Author Topic: chassis top rail has bowed outwards  (Read 756 times)

Offline longtimeracer

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chassis top rail has bowed outwards
« on: November 13, 2020, 05:02:35 AM »
Got a bit of a conundrum with my FED, its a 150" mild steel chassis with an injected Chevy small block. The chassis is 5 years old, built to SFI 7.50. Only done 30 runs as I only do 3 meetings a year, its a hobby car, not ultra serious but I don't stint on what it needs. Its a regular low 9 second car but got it into the 8s in 2019. Taking the motor out, I noticed that the offside top chassis rail(that's the right-side from the drivers seat) is bowed out by about 3/4". At the front the motor mounts on saddle brackets held with Micalor hose type clips. I'm thinking that in a wheel stand the right side front motor mount slipped because of the weight of the motor and then pushed the chassis rail out? Also the torque reaction of the motor would tend to push the motor down and push against the right hand side chassis rail which might worsen the effect of a wheel stand. These are thoughts that I've had. Regarding saddle mounts, wouldn't these work better if dowelled? Of course I've got to get it fixed or may be front halved? I would be very interested in what you guys think, having a bit more experience than me, thanks.

Offline longtimeracer

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Re: chassis top rail has bowed outwards
« Reply #1 on: November 14, 2020, 03:43:56 AM »
Hi Roo Man, what do you think? Value your comments

Offline MaggiFinn

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Re: chassis top rail has bowed outwards
« Reply #2 on: November 27, 2020, 01:59:13 PM »
I think the tube that holds the steering box should be fastened to both top rails...


Offline longtimeracer

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Re: chassis top rail has bowed outwards
« Reply #3 on: November 30, 2020, 05:41:57 AM »
Hi Magnus, the steering box is tied to both top chassis rails, the bowing out started in front of the motor and the chassis builder has concluded that a wheel stand did this when the engine came down with the chassis and the weight sprung the top rail out, its also made a a slight curve on the LOWER frame rail on the opposite side, aren't wheelies great :-\. I'm having to front end the chassis now, with extra bracing.

Offline JrFuel Hayden

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Re: chassis top rail has bowed outwards
« Reply #4 on: November 30, 2020, 03:00:43 PM »
Our Heritage JF chassis had the top rail bow out in front of the engine so we just added a couple of cross bars , helped make the chassis stiffer and helped with the tire shake.
We also added another 20 lbs to the front to control the wheelies better and we run our wheelie bar about 1 1/2" off the track. 
Jon C. Hansen

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Offline Curly1

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Re: chassis top rail has bowed outwards
« Reply #5 on: December 08, 2020, 07:06:56 PM »
You need to be able to control the wheelies. On my 225" FED I can pick up front wheels 4 feet high and carry them out well past 60 foot? or with just 25 Lbs on front and no other changes will pull them up 4 inches and maybe carry them 2 feet? I do not even run my wheelie bar any more I use weight up front to control wheelies.