Repair of oil feed pipe threads in crankcase

segt · Post by **segt** » Thu Dec 02, 2004 1:30 pm

I am stripping down a G3L 1950 (candlestick rear suspension) and starting on the long processs of restoring a bike used/abused as a farm bike in the south-west of Western Australia. It has been stored in a shed for 15 years since working on the farm. [:(]
I would appreciate some ideas on how best to fix a missing section of casting where the oil fed pipes enter the crankcase. I guess this is a common problem with threads in to alloy. The main damage is to the casting where the upper return pipe enters: an area of about 10 mm X 10 mm is missing. I thought it may be best to weld in a new section of pipe with a modern threaded fitting attached, or is it better to rebuild the casting & rethread with the old thread profile.
I am not sure of the thread type used on the oil pipes or is it best to solder modern fiiting to the old oil pipe. Is it possible to include photographs on the forum.
Cheers from WA

TommoT · Post by **TommoT** » Mon Dec 06, 2004 10:02 pm

Peter,
I would get a qualified aluminium welder to build up the area and re-thread to original spec.. It makes future repairs and ordering of spares a lot easier than trying to remember what kind of mod you made. This is also a highly visible area of the engine, so you might want to retain original appearance. You could at the same fit a steel thread, perhaps some kind of helicoil to make the thread stronger, since damage often occurs from cross threading or using too heavy a spanner hand! Sorry I don't remember the thread size, but it could be a british pipe thread of some sort.

But it's your choice, if you fit a modern crossover or thread you can choose whatever system you like and perhaps improve access and oil
tightness.

Regards,
Tom M. (TM)

segt · Post by **segt** » Tue Dec 07, 2004 1:26 am

Tom,
Many thanks for the advice. I think I will try to retain the original thread in the casting.
Regards

33d6 · Post by **33d6** » Sat Dec 11, 2004 1:44 am

Hi Pete,
Tom is quite right, to prevent a recurrence install a helicoil/recoil insert after the welding repair. Helicoil is just a trade name as is Recoil, they both do the same thing except that Recoil is Australian made (made here in Melbourne, centre of the universe) and helicoil is imported. I've always found Recoils to be much cheaper. And it is a common British Standard Pipe thread size. I can't recall precisely which size without leaving the computer but it's no drama.
I believe leaving it standard is by far the sanest approach. It works, it fits, it doesn't leak if done right and it's easiest!
One last thing, its a professional job. If you haven't the skills yourself don't use a mate who knows someone. Don't take short cuts, get a knowledgeable engineering firm to do it. Your local vintage motorcycle club will be able to recommend someone.
Cheers, Bob

Peter Lecompte · Post by **Peter Lecompte** » Thu Jan 06, 2011 3:31 am

Hi,
just a bit more on this thread. Has anyone actually done this repair of using recoil/helicoil on the crankcase oil pipes threads. Mine on a 1949 18 cases are damaged by crossthreading. Help and ideas are most welcome. I am in Australia. Thanks Peter

Don Madden · Post by **Don Madden** » Thu Jan 06, 2011 5:31 pm

Please note that the pipe does not seal to the threads. The pipes have reverse flare, cone shaped, formed in the ends which the nuts clamp onto taper seats in the case half. Tooling for this is not available in North America, to my knowledge & probably rest of world as well. It is obsolete in the UK & EU regulations make anything non-metric difficult to produce. I have experamented with tubing compression sleeves but have not found any off-the-shelf hardware here to fit. You can seal the gland nut with teflon tape but must still seal the pipe to the nut, which must turn. The pipes are 3/8in to match the drilling in the case & repairs should not restict them. Late 50s had an adaptor to 1/2in to acommodate larger hoses but did not change the 3/8in in the case.

Comments on a solution are invited. Cheers, Don.

Peter Lecompte · Post by **Peter Lecompte** » Tue Feb 08, 2011 12:00 am

Hi, i have just cleaned out both of the threads with a 1/4" BSPT (taper) Tap. This is on a crankcase marked 49/18. I then tried some old fittings and they seemed able to be tightened. I have seen those adaptors you mention Don on 3 other crancases, Matchless 41, 49 and 50. The adaptor is only on the lower hole which has a larger drilling at the base of the female threaded hole. I am likely to make up my own oil pipes. What sizes are recomended for best oil flows for the feed and return? Thanks Peter

wilko · Post by **wilko** » Tue Feb 08, 2011 12:00 am

This is my setup. [IMG]http://i244.photobucket.com/albums/gg3/ ... 0_0713.jpg[/IMG]

Peter Lecompte · Post by **Peter Lecompte** » Tue Feb 08, 2011 2:20 am

Yes, that is a setup I have seen on a few crankcases. This gives a clearance to tighten the nuts and also allows for the larger diamter bottom pipe. It also means that the lower pipe end is a female fitting, not male! I have that adaptor amongst some spares. Great picture, great information. thank you, Peter

GOLDSTAR · Post by **GOLDSTAR** » Tue Feb 08, 2011 9:05 am

As I said on the earlier post and it may assist if only to give a lateral view I used hydraulic/air rubber hose for my pipes and was able to obtain correctly threaded connections from the same supplier, all works OK but of course would not impress the anoraks, kind regards