Cub 123 - OEM head?
 

I have two motors for the same Cub 123. One is the motor that came with the Cub, which was removed ca.1983, when the exhaust valve started sticking. The other motor came out of a newer Cub, and was installed in the 123 by the previous owner. He borrowed much of the shrouding, bracketry, etc. from the original motor to install on the new motor, at the time.

The new motor is shot (broken connecting rod), and now I'm trying to put the original motor back, replacing the valves and guides in the process. Trouble is... I can't figure out which head is the right one for this tractor, as the two are different, and the PO can't remember if he moved the original head to the new motor at the time of the swap 30 years ago.

One has all bolts and studs deeply recessed into the fins, and uses unthreaded spacers on the long studs to set the height of the shroud that covers the head. The other has bosses in the head, which would almost make those spacers unnecessary, but would put the shroud much closer to the head. I will try to get pic's to post tonight.

I sort of remember someone saying something about them changing the spacing on that head shroud, because it was set too close on the early engines, leading to trapped grass and engine fires. For this reason, I suspect whichever sets that shroud higher is better... but how interchangeable are K301AS heads?

Thanks, guys!

They should swap right out from eachother.

Your motor came originally with the high boss head.You will no longer need the spacers.And yes the tin sits directly on the head.

Cool, thanks guys! I remember the old owner mentioning this. So, the high boss head with the tin sitting directly on the head is the original, but maybe not preferred. If the heads are interchangeable, I'd consider putting the newer head with the spacers on the old motor, to go with the newer (assume improved) design.

Any reason why I wouldn't want to do that?

As long as you use the studs in the same position on the block and the correct shroud that goes with the low boss head,just watch if the studs are hitting the bottom of the gas tank as those are shorter. I do not see a problem.

Cool. Thanks!