Knucklehead Rocker Lower Tins Question

[MMasa]

I looked in Palmer’s 2nd edition (I don’t have 3rd yet) and didn’t find an answer.
Im sorting out the intake and exhaust lower tins for both a 39 build and a 47 build.
My question is that I’ve noticed a difference on the “rabbit ear” end where there’s a step in the stamping. It’s only on two of the couple dozen lowers that I have.
Whats the deal with that and what’s the application of the stepped style.
Thanks
Mark

[bobphd]

I believe that the ones with the step are the over the counter ones that were available for replacement of the troublesome 36-37 baby jar covers . I am not sure on this or why the step but I believe I read that somewhere. I do know that I have used ones with and without the steps on many heads without issue.
Bob

[Jerry Wieland]

I believe that the ones with the step are the over the counter ones that were available for replacement of the troublesome 36-37 baby jar covers . I am not sure on this or why the step but I believe I read that somewhere. I do know that I have used ones with and without the steps on many heads without issue.
Bob

Bob The step tins were used to retrofit the later tins to the early heads. I also think early 1938 used the late 37 type head and would have also needed the step tins. Jerry

[MMasa]

Ok, thanks for the replies guys.
So they’re all interchangeable and usable on any year head?
Mark

[Carl Olsen]

The stepped tins are for 36-39 heads, but will work on later heads, but the later non stepped will not work on the early heads.
Carl

[jorrow]

Can someone post pictures please?

[bobphd]

Thanks Carl and Jerry for the info. If the picture works it shows stepped and non stepped covers.
Bob

[MMasa]

So just to be clear, stepped covers never came on a new bike from the factory. They were just used when retrofitting the new style of cover onto 1936-1938 heads?
Mark

[jorrow]

The stepped tins are for 36-39 heads, but will work on later heads, but the later non stepped will not work on the early heads.
Carl

The stepped tins will work on the 36-38 heads without fin modification?

[bobphd]

According to shop Dope 172 Jan 20, 1938 , 36 and 37 heads need to be ground for clearance when installing the 38 type covers. According to Carl the 38 and 39 heads also need the stepped covers and I assume he is correct and there must be a difference in the “rabbit ears” on the head castings. I cannot tell on my 36 or 39 if they have the stepped covers as they are assembled running motorcycles, but I also assume that the 39 has the original covers it came with and the 36 probably the covers that were fitted when it was modified who knows when . Only if the covers were damaged would I have replaced them and if I did I did not know about the step difference and don’t remember yesterday let alone 10 plus years ago. Anyway , this is an interesting topic and I have learned something , I think.
Bob

[Jerry Wieland]

According to shop Dope 172 Jan 20, 1938 , 36 and 37 heads need to be ground for clearance when installing the 38 type covers. According to Carl the 38 and 39 heads also need the stepped covers and I assume he is correct and there must be a difference in the “rabbit ears” on the head castings. I cannot tell on my 36 or 39 if they have the stepped covers as they are assembled running motorcycles, but I also assume that the 39 has the original covers it came with and the 36 probably the covers that were fitted when it was modified who knows when . Only if the covers were damaged would I have replaced them and if I did I did not know about the step difference and don’t remember yesterday let alone 10 plus years ago. Anyway , this is an interesting topic and I have learned something , I think.
Bob

Bob Later 38 and 39 heads do not need the step tins. Jerry