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.