weird chain problem-AR28 chassis

[Joe Rosse]

Anyone have a problem with chains popping off an AR-28 chassis with a Rotax Jr engine and a Free Line mount?

We've had a series of strange situations in which the chain is adjusted just fine when it goes out and then gets loose--often enough to fall off. Last race was the weirdest, because this happened and my son was able to replace the chain by hand and it was still too loose to use. But after putting the kart on a stand and bringing it back to the pits, the chain was perfectly adjusted, and the motor mounts were tight. I don't know how the motor could have moved backwards because I've installed an adjusting/tensioning bolt to keep the motor from moving backwards. I backed off the bolt about 1/16" of an inch so it wouldn't bind up the chassis, but would still keep the motor from moving back.

What the heck is going on??!!

I talked to another racer who said he'd had the same problem with a chassis he'd run before. Like the AR28, this chassis was supposed to be quite flexible, and his impression was that there was so much flex that the engine would move back, loosening or removing the chain, and then move back up again. His solution was to install a locking collar in front of the engine, as well as the tightening bolt in the rear, so that it couldn't move very far in either direction.

I'm willing to try that, though it doesn't make much sense to me. Anyone else experience this???

[Dave Thompson]

Couple things come to mind.

1 Ck and make sure mount is not resting on cross bar, If so machine mount so it sits flat on frame.

2 If a chain comes off it is usually bent and is junk dont try and reuse it It will only lead to problems like this

Dave

www.davesperf.com

[Garry Lobaugh]

I do believe that Dave has the bases covered for starters. Another issue is to make sure the roll of the chain vs. the sprocket carrier is perfect. The new Free Line alignment tools help in the alignment, plus double check to see that the bolts holding the sprocket to the carrier are perfectly aligned on the carrier. We have not had a problem with the flexing aspect and a chain popping off. Most often, it was a chain problem to begin with and as Dave suggests, if one gets thrown off once, put a new one on for the race and save the other one for a swap meet. Garry

[Joe Rosse]

Dave,

I think you may have it. The motor mount does sit on the cross-member, there's no way around that. I was concerned about the fit, so I ground the welds on top and bottom flat so the motor mount slides better. But I'm betting that you're thinking that the cross-member flexes and pushes on the motor, right? So tomorrow, I'm going to pull the mount and machine it to provide more clearance.

Boy, my son will sure be happy if that gets him through the race on Sunday!!

[Jean Stafford]

We also noticed the same problem with the chains last year on our QC31. Seesm that each time the driver went onto the track for the first lap, we lost the chain.

We finally setteled the drived down and convienced him to proceed slowly for the first lap, including entering the track like "Little E", and sliding the Kart. This solved our problem.

The Chassis are designed to withstand the rigors of racing, not necessarily "freestyle" activities.

Like Garry said, if it comes off, keep it for the swap meet. The 219 series chain is a little more fragile than #35 or #41.
Jean Stafford
www.staffordsracing.com

[Joe Rosse]

Thanks to everyone for all the help. I decided to replace both the sprocket and the chain, and threw on a chain guard for good measure, and all was well. In fact, it survived a crash that bent the axle!