Aluminium c/block

[lotus 30]

I have a ali cylinder block. (coventry climax) which has put a leg out of bed
There is a fair size hole in the side. i think it is LM25 heat treated. No major
arteries are bust so it is just to stop the oil getting out. can i patch it with some rolled plate or should i try and find some cast material to patch it. Then when welding, is it best to pre heat the block. i have another which has been repaired badly and it has put the mains out of line. it now needs line boring.
Would it be worth putting in a crank that needs a grind with old oversize shells,
and locking down the mains that way to have a heat sink and to stiffen the block.also should i preheat it before welding and cool slowly. thats all not much to ask andyb

 

[rtbcomp]

You'll need undersize shells if you go down that route.

 

[lotus 30]

over size Backed shells are not available for c/climax thats why i want to try and keep the block inline during the repair

 

[hotrodder]

If the fuel tank was trying to run before learning to walk repairing a windowed crankcase is entering the TT before learning to ride a bike...

An old lump of cast ally that's spent it's life in contact with oil often 'bleeds oil' when heated i.e. doesn't matter how clean you get it before starting, the castings are often porous enough to have soaked up oil and will sweat it out when heated. Getting a clean weldpool is half the challenge, often involves repeatedly boiling the crud out and then grinding it off with a carbide burr in a die grinder

Sticking a patch over the hole is typically easier from a welding POV but chances are they'll be various cracks in the area from when the piston and rod made their escape... some obvious, some less so unless inspected with dye penetrant etc. Plating over cracks typically results in the cracks continuing to grow. Miss any and they'll often grow very quickly when you start welding. Personally i usually clean up the hole to a regular shape and butt weld a piece in

Preheat depends on complexity of casting (intricate/lots of stiffening ribs = more likely to crack due to uneven expansion/contraction) and whether the machine has enough guts to cope with a large chunk of ally/the local wall thickness. Min of getting the entire thing warm (~50/60C), max of 200 C. Just let it cool naturally. Any chunk of ally plate will do for a patch, preferably not a 5xxx series. 4043 filler wire

 

[lotus 30]

Thank you hotrodder, my machine is an old boc adr so plenty of amps available. i do have crack detecting dye. thanks for the advice as these blocks are getting harder to find. I thought it might be easier to weld a big lump of cast than my fuel tank. by the way i have pressure tested the fuel tank with comp air and soapy water and had a few leaks but soon rectified them. andy b

 

[FranV8]

Good to hear you're having some success!

 

[langy]

The way we repaired ally blocks was to leave the crank in situ repair then the block would be line bored

 

[lotus 30]

You may feel like i have no idea but i have gas welded aluminium in the past 20 gauge at that. so i do have a feel for the job in hand just got to get used to the tig. and yes i reckon the block will have to be line bored i will take it to south cirney as they may be able to keep the standard backed shells. as i have said there are no 10thou backed shells available . not like the ford engines i am used to.andy b

 

[justmental]

seen plenty of engine blocks welded at the track at santapod and all of them was with the cranks in place.