Royal Enfield Owners Club,  Humberside Area
Back to the

Bullet crankcase drainplugs.

A modification to secure drain plugs.

There are instances of crankcase drainplugs stripping threads in the (fairly soft) alloy of the crankcase. This isn't helped by the fact that the drain plug relies on only 5 threads. If the crankcase threads do strip it's a tricky job to repair them.
While this modification isn't a fix for stripped threads, it should stop them from stripping in the first place.

First of all, get yourselves some Dowty washers.

drainplugwash.jpg (13557 bytes)Available from Hitchcocks (Accessories/Engine/Oil seals) or other engineering suppliers.

These have a neoprene seal bonded in to them which seal a lot better than the original copper washers. Dowty washers seal with a lot less torque than copper washers, and in fact will seal with less torque than I consider safe to prevent the plug vibrating loose - much safer if they were wired on. I used to use Dowty washers at work to seal reducing valves onto compressed gas cylinders. They will seal against many atmospheres of pressure with not much more than hand tight torque.

drainplug01.jpg (236329 bytes) 

Drill a small hole in the plug on a suitable flat which will hold the plug tight when it's wired.

drainplug02.jpg (210948 bytes)

Refit the plug and just nip it up. Drill a small hole in the engine fin to secure the rear plug and wire it on with a bit of malleable wire.
The best stuff to use is proper locking wire which resists breaking when twisted a lot.
WARNING pick up those offcuts of wire as they are sharp and can end up in tyres!
You'll see why you need to choose which flat to drill so that the wire stops the plug unscrewing.

drainplug03.jpg (204271 bytes)

And a small hole in the engine plate to secure the front one.
(yes, I drilled the wrong flat the first time on this one)

I know it looks a bit untidy but it really isn't that noticeable when viewed from above.

drainplug04.jpg (233778 bytes)

You can now put just enough torque on the plugs to seal the Dowty washers without fear of stripping the threads.

I'll do the oil tank drain plug as well when I next change the oil.