1926 EW engine to frame bolts

[MattF]

Hi,
Can someone tell me please what size / type are the two bolts that secure the engine to the frame of a 1926 EW 350.
Thanks.....Matt

[EW-Ron]

The 'bolts' on my unrestored EW would seem to be studs and nuts.
Not yet explored what they are ...

https://i.postimg.cc/xT5Y1L53/EW-engine-frame-stud.jpg


Image added to Forum server - Dave, 01Jun2023

[MattF]

Hi EW Ron, thanks for taking the time to reply. I did not know that they were Studs and nuts. The bike I bought is a "rolling chassis". The engine was removed for a rebore by the previous owner. I have a box of " bits" and will take a look . I may have them.
Stay Safe...Matt

[MattF]

Hi, no sign of the Studs and nuts. They have gone AWOL. Any help in this would be appreciated by a first time Vintage bike owner.
Thanks again.

[EW-Ron]

OK, removing said nut - it came off surprisingly easily - wasn't especially tight,
and ran down off its thread quite smoothly.
Its 3/8", and goes onto a 3/8 BSF bolt - 20 tpi 
NB Sorta goes on fully but then doesn't want to proceed.

This is a nice clean BSF bolt, and std BSF nuts go onto quite readily and smoothly.
Same result with a number of BSF bolts I tried.

Makes me wonder if its 20 tpi Cycle Thread coarse.   ???
So 60°, not the 55° of BSF
https://britishfasteners.com/threads-bsc

Might throw this over to the learned gentlemen  (Duggites ?)  here
I'd hate to suggest BSF if its not ....

https://i.postimg.cc/FzkgTsgF/Douglas-3-8ths-20-tpi.jpg


Image added to Forum server - Dave, 01Jun2023

[MattF]

Hi EW Ron...thanks for going to the trouble of removing the stud for me. I can get both the nuts and the studs here locally.
Take care.
Matt.

[EW-Ron]

For clarity, I only removed the nut.
Without taking the engine out of the frame, those studs look to be very solidly in there.

I think we (You !) need to further explore whether those studs are 3/8 BSF or 3/8 20 tpi coarse cycle thread.
Either one is a possibility - the 55° of BSF v's  60° may not seem like much, but this is a rather critical application,
and the wrong one could damage the thread in the alloy engine mounting points.

I'll try to run a new 3/8 BSF nut onto the stud tomorrow (in daylight)
If it goes on cleanly, it would be good to verify.
I don't have a 3/8 20 tpi cycle thread coarse to try.
They would be a special order.
I have met the occasional other 20 tpi cycle thread on other bikes.
When you meet something odd, its best to investigate, and not force it ....

[EW-Ron]

You could - very carefully - try to thread a 3/8 BSF bolt into the threaded crankcase holes.
If you meet any reluctance - whatsoever - cease and desist.

I have noted that manufacturers, if they don't generally use BSF, will go to any lengths to avoid using them. !
Inc using the aforesaid 20 tpi coarse cycle thread.
Always a possibility ....

Note well the comment
https://britishfasteners.com/threads-bsc
"We have numerous taps and dies in BSC with 20 tpi threads."
"Angle of thread = 60°  "

[MattF]

Your replies are noted at this end Ron and I will proceed with caution. I am in no rush with this. I may hear from you again.
Thanks for all of your time..
Matt

[EW-Ron]

Tell us how it goes.
From the deafening silence here, its almost like no-one has ever removed these studs to
see/say what they are ??

The Owners Club seems to like keeping it secret what spares they hold too,  which is a bit
unfortunate for bikes being restored - so is it worth joining at this stage in proceedings ?

[Daren W Australia]

Spare list from club is here https://douglasmcc.co.uk/pre-war-douglas-spares/

[Doug]

Douglas did use Whitworth coarse threads in cases where they were tapping into aluminum (or aluminium). The ohv engines use 5/16-18  for cylinder studs. Both ohv and sv engines used the same thread for magneto hold down studs into aluminum. The 350EW, B29, L29, L3, H3, C32, A31/32 used 1/2-12 for the crankcase mounting inserts (more on that momentarily). The 250/350 Aero used 9/16 Whitworth for the crankcase mounting clamp bolts. In the cases above factory drawings state "1/2 Whit", "5/16 Whit", or "9/16 Whit" as the case might be. However drawings for 3-speed gearcases for the 350EW, 600EW, and the S5/S6/T6, are annotated just "3/8-20". No mention of thread series such as Whitworth (fine) or CEI/BSC-20. And contrary to the aforementioned practice, and good engineering practice, of using a coarse thread in soft, ductile materials. It would be a good experiment to inspect the thread profile of some original gearcase bolts.

