The V8 Owners Forum -

Hey, I have got to machine nearly 70mm off the front of my ZF bellhousing, and have done a drawing of the new flange I require to weld on to mate to the lump. Only question is- what thickness for the flange? It is a good couple of inches thick on the diameter, but plate thickness would 16mm be enough or safer to go with 20mm to eradicate chances of warping?

Any advice appreciated!

Hi Tom
16mm would be plenty thick enough, how thick is the housing in that area? bet it is than 6 maybe 8 mm. My engine plate is 10mm and is about the same as the powerglide flange, and the engine plate is much better metal than the bell housing. OK your engine may be a little heavier than the chevy but even so 10 or 12mm should be plenty, 16mm if you must, my only worry using metal that thick would be getting a good even weld.
best regards
Mike

Hi Mike, I was really just concerned about it warping, as it's so big I don't think I can mill it afterwards, but it probably doesn't really matter if it is a a fraction out (warped) anyway?

Maybe I'll go for 12mm then- it's an expensive piece to get cut!

Hi Tom
with less material you have to put less heat into the work to weld it, it is a compromise of inherent stiffness against heat. As I say I would go for 10 to 12mm but bolt it to something big and flat while you weld it.
best regards
Mike

I think you are right to be concerned about warping - you need to really clamp it against something very solid if you can.

I don't think there will be much difference in heat in a big lump of ally Mike, it will take a while to warm up first whether it is 10mm or 16mm. If actual strength isn't an issue, I think I will go for 12mm then (cost for flange probably closer to £100 then!) , and clamp it to something big whilst welding.

Cheers guys.

You could always pre-heat it with a propane torch then weld it. This will greatly reduce warping and relieve a lot of the stresses that lead to cracking.

topcatcustom wrote:Hey, I have got to machine nearly 70mm off the front of my ZF bellhousing, and have done a drawing of the new flange I require to weld on to mate to the lump. Only question is- what thickness for the flange? It is a good couple of inches thick on the diameter, but plate thickness would 16mm be enough or safer to go with 20mm to eradicate chances of warping?

Any advice appreciated!

I'm interested in this. Is it go get rid of the spacer used between drive plate and torque converter on the RR, etc? To make the box shorter for a RWD app?

Hi John, I asually pre heat with oxy acetylene gently first anyway, welds much better when it is hot already!

Dave this is so it will fit on my 8 cy Nash engine, the flywheel on it sits approx 2.5" inside the end and I don't fancy running a spacer that big!!

I haven't got to that level of welding yet, but I have read up on it and they usually preheat the whole piece to get the expansion right so it doesn't develop stress points as it cools. It's normally for cylinder heads etc but it should work here too.

I used 12mm ali on the back of my bellhousing but skimmed it flat and machined all the holes and profile after welding.

It did distort a bit with all the heat involved.

It is welded inside and out to make sure of strength.





Edit to add I didn't do the welding

This guy in Clacton sorted it for me

https://www.facebook.com/RedTorchWelding

Nice, I think the biggest problem I have will be lining it up dead centre! Had it made in 15mm in the end.

Getting it on centre is tricky.

I used the dowel holes on the engine side as a reference point and machined the big diameter in the centre first.

I then bolted the bellhousing to the engine and mounted a mag base and dial test indicator on the flywheel to check the bellhousing reference diameter for run out.

It did need tweeking to get it spot on.

I've had the flange cut with "crosshairs" included, and enough room to drill a pre centred hole in the middle to at least an inch, I plan to drill and ream this to a snug fit over the gearbox input shaft, which should hold it perfectly inline, the rotate is not as important, within a couple of degrees should be fine. I'm hoping this is a pretty fool proof plan!! I need to cut a couple of inches off the front so the input shaft should just be long enough to centre it up.

Should always pre-heat big ally objects prior to tig welding, as you can imagine ally is a great heatsink and if its stone cold it just sucks all the heat out of the weld.