Topic: Lets clear up early/late K heads with late F cylinders...

[MRieck]

once and for all. First, the 77/78F2/3 heads shared a common head drain back hole which early K,F and late K heads did not. This eliminated the middle drain back holes in the F2/3 heads. The 4 studs next to the eliminated drain back holes require cap nuts and copper sealing washers on the F2/3 head only. The late F2/3, 77/78 cylinders CAN accomodate the knock pins(or dowels) and the rubber gaskets which allows you to run these early/late K and earlyF/F1(75/76) heads. The later F2/3 castings are good as they are more stout but this does add weight. Trying to run a Wiseco 836 kit with an F2/3 head will result in low compression secondary to the increased volume of the F2/3 chamber. Bottom line....early/late K and early F1(75/76) heads will work on late (F2/F3) cylinders and early/late K and F1 upper cases with mild opening (joining) of the F2/F3 two inner drain back holes at the base of the cylinder.

[scondon]

Wow, you said it all in one paragraph. I'm copying the link to my desktop, FAQ! FAQ! FAQ!

[mick750F]

   I hope Sam sees this post.

Mike

[Clyde]

Mike, Excellent summary.
What about K/F1 heads with F2 cylinder/pistons. Is this a problem?

[mick750F]

Mike, Excellent summary.
What about K/F1 heads with F2 cylinder/pistons. Is this a problem?

 

[SteveD CB500F]

Dr Rieck - I have put this in the Engine FAQs and will follow up with any further gems...

[dusterdude]

damn clyde,now you done gone and opened up a whole nother can of worms.

[MRieck]

Dr Rieck - I have put this in the Engine FAQs and will follow up with any further gems...

Thanks Steve.

[MRieck]

Mike, Excellent summary.
What about K/F1 heads with F2 cylinder/pistons. Is this a problem?

Do you mean F2 heads with early K/F cylinders? If so yes you can do it. Use the cap nuts with copper washers as outlined earlier and eliminate the 4 inner cylinder knock pins(dowels) and rubber seals. Even easier BUT the F2/F3 heads are basically usless with an 836 kit so most folks do the K/F1 head on the F2/F3 cylinders. In all honesty the problems with the F2/F3 heads(retainers, guide wear, chamber size) greatly outweigh the benefits( larger valves).

[GoatBaSS]

Several reactions:
#1 Wha?
#2 Uh, Wha?
#3 Thank You!
#4 Uh O.K.
Man talk about sideswiped by a truck. I feel violated. I am truly stupid.

[MRieck]

Several reactions:
#1 Wha?
#2 Uh, Wha?
#3 Thank You!
#4 Uh O.K.
Man talk about sideswiped by a truck. I feel violated. I am truly stupid.

That's funny.

[Clyde]

Mike,
I was more asking about K/F1 heads with F2 pistons. Is there a clearance problem or too high compression?
Cheers Clyde

[mick750F]

Mike,
I was more asking about K/F1 heads with F2 pistons. Is there a clearance problem or too high compression?
Cheers Clyde

   Watch out Clyde, that truck is on its way back. I've got to assume that you're not understanding Mike's post, because it pretty much answers your question. Or perhaps you are a glutton for punishment? Or perhaps I'm not getting your question...
   
  From the good doctor MRieck...."The late F2/3, 77/78 cylinders CAN accomodate the knock pins(or dowels) and the rubber gaskets which allows you to run these early/late K and earlyF/F1(75/76) heads."

   Got it?

Mike

[MRieck]

Mike,
I was more asking about K/F1 heads with F2 pistons. Is there a clearance problem or too high compression?
Cheers Clyde

Yes, compression will get too high. There could be problems with valve reliefs secondary to the slightly different valve angle of the F2 head BUT I tend to doubt that.

[750]

Sorry to add to a really old thread. Though, I guess better that than to create a new one.  I have a follow up question... Does all of this information mean that basically any early k and any early F heads and cylinders can be swapped around at will? IN turn, does this mean that any late K head and cylinders can be swapped with any head and cylinder only to exclude the F2-F3?  I do apologize if I have confused anyone but I really am curious what cylinders and heads I can put with my K7 and K8. If I could compile all of this information I'd build an excel file to stop the confusion for everyone. It would be really easy and we could even add in what cases work with what engines.

[cobra2411]

Yeah I'd kinda like to know too. What about early / late K and F0 / F1 heads? Any better then the other? Any difference between say a k4 and F1 head as far as ports and flow?

