Why does a chassis wear out?

Rodney Ebersole · Posted: Sun Aug 12, 2001 5:39 am Post subject: Why does a chassis wear out?

I wasn't joking, if you want to learn more about cryo treatment which goes hand and hand with heat treating here are a few links to web sites with info. My part time business http://www.coloradocryo.com . The company I bought my processor from http://www.300below and http://www.heattreatingonline.com/index.ht I do use sort of a tripple batch cookie recipe when I cook it in the oven

Tim Brand · Joined: 18 Oct 2001 Posts: 53 Location: Pacifica, CA

Very interesting thread.

So where does this leave the newbie who wants to get started but doesn't want to start out with a new kart?

I found a nice '97 Trackmagic, KT100, in fine shape that a very nice racer will be selling at the end of the season (he's changing classes). It comes with lots of spare parts and the price is right. Is the chassis too old? Should I get a newer one? Does it really make a difference for the amateur club racer?

I heard some negative stuff from a friend about that year chassis from Trackmagic ... anyone else hear anything?

I kind of think that even if it is a mid-pack kart, I'll still have a blast and my son can still go to college.

Any comments?

Thanks,
Tim

Pat Calhoun · Posted: Sun Oct 21, 2001 5:08 am Post subject: Why does a chassis wear out?

I bet if you put Scott Speed in a 1997 chassis, and still had his team he'd still be the one to beat..... 2.5 cents

Pat

Steve Moore · Posted: Sun Oct 21, 2001 5:17 am Post subject: Why does a chassis wear out?

The real money is in the engine and spares.

If you don't like the chassis, you can always buy someone else's roller.

To paraphrase Scott Speed, people who know how can make any chassis work. Of course, the inverse to that also applies; people who don't can't.

Starting out, a kart that is clean and well maintained and doesn't nickel and dime you to death will do you right.

Tim Brand · Joined: 18 Oct 2001 Posts: 53 Location: Pacifica, CA

Thanks for the replies guys. It's pretty much what I figured. Trackmagic has a really good reputation for quality and support. I think I'll be very happy with it to start out with as a newbie.

Tim

Kenny Bolen · Posted: Sun Oct 21, 2001 11:38 am Post subject: Why does a chassis wear out?

I just hug my old '97 Trackmagic, hang a "New Kart Smell" air freshner off the fairing and go!

Todd Godwin · Posted: Sun Oct 21, 2001 4:39 pm Post subject: Why does a chassis wear out?

I know of one manufacturer who has the capability to test a chassis for "flex out". He took a chassis which had been ridden 30 or so times in a season and compared it to a new one out of the jig and could see no difference on his test apparatus. As for a kart slowing down, there are hundreds of variables which change in a race day; even more over a season or two which make the process of comparing lap times pretty unreliable. One thing this manufacturer said that makes lots of sense is that if you think about it, the chassis is pretty stiff and strong compared to many other components on the kart like the spindles, seat struts, etc. Given this, he did recommend that he front end be rebuilt on a regular basis.

Roger Miller · Posted: Sun Oct 21, 2001 8:17 pm Post subject: Why does a chassis wear out?

We have a '97 TrackMagic that was used for Sprint racing for 3 seasons and has now completed its second Road Race Season - and brought home a Duffy from Portland. Seems to work just fine. Of course, Road Racing isn't the same demand as sprinting, I know.

Also, we have a Margay that completed it's second season of Sprint racing, and in it's last three races, placed third in an IKF Regional (best finish of the seasom), 1st a club race tuning up for the last Regional, and then the following week, qualified 5th, led the most laps in both the heat and the main. Didn't win due to slight driving incident that forced the chain to come off. Darn! but the point is, the chassis (plural) haven't seemed to drop off, and, the major variable, the driver, has continued to improve.

