Repairing cracks in flywheel

Hi! I’ve just acquired a lovely Thompson Gem No 2. While moving it (a bit of an ordeal!) I noticed some cracks on the flywheel (I believe on both sides).

- Is this something I should be worried about?
- Could I strengthen it using some JB Weld or similar steel epoxy?

I understand that the optimal solution would be for it to be fired up and welded by a professional but I’m afraid the cost would be prohibitive for my more casual use of the press.

What’s the best way to make this safe if it isn’t now?

(I can’t seem to be able to attach pictures, so here’s a link to see the cracks:

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Based on what the photos show I wouldn’t worry about it. If it were a spoked flywheel on a motorized press I might be concerned about it breaking at speed. Do the cracks extend all the way to the hub of the flywheel? I’d print on it for a bit (months maybe?) and see if the cracks grow.


Thanks for taking a look Bradley! Yes, definitely not motorised. However, i do think the cracks have come quite close to the hub on one side at least. A bit of JB Weld would ease my mind I think, but don’t want it to be a problem (or useless) in the long run.

That is a very nice press.
My opinion is that JB Weld would only be a cosmetic repair, if you feel better about it, then go ahead. But first, I would drill a small hole at the very end of each crack to stop it from propagating. The hole should go right through the flywheel, on the side of the crack away from the hub. Then fill that hole cosmetically with JB.
I’m not an expert in cast iron repair, however, I believe welding this would take a lot of work for little gain, especially since the whole flywheel would probably have to be pre-heated up before welding and carefully cooled after. As mentioned previously, if it is non-motorized, you are not taking a lot of risk.

Grind the cracks in a v pattern, deep enough to see the crack gone, weld with nickel rod, I have repaired multiple cast Iron Wheels like that and they perform flawless

As long as the rim isn’t compromised, stress-relieve the ends of the cracks (by drilling a small hole, doesn’t need to be more 1/8”) then unless parts of the f/w are shifting I wouldn’t worry much about it.

BTW it’s possible to MIG weld cast iron- preheat then make very short beads (1/2” or less).

Thanks al!

Rim looks ok but will double check once I’m in the workshop. Drilling a small hole at the end of the crack and filling that with JB Weld sounds like a smart move. I’d love to have this done by a pro (in London, UK) but will see how it goes.

As for grinding the crack, I’ll take another look and make sure the crack is not in the same place on both sides which might be a bigger issue.

Nevertheless, happy to hear that this doesn’t seem (too) dangerous. Will take a look in the coming weeks and report. If anyone has any other valuable pieces of advice, I’m all ears!