Topic: k2 head on a k7 engine??

[HB-1fan]

Replacing a k2 engine with a k7 that had no valve train. Can I put the k2 head and valve train on the k7 engine? Or can I simply just put the k2 valve train on the k7 head.
  Is there any difference in cam sprockets through the years?
The k2 engine had been apart before, has overbore ART pistons in it and some minor work(no milling) done to the head. The cam looks like a honda cam and is marked only "K5" anyone know what year it might be?

Thanks for any help,
Rick

[StevieMac]

I think you need to change the whole top end but I'm not 100% sure.  I think the K7 head would work but you would have lower compression due to revised pistons on the later models.

[Clyde]

K7 and K2 heads should interchange OK.
The changed compression ratio (9.0 for the K2  vs 9.2 for the K7) is because of the K7 pistons (same as the F1), which were slightly raised compared to the earlier pistons.
The difference is that the later heads had dowel/locating sleeves and rubbers around the studs to help eliminate oil leaks.
I would tend to use the K7 head with the K2 cam towers/valve train etc. Only because the later system had less problems with head gasket leaks.
If you use a genuine Honda head gasket and also make sure you replace the rubber buttons/seals underneath the cam towers, then you should be OK.
Regds Clyde

[HB-1fan]

 Thanks for that info clyde. Thats the direction I was heading. The k2 cam is marked R5. Is that correct for k2 and is it ok to us with the k7 pistons?

Rick

[Jerry Rxman Griffin aka MuthaF'er]

Not only are the pistons higher compression with a slight raised top but you will probably find the K7 head has 392 cast into it on the top fin intake side between #2 & #3. I have a 392 head sitting next to an earlier K head (not sure what year however). The 392 also has K8 hand stamped next to the 392. It did come from a K8. The 392 combustion chamber profile is more hemi shaped. It does not have the shrouding around the plug hole or valves like my earlier head. Compare the 2 heads when you have the chance.

If it were me, I'd use the K7 head, pistons, and possibly cam. The K7 cam should be hotter due to 5 degrees more duration on intake but the int & exh opening comes on 5 degrees later. I'm not the cam guy for sure and I don't know how the +5 degrees on opening of int & exh would exhibit itself. The Honda shop manual specs are the same for the K1-4 with no cam differences noted until K7. They do not list specs for the K0 which was considered hotter than the other 750s until the F0, F1, K7, K8 era. Either cam would fit however.   

General consensus is the cam markings have no bearing on the grind. That'd be too damn easy. I think the cam grinds were Honda's one big secret. An obvious sales ploy. The first K was hot and then detuned just as my old 68 350 (first year also) had a hotter cam before detuning.

[MRieck]

The valve keepers and retainers are different on the K&/8 head as well. It really doesn't make a difference with stock cams. As RX mentioned...the chambers are better and the castring is far more stout than early versions (69 to 73 or 74). I think the guides sit alittle higher in the head too....not much but maybe .010 or so. They are a very solid piece that can be converted to early valves.

[Clyde]

According to my  Honda parts book (and also microfiche) the K7 valves, valve retainers and keepers should be the same as the F1 and earlier. Honda changed them to the F2 type for the K8 (goodness knows why?) I have used a K7 head before on an K2 without any problem and do not remember the valves as being different.
Rick, I would be interested if you can check this as you have both heads together. If you compare the top of the valves and check if there is a difference.
The reason I would be interested is that I know where there is a K7 head with a set of new valves and I could use the valves. If they are different to the early ones then I will pass on it. It is too far away to go and have a look and the owner does not know anything about engines.
Thanks Clyde

[Jerry Rxman Griffin aka MuthaF'er]

Clyde,

My 2 heads are (1) stock K8 -392 28mm exhaust & 32mm intake (2) older K head not stock 28mm exh & 33.5mm int.

I pulled up Service Honda's fiche. The K8 is a hybrid F2 & K7/F0/F1 head. The K8 head itself is the same as K7/F1/F0. The K8 & K7 have the same part numbers for the valves and springs. The differences between the K8 & K7 are: K8 used F2 spring seats, retainers, keepers with K7 valves and springs. So, it appears the valves did not change from 69K through 78K and includes F0 & F1. The only different valves were on the F2 & F3.

Hope this helps. 

[MRieck]

I know K8 valves have the same narrow keeper groove, retainers and keepers as the F2. I'm very, very sure the K7 uses the same valves (with the narrow keeper groove etc) as the K8. The valve diameter is the same for all K's....just the keeper groove with the necessary parts changes. I have had to switch to the later valve style when doing performance cams etc in the late K heads.

[Clyde]

When I rebuilt an F2 motor three years ago I had to replace the exhaust valve guides and also a few valves. The valves are  different in that the shafts are machined differently for the different types of retainers with narrower keepers (and of course the F2 valves are slightly larger).
I originally thought the K valves did not change through the K range, but am now convinced they did change at least for the K8.
I have used a K7 head before and from memory the valves used the same keepers/retainers as my K2/F1.
Mike's posting about a K8 some months ago, is what got me looking into this.

I have never worked on a K8 so cannot be sure, but my parts book shows  different valves for the K8, which is logical as the older valves could not be used with the newer valve retainerskeepers.
The K8 valves must be rarer than F2 valves or rocking horse s??t. I had enough problems getting some valves for the F2.
Clyde

[Jerry Rxman Griffin aka MuthaF'er]

After reading Mike's and Clyde's posts I went back to the Service Honda fiche. As far as valves go this is what I found:

77K Int 14711-ME2-000 or 14711-300-005 (Mitsubishi)
78K Int 14711-300-015

77K Exh 14721-300-005
78K Exh 14721-300-015

I may have falsely assumed the last 3 numbers were not relevant ?! Did I intrepret this wrong? Don't want to screw anyone up !!!

[MRieck]

When I rebuilt an F2 motor three years ago I had to replace the exhaust valve guides and also a few valves. The valves are  different in that the shafts are machined differently for the different types of retainers with narrower keepers (and of course the F2 valves are slightly larger).
I originally thought the K valves did not change through the K range, but am now convinced they did change at least for the K8.
I have used a K7 head before and from memory the valves used the same keepers/retainers as my K2/F1.
Mike's posting about a K8 some months ago, is what got me looking into this.

I have never worked on a K8 so cannot be sure, but my parts book shows  different valves for the K8, which is logical as the older valves could not be used with the newer valve retainerskeepers.
The K8 valves must be rarer than F2 valves or rocking horse s??t. I had enough problems getting some valves for the F2.
Clyde

I've got a bunch of K8 valves sitting here. Not so much of a problem as the earlier valves can be used with the appropriate retainers and keepers. You can also use aftermarket oversize valves and Ti retainers which is a real plus. The K8 head is good to hop up because of the chamber shape. As for the K7 valves....can someone give a definitive answer. I could have sworn the last one I did....which was a while ago...had the narrow groove. Maybe there was a mid production change like the F1 top ring. Thanks again for that info Clyde ( and Upperlake) as you guys saved the day.
   Mike

[Jerry Rxman Griffin aka MuthaF'er]

Service Honda fiche has the same parts numbers for K7 valves as F0 & F1 if thats any help. I don't have a K7  head to take measurements from however.