Welding light-alloy casting -advice please!

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VicMallows

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The BW7 gearbox on my BUKH20 has a fatigue fracture in the area of the STB engine mounting bolt holes (WHY is the rear of the very heavy engine supported on the light alloy front gearbox casting, rather than than the cast-iron block?? :(

Advise Please!... I assume this can be welded? How difficult is this and do I need to find a specialist welder? Any specific questions I should be asking of the welder?

If you have any specific recommendations for a welder in the Solent area (preferably Chi Hbr area) that would be great.

Thanks, Vic
 
In a previous employment, we used to have problems with fatigue cracks in sand cast aluminium engine blocks. Provided you can get the area (and the crack) adequately de-greased, TIG welding should work. If it's possible, it might be worth considering adding an Aluminium web (just a bit of extrusion - doesn't have to be cast), whilst the welder is doing the job.

Depending on the power of his welding set, he might find that the aluminium conducts the heat away too fast at the start - in which case, he might need an assistant to get some initial heat into it with an oxy-acetylene set or similar.
 
Vic,

try Chris Silverthorne at C&B marine, his workshop is beside Chichester Marina at the far CYC end, has done a few bits for me, excellent and I think surprisingly reasonable.

If he doesn't do a visiting service he'll surely have advice;

01243 511273

No connection.
 
Vic, Be very careful that whoever does the job for you does not warp or distort the casing. I would prefer to reassemle the casing and bolt teh whole casing down to a heavy steel plate to minimise any distortion or at least to the bell housing. As you indicated there was a considerable oil leak one can only assume the "crack" goes all the way through the casing. The "crack" will need ground out and the surfaces washed with solvent to remove all the oil (Tric or acetone are my favourites or even zylene :eek:) - I do not have my manual handy and cannot remember clearly the configuration or even if there is a bell housing on those g'boxes. As it will envolve a full pen weld do ensure the welder applies a back purge. I would also look at stripping the box completely and rebuilding after the weld repair IIRC they are relatively simple boxes.

Have fun and do post the results - possibly with lots of photos!
 
Thanks for all the advice. I have gone with Seajet's recommendation: attitude good and he was happy to spend time discussing the job, so fingers crossed!

Photos: yes I have the 'before' shots and will post all in due course.

Vic
 
VicMallows said:
The BW7 gearbox on my BUKH20 has a fatigue fracture in the area of the STB engine mounting bolt holes (WHY is the rear of the very heavy engine supported on the light alloy front gearbox casting, rather than than the cast-iron block?? :(

Advise Please!... I assume this can be welded? How difficult is this and do I need to find a specialist welder? Any specific questions I should be asking of the welder?

If you have any specific recommendations for a welder in the Solent area (preferably Chi Hbr area) that would be great.

Thanks, Vic
Click to expand...
Hi Vic, as per my other message, what was the outcome on this. With hindsight, would you consider fitting a new engine?
 
Make sure the welder uses a stainless steel wire brush to clean the crack/area to be welded to remove any carbon/oxidation
the welder should know that the tig plant should be on a/c current and not dc and the tungsten tips used are zirconiated and not thoriated - best way to remember dc comics has the thor charachter so dc current is thoriated ac current is zirconiated.

you could also use mig welding but make sure the wire liner is either brand new or has only be used on alloy again dependant on scenario

jon
 
Seajet said:
Vic,

try Chris Silverthorne at C&B marine, his workshop is beside Chichester Marina at the far CYC end, has done a few bits for me, excellent and I think surprisingly reasonable.

If he doesn't do a visiting service he'll surely have advice;

01243 511273

No connection.
Click to expand...
Hi Seajet, do you know if Vic is still around the Chichester area?
 
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