1940 frame question

[Steve Little]

Hi.
I logged in to post an issue with a 36-40 clutch and noticed 2 private messages.
I haven’t signed in to my AMCA account for a while, but I still read the forum on a weekly basis and am interested in the club and all things that go “tippityfart” with engines and wheels.

I hope I don’t offend the enquirer, but thought I would answer one of the questions through this public forum, for all members to check, maybe add to, and hopefully to benefit from.

Enquiry as follows:
Hi Steve,
I hope this message finds you well. I haven't seen you on the AMCA forum for awhile.
I asked this question on the AMCA forum a while ago but never got an answer that really answered the question.
Is there a simple way to check the neck angle on a bare 40 EL frame.
No front forks. Also what should the angle be?
Thank you in advance.

1936 through 1940 frames were designed, drawn, and manufactured at 25 degrees.
But I think it would be nearly impossible to find a frame that came through the original manufacture process, and still be 25 degrees.
The good frames that I checked through 25 years of frame work, were 25 degrees & 30 minutes, with some closer to, but not quite, 26 degrees.
The change in neck angle was due to contraction of tubing after the brazing process, and then the subsequent quench process that followed in the brine bath.
The 1936-1944 (brazed seat post) frames were placed in a brine bath and drawn up to 30 rockwell.

I found, that original, perfect, frames will not fit into a jig that is made exactly to Harley frame dimensions.
This is because the engine mounts were re-cut to correct for warpage after the frame had cooled down. The neck bearing cup areas, were also re-cut at this time to correct “out of roundness”.
The area that contracted the most were the rear tubes, which caused the axle carriers to point upwards slightly.

I think the easiest way for you to check that frame is copy the Harley method in the early service manual.
Place it on a good flat surface with some even blocks under the bottom frame tubes.
Put a piece of good quality “straight” tube or bright bar (about 3 foot long) through the neck cups.
Make sure the holes in the cups measure the same size.
Rest the tube against the back edge of the top and bottom bearing cup holes.
Sit a 2 foot plate square on the table and place against the side of the tube.
The vertical line of the plate square is zero.
Using a vernia protractor, measure the angle from the vertical plate square to the tube. This is the degree of neck angle.

Factors that will alter the neck angle:
Any bend in the two front down tubes.
Check them with a 12” ruler. If you see any gap it will alter the angle of the neck.
Check the backbone. Any hump or hollow will affect the rake of the neck

Comments, questions and suggestions are encouraged, welcomed, and ultimately provide involvement and life in the club forum.

Regards Steve

[Old Ugly 40]

Hi Steve and thank you.
That is the answer I am looking for. I have the frame sitting on a metal table that has another plate on top that has 6 adjusting bolts so it can be adjusted flat
so it should be fairly easy to follow your instructions. Unfortunately it is on the back burner till next winter. I am recovering from back surgery and have other things
to catch up on.
I have no problem with this being answered here as it may help others and it is good general info from someone that knows. I have read and book marked any of
your posts concerning this type of frame. Thank you for the excellent information.
I looked at my clutch but there is no way to tell if the stud holes are threaded or not. Hopefully there will be some more input about this just for general info.
Good luck and thanks again.

Old Ugly 40
Rod

[RichO]

Hi Steve, I ride a 1940 x-California Highway Patrol EL. It still had the tool box mount on the left side, three post coil, and M-25 carb w/bombsite to overcome the 1 5/16" venturi when I got it. The backbone from neck to seat post had been bumped to correct the handling problem the 16" tires created for the CHP because of the steep next angle. It makes fitting the tanks and instrument cluster interesting. Always enjoy your posts. P.S. I always install a M-35 1 1/8' venture in an M-25 body to get more velocity and better mix plus the 18" tires for better handling. I love the 40 El's. This is my second one. So many first or last year changes and that large upper end really let's them breath. Congrats on your mates first AMCA Chapter down under. Regards, Rich P.S.S. My next angle after the dealer or factory bump?????

[T. Cotten]

Dr. Sprocket!

An M-25 Linkert will not accept an OEM "bombsight", as there will be no air correction circuit to the main nozzle.
We must presume you installed some modern hybrid?
Why would you want to "overcome" the original design?

Did it go too fast?

