Triumphrat

slowride

I have a gas tank on a 1978 T140E that has had one of the bung holes retaped to fit an aftermarket petcock. This 30 something year old generic petcock has now failed and I need to replace it – there is no identification on it that I can find except “made in Italy”. The size of the male thread seemed to be the same as the original so I ordered a replacement of the original from northern eagle and then found out that the threads weren’t the same.
The tank end threads on the adapter for the old failed petcock measure .514 inches – about .020 to big, and a totally different thread. The petcock end of the adaptor has male threads that measure .625 or so and are relatively fine, but I don’t know if these are some sort of standard thread for a possible replacement or not.
My question is can I drill out the bung hole and retap it for a larger petcock, such as a HD style Pingel? How much metal is around that hole? Could I go as large as 3/8 inch NPT?
Any advice or alternative solutions would be much appreciated, thanks in advance.

Mr.Pete

The tank threads should be 1/4" BSPF.That's a parallel thread 19 tpi,about 0.518" O.D.

slowride

Thank you for that information. What a relief. The adaptor that was in the tank measures .514 and sealed up fine with some Teflon tape, and I was assuming that the new replacement was the correct size at .492 – I would say quite a bit too small for tape or sealer! I can’t believe the machining on a part as vital as a petcock would be that sloppy.
I want to run with both petcocks open and would still prefer a reserve, so a 3 way would be nice – even though in 34 years with this bike I have never had to use the reserve.
Since it appears I will have to buy another one, any suggestions for a supplier for either an original that is for sure going to be the right size or a different 3 way? The Pingels look good but at around $100 are a bit steep.

Morris the Cat

Make sure to use the yellow version tape as it's designed for gas!

__________________

Morris of Main Street

Snakeoil

If I am not mistaken, HD used a petcock that was 1/4 NPT which I believe is a tapered 19 TPI thread of close diameter to the straight BSP thread. I'd have to look it up to be sure. If you are handy or have a friend with a lathe, you might be able to machine the tapered thread to a straight thread so it will fit. The HD petcock I'm thinking of was used on early 70's Superglides. It has a reserve.

Check a vendor like J&P Cycle. They have all kinds of custom stuff and OEM repop stuff for HD.

Another possibility is to adapt a common Jap bike petcock. You would have to machine an adapter to screw into your tank and provide mounting for the petcock. Difficulty would depend on the design of the petcock you choose.

NEW INFO: I went to the J&P site out of curiosity. Here's all the HD petcocks they list.
http://www.jpcycles.com/vintage-harl...28004844&Nao=0

The one I was thinking of is this one.
http://www.jpcycles.com/product/4100030

I looked at the specs for some of the others and noticed some fit a 22mm thread.

I had forgotten that later model HDs used a bung with a male thread, meaning the petcock has a female thread. You could make an adapter that screws into your tank and provides the male thread to which the HD petcock would screw onto. Of course, this also requires a friend with a lathe to make the adapter. You also have to assure that the tube and fuel screen will fit thru your adapter.

regards,
Rob

slowride

Thank you everyone for all the help. Now that I know the proper size of the ¼ BSPF threads and the problem is with the new petcock not my tank, I should be able to find something that will be suitable. As far as adapting an older style HD petcock, I believe Pengel will sell adaptors separately, or I may just bite the bullet and buy the petcock from them and be done with it. The sooner I get back in riding condition the better.
Once again this forum has saved me a lot of frustration and time.