Other exceptions to using coasre threads in aluminum are the cam spindle outrigger plate bolts for things like the A31/32 and the Aero series, which used Douglas' own 5/16-25 thread. Timing cover studs and screws were frequently 3/17-27. These though do not tend to be torqued as high and crankcase and engine mounting points.

In situations where a strong purchase was required as well as the expectation of removing and installing the fastener multiple times, Douglas would fit a threaded insert. They did not trust the wear properties of their own aluminum! Given that the bolt or stud is threading into steel, the above premise does not apply.

According to the EW spare list, they mention both an Anchorage Bolt (7596) and Anchorage Stud & Nut For Stud (9251 & z/467) So a bit confusing as to if it should be a bolt or stud, maybe both were used at different times. The anchorage bolt for the gear case is 7741. Had it been the same number as the engine mounting bolt, then checking the profile on a gear box bolt would be I think 99.9% conclusive. As it is, I think it would be 99%. Nut z/467 is also 3/8-20 and dates back to the 2-3/4hp era. Those threads that nut is used on that I have checked had a 60 degree thread profile.

-Doug

[EW-Ron]

Those threads that nut is used on that I have checked had a 60 degree thread profile.

Which would make them 3/8 20 tpi Cycle Thread Coarse, rather then 55 degree BSF.

Spare list from club is here https://douglasmcc.co.uk/pre-war-douglas-spares/

Aha !  Thanks Daren.
Don't know how I didn't come across this ...

[MattF]

Hi, update...It seems the holes on the bottom of my engine have HeliCoils inserted. The last owner sent the engine to be rebored and rebuilt in the late 90s and this may have been done then. The engine was never put back in the frame. I had someone take a look for me and after a quick measurement stated that they appear to be 7/16 UNC. He tried a 7/16 bolt and it went onto 2/3 threads only. I made further enquiries and I have a member of a Club I am in calling the weekend and hopefully he will be able to progress matters for me. He is familiar with HeliCoils etc.
I will try and post pics of what I have.
Thanks...Matt

[EW-Ron]

Gee, that gives an extra measure of complication.

Could be worth trying metric then, just out of curiousity.
M12* is remarkably similar to 7/16 Whit/UNC
*(there are different pitches of metric !)

At least the mounts are in a healthy state.
When you find the correct hardware !
Good Luck.

[eddie]

Hi Matt,
             The fact that the mounting lugs on the engine have been 'Helicoiled' may be adding to the confusion as to what the original thread would have been. I have been looking through my copies of the surviving works drawings, but cant find any for the EW crankcases. However, there are some drawings for the later 350 engines, and all the lugs are listed as being tapped 1/2"BSW - so Douglas were using the Whitworth thread in the alloy castings prewar. The usual practice was to have studs with coarse threads (BSW) in the castings and a finer (BSF) thread for the nuts.

  Hope this helps,
                          Regards,
                                        Eddie.

[graeme]

I would definitely be checking the metric sizes

[EW-Ron]

The helicoils could be anything, so its worth trying anything and everything !
Aye, metric not ruled out, by any means ...

The studs in my EW are 3/8", and if damaged taking them out to ~7/16" makes sense. (M12 ?)
1/2" must have come later.
BSW makes sense. But printed evidence of this for Douglas for the 1920s is yet to materialise ?
That 20 tpi Cycle Thread coarse gets some mentions for the TS models, for quite some years.

[EW-Ron]

However, there are some drawings for the later 350 engines, and all the lugs are listed as being tapped 1/2"BSW - so Douglas were using the Whitworth thread in the alloy castings prewar.

PPS Something to keep a close eye on with 1/2" BSW threads is that they are 12 tpi.
Where as UNC 1/2" threads are 13 tpi
This can be a soul destroying (and thread destroying) difference !

1/2" is the ONLY case where BSW/Whit and UNC  differ like this ...
Otherwise they are more or less interchangeable
Sorta sorta sorta
If you ignore the 55 and 60 degree aspect .
They will all thread onto/into each other fully, if not perfectly

[MattF]

Update....sorted. Turns out they are 12 Metric with a 1.75 mm thread pitch.
I will get Studs and nuts for them.
Thanks to those who took the time to give me advice.It is greatly appreciated.
Matt