....Cotten

[Steve Little]

Hi Rod. I,m pleased I could help, and a little bit amazed that I could write the information in a relatively short fashion. I know that sometimes I have a tendency to fill the page.

Hi Rich.
Those frames are really interesting to look at when they are stripped of tanks. I think the bends in the backbone were cold pressed in a die set. When I had the frame business we had a big electric over hydraulic press and did a lot of the forming of the frame tubes in in the die sets we had made. We could set the relief valve as high or low as needed. We would bolt the die sets into the press and press the first couple of tubes to see what minimum pressure was needed to get the correct pressure to form the tube and close up the gap between the die set. We did not try to recreate the backbone bends like your frame has, but they are very close together, and it is 1 1/2" tube. My guess is it would take monstrouse pressure to form them.
Regards Steve
ps. The front down tubes are the gauwdy part of that design....but interesting just the same.

[RichO]

Dear Mr. Cotton, The bike had the HARLEY bombsite installed in the M-25 when I bought it. The problem for US that ride 1940 EL's with stock M-25's (I removed the bombsite to make it original, silly me) is that they take in to large a lump of air which doesn't mix well with the fuel and they bog down. That's why in 1939 and back to it in 1941 they had 1 1/8th venturi's in stead of the 1 5/16th they tried in 1940. Just like the brass manifold that distorted and they went back to steel ones. Many old rider's of 1940 models have verified this problem. The CHP used the bombsite to get a faster pull in and mix of fuel and air. Just like 1940 frames had to be bumped on the backbone bar to increase the neck angle because with the new optional 16" tires the CHP bikes at speed got intense front fork wobbles. In 1941 the neck angle was increased in production. 1940 models are a different breed of cat. Lot's of last year/ first year parts. Many miles in the saddle will let a rider know what worked and didn't. P.S. The CHO carb's as you certainly know had a fixed high speed circuit so the boy's in blue couldn't lean it out and destroy the motor.

[T. Cotten]

You don't get it Rich...

The OEM bombsight does not have an annular groove around its outside for the air correction circuit.
Bodies for bombsight models, such as the M53 (NOT A 1) had a separate gallery drilled to feed the nozzle, and a completely different nozzle as well.

M25s run just fine with their original venturies, as History has proven.

And don't look now, but brass manifolds were NOT, I repeat, NOT early '40s!

Many, many cross my benches, and virtually every one is for a '47 OHV, except a couple of '46 U and G models.

Think about it: On the verge of war, why would a strategic material such as brass be used to replace cheap and easy cast steel?
After the War, brass was abundant ordinance scrap, and the castings were prone to porosities in bizarre places, because it was fouled by gunpowder. (attached)

And don't forget, 1940 OHVs had a short manifold as shown on the left in my last attachment. They were never, ever brass or bronze.

Seriously, I do this for a living.

....Cotten

[RichO]

Tom, I misspoke, I stand corrected, I never claim to be and expert on anything (don't like to paint myself into that corner). Coming up on my 70th year it takes more time to recall exactly what happen yesterday well alone 15 years ago. I now remember I had to source an M-25 as the machine did come with a M-53 bombsite carb. I was told it should use a brass manifold but chose to install a steel one. Why would the factory go from 1 1/8" to 1 5/16" (because of the new big port top end?) back to 1 1/8th? Steve, I'm sorry your thread got highjacked. For Tom this final comment. "Didn't it go fast enough?" "Why would you want to "overcome" the original design?" "Don't you get it?" "Seriously I do this for a living." Snarky Tom I certainly hope you never error, make a mistake, or misspeak. Unlike the Harley-Davidson factory that has more than several times in it's history, made design errors and put them in production hence their need for corrections and design changes.

[T. Cotten]

Just call me "Snarky", The Gadfly from the Dumpster,... Folks.

The internet is already the great mis-information highway, and somebody has to speak up before somebody else actually believes it.

....Cotten

[DANPATCH]

Steve good to se you on the forum . Really miss the parts you made . I Pray you health will improve .Dan Patch

[Steve Little]

Steve good to se you on the forum . Really miss the parts you made . I Pray you health will improve .Dan Patch

G'day Dan.
Thanks for the well wish. Inching forward and getting better every day.
Regards Steve