers off the side of the motor. Replace as necessary.

• Procure a shop manual from Yamaha if you can. The aftermarket manuals leave something to be desired.

Answer 2

Well I don't know if this applies to all motorcycles but my GSX-R 600 K7 manual says that you need to change the cam chain:

• When the distance between some pins of the chain is out of tolerance.
• When the tensioner reaches the end and cannot stretch out any further.
• When the chain is broken.
• When some other visible damage is noticeable.
• When you replace the cam chain sprockets.

Also when you build the cam chain tensioner back, you have to retract the tensioner by clicking on the pin and pull the bar back. So you can mount the tensioner unstretched.

The last step is to put the spring back and push it back and then screw the bolt back. The tensioner will stretch out properly.

If you remove the cam chain tensioner without unstressing it first, then it will stretch out fully. If you put it back like this it will overstretch the cam chain and it will result in serious damage.

Again, I'm not sure if this applies to all engines.