Baldrick
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| posted on 10/3/08 at 01:17 PM |
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Stripped Drain Plug Thread
The Gearbox drain plug hole on my old motorbike has stripped threads. The gearbox is Ally and the plug is steel. I need to repair and I guess there
are a number of options.
1. Run new ally weld onto the old hole and then recut threads.
2. Recut the thread larger and get a larger plug
3. Helicoil insert down to original thread size.
Which do you think is the best/easiest solution. Is it true that a helicoil would not be suitable because oil would still leak? I've used them
before but not in this sort of application.
Thanks,
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RazMan
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| posted on 10/3/08 at 01:19 PM |
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The easiest option would be to redrill and tap to a larger size imo, but that depends on whether you have sufficient metal to take the larger thread.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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speedyxjs
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| posted on 10/3/08 at 01:20 PM |
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I have no idea what helicoil is but i would think recutting a larger thread and getting a larger plug would be the easiest
How long can i resist the temptation to drop a V8 in?
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MikeCapon
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| posted on 10/3/08 at 01:22 PM |
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A helicoil should not provoke a leak as the sealing happens between the compressed face of the plug and the flat face surrounding the tapped hole. Is
there not a fibre/copper washer there?
www.shock-factory.co.uk
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owelly
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| posted on 10/3/08 at 01:43 PM |
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Or there is another alternative........
Use a tapered thread plug.
Whatever is the best size for your hole (!!) and as long as there is enough maet around the hole.
http://www.ppcmag.co.uk
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r1_pete
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| posted on 10/3/08 at 01:45 PM |
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I've repaired similar in the past using a BSPT (Tapered BSP) plug, after re-tapping of course. Minimises the risk of stripping again as there is
no shoulder to over tighten against.
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bonzoronnie
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| posted on 10/3/08 at 02:56 PM |
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Another vote for a re-tap 
Ronnie
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britishtrident
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| posted on 10/3/08 at 05:14 PM |
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I would tap oversize --- try BSP tapered
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Baldrick
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| posted on 11/3/08 at 08:03 PM |
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Any idea where I would get a BSP tapered plug? Are they easy to get hold of? Current plug is 1/2" I think.
Thanks for all the input
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907
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| posted on 11/3/08 at 08:22 PM |
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I once owned a ZX10 that had a parallel thread drain plug with a copper washer.
The copper washer had worn to a sort of cone shape. When I tightened it the coned washer caused the ally sump to split.
I still hear that metallic ping in my dreams. 
For this reason I would not advise a tapered plug in ally.
I would use a straight thread and a NEW copper washer.
Paul G
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