1927 J model steering head thread size

[ChrisLewis]

Hi

First technical post !

I need the thread size for the rear fork steering head please
Don't know the American technical term (Yet !)
This is the thread where the screw down bearing cup fits on the rear fork
I have purchased two bearing cups, one from the US and one from Europe
Neither fit, I think they are close but hey no cigar !

Even better anybody know where I can buy the tap and dye for this thread ?

Thanks in anticipation !

I have ordered manuals and part books and am hoping I can gain further information on thread sizes from them.
(Waiting for delivery)

[TechNoir]

Chris,

I note that Bob Luland has replied to this on another forum re the thread size but here is what I would do in your shoes.

First buy yourself a vernier or digital caliper so you can measure things to a reasonable degree of accuracy and then look after it (i.e. don’t drop it etc). You don’t need to go high end but don’t go cheap either. Chronos do one for about £40 which is good enough for most things, link here, although its showing out of stock at the moment. At the same time buy some thread pitch gauges. With these two tools you should be able to identify threads.

Second, find a local engineering company who will look at your stem and cup. I think that it should be reasonably simple to get the two to fit together as long as they are the same pitch which i would be surprised if they weren’t. I would also be surprised if a decent engineer couldn’t sort it out for you. I use a local firm for stuff that I cant do myself and they are always very helpful and don’t charge an arm an a leg. You WILL find somewhere similar near to you.

The first place where most people go for taps and dies is Tracy Tools. They do 90% of the stuff I have ever needed including lots of bastard threads. I looked for and couldn’t find a 1.125 x 40 die on their site although I wasn’t surprised that I couldn’t its, like Bob said, a bastard thread. If Tracy dont do it then google is your friend but again I couldnt see the one you were looking for on a quick search.

1.125 is 1 1/8" so would be a more common size than 1.120" so a 1.120 x 40 die is going to be like hens teeth. A lathe is the way to go for cutting this thread.

John

[ChrisLewis]

Hi John

In full agreement, I have ordered the items, but I will no doubt be using local machine shops.
Thanks

Chris

[Steve Slocombe]

Dear Chris, Harley described the VL/JD main fork stem thread as 1 9/64" x 24 tpi V-form thread in the 1932 dealer accessory catalog, and that is not one you find on every street corner. I've got a 1 1/8" x 24 tpi die here if you want to borrow it, which seems to do a good job of cleaning up the fork stem threads.