Paul Harraka · Joined: 28 Aug 2001 Posts: 1345

The reason you need to stress relieve 4130 chromoly tubing is due to the very reason that it is stronger than 1018 tubing, and that is that the molecules are packed much tighter together in the 4130. This tighter molecular structure causes the heat from the welded area to be drawn out much more rapidly than in 1018-1020 mild steel tubing. This results in a brittle area around the weld which stress relieving,( post heating) will negate. However, if you pre-heat the area a few inches on both sides of the area that is being welded BEFORE you weld, you will prevent the heat from being "sucked out" too rapidly and you won't have to stress relieve. Also, NASCAR chassis and roll cages are made out of 1018-1020 mild steel tubing, that is why they are mig welded with no stress relieving necessary. NASCAR rules forbid the use of 4130 alloy tubing in the roll cages or frame. 4130 is only allowed in suspension components. World of outlaw frames and roll cages are made from 4130 alloy tubing and are either pre-heated prior to welding or are post heated to stress relieve the welded areas. If they weren't the welds would crack or the frame would break around the welded areas.
In my opinion, a go-kart frame should be made from 4130 alloy steel in order to flex and return properly. 4130 has a better "memory" than 1018 mild steel. It isn't necessary to tig weld them so long as you pre-heat or post-heat the frame. My son, Paulie's, Invader karts are made from 4130 and are Mig welded and we have NEVER had a frame failure in 4 years. How long a frame lasts depends on the grade of tubing used, the O.D. and wall thickness of the tubing, and the weight class the frame is run in. Weight is the biggest " killer " of a good chassis.

Martin Secrest · Posted: Mon Oct 22, 2001 9:19 pm Post subject: Why does a chassis wear out?

quote:
Originally posted by Steve Moore:

Starting out, a kart that is clean and well maintained and doesn't nickel and dime you to death will do you right.

Boy, for a newbie, I couldn't agree more with this sentiment. To be talking about the nuances of chassis "spring rates" for your first season of karting is rather unrealistic. As you've surmised, you'll want to be more concerned with staying on the pavement, and keeping your kart from falling apart, should you be able successfully to do the former.

If you're a new karter with a bad machine, you'll spend most of your time wrenching in the pits or waiting in the weeds. Ask me how I learned that lesson (insert emoticon of choice).

Dax Blake · Posted: Wed Oct 24, 2001 6:01 am Post subject: Why does a chassis wear out?

Someone related springs and shocks on a car to the spring of a kart chassis. The following is straight from a TrueSports catalog. Truesports specializes in shocks and springs.

"How do I know when a spring is bad?

Unless the physical dimensions of the spring have been altered (i.e. wire thickness, number of active coils, inside diameter, etc.) the spring rate will always remain the same. Springs do not "lose" rate. However, springs can lose free height or "sag". Verify the free hieght of your springs frequently and replace parts that are out of tolerance."

Hope this adds a little light to the subject.

Dax

Rodney Ebersole · Posted: Wed Oct 24, 2001 6:54 am Post subject: Why does a chassis wear out?

It really didn't shed any light for me. How can a spring that has saged still have the same spring rate? To get rate we must have travel. As travel increases rate increases untill its bottomed or bent.

Stephen Buckley · Joined: 18 Jul 2001 Posts: 861

Chuck,

I have two Italkarts. I was told today that they are made for Claudio at Parolin?????

chall · Joined: 25 Aug 2001 Posts: 16

For years now bike racers have been complaining about frames becoming soft and "whippy", and just as long engineers have ben saying that it's impossible. I think the question of stress changes is going to be answered definitively for many years. As for "heat treating" Watch what you mean when you use that term, it encompasses a large group of very different process. The act of heating and then controlled cooling of the weld area is "normalizing". You might get away with not normalizing a weld in 4130 and you might not, it depends on the stress applied to the joint and how hard the joint is after welding. You can measure hardness and then take that info to an engineering book and look up "fatigue limit" and lots of other useful info about 4130 at that state of hardness. If you have used 4130 as filler you will know just what you are dealing with, if you used something else only time or experience will tell. So what filler metals are being used? 4130, Oxy32, ER70S6, coat hanger?

Chris hall

Mike Goebel · Posted: Wed Oct 24, 2001 5:49 pm Post subject: Why does a chassis wear out?

quote:
Originally posted by Rodney Ebersole:
To get rate we must have travel. As travel increases rate increases untill its bottomed or bent.

Actually spring rate is typically constant, linear. Then force increases not rate with deflection. Ok say a spring has sagged one inch and the spring rate is 100 lb/in. Force has not changed, rate has not changed. Throw another 100 lb on and the spring will deflect an inch. How about them valve springs huh? They see some cycles. My car has 232K miles on it.

Mike G.