Monday 19 November 2012

Cracked heads!

-By Juris in Latvia- I have read Paul’s questions regarding repairing cast iron cylinder heads and I can tell that there are at least two ways of repairing the crack, apart from welding it in the old-fashioned way with pre-heating in an oven and afterheating in the same oven.

A nasty crack
Another nasty crack
...and another!

One of these methods is called stitching with Lock-N-Stitch plugs which have a sawtooth and a dovetail – both acting against each other to contract the crack. The repair, if correctly made can be very strong. It is enough to use one such bolt to repair a crack between two valve plug holes in a sidevalve engine. This method requires special expensive American Lock-N-Stitch tooling, those special plugs and some experience and know-how.

Preparing for flame powder spray
Stitch between the openings; cracks repaired

The second method I have practiced for many years is 'flame powder spray' using a special oxy-acetylene torch with a container mounted on the oxygen pipe. Nickel powder is released by a special trigger when required during the heating process of the part. The nickel powder consists of round particles and when it melts it diffuses into cast iron, steel or stainless steel, making a nice, strong joint without any pores. Over the years I have saved quite a few scrap cylinder heads and cylinders which were supposed to be irrepairable – also for my UK friends and customers. I am using a British made MAC flame powder spray torch for the job and it has proved to be successful. Sometimes it is necessary to brake away the cylinder ribs, do the flame spray weld and then add the ribs back by silver or bronze brazing as per attached photos. Please also see this link to the Douglas website. The flame powder spray method can also be used to build metal on severely corroded parts before plating, also for repairing worn shafts and other things. Contact me on my website for further information.

Cleaning up the weld