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How to measure a cam chain?

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I am having trouble with the timing chain on my son's 2003 CRF230F. It keeps falling off the bottom sprocket when we try to align the cam sprocket. I don't recall it having this trouble before or my other bikes doing this. Is there a way to measure the cam chain for stetching? I seem to remember a method for checking the cam chain on my old XR250. Or should I just go ahead and replace it and the guides. The guides don't look worn and are not broken.

TIA,

Jim

Edited by 426Dude

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If the tensioners are ok, then order a new OEM chain and place it on top of the old one to compare lengths.

Even with the flywheel marks spot on, it's pretty common that the lines on the cam sprocket are not lined up perfectly

It is correct to have the cam in a SLIGHTLY retarded position rather than advanced. Meaning, the front line on the cam sprocket may be just a hair above the cylinder head casting and the rear line maybe just a hair below.

The more stretched/worn the chain is, the more pronounced this misalignment will be.

No matter if it's new or how much it is stretched, you can never be 100% positive that the cam timing is exactly correct unless the camshaft is properly "degreed in"

Personally I like all mine set up 1 - 2 degrees advanced.

That way, as the chain and sprockets wear, the cam timing will wear into perfect and hold its tune a lot longer with the added benefit of a very slight low end torque enhancement.

Of course these engines are not normally very hard on cam chains so one can expect the cam timing to be within specs for many miles/years.

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Thanks adnohguy, I'll take your advice and get a new chain. Cheap insurance.

One more question. When I am lining up the timing marks should the tensioner be in and extended? Or are the timing marks aligned before releasing the tensioner?

Thanks again,

Jim

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Easy check for stretch is to put the chain on the top sprocket.  Then lift in the center of the top sprocket.  If the chain is worn out it will lift a bit off of the sprocket, if it is not worn then it will only lift a tiny bit with the chain wrapped around the sides of the sprocket.  You can do the same with a rear drive chain.  Just grab it at the back of the sprocket and pull out.  It should stay pretty close to the sprocket.  If it easily lifts from the sprocket then it is worn out.

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Set your cam timing without the tensioner installed. You can use your finger or a screwdriver handle or what ever to push into the tensioner hole to put pressure on the chain tensioner slipper to make sure you have everything properly aligned to your satisfaction. Then install your tensioner after that.

Just to double check that nothing has changed, turn the crankshaft (counter clockwise) a minimum of 4 - 6 revolutions and double check your timing again.

That's it, your good to go.

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