Kart Frame Flex in Heat

[Evan FraserParticipant]

Hi EKN forums,

I’ve been having major binding issues since it got hot here in BC. The kart is almost completely unresponsive to tuning. The only thing that freed it at all was running the rear tires at 20+ PSI. Have any of you experienced increased frame stiffness or something that effects flex in higher temperatures? I was very competitive until the temperature went up and am now sad!

Thank guys.

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[TJ KoyenModerator]

The heat isn’t changing your frame stiffness, but it definitely could be affecting how your kart handles.

What have you tried adjusting?

Driver/Coach/Wrench : Innovative Performance/Exprit
Owner : Oktane Visual - www.oktanevisual.com
www.facebook.com/oktanevisual
www.instagram.com/oktanevisual

[Evan FraserParticipant]

Everything I can think of to take grip out. Front track in, decrease Ackerman, remove caster (neutral pills), no seat struts, seat loose and tight, seat position forward, front torsion bar out and in, rear track at max, bumper loose, rear ride low, mid and high, third bearing out and in, probably more I haven’t thought of. My entry speed is the same or faster than other karts but my exit is awful.

I’m also on a new short block and followed recommended break in after my last one started leaking from the usual place.

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[TJ KoyenModerator]

If the kart is binding, it’s because the inside rear isn’t lifting. You’re taking the correct steps and making the right adjustments to compensate for the track gripping up, but a lot of those changes are counterproductive to getting the inside rear to stay up.

I’ve always found that once you change everything and get real far out of the tuning window, things don’t work as they should. If you’ve made all those adjustments and the kart still won’t work, go back to baseline setup and start over.

And it seems like a cop out on my part, but if you went down one path of tuning and it didn’t work, try making the opposite adjustments and see if they work. Start putting front grip back in and see if that will keep the inside rear off the ground better.

Driver/Coach/Wrench : Innovative Performance/Exprit
Owner : Oktane Visual - www.oktanevisual.com
www.facebook.com/oktanevisual
www.instagram.com/oktanevisual

[Walt GiffordParticipant]

Have you tried 8 psi and mag wheels, do you have beadlocks?

FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience

[William MartinParticipant]

Your kart is in heat? Is that where baby karts come from? :-)

 

[Gary LawsonParticipant]

Give details of the kart/engine you are using and the setup you normally use.

[Evan FraserParticipant]

TJ: All those adjustments were made one at a time and tested but I agree with going back to baseline and doing the opposite. I think I’ll try to go more towards jacking effect and less towards grip reduction.

Walt: Nope, just aluminum, 185mm.

Gary: In my sig. Formula K FK01, LO206. Normal baseline is two front spacers, neutral front pills, no torsion bars, max rear track, mid height all around, seat tight bumper loose.

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[Tim KoyenParticipant]

And just to clarify, the heat isn’t affecting the material your kart is made of, it’s creating much more grip in the tires, which is what is making the kart handle poorly.

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[Jim DerrigParticipant]

In my experience “binding” is related more to mid-corner speed than to entry speed.  My guess is that you are entering the corner, getting axle hop and lifting, and then finding that your exist speed sucks.  Concentrate very hard on maintaing speed after entry, getting on the throttle early and keeping the kart right on the edge of the traction circle.

Also, I’ve had some success decreasing the air pressure in the outside rear tire (drivers left for counterclockwise circuits, right for clockwise) by as little as ¼ psi.  Check your pressure immediately after your next run.  If the outside rear tire pressure is higher than the inside, reduce the psi to make it more even.  I started doing this when I noticed that my axle binding problem was much more pronounced on turns corresponding to the track direction.

[Evan FraserParticipant]

Jim: Thanks for the advice, I do try to balance my pressures (we get distinctly higher temperatures on the left side) but I’ll give it some closer focus. Also LO206 on our track doesn’t lift anywhere but I’ve experimented with it to see if it helps. Usually I run the entire race at WOT and balance with the brakes. Hopping doesn’t scare me, I was racing Rok GP before this year :D

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[Brock WeissParticipant]

I went through the same thing you did last year and I tried everything you did. This year I went with a harder axle on the kart drives perfect and we no grip issues at all

granted we have a Tony Kart so we put in a hard axle and the kart has no binding or grip issues at all.

