Date: Sun, 16 Aug 1998 18:27:23 -0700
From: Dennis Dyck
I am just in the process of finishing the replacement of 8 broken fins onto a 51 Norton ES2 head and barrel (cast iron) and thought I would pass on a few things I've learned in this process. I will be brief as possible, if anyone wishes more detailed info please email me off the list. First thing is to grind the broken edge on the head or barrel to a nice smooth profile. I found that using an angle grinder with a cut-off disc works quite nicely, fits easily between the fins, and you can use the disc as a template to help shape the new fins.
Once this part is done you have to cut a new fin to fit. I used an old Triumph 650 cast-iron barrel as a donor. Fins will break off easily with a hammer and chisel. (Wear safety glasses!). Select a piece whose thickness profile closely matches the area you wish to replace. Either use the cut-off disc as a template (if it's still about the same diameter) or draw a template on a thin card. Cut out the template and trace the shape on the fin. Grind the donor piece to the desired shape, leaving it about 1/8 inch larger than necessary. You can at this point also grind or file the donor to the correct thickness, but don't profile the edges. The reason that you don't want to file the donor piece to the exact size and profile is that if the edges are thin, you risk the possibility of burning through them when they are welded.
Once you have all the pieces cut and ground, find a reliable person who has experience welding cast-iron. Don't know much about welding except he used a Nickel rod. Difficult to get at fins can only be tacked on the edges. Hopefully mine won't break off when I get the beast running. After the welding job is done you can grind the bead off with a cut-off disc (carefully!) and also carefully grind or file the repaired fin the desired shape and profile. Some of these metal epoxies like Liquid Steel can be used to fill in the gaps, then sanded down to give a nice finished look. Fins may "pull down" when they are tacked on so be sure they are supported or clamped in the right position during welding. Your welder will be aware of this.
All of this filing and grinding can be a tedious job but turning an almost piece of scrap into a functional piece of iron can be very satisfying. I am sure that other list members have some other ideas and on doing this work, I'd be pleased to hear them 'cause I got some other engines under the bench waiting for their turn. Has anyone tried brazing instead of arc welding? Can this be done with a MIG welder?
Hope all of this makes some sense.
Cheers, Dennis.
"Every man has to shoot his own dog"