Driving pistons cracked on Bauer KA20

[drcolyn]

I am busy restoring a KA20 and during dismantling dropped one of the driving pistons and it had a light crack at bottom end of the piston. It seemed like very bad luck at the moment but a local engine rebuilder welded the aluminium chop chop. What was more important is that after getting it back I took a close look at the quality of the welding and discovered the top has 3 hairline crackes running outwards from the point of impact with the floating piston. The cracks can be seen from the bottom as well. If I put it back it might have caused a lot of damage later during a catastrofic failure. Is this type of wear on driving pistons normal after 600 hours of operation. I noticed the compressor was worked on before and badly tuned (the oil regulating valve was not adjusted to give back pressure at all and the 4 stage floating piston is worn and scoured. What can be done to prevent this type of wear?

 

[CraigAClark]

If the guide piston is cracked where it meets the final floating and the floater and sleeve are scored, you are taking a big risk trying to reuse them, IMHO. I would imagine the "0" oil pressure had quite a bit to due with the results you are observing.

Craig