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 Post subject: RX3 Strengthening
PostPosted: Sun Nov 09, 2003 2:13 pm 
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Mazda Approved Mechanic
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We are just rebuilding our RX3 rally car, and I was wondering where other people have strengthened their '3's.

So far we are stitch welding most of the front ent, strut towers and so on.
Plating the chassis rails. And welding a ring around the gear stick opening.

Maybe some of the drag guys have more experience in this?
Where have you found your '3 cracking/bending/breaking?


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PostPosted: Sun Nov 09, 2003 4:50 pm 
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Get a Girlfriend
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Poor old 3 being gravel bashed :cry:


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PostPosted: Sun Nov 09, 2003 9:33 pm 
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The Bug Has Bitten

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Sorry Daveee cant answer your question but is a question I have wondered about.

Could you tell me whats involved with stitch welding a car?

If you cant do it yourself can a rotary workshop perform this?

Cant be certain but would adding a strut tower help? and adding a support to the rear of the car between the shock tops be a good idea also?


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PostPosted: Mon Nov 10, 2003 11:08 am 
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RE10, it's a bit more sophisticated than "gravel bashing". In my mind it's better that these cars get used, rather than;
a) Being cut up and tubbed for drag racing.
b) Being super powerful road cars that can never use the power, and when they do finally hit the track (with corners), post some shithouse times.

After all, it's only metal.

SnailTrail, Stichwelding the car is to give added strength to the crappy 30+ yo welds. It's just a process of welding down the various seams of the car doing say 5cm of weld, then a 5cm gap then another 5cm of weld an so on. It's simply to make the car stiffer. (So it not only lasts longer, but you get more stable suspention pickup points, which = good).

Any body shop could do it. In fact, you can do it yourself if you are any good with a welder.

I assume you mean a strut tower brace, yes it would help a lot. you want it pretty much straight across between the towers, so that the forces are not on the front or the back of the tower, so that it doesn't try to "turn" the towers. Hence stuffing up suspention alighnment.

I'm pretty sure on RX3's the fuel tank sits bang between the strut tops. I can't remember how high it sits, but I think it's high enough to stop you being able to run a straight bar across from tower to tower.

Also in front of the fuel tank are these little wimpy , pressed steel cross braces. They run from where the parcel shelf meets the body near the door and down to the middle of the backseat. It *could* be useful replacing these with soemthing stronger... alhough I don't really know.

And finally, Hey Spac, did you do *any* seam welding on the 808? I seem to remember it falling apart?


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PostPosted: Mon Nov 10, 2003 11:25 am 
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Spitting Seals
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Spac did a nice job on my 929 shell....... :D

Saved me getting the welder out....................thanks mate...


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PostPosted: Mon Nov 10, 2003 12:00 pm 
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I doubt any of the rotor shops would be interested... too much work, too much of a "fabrication" type job, too grotty.
Instead, try panel beaters, pro welders or roll-cage manufacturers.

Daveee,
Yeah, the 808 was in a sad way in its later days. It wasn't welded up from "new", and never had decent suspension in it. FWIW, the boggered bits were:
radiator support seperating from inner guard (dri).
inner guard behind strut tower collapsing (nav).
boot opening becoming parallelogram.
Rear shock tower cracking (dri).
Ugly cracks in inner guard in front of strut tower (dri and nav. Mostly dri).


I reckon hardly any of this would have been an issue if it had been welded up BEFORE being rallied. I wouldn't build another car without plating the rails up - the RX-2s and -3s are too weak around the steering box, the suspension x-member, and the sway bar mounts (ie basically everywhere).
The other thing that's a good idea is welding in the engine x-member, and then mounting an extra pair of sway bar mounts just inboard of the originals - its fairly easy to pull the bolts out of the chassis rails on big hits. This mod also stops the chassis rails from "walking" - moving up and down at the ends independantly - which is what caused most of the 808's front end problems.

But nothing will go close to helping the way a decent weld-in cage will. Seeing as it has an old log book, you should look long and hard at doing the Stanza style "pipe cage". Pete reckons his cost him ~$300 in total (materials + bending), and I can tell you that the Stanza would be in several seperate parts by now if it still had the alloy cage in it.

Hope sense make.

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Last edited by Spac on Mon Nov 10, 2003 3:48 pm, edited 1 time in total.

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PostPosted: Mon Nov 10, 2003 12:34 pm 
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Epitrochoid Shaped Head

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Ive done this with my previos offroad 4wd stuff. Mine was so bad the body mounts all split, the chassis went one way the body the other - end result the gear lever was sheared in two by relative movement! Numerous cracks in stress raiser type positions elsewhere.

This was all fixed through basic analysis of what the stress raisers for, and reducing the amount of load going into them. You cant change the force practically, so in the equation f=ma the best option is to increase the surface area the force is applied too.

So in went lots of reinforcing plates everywhere.

Ever since it was jumped, smashed on rocks and all the rest of it not one crack.


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