Primer Cups

[bselph]

What is the difference between the primer cups for a VL vs a J model?

[Robert Luland]

NONE! What's the difference between a VL and a 37 U Primer? NONE! They were all the same. Bob L

[bselph]

That's what I thought. Competition Distributing shows two different styles. The J model has a short non threaded section that protrudes into the cylinder.

[Robert Luland]

I find it weird that the factory would have something protrude into the combustion chamber. Got to go look at this item.

[MMasa]

Bselph
Somewhere around 1930 there was a change to the shape of the "knob" of the primer. All primers I have ever seen on JD's are flat topped with just a small countersink around the primer hole. The later style has the whole top face of the knob "cupped". It's almost like a bowl. I'll have to put the two styles side by side to see if there is a difference in the length.
Mark

[Peter Cooke]

Mark is correct.

See post #48 of the link

http://www.antiquemotorcycle.org/bbo...toration/page5

[Robert Luland]

Well, now I know my 37 came with the wrong ones in it. Bob L

[MMasa]

Peter
Thanks for the link. Saved me from posting some pics. That was exactly the feature I was describing.
Mark

[bselph]

Slocombe just confirmed that in 1930 the face changed from being flat to cupped. Still not sure about the unthreaded area on the bottom.