Chain keeps tightening

[Rujack]

The chain on my son’s 70cc keeps tightening while riding. It’s a 2021 SSR that I bought new a couple of months ago. Yesterday I replaced the stock chain with a pro taper as it seemed the stock chain was binding, but clearly something else is going on.

Today I’m going to check the axle for straightness and the spacers for 90 degrees.

Is there anything else recommended to check?

[Mudflap]

Engine mounting bolts.

[Thumper]

Maybe the axel pushes back when you tighten the axel bolt (swingarms push back)???

Try setting it loose, then tighten the axel bolt.

[TominMO]

Most likely is that your procedure for tightening the chain is incorrect.

When the swingarm is horizontal, parallel to the ground, the chain is at its tightest--i.e. the rear sprocket is at its greatest distance from the front sprocket. Anything above or below horizontal, and the rear sprocket is closer to the front one. Simple geometry. The mistake many people make is adjusting it without a rider on the bike, and the swingarm is hanging down at a 30 degree angle or something, not level. So then it tightens as it goes up to level, with a rider on board.

Make your adjustment, then check it with your son sitting on the bike. With experience, you will know how much slack to leave in without him on it.

As far as checking whether the axle is straight, the foolproof method is to measure, on both sides, the distance from the center of the swingarm pivot bolt in front to the center of the rear axle nut. Obviously you should get the same number.

Here is a good video on adjusting your chain:

[ProDigit]

Agree with above,
Also, when you have the correct chain tension (1-1.25"), and tighten the rear wheel axle, the chain will tighten by about 1/4th to 1/2 in.
This is due to the arms (rear fork legs) bending towards one another, and the wheel axle being moved backwards as a result.

[Thumper]

Originally Posted by ProDigit

Agree with above,
Also, when you have the correct chain tension (1-1.25"), and tighten the rear wheel axle, the chain will tighten by about 1/4th to 1/2 in.
This is due to the arms (rear fork legs) bending towards one another, and the wheel axle being moved backwards as a result.

This and TominMOs response do not adress the fact that OP sez it gets TIGHTER while riding.

Give the OP a break. It is tightening After he thinks he has set the adjusters to the spec (~2 to 2.5cm flex). Some swingarms are broad when loose, they come together pushing the axel back. This could easily result in chain tensioning.

So start LOOSER, and once the axel bolt is tensioned, maybe tension will be OK.

[TominMO]

Originally Posted by Thumper

This and TominMOs response do not address the fact that OP sez it gets TIGHTER while riding.

Give the OP a break. It is tightening After he thinks he has set the adjusters to the spec (~2 to 2.5cm flex). Some swingarms are broad when loose, they come together pushing the axel back. This could easily result in chain tensioning.

So start LOOSER, and once the axel bolt is tensioned, maybe tension will be OK.

Actually it can't "get tighter" while riding. It was just set wrong, and since he didn't test it with a rider sitting on the bike after the adjustment, it seemed to get tighter while riding. He just wasn't aware how this all works. Everyone starts out as a noob.

[Thumper]

Tom...
The swingarm is typically below parallel when on the side stand. As you sit on the bike, the swingarm moves closer to parallel, at parallel, or past parallel as your weight causes the swingarm to flex up (parallel as in pointing directly at the front sprocket)... Depending on your setup, and your weight, the swingarm can end up AT the parallel position, which is the longest distance from the front sprocket. So yes, it CAN get tighter when you sit on the bike, and typically, it does indeed since it was below parallel when you adjusted it. It is true.

OK, it doesn't "get tighter as you are riding it". The tension depends on the position of the swingarm.

If the OP set the chain too tight to begin with, then it can really get way too tight if the swingarm was way below parallel when he tensioned it.

On your bike, have someone place weight on your bike while you continuously monitor tension on the chain, and you will see what I mean. As the swingarm compresses the rear suspension, the chain is tightest when the swingarm is aligned pointing directly at the front sprocket.

[J4Fun]

Guys, I think I would be doing a close examination of the brakes…

[TominMO]

Originally Posted by Thumper

Tom...
The swingarm is typically below parallel when on the side stand. As you sit on the bike, the swingarm moves closer to parallel, at parallel, or past parallel as your weight causes the swingarm to flex up (parallel as in pointing directly at the front sprocket)... Depending on your setup, and your weight, the swingarm can end up AT the parallel position, which is the longest distance from the front sprocket. So yes, it CAN get tighter when you sit on the bike, and typically, it does indeed since it was below parallel when you adjusted it. It is true.

OK, it doesn't "get tighter as you are riding it". The tension depends on the position of the swingarm.

If the OP set the chain too tight to begin with, then it can really get way too tight if the swingarm was way below parallel when he tensioned it.

On your bike, have someone place weight on your bike while you continuously monitor tension on the chain, and you will see what I mean. As the swingarm compresses the rear suspension, the chain is tightest when the swingarm is aligned pointing directly at the front sprocket.

I think we are saying the same thing. I agree with what you are saying, and none of it contradicts what I said.

[Thumper]

I agree with you Tom.

We are saying the same thing.

The first sentence in the first post is compatible with our diagnosis... With the exception that we don't think it is happening while the kid is riding it.

[bigdano711]

I really like this guy's method. Since I started using the "rag in the chain" method, I've had a MUCH easier time getting my chain adjusted. I also do the adjustment while on the side-stand, so I go for 30-35mm, the upper end of the adjustment range called for on the Hawk 250.

[ProDigit]

Originally Posted by Thumper

I agree with you Tom.

We are saying the same thing.

The first sentence in the first post is compatible with our diagnosis... With the exception that we don't think it is happening while the kid is riding it.

Yeah, my understanding is the same. A chain doesn't keep tightening when riding.
My understanding was that he set the chain up correctly when working on it, and then noticed while riding that it was tight.

[TominMO]

Originally Posted by bigdano711

I really like this guy's method. Since I started using the "rag in the chain" method, I've had a MUCH easier time getting my chain adjusted. I also do the adjustment while on the side-stand, so I go for 30-35mm, the upper end of the adjustment range called for on the Hawk 250.

Yeah, that's a good video. Thanks.

The reason the chain gets tighter or looser depending on swingarm angle is that the front sprocket is in front of the swingarm pivot bolt. This is what causes the differences in distance between the rear sprocket and the front one. If you took off the rear wheel and the drive chain, lifted the bike up, and swung the swingarm as far down and forward as possible, you would easily see why this is so.

Proper chain tension is a balance between not having it so loose that it could come off a sprocket, and not so tight that it causes various stress problems.

[Thumper]

Originally Posted by ProDigit

Yeah, my understanding is the same. A chain doesn't keep tightening when riding.
My understanding was that he set the chain up correctly when working on it, and then noticed while riding that it was tight.

The funny thing is that you can't actually notice that it is tighter while riding it. I mean it is physically impossible

But, I guess that you can observe it getting tighter when your son sits on it