Lovely, on the sportster K&B markings varied over the production life. OK some of them were marked with the three digit numbers with the last two digits being the displacement in the location above. Some had a multiple digit (about six) on the side of one of the mount lugs and the last two numbers were the displacement. I have a large number of all four sizes of the sportsters and I just checked them all and they had some form of stamping but Iwould not be surprised if a number pased through and missed this step.

First of all lets confirm this is a Sporster and not a piece of one of the outboards that some were also four bolt heads. The Sportster was a sleeveless cylinder that has a seam and separates just above the raised K&B marks. If your engine has: a conventional looking thrust washer for the prop (ruling out an outboard), has a cylinder base seam and has a round cylindrical muffler that looks as though its made out of tubing with a separate cast header piece from the head to the muffler I am sure it is a sportster. Now since you say it is smaller than your
.40 it is very probably a 20/28. The .45 Sporster is quite large for its displacement and most folks think it is a .60 at first glance. All the parts on 20/28 are interchangeable except the piston and cylinder (this is probably why they used no moulded size markings) and the engines perform almost the same. They are excellent little engines that are not quite as powerfull as some more modern stuff but do serve well. For either the 20 or 28 you can prop about the same, 9x4, 9x5 or a narrow blade 9x6.

I have a pair of twentys on a twin bashed forty size trainer that does well with 9x4's and has even performed single engine takeoffs and untill last year had raced in our local twenty five size Quickee pylon races very successfully with a .28 pulling an APC 9.25 x 6 Narrow.


John