I am just in the process of giving my M20 a good check after a busy year and I've found an oil leak from the timing cover. There is a hairline crack where the oil valve spring bolt screws in presumably from over tightening at some stage. The crack is on the underside of the case directly below the spring position and seems to go through to the thread.
Does it need a professional repair? or can it be soldiered?
That's a difficult one to repair..It would need to be welded and that raises various problems...
The thread will probably need to be cleaned out and recut after welding..The weld tends to penetrate...Also the contamination of oil, impurities in the castings and the possibility you have a wartime cover with a higher than normal zinc content in the alloy mix can all lead to a compromised/failed weld....
Personally I would look to replace the cover with an undamaged one...They aren't particularly rare...Ian
Stuff like Lumiweld , Aluweld etc which are all basically a solder should do the job, if and only if you can get the cover clean enough and that is no mean feat.
Due to oil in pores it is very difficult to electric weld aluminium castings
I used Lumiweld on a crankcase some years ago and it worked OK. It also doesn’t seem to stick to steel so you can put a bolt into a broken threaded hole and it will form around the bolt which can then be screwed out (at least it did for me). Getting everything clean is, as mentioned, the hard part.
As Ian said, a sound replacement is probably less hassle and not particularly expensive.
There is also the future to consider if any repair made fails at a future date...Replacement covers won't be so common then..
As an aside I have found than many internal threads get damaged simply because they are clagged up with sealant, oil and grease deposits, bits of gasket, paint deposits etc.etc...and that's apart from the fact they frequently have damaged fasteners forced into them...
That makes any taps and dies that are bought a good investment...When rebuilding bikes I routinely tap out all the threads and inspect the threads on any reused fasteners very carefully prior to fitting...If it's tight to screw in when fitting there's something wrong with one of the threads!
Though the taps and dies required are many, covering different sizes and threads, they can be acquired gradually over time to spread the costs...Ian
