Repairing 4F crankcase

[TimCee]

Hi,
This is my first post. I'm grateful in advance for your help.

The top front lug has broken off the crankcase of my 1935 4F, approximately along a diameter of the mounting hole (see attached pic). I am considering rebuilding it by welding. I have seen advice in the forum about welding aluminium (eg http://forum.arielownersmcc.com/viewt ... ium#p31721). I'm aware of the general principles of welding Aluminium castings. I've also been in communication with a few members about the idea. This looks like a specialist job.

- Does anyone know anything about the metallurgy of the crankcases of this period?
- Has anyone got any experience of performing a repair to a similar casting which they could share?


Many thanks.

TimCee
1935 600cc 4F

[adrie.degraaff]

The most important thing is that the crankcase must be very hot during the welding.

[paul.jameson]

1) Has the bike been used to pull a sidecar?
2) Do you intend to pull a sidecar with the bike?

If the answers are Yes, No, I might consider leaving well alone. If the answers are No, Yes, you need to do something.

[ColinPeck]

I saw this video and thought I'd give it a try, it works just like the video shows.

https://www.youtube.com/watch?v=Swyglwk ... ZSUjtsTC8w

I tried several test pieces including using a steel strip to re-mold a broken lug, every test went well. I had to repair a 4" split in a Bantam crankcase, the crank flywheel had rusted badly and blew the crankcase in a circular crack. I V'd it out, tinned it and the the repair came out very well. It was a bit like doing lead work just with a higher temperature, it's surprising how much heat dissipation occurred with all the test pieces and this repair. That said the overall temperature is much lower than welding.
After filing up and sanding the repaired crack you wouldn't know it was there and a perfect seal with no leaks. The product is much tougher than the surrounding alli. and I won't hesitate to use it for almost any alli. repairs.
I also did the test using a bolt in a half broken lug, the resulting thread was perfectly usable without having to run a tap through it.

Colin

[Bob.Murphy]

This looks like 'Lumiweld' that I have used. It requires a stainless steel brush to clean the workpiece before and during the repair in order to get fusion.

I see that some of the 'HTS-2000' adverts also offer stainless brushes, so I guess the Chemistry is the same.

I have had good results with 'Lumiweld'.

Bob.

[john.whiting]

If you have spare crankcases,by all means use "Lumiweld".If not,take the cases to a pro old bike welder who will have a high amp TIG,the correct filler rod, the necessary knowlege and experience,and do the job properly.Regards John.

[TimCee]

Thanks All.

Paul,
Yes, I think the bike has towed a sidecar in its past. No, I don't intend to.

John,
What would be the correct welding rod to use?

Does anyone know the metallurgy of this vnitage of chaincase?

Thanks

Tim

[nevhunter]

It's not a difficult situation to weld. It's essentially on a corner so less likely to cause warpage or cracking. The quality of the original metal is important. If there's a lot of porosity it's potentially more difficult to get a clean weld. TIG welding these days is common with proper pre heat and careful cooling, very successful. You usually use a 5% to 10% silicon AL rod with most of those alloys. It's a high loaded lug and should be restored to full strength. Half of it is still there. You build the rest of it up with filler rod. Nev

[john.whiting]

In a lot of prewar alloys,there was a fair copper content.The expert will have pieces of compatible crankcase to use as filler,if the alloy is a tricky one.I see a lot of old repairs that were succesfully done using oxy/acetylene.But some have over the years disintegrated because of oxide inclusions causing a entry path for corrosion.This is the tricky part of oxy welding ally,the oxide is the same weight as the metal,and does not separate from the weldpool.TIG welding using square wave AC ejects the oxide from the weld pool and cleans the metal.But a high current and a watercooled torch is needed.Regards John.

[Brian.Fosh]

I would take it to an engine restorer like T&L in Bedford.

Brian