ET: Engine (Twin) Chopped engine, reunited with original gearbox.

greg brillus

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Thanks for the replies guy's........yes i don't think it has been a common thing to reunite an engine and gearbox. It is probably far too much work to carry out unless the engine is a rare one or you are able to carry out the repairs yourself. My thoughts are that you really need to jig the crankcase and gear box half as a pair and be able to get to the inside and outside.........If you did it this way, I feel the distortion would possibly be less, as you could alternate the welding from the inside and outside a bit at a time. I have 3 chopped crankcases, one original gearbox.......one of the cases is a genuine series "B" Shadow engine.........it is the one where the entire section of the inner primary housing has been cut off........this is the case we want to reunite with the gearbox.
 

Black Flash

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If I remember correctly, Bob Dunn had castings made that he welded back on.
Maybe worth a try asking him. Probably best to write a letter.
 

Pushrod Twin

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Yep, it's scary! Hence my reluctance to follow through with the idea. I think Vince's idea of using a thick jig plate is smart, but I would lean towards making an aluminium one for exactly the reason he recognised, it will expand at the same rate as the casings. Vince also recognised the process required, pre-heat, weld, post cool. The original Vincent case material actually welds quite well.
Then there is the decision to be made regarding post weld heat treatment. This was the part which scared me off as I was heat treating aircraft parts during the period of my career when I started work on my B cases. Heating the serviceable engine front half case to something near 500 C and biffing it in a tank of water knowing that it was going to change shape put me off. I could never be sure that the distortion could be machined out of it.
 

Vincent Brake

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Yes one can skim the whole lot.
Cylinder surface and mains in one go.
Never more as 0.3mm..
I have done about 5-6 cases both the ugly whoop whoop warping D...
But only once i had to sand the mating faces by total 0.5 mm.
That took some time.
Than after done all saw the gear selector silly half bevel thingy needed to be 0.3 mm deeper.

Of course only saw when whole lot was joined....

Learing curve...
 

Phil Davies

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Sorry to be a late starter to this thread.
Bob did not make any castings.
What happend was a customer had a set of brand new cases and he wanted to remove the gearbox and for Bob to build the engine, which Bob did, Bob being Bob he kept the 'new' gearbox shell as a curio.

Subsequently an owner from Norway with a chopped Shadow engine asked Bob if it was ever possible to find and attach a gearbox back on for a standard chassis set up - Bob produced the 'new' gearbox shell and duly set about welding it on to the Shadow engine. Bob had to shorten an original outer chaincase by 1/32 from the middle to make it fit the repaired engine - what a fantastic achievement.
I saw the finished item and you had to look very hard to be able to know!
That was Bob at his old usual outstanding best, happy days.
 

Phil Davies

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I know he did use a lot of 'warming heat' to reduce temperature differentials and hot spots and welded in precise short runs at a time, the welder was a TIG welder (you would not use anything else really), which make of welder I cannot recall, but it was big and did look like something from a Star Wars space ship flight deck, which Bob said allowed him to weld anything he wished, how he wished.
 

Cyborg

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It would have been interesting to watch. I assumed it would be TIG, but I do remember my oxy acetylene instructor welding up cast aluminum. I will never get close to his level of skill. I imagine you would need a fairly healthy TIG along with a water cooled torch to tackle something like that. Maybe some helium added to the mix.
 

eglijim

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I have no direct experience but have heard good things about using the new generation of handheld laser welders which seem to allow even novice fabricators produce high quality joins . The advantage for Aluminium is supposedly a clean and fast weld with a very small and limited heat affected zone and depending on the head used a wide "wobble"bead can be produced . A1500 Watt machine is ( I am told) capable of producing a weld depth of up to 10mm in aluminium. Maybe a local search to see who has appropriate equipment and experience would be worthwhile but I understand the reluctance to commit as you will only get one chance and it must be right first time.
 
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