Welding the Chassis

[sirtommy]

I am just writing to enquire about the best time to fully weld the chassis. Anyone got any advice.


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[HandyAndy]

Hi Tommy,
I,ve just had a look at your blog photos etc, I read that you intend fitting the Type 9 gearbox ( located a box at the scrap yard etc), if you still intend to fit the Type 9 then i hope you don,t mind me mentioning that you have placed part U7 slightly in the wrong place, it needs to go slightly over to the passenger side,
Tho if you are fitting the MT75 box then ignore what i,ve said

As for fully welding.....when you have tacked the full main frame together with the rear diff cage too then thats the best time to fully weld it,
BUT
before you do .....check all measurements are correct as per the book dimensions, including all diagonal dimensions, its worth taking the time to ensure all is correct before fully welding anything.

Hope this helps,
Chassis looks good in your blog photos

cheers
andy

[Wynand]

If I may chine in,

Being a boilermaker for 35 years I had my share of welding and paid my dues.
The first thing to do with your chassis is to keep it form twisting/warping whilst welding.
Get the chassis clamped down good - in my case I built mine on a 1.25m x 2.5m steel table with 10mm plate top. The frame was tack welded to that before welding.
If you do not have the luxury of a steel plate to attach the frame to, clamp to wooden table but be sure the wood is fasten to solid frame.
Start welding frame as she sits on table/jig. It is important to stagger your welds - IOW, do only a 25mm run on joint, move to other part of car, do the same etc. This is to prevent excessive heat buildup on a joint/steel that may result in warping when the steel cools and retracts - it is cumbersome but the results well worth it. This is the most important stage of the welding issue. (test: take a half meter off cut tube, do a few welds on one side only and see how it pulls into a banana shape)
DO NOT WELD ONE SIDE ON THE CHASSIS ONLY - this will result in a car good for scrap - stagger welds as mention all over chassis.
About 80% plus welding can be completed whilst the frame is secured and when it is taken off, it should be straight, turn over and weld bottom welds.

A MIG welding machine makes this very easy since weld can be done vertical down without any loss off strength but do not do this with arc welding. There will be a lack of penetration and chances good to trap flux in welds...
If using an normal arc welder, err the amps a bit on the high side as this simplify vertical up welds when using broken arc technique which is the way to go with the thin wall steel tube used on chassis.

Hope this helps.

[spud69]

A good way to clamp your chassis is to get 3 lengths of 25mm box and lay them across your bottom rails on your build table and screw them down to your table with some no. 10 screws. As said, weld as much as you can on alternate sides and should keep it pretty un-twisted.

AndyH

[sirtommy]

That seems sound advice. Under my board which is 20mm glasfibre reinforced plywood there is a metal table which measures 2200X760. So seing as the chassis is only 2360x1118 at the largest measurements do you think it will be ok to to clamp to the board as the overhang is not that great? Or will it bend that overhang?

[sirtommy]

I forgot, i meant to ask andy or any other member from there experience which gearbox is best? Pro's? Con's?

[spud69]

No the overhang certainly wont bend up, you'll be fine with that.

The Type 9 is a good choice upto 200hp, not many people go beyond that, with a short shift gear lever mod it give a nice positive gear change and is also the smaller option so gives you more pedal box area. The MT-75 is a good gearbox and will take more power but has a larger bell housing which will mean tranny tunnel mods and loosing some pedal box room.

AndyH

[alga]

Come on, do a search, it's been discussed plenty of times.

In short, Type 9 is the more popular, the chassis has been designed for it, it's more compact. But it's specced for up to around 200 Nm of torque, although apparently it's handling more without much trouble. Bellhousings are separate from the box, so you could get aftermarket bellhousings to mate to other engines. MT-75 is a newer design, holds up more torque, has an integral bellhousing, but a bit bulkier. It will eat around 3 cm out of your pedal box width, which is not very wide to start with.