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[PeteF]

Don't overdo the heat, you can welt copper with propane!

[Adrian]

I was taught to anneal copper gaskets but heating them until red hot then plunging them in cold water.



Assuming the threads in the alloy and on the plug are still good, your other option will be to clean the threads thoroughly with a good solvent and apply a thread sealing compound (PTFE comes in tubes as well as reels) to provide back-up for whatever washer you end up using. You local industrial hose shop will have some.



A.

[Leon Novello]

This sounds like there is a hairline crack in the casing which opens when the drain plug is tightened. Lightly sandpaper around the hole to get it spotlessly clean then get out your magnifying glass.

[PeteF]

Adrian, copper doesn't care if it's quenched or not but quenching does tend to remove the oxide (or most of it)

[Jamesy]

Lord Toady cheap option, easy option first. Fit copper washer don't bother annealing it. Fit, test,then take it from there.

[Jamesy]

There's a host of various size sealing copper washers on eBay.

[stinkwheel]

Does sound like the facing is defective (or cracked). They use a really chunky copper/rubber composite crush washer on fuel taps. I wonder if one of those would take up the slack? a 1/4" one is part: 5662.



I'd have a really good look for any cracks though. Re-facing the drain hole would be the ideal solution, a local mechanics may have a sump plug facing tool but you can nearly bet on a bullet gearbox being an oddball thread. If it's very bad though, I wonder if some wet and dry on a flat steel/alloy block would take the worst of any high spots off and allow your sealing washer to take up the slack.

[Lord-Toady]

Meh I have put on my annealed copper washer using my finger and the old plug to keep the oil in to save it all draining out while swapping the washer. I did the plug up a little over hand tight and cleaned everything up with a rag. A couple of hours later I still had a drip on the plug so gave it another 1/4 turn with the ratchet. This morning I still have a drip but on close inspection it almost looks like oil might be seeping from seams all over the place and ending up on the plug since its the lowest point. I am using 140 weight gear oil as someone on here said it would be similar weight to a mix of oil and grease. I am thinking of draining the whole lot out and just packing with grease instead as grease cant leak out. For now anyway until I can take the gearbox off and rebuild with new seals and have a proper look at the drain plug mating surface.

[Lord-Toady]

I dont think it is leaking from the drain plug now looking again it looks like it is leaking from the front cover allen key bolt and the seam where the gearbox front cover attaches to the gearbox. It shouldnt be leaking into that front cover. Maybe 00 grease is the best option for now.

[Lord-Toady]

I cleaned all that with a rag and now you can see the fresh yellow oil on the boss above the drain plug so it is running down the casing and ending up on the drain plug.