Im not sure which axle you would use to put in soft or hard as OTK karts are different than most. But basically what I’m saying is I had the same issue as you did the same setup changes as you and the. Finally I put a harder axle in and problem solved

maybe someone else can weigh in on if going to a different axle would help you as I don’t want to give you the wrong advice

[Brian MeadParticipant]

Evan – Carefully check the frame paint for cracks. You may have a boken frame somewhere. It should have responded in some fashion. Frames are usually thought to be shot if they don’t respond to anything and there are no cracks anywhere.

[Pat CollinsParticipant]

Evan Fraser

We just ran into this last week before running our Arrow x9. With the kart sitting on the ground turn the wheel lock to lock and see if both inside rear wheels get light. And see if the opposite front wheel has lifted slightly. Our Arrow had one side stay planted on the ground the other was lifting. We had full caster in at the time to perform check. What we had to do is bend down the front side corner to get it to plant the wheel properly. You have to support the good side front corner on a jackstand or floor jack. Have someone stand on the back axle/ wheels while holding onto the seat. Then someone can bounce carefully on the offending corner. It took us 3 tweaks and we had a kart that would jack on both sides equally. We figured this corner was tweaked from a slight corner shunt in Feb of this year.

 

Pat Collins

PS I will try to find the link to a video I found that helped us Troubleshoot this problem…..

[Pat CollinsParticipant]

Evan

 

Here is a link to the video I found that helped us out.

http://www.kartingmentor.com/tutorials/basic-tuning/bent-chassis-test/

I know how we did our adjustment may not be the accepted way to get this done. But I was out of time and needed to get the kart sorted. Hope this might help you out….. :)

 

Pat Collins

[Evan FraserParticipant]

Thanks Pat. My snipers tell me I’m either bent or off center. I’ll also check for cracks. Failing all that my plan is to change my tuning goal from grip reduction to jacking effect. Next race in August so I hope to get some practice before then.

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[Rob KozakowskiParticipant]

Obviously, start with getting the frame / components straight.

My first question would be what axle?

ASN Canada rules?  50″ max width?  I’m guessing you have a 50mm axle?  If that’s what you’re running, if you don’t have it in there already, I’d start by going with a soft or super soft axle to try to get that narrow rear end to flex as much as possible – and remove / detach the middle axle bearing. If you’ve got a medium/hard axle in there, it may lift quickly with a stiff rear for decent entry, but sit back down too soon on exit, especially with the combo of lower HP and lower weight and narrower width of the Canadian-rules LO206, compared to the Rok GP.

If I’m guessing correctly, the reason high air pressures are helping is that the sidewalls are no longer flexing under side loads, and instead of generating side bite, the tires are now just sliding which will help the kart rotate – the kart might not be binding as bad on exit, but you’re not getting the forward drive either.  With lower pressures, I’d guess you get the side bite, and with the back end setting back down too fast, you’re probably having to add more steering input and killing your exit.

A soft axle is almost a “must” for the 4-cycles at 50″.

[Evan FraserParticipant]

Rob:

Sort of ASN Canada Rules.  We run 55″ rear at our club.  I did have a super soft axle in too and that didn’t help, I just couldn’t get the lift.  Considering this is a 2-cycle chassis I do have 50mm rear parts.  I’m going to experiment this weekend on jacking effect through caster and ackerman adjustments and adding in seat struts to the outside of the bearing carriers to get the damn rear to lift.

One thing I noticed when replacing the rear axle is that when securing the two bearing carriers when I tightened the top bolts on one of them the axle started dragging.  I shimmed the top bolts to stand the carrier up more and it didn’t drag.  Are my pinch bolts too tight and not allowing the bearings to twist?

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[Evan FraserParticipant]

I was out for testing this weekend and had no luck.  I added seat struts and added caster and ackerman to the front.  I widened the front track to max and installed the front bar at one point for testing and when the wheel was turned to lock the opposite rear wheel wouldn’t just get light, it would lift off the ground, so the jacking is certainly there.  I had one guy tell me that I was lifting the inside rear on entry and then it would plant itself back down and stick.  I still have ridiculous understeer at all points in the corner.  I’m so stuck that the kart only accelerates in a straight line.  I even took all my lead off and moved my seat back so my struts are nearly vertical to the mounting points on the bearing carriers.

