ET: Engine (Twin) Exhaust cam follower 7/16 x 20 TPI thread.

[A_HRD]

20 tpi Cycle is 60 degrees (as is the 26 tpi BSCy/CEI).
But 20 tpi Cycle WHITFORM is 55 degrees.
Most 20 tpi threads used on Vincents are the latter (ie Whitform).
As Marcus says, you can buy them from Tracy Tools - see link below:

https://www.tracytools.com/taps-and-dies/whitform-taps-dies

If you are cutting new threads don't waste your money on carbon steel taps/dies; use HSS ones. Carbon steel is ok for cleaning-up existing or damaged threads. But even HSS won't work on hardened steel.

Peter B

 

[greg brillus]

Thanks for all the help guy's............It is my opinion that the thread in question in that part of the engine apart from the oil pump bore, is probably one of the most awkward ones to repair, especially on a die cast engine where the material around it is very thin. Cheers.............Greg.

 

[Bill Thomas]

i find they are all a bit on the piss in the cases, so doe not lay flat on the cam, causing wh#@tever. due to the thread being on: yes where...
so I drill the cases deeper, 9,54 hone, and make me a hardend axle, one end M5 female and make up a the afore mentioned thread on a small piece with 5, 3mm hole. glue in. bolt in.
slightly oversise rod (and hone the follower...) screw in and there we go

Any chance of a photo, Sounds interesting, My L/ning rep' engine when I built it, Had that damage, Very bad,
Bob Dunn made a brass insert some how.
Cheers Bill.

 

[clevtrev]

20 tpi Cycle is 60 degrees (as is the 26 tpi BSCy/CEI).
But 20 tpi Cycle WHITFORM is 55 degrees.
Most 20 tpi threads used on Vincents are the latter (ie Whitform).
As Marcus says, you can buy them from Tracy Tools - see link below:

https://www.tracytools.com/taps-and-dies/whitform-taps-dies

If you are cutting new threads don't waste your money on carbon steel taps/dies; use HSS ones. Carbon steel is ok for cleaning-up existing or damaged threads. But even HSS won't work on hardened steel.

Peter B

No such animal as a 20 TPI Bsc thread with 60 degree angle.
The 20 TPI series as per BS 811 is a Whitworth form 55 degree thread.
Anyone wanting a copy e-mail me. That is send your e-mail address in a conversation.

 

[ClassicBiker]

No such animal as a 20 TPI Bsc thread with 60 degree angle.
The 20 TPI series as per BS 811 is a Whitworth form 55 degree thread.
Anyone wanting a copy e-mail me. That is send your e-mail address in a conversation.

Machinery's handbook from 1917 doesn't list a 7/16 Cycle thread at all. I had to go that far back to find the thread depth formula (depth = 0.5327P) to cut them on my lathe. In the course of searching I found the attached diagram but I wanted something a little more concrete for thread depth, hence the handbook from 1917. That's when I found that Motalia had studs listed as 7/16 x 20 cycle. http://www.motalia.co.uk/Catalogues/Bolts/ipage.html
So given that Harley and Indian used 24 tpi on most diameters of the fasteners they used early on, I would suspect some manufactures may have specified threads forms that were non-standard at sometime or not commonly used in a given application.
Otherwise how to do you explain using a pipe thread for a tappet adjuster?
Nothing surprises me when it comes to manufacturing companies. Want to make it an item proprietary? Give it a unique thread then they have to come to you for spares.
Speaking of which has anyone asked the VOC Spares Company what thread is specified on the drawings they work too?
Steven

 

[Sakura]

The only divergence in non metric motorcycle threads from 55 are
UNC which has 60 degree threads and a flatter crest than whitworth but except for 1/2" is same TPI as whit
Also BSC or its predecessor CEI is 60 see:

There are many different thread forms and angles and the above is an oversimplification. BA is 47 1/2°,. UNF, ANF, ANC 60°, BSB 55° @ 26tpi and so it goes on.

 

[Sakura]

If you are cutting new threads don't waste your money on carbon steel taps/dies; use HSS ones. Carbon steel is ok for cleaning-up existing or damaged threads.

Peter B

Good quality carbon steel taps and dies are perfectly capable of cutting threads in steel and stainless steel. Carbon steel actually takes a keener edge than hss. I used my first set of 26tpi from Tracy Tools for many years on ss. CS taps and dies will be good enough for occasional thread cutting. HSS for heavier usage.

 

[greg brillus]

I'll try and get a picture on here of the repair..........Done by my machinist..........very well done, had to weld the area first. This was the result of the follower spindle coming loose in service...........not pretty.