It's true that with Harley-Dee it's risky to say NEVER. I've said that myself. And it does seem that some sidecar marked "S" motors may exist. But these don't conform to H-D's own numbering system and that's what I'm referring to. Not that they don't exist, but that by H-D's own accounting they should not exist. No judgement. Just observation.
Let's take the above described "34VDS1371" motor number that Steve saw on the Alcazar museum bike in Spain. I accept that. However, I have in front of me a photocopy of an orginal H-D "Layout of 1935 Motorcycle Models & Model Numbers" issued by the Engineering Department, dated June 11, 1935. Documentation from the hog's mouth, so to speak. This states that "Model No. 35VDS (74 cu. in. Sidecar Twin) Assem. Pt. No. XL-11" used engines with motor numbers stamped "35VD1000" and up. This was the exact same system they used every year with all sidecar models. The "S" did NOT appear in the motor number by their own admission. They say this over and over, year after year. It's gotta be true.
Therefore, if these two "S" marked motor numbers do exist--and I'm not saying they don't--then there must another explanation for the discrepency. What could that be? I'm not sure. Maybe the "S" was stamped on the motor in error and it got by. We've seen motor numbers stamped upside down, sideways, etc. Or is there some other explanation?
I'm not criticizing anyone, just trying to give the most accurate information about the motor numbering system used by sometimes wacky but always loveable Harley-Davidson. By the factory's own reckoning, no sidecar stamped S motor "should" exist.