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  #1  
Old 19-12-17, 18:01
Lolat492 Lolat492 is online now
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Welding alum alloy (gearbox) castings?

It's winter, my Lola is all done and ready for 2018.
So my mind is drifting, hence this possible scenario I could do with some practical advice please.

Imagine:
AUDI A4 manual gearbox (about 2005) with the 'bell housing' cut off exposing the input shaft.
Porsche aluminium alloy bell housing (about 1986) cut to face onto the cut A4 box case allowing me to use the 911 clutch assembly and starter motor etc.

These two cut castings need to be welded together (where they touch) and then filler pieces added to give a 'whole' peripheric weld.

This would give me a great shifting gearbox (compared to the Porsche box I have).

Would these two alloys be weldable? I have no idea if both or one has a high silicon content etc.

Audi box:

https://www.proxyparts.com/upload/pa...87/large/0.jpg

Porsche box:

https://patrickms.s3.amazonaws.com/p...ANSMISSION.jpg
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Old 19-12-17, 20:02
No Imagination No Imagination is offline
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Various Tig related web sites showthe type of filler rod necessay for welding dissimilar alloys, e.g.https://www.westbrookwelding.co.uk/W...final%2052.pdf

By implication if it is feasible to get a small sample from each tested (pretty sure welding professionals must have access to this?), then the appropriate filler can be chosen and job's a good 'un. Probably sensible to include the cost of checking and machining the flat surfaces post welding.............
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Old 19-12-17, 23:44
Lolat492 Lolat492 is online now
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Thank you, I had looked at several threads and all came down to filler rods.
I think the silicon content is something to know before choosing the rods, and a good welder!
The castings would be quite thick walled, and I was hoping to avoid any pre-heating of either part and certainly any post welding machining.

All a bit of a flight of fancy, but would like to get a cheap AUDI or Passat box off eeBTDBTDBTDBTDyy (£100 delivered) and buy some new hack saw blades.

Strip the box and machine the case and the Porsche case (which I happen to have in the shed).
The gearbox I had in my A4 some years ago was a dream compared to my Lola's box....
Driveshafts would be a major task due to the odd design of the March F2 units in the car and the CV's used.
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Old 20-12-17, 10:31
tiganut tiganut is offline
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Quote:
Originally Posted by No Imagination View Post
Various Tig related web sites showthe type of filler rod necessay for welding dissimilar alloys, e.g.https://www.westbrookwelding.co.uk/W...final%2052.pdf

By implication if it is feasible to get a small sample from each tested (pretty sure welding professionals must have access to this?), then the appropriate filler can be chosen and job's a good 'un. Probably sensible to include the cost of checking and machining the flat surfaces post welding.............
Good old fashioned trial & error,works every time.
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Old 20-12-17, 16:22
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david.seaton david.seaton is offline
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I thought about that sort of thing to mate the BMW to a Hewland box as I had an old BMW bellhousing and a Rover to Hewland adaptor lying about.
In the end I got a clever man with a big expensive machine to just knock up the whole adaptor from a big billet of alloy.
A lot of trial fittings and doing alterations in small stages, but in the end it was a lovely looking thing and did the job perfectly.
I was afraid that if I tried to make something by welding bits together, it would be very hard to get it totally accurate and I would end up with spigot or gearbox wear from any tiny misalignment.
I have no doubt it could be done, but I think it would require a lot of patience - probably more than I have these days !
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Old 20-12-17, 17:33
shortie2 shortie2 is offline
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yes it can be done but everything will need stripped back to bare casings and scrupulously cleaned, they will need preheated before welding other wise they will distort or crack at the welds or both
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Old 20-12-17, 17:51
Lolat492 Lolat492 is online now
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I assumed the AUDI case would be stripped out if nothing else to assist it being mounted on a big milling machine.
My thought was to weld 2 plain plates, one to each casting with a centre hole to snugly fit to the AUDI input shaft and similarly to the 911 casting. A custom dowel would then pass through both of these holes (the input shafts I think are the same dia where the clutch pressure plates mount on their splines.

This should centralise the two.
The 911 mounts to a large dia rebate/shoulder on the engine and the gearbox and bolts tight via 4 simple M8 bolts. The diameters assure concentricity on the 911 side.
I think the AUDI is located via dowels and a shoulder also.

It would all be faffing about, but you could get there if you can find a small engineering company to work with, hard to find these days, even in Birmingham.
A man with a cnc and a means to measure the mating faces of both castings is ideal, and expensive.
I'm not ready to spend a lot on this!
Both of the interfaces of the castings would be out of the oil side of the gearboxes so relatively clean.
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  #8  
Old 24-12-17, 14:15
stevieturbo stevieturbo is offline
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I think welding would be the relatively easy part, ensuring alignment would be the difficult part.

Craig at Dynotorque is a good welder and does lots of engine conversions etc, maybe he could advise or perform the work.
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  #9  
Old 24-12-17, 17:17
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RichardBrant RichardBrant is offline
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Craig @ Dyno Torque is a good shout he does some serious alloy welding and this type of modification is right up his street.
He fitted an LS3 to a 996 911 while keeping the Porsche gearbox.
Rich
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  #10  
Old 31-12-17, 17:24
TonyBatten TonyBatten is offline
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The normal method to bolt a mismatched engine and gearbox together is to make an adaptor plate.
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