Topic: K v's F engine - interchangeability

[NickO]

Can someone please give me "chapter & verse" on what is or is not interchangeable between the K and F series engines please?

From what I understand, I believe that you have to use both the head and block (i.e all the top half) from one type together and that an F top end will fit a K bottom end and vice versa, is this correct? If so what are the reasons for not being able, say, to use a K head with F barrels? I have a few sets of what I believe to be F1 barrels and I am planning to get the iron liners replaced with aluminium ones and Nickasil plated, but I don't want to waste the cash if I need K barrels!

Is there any easy way to tell K & F heads and barrels apart (on a stripped engine)?

Also, I'm looking for a good set of F2 cases, (I need these for the bigger bearing on the output shaft). If the engine number begins 26*****, am I guaranteed these will be the right ones? Was this modification only on the F2 cases?

Thanks in advance guys.......

[mlinder]

Pretty sure it's just head and piston. Think they will bolt up to each other, but you need pistons because of combustion chamber design differences.

[Tim2005]

It's the F2s that had the combustion chamber change. I believe that there's a difference with oil return holes too, so while you can put an early head on later barrels you can't put a later head on earlier barrels - would be useful if someone could confirm this & whether that change was with F2 or was earlier. 

Otherwise I believe you are ok to use a K head with F1 barrels. I'm looking at doing this myself with a very early K0/K1 head onto some later K or F1 barrels too, and have been looking & measuring and have not found any differences.

[jweeks]

You can put a "F" head on earlier blocks. If I remember correctly, there are two head bolt holes that are oil returns on "K" heads that aren't sealed passages on the ""F" design. Putting a sleeve into the head for those two head bolts will seal up the head. I run a "F" head on a "Gort" block for my drag bike. When you get over 1,000 cc, the increased air flow of the "F" head has advantages. On smaller displacement motors the bigger ports with slower airflow hurts your lower rpms. Piston head designs will vary with the desired compression ratio desired. Hope this helps!

                                                                     Jon Weeks