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DR650 chain loosening

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I have two DR650 Suzukis. One 1998 with 60,000 miles on it and my 05 with 11,000 miles I motarded.

I have been through some chains and sprockets. Usually around 10-13k they just start stretching, and stretching and I have adjusted the 05 about 4 clicks on the adjuster and its still stretching. I am not over tightening the chain when I set it.

Its stock chain 525. I had 520 on the older bike once and it stretched the whole time it was on there.

These 525's seem to go a long time without needing to be adjusted then all of a sudden they need constant attention. My sprockets are in good condition and will be replaced with the new chain, my front one is 16 tooth and is only about 3,000 miles old.

I was wondering if someone could shed some real light on why these things do this all of a sudden.

I do work these bikes and they do have jet kits and every thing possible to make them produce the max power they can, and I use it ,but no abusively.

Thanks for any comments

Andrew.

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These 525's seem to go a long time without needing to be adjusted then all of a sudden they need constant attention. My sprockets are in good condition and will be replaced with the new chain, my front one is 16 tooth and is only about 3,000 miles old.

I was wondering if someone could shed some real light on why these things do this all of a sudden.

Modern high-quality sealed chains are pretty amazing compared to what was available in the past but they still have to endure a lot. They last pretty well until the grease inside leaks out , then they start to wear rapidly. As they lengthen they no longer fit the sprockets well and the forces increase exponentially and more rapid wear follows. I generally replace the chain and sprockets soon after I notice the chain is needing more frequent adjustments.

Mike

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I'll try to shed a little light on this.

First of all a chain doesn't really 'stretch'. What happens is the pin and bushing of each link wears a little bit. The wear makes the chain get longer because there is a tiny bit more distance between each chain roller.

When everything is new, as the chain wraps around the sprocket every roller and every tooth carries an evenly shared amount of the driving force. Since the chain rollers of the worn chain are a bit further apart this changes the actual chain pitch so it no longer perfectly matches the sprocket. When the worn chain doesn't fit the sprocket perfectly any more the force is carried by fewer chain rollers and sprocket teeth. A severely worn chain might only pull on one or two teeth at the top of the sprocket while the rest of the chain that wraps around the sprocket is hanging loose.

As the chain wears the actual force transmitted through each roller and tooth increases causing the chain to wear faster and faster. This exponential wear happens to the sprockets too but it isn't as obvious.

Another factor is that as the chain pins and bushing grind against each other the ground up steel can get trapped in the chain bushings and add to the wear rate.

It's not unusual to see a red powdery substance around the links of a worn chain. This is 'rust powder'. It's the steel that has worn away from inside the links. You also see the same stuff around loose bolts. The ground up powdered steel oxidizes almost immediately and leaves dirty red-brown deposits.

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