At this point I’m thinking of taking the front and rear apart completely and checking everything before I put it back on.  While I have very little rolling resistance going straight I’m beginning to wonder if one of my bearings is locking up when twisted.

I did also inspect the frame and while I do have some cracked paint the tubing underneath it appears to be intact.

I took a friend’s kart out for a spin and knocked 2.5s off my lap time.  He took mine out and lost 3s.  At least I know I don’t just suck horribly :D

Thanks again guys.

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[Brian MeadParticipant]

Evan – if you could, have someone set in the kart and then look at the frame. Also,
the frame can crack on the underside as well. The frame wasn’t loaded up unless you had someone in it as it would be on the track.

[TJ KoyenModerator]

Sounds like your kart is cracked or something is seriously amiss with the frame in some way.

Rule out all other possible things, such as axle shifting/brakes dragging while turning, damaged components etc.

No kart should be 3s off. Even a very poorly handling kart should be closer than that.

Driver/Coach/Wrench : Innovative Performance/Exprit
Owner : Oktane Visual - www.oktanevisual.com
www.facebook.com/oktanevisual
www.instagram.com/oktanevisual

[Walt GiffordParticipant]

Have you had the kart on scales, have you checked the roll out?

Gif

FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience

[Evan FraserParticipant]

Roll is straight, haven’t checked it on scales.  I’m going to take a good hard look at everything when I take it apart this weekend.

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[Evan FraserParticipant]

I think I’ve found my problem.  One rear bearing is shot, and all three rear bearings are frozen in their carriers.  Can’t get them out or to even move.  I also went over the frame by look and feel and found no cracking.  There was a slight deformation under one of the motor mounts where it’s crushed a tiny bit but that’s it.

Thanks for all your help guys.  I’m going to replace these bearings and see where that gets me.

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[Evan FraserParticipant]

Hi again guys,

The plot thickens.  I was able to get the bearings out by sticking the cassettes in a vice and using a hammer handle to force them to twist.  It took a fair bit of doing.  I purchased new bearings and when I went to put them in discovered they’re just as tight.  I don’t mean a bit snug I mean impossible to twist into place by hand.  This suggests to me that the cassettes are deformed, possibly overtightened at some point.  So my question:

These are aluminum cassettes.  This is where the pinch bolt goes through.  Can anyone think of a way to force it to spread back out?  I’ve put a nut in there on the pinch bolt and attempted to loosen the nut on the bolt but that just tries to stretch the bolt.

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[Larry HayashigawaParticipant]

This might work.  Put some lapping compound in the cassette, clamp the cassette in a vise, insert a bearing you are willing to sacrifice into the cassette and work the old bearing inside the cassette with the axle.  Before starting, make sure the surface of the outside of the bearing is smooth.

[Gary LawsonParticipant]

From what I have seen cassettes for most karts are extremely tight and a mallet is usually needed to remove the bearings. You may want to contact the manufacturer to see if loosening them is a good idea since this is apparently how they were made to begin with.

[Evan FraserParticipant]

Gary I could be wrong but I thought the idea was that these bearings should be free to rotate in the cassette to allow for the axle to flex, otherwise they’ll hold the axle dead straight or worse bind it if the bearings are out of alignment.  On my last two karts (a Tony and a CRG) the bearings could be rotated easily by hand in the cassette so I’m basing my conclusions off of that.

These took more than a mallet (I tried that), they took such a beating that the outer covers of the bearings actually buckled slightly from the pressure we applied to the inside of the bearing.

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[Evan FraserParticipant]

For anyone wondering about the end result of all this:

I started by removing some of the material between the inner and outer surface of the pinch point, with no success.  Then I machined out the inside of the cassettes with wire brushes and emery cloth, found it much easier to insert the bearings but was still tight at the pinch point.  I then split the cassette completely at the pinch point.

I was on track for the next race weekend and the difference was huge.  I am now free out of the corners and able to turn much better and accelerate out of the corners again.  End result was that bearings unable to twist in their cassettes = bind, at least in a low power class.  I’m going to take a bit more material off and polish the inner race of the cassettes up nicely as there’s a bit more I can get out of them.

Evan Fraser

#43 - Formula K FK01 / Briggs LO206

West Coast Kart Club

[Gary LawsonParticipant]

Interesting. Both arrow and tony kart cassettes are so tight you cannot remove them with your hands. Unless they are very used. Yours did sound severe though.

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