I am just cleaning my crankcases halves up and having checked the two main oil pipes female threads, the feed and return are really not very nice. I guess some squaddie has crossed the threads over the years. One does tighten up the pipe on the olive but the other one is not quite tigtening the pipe in place. I assume its a problem on most of the WD alloy cased bikes and I wonder whether there is a fix. Has anyone done helicoils or similar or maybe able to suggest a solution. thanks Andrew

email (option): andrew.honychurch@btinternet.com

Hey Andrew, I'm sure those threads are 1/4"BSP. Helicoils are available.
Cheers, Mick.

email (option): mick@motorbikemike.org.uk

I was rather wondering how they would work given the countersunk bottom and centralising the new thread in the casing when you drill it. In simple terms it could be very easy to mess up, and was rather hoping someone out there would say "yeah we always helicoil them"

Anwyay it it is BSP then we should be ok. I will try to look at the parts book and see whether I can confirm the thread thats the starting point! thanks Mick

email (option): andrew.honychurch@btinternet.com

Have you tried to run the correct tap up them? Usually the top couple of threads are the only ones damaged and if you try to run a tap up them ensuring it goes in straight it may just save them.

email (option): davmax@ntlworld.com

Don't know about war models but there is an extension on the bottom fitting to allow a little room for spanner tightening.

I have not tried a tap as yet but will. The thread just looks weak and twisted. I will post up a photo tomorrow so you can see the problem. I just don't want to rebuild the engine and find out some time in the future that I should have done the job properly when I had it in bits.

I would recommend anyone buying cases unseen not to. These threads are nearly always mangled by heavyhandedness.

do you think they may be 1/8th BSP rather than 1/4? My father reckons his 1/8th BSP tap has an external diameter of approximately .375in which would seem about right.

email (option): andrew.honychurch@btinternet.com

Hi Andrew, I'm no Matchless expert but they may not be BSP at all..1/8 BSP is a very fine thread (28 TPI.) with an outside diameter of .304".
1/4 BSP is 19 TPI with an outside diameter of .518".
Other possible candidates are 3/8" BSW (Whitworth) which is 16 TPI and 3/8" BSF (British Standard Fine) which is 20 TPI.
Really you should start by measuring the OD of the fitting that screws into the thread and counting the number of teeth per inch to deduce exactly what you are dealing with...Ian

email (option): ian@wright52.plus.com

Hi Andrew,

My cases are apart at the moment. I'll check then out and PM you.

I have thread charts I can send you also.

Cheers

email (option): britool51@hotmail.com

Hi Robb.. You should post the information on here as well so all the Matchbox owners have it..Ian

email (option): ian@wright52.plus.com

Thank Ian. I will! Sometime I just don't think things all the way through.

Cheers

email (option): britool51@hotmail.com

Hi Andrew,

I also believe there are 1/4 BSP. They measure correctly for that.

Cheers

email (option): britool51@hotmail.com

Just to confirm the threads are 1/4 BSP, well I am 99% sure they are. One more question to all you engineers out there. Looking at the pipe nut it is a tapered fitting. So my question is, will the thread in the crankcase be parallel, or will it have been tapped with a special tap. What I dont want to do is run this tap down and take too much out as I will make a bad job even worse!

email (option): andrew.honychurch@btinternet.com