Oil contaminated Alloy castings

By bmwmyplace Date 01-07-2005 10:32

I have a rare rear drive casting on my 1926 BMW motorcycle which needs to be repaired...it has been cleaned and the cracks ground out using a tungsten burr....the problem arrises after the preheat 200C first touch of the tig reveals oil contamination in the casting...and it wont weld.....I have been told to boil the casting in soapy water for at least 8 hours which I am doing...are there any other suggestion ..Regards Peter Down under.

By awill4wd (**)

Date 01-08-2005 22:58

Peter, I have also encountered problems with welding BMW motorbike castings, notably, I suppose they would be called rocker covers off a 1950's era bike.
The castings felt heavier than normal aluminium castings so that gave me some doubts from the start and I was to be proved correct. No matter what method I tried (pulse/no pulse, high AC cleaning/low AC cleaning, hybrid wave forms etc) the result finally beat me and I had to give in.
Does the casting you're welding feel noticably heavier than it should for an aluminium casting? If so, perhaps it's made of the same material.
Regards Andrew. (also from down under (Melbourne))

By bmwmyplace Date 01-09-2005 06:50

Thanks Andrew....now I would have thought for sure that you would not have any problem welding that circa bmw rocker covers....as I know of several that have been welded.... were they one or two piece ?....

I have BMWs from 1926 1997 and at least one from every decade plus a few doubles....so I know there is a wide variety of alloy types ...some that weld well and others that are hopeless...the wosrt seems to be that of WW2 when I guess they used what ever could be smelted.....

I feel certain that the particular alloy I am trying to weld should be ok its just that it is full of oil..... ..so far I have boiled it for three days with a little dishwash liquid.....and a lot of oil came the suface of the casting just like if it was your wifes roasting pan.....

I then put it in the dishwasher and this got rid of the surface oil ( all the brown spots)..... so today it is back into the boiling water to see if any more spots come out ...I will repeat this till it is clear then give it a try...

I will post the results ..... keep your fingers crossed.. I also read on one of the welding supply company sites that it may be better to weld a casting 3/16 to 5/15 with a mig.....? I understood it to say that the mig uses less heat...did I understand this correctly ? anyone......Regards peter

By billvanderhoof (****)

Date 01-10-2005 04:38

You might be able to bake the oil out but be careful. The temperatures and times required to fully volitilize the oil may also anneal the part. Warping is also a possibility although clamping the part in a fixture would help control that. Vacuum while the bake proceeds might help too but I'm starting to get a little far out now.
Bill