[scottly]

What about K7-K8 heads? Are they the same as F2 as far as combustion chamber volume? In short, can I fit a K7 head on my K1 836 (Wiseco?) without putting my compression (10.5?) in the bottom of the dumpster?

[Jerry Rxman Griffin aka MuthaF'er]

F/F1/K7/K8 heads are all a -392 head with a different combustion chamber shape than the earlier heads, more hemi appearing without the shrouding. These engines had 9.2 CR vs 9.0 possibly due to the chamber design. It has been said this was due to the piston tops but I have both piston styles labeled as -392 and have NOT seen any measurements of volume to compare the two head designs. Therefore without chamber volume measurements I'd say it is inconclusive as to whether it is the chamber shape or the pistons that created the CR bump. F2 is a definite different volume. I'd use a -392 head over an earlier head.

[cobra2411]

You mean F2/F3 not F/F1 right?

[Jerry Rxman Griffin aka MuthaF'er]

Complicated but not really complicated. Difficult to compare 3 styles of heads here and answer your specific questions. Heads - (1) early K  (2) late 77/78 K which is the same -392 part number head originally used on the 75/76 CB750F and (3) 77/78 F2/F3.

PM me with a more specific question.  I don't want to get you more confused.

[cobra2411]

Oh I thought there where only 2 types of heads K and F2/3... Didn't know my F1 was different then an early K head. So they introduced the 392 head on the F0/1 and then the K7/8?

[Jerry Rxman Griffin aka MuthaF'er]

F and F1 head are basically the same as the earlier heads except the combustion chamber was reshaped and may/may not have the same volume. I have not seen nor done any volume measurements to verify any differences if they do exist. It is possible that the new shape accounted for some of the increase in compression ratio.

-392 head pix - used on 75/76 F's and 77/78 K's

[74750k4]

Hi,

I have  a 750K4 that needs head work...  guides in particular. I think the rings are not sealing particularly well either.
I have a 77 parts engine with 392 heads. I'm considering swapping the whole top end...  piston/cylinders, and the 392 heads. Any opinions?
I read about beefing up the guides on the 392's, as that was a weak point. Using the whole setup (P/C, head) from the 77, sounds like an upgrade, but still not thoroughly convinced. I'm hoping someone will sound off, with some substantiated input.

Thanks!

Martin

[Retro Rocket]

I read about beefing up the guides on the 392's

As far as i know the 392's didn't have the guide problem, it was the F2,F3 heads that were problematic.....

[HondaMan]

Hi,

I have  a 750K4 that needs head work...  guides in particular. I think the rings are not sealing particularly well either.
I have a 77 parts engine with 392 heads. I'm considering swapping the whole top end...  piston/cylinders, and the 392 heads. Any opinions?
I read about beefing up the guides on the 392's, as that was a weak point. Using the whole setup (P/C, head) from the 77, sounds like an upgrade, but still not thoroughly convinced. I'm hoping someone will sound off, with some substantiated input.

Thanks!

Martin

It might be simpler for you to bore the K4 cylinders a step and have the guides replaced and valve faces reground. If you also clear away the flash in the cooling fins on the [typical] K4 engine and deshroud the valves, then remove the 8 little 5mm bolts in the rocker shafts (as long as it is apart anyway). Doing these simple things to a typical K4 engine greatly extends their wear life and can pick up as much as 5 HP over the previous bores (10% is typical), leaving you with an all-stock engine for future reference and parts management.

Generally, the "F" engines see short exhaust valve guide life, because the materials used in the guides are not as durable as in the earlier engines. Also, the "F" engines with the PD carbs ran quite lean, which made the wear issue worse.

In the last 4 years, I have rebuilt 4 of the K7 engines. All 4 needed exhaust guides, severely worn. In that same time, I have been through 5 early "K" engines, none of which needed guides or valves, and all of which had much higher mileage than the K7 versions. I have also been through two F2 engines: both needed all of the guides replaced, and most of the exhaust valves, due to valve stem wear. This is typical of the differences between the engines.

Generally, the post-1976 engines make a little more HP than the pre-1976 "K" versions, in stock configuration. Typical [published] figures ranged from 72-77 HP for the post-1976 engines (F2/3 being the highest), 67 HP for the earlier ones (although many K3-K5 engines were in the 50+ HP range in real life), with the K0/K1 being the highest. In all cases today, with more than 10k miles on the engines, boring to even 0.25mm oversize will restore much lost power because the bores are not round, due to the metals used. A new bore brings back the original power, and greatly extends their life.