My best buddy just bought a 1940 Scout to rebuild. He asked me to make a shift knob.
can someone tell me the thread size and how much room do I have between the shift lever and the tank
much appreciated for any help
It should be 3/8-24 if it is stock and has not been rethreaded or cut off and modified. As far as clearance you can find knobs in different dimensions that work, the majority are in the 1 1/2 to 2 inch range. Clearance is usually not as much of an issue as what is comfortable in the riders hand.
A good place to get ideas and to see what is out there is to look on jerrygreersengineering.com and pick your model and go to shift knobs or skoobyzzstuff.com
You will see many ideas. I usually make my own and use different things, If I can get to it in the next day or so I will try to post a picture of the one on my 40 Scout I just did, it has a 1940 AMA Gypsy Tour original medallion on it.
There are numerous places to find items to use, swap meets and flea markets often turn up oddities. Another great source is flea bay, just put in AMA pins etc. and you will find offerings of all shapes, sizes and years. Indian head or buffalo head coins are another interesting thing to use, just get the correct year for the bike.
I would have him check his shifter before you put hours and hours into making a knob to find out someone buggered it up and rethreaded it or wanted to use a knob they had that was a different thread and ran a tap over it. You will find out, and so will he that it is rare to find a motorcycle that has been around for 80 years that doesn't have many items that have been altered and often not for the best. I have a 37 and a 38 scout that I road race as well as a couple of 40's HD's and it is scary what you find.