K&B parts compatability

[Andre girouard]

Hello. I recently acquired 2 k&b engines.An outboard and an aircraft engine both are 3.5 cc.Are the parts interchangeable? Such as piston/sleeve etc.What version outboard is this? Is this a 12mm or 13mm motor ? (What measurement does this refer to) ? I believe the aircraft engine is ,# 8380 on the box, but mecoa has no such number. Thanks.

 

[RobertDoak]

Andre...the mecoa web site has a ton of "hidden" info on the K&B engines....but to answer your immediate questions...the engines you have are 13mm engines...the giveaways to look for are the webbing around the motor mounting lug and the exhaust area where it meets the lower...there is a difference in the cranks between the aero engine and the outboard...and I think it's the rotation...not 100% sure on that but something definitely about the intake port on the crank...the sleeve and piston may work...there are timing differences between the outboard and aero sleeves...I was a k&b fan for many years...and the late Rod Geraghty taught me a lifetime of info on these motors...they run well and are very dependable engines...with some mild porting and a tune pipe they can come alive...

 

[LohringMiller]

The outboard has a reverse rotation crankshaft. That way both engines turn their propellers the same way, counterclockwise.

Lohring Miller

 

[Kez]

I believe these engines likely have 12mm cranks. Early K&Bs had no web on the mounting lugs as Robert has pointed out. Those engines had thinner sleeves. They later added the web to the mounting lugs. Your aero engine is front that vintage. After that, they filled in the exhaust flange mounting holes. Your outboard is one of those. It was not until much later that they came up with the 13mm crank. You cannot tell from the outside but my guess is that both your engines have the 12mm crank with a pressed in crank pin. The 13mm cranks are one piece forged.
12mm and 13mm refers to the crank diameter.

 

[rhomodel]

Just take them apart ( which I think you have to do anyhow to inspect them and ensure all is still ok) and measure the diameter of the crank if 12 mm, or slightly under half inch it is 12 mm, if 13 mm,, or slightly over half inch it is 13 mm ( or the inside of the bearings...)

 

[RobertDoak]

An easier way...just remove the piston sleeve...if it measures .765" O.D. it's the 13mm version..if it's .750" is the 12mm version ...but in the grand scheme of things...it really doesn't matter 12mm/13mm...both will run fine...

 

[Daniel's Racing]

Both of those do have the cast in brace on mounting lugs. 13mm ???
The early outboards had exhaust throttles. Not sure if they went to carb the same time as the crank changed though.

 

[Grimracer]

based on the width of the head button.. they are 12mm