Sorting through some K&B 3.5 engines I’ve acquired over time, I found that one is,in fact, a 3.25. It has the shorter stroke crank, and the face of the head has been machined to get the correct clearance.
The 3.5 on the side has been removed and left blank. The side of one lug has been engraved with the word ‘small’. There’s also what looks like ‘SS’ or ’55’ in the case.
Also the conrod is different to those on my other engines, having a single oilway on the top of the big end.
It’s the later type case with the larger 0.765″ sleeve.
Any K&B experts out there know if this a factory engine, or could it be a conversion from a 3.5?
Also, there is some slight conrod play. I’ll order a new one from MECOA, unless anyone has an unwanted spare one to sell.