Topic: CB750 K5/K6 vs CB750 F/F1 head

[macvit7906]

Anybody have a picture side by side of a K5/K6 head next to a F0/F1 head?

I have two parts bikes that are supposed to be 750F but I'm finding differences between engines.

For the head specifically, one has exhaust studs installed in the head that the clamps go over, the other head had 8 bolts holding the exhaust clamps in, that unscrewed and came out like normal bolts.

Anybody have experience with this? Trying to determine which parts are actually F vs K5/K6

[Jerry Rxman Griffin aka MuthaF'er]

A 75/76 F head will probably have a 392 cast into the top fin intake side by #3. You can use either bolts or studs so you really can't go by that but the 75/76 F head uses studs.

[Bankerdanny]

It isn't unusual to find that someone has replaced the header studs with bolts, I would not use that as an indicator that the head is off of a different engine.

[macvit7906]

Thanks guys. I'll look for the 392 casting, If I can't find, I'll post some pics

[HondaMan]

Honda swapped heads, cylinders, pistons and cams between the K6 and the F0. I have found them interchanged on virgin engines. The 'story' went like this: when the F0 was introduced, the market was underwhelmed and sales fell flat by February. The dealers were all crying out for more of the 4-pipers, and the K6 was born. This bike often has patched-together F0 wiring harnesses in it, confused wire colors with little jumpers plugging things together, F0 heads and cylinders and cams, and F0 bottom ends with K5 heads, pistons, and cams. The hotrod K6 has the F0 pistons inside of K5 cylinders and a K5 head & cam on top: this has compression ratios like 9.7:1 and compression test numbers like 150 PSI cold!

[macvit7906]

Honda swapped heads, cylinders, pistons and cams between the K6 and the F0. I have found them interchanged on virgin engines. The 'story' went like this: when the F0 was introduced, the market was underwhelmed and sales fell flat by February. The dealers were all crying out for more of the 4-pipers, and the K6 was born. This bike often has patched-together F0 wiring harnesses in it, confused wire colors with little jumpers plugging things together, F0 heads and cylinders and cams, and F0 bottom ends with K5 heads, pistons, and cams. The hotrod K6 has the F0 pistons inside of K5 cylinders and a K5 head & cam on top: this has compression ratios like 9.7:1 and compression test numbers like 150 PSI cold!

HondaMan,

Thanks for all the info so far.

Here are some pictures of both heads and some differences I found. Hopefully this can help identify which model is which.

At the end of the day, the Head and cylinder is getting vapor blasted, then sent to MR for porting, surfacing, and an 836cc kit, so I am just trying to determine which head is the best to use.

The carbs I'll be using are stamped 064A (CB750F)

Head 1 looks to be stamped "X7S" and has oblong columns between the fins

Head 2 looks to be stamped "C23" (reading from the front of the bike) and has thinner circular columns between the fins

[macvit7906]

Head 2 pictures:

[RSchaefer]

My (certain from the factory) F0 has "X3" on the head, no "S," and the oblong columns.  It would appear your "Head #1" is from the F0/1, not sure what the difference is between X3 verses X7S