Topic: 78K head with early model cylinders

[750]

Just bought some parts from a dealer I know.  RC315 cam in a 750 head, 736 wisco piston kit to include cylinders bored for the pistons.  Everything is in great shape.  I'd like to use the cylinders on my K8 cases.  Is there a good way to identify what year cylinders are?  How do I know if the cylinders are compatible with my K8?  How do I Identify what year head it is?  The only markings I can find on the head are HHO on the top intake side and B148 on the bottom intake side and I can't find any markings on the cylinder. 
Any help would be huge
Thanks Guys

[754]

Real early cylinder have different looking holes underneath, when looking at the base gasket surface, between the pairs of sleeves. Early have sharp corners, later have rounded.

 Heads after 73 have 3 rectangular or oval struts between the fins, loking at the outer edge of the fins, earlier have 4 round skinny ones. Top leading edge of  top fin above exhaist is different too, 73 & up is a straight line and two angled lines (earlier is nore of a curved notch) After around 77 ? there is a logo cast in to top of the highest fin on intake side, in the middle.

 If you want to sell the 315 cam, let me know please.

[750]

Thanks, if I can't make this combination work I may have the works up for sale. Is there somewhere on this site that will tell me what heads are compatible with what cylinders and what cylinders are compatible with what cases or can one put any combination together?? Is there somewhere on this site that will help me identify what cylinders and head I have??
Thanks again

[the technological J]

take a look through the last couple days posts... it seems to be popular latetly...but i think most k models are interchangeable and f and a's are in thier own world

[750]

take a look through the last couple days posts... it seems to be popular latetly...but i think most k models are interchangeable and f and a's are in thier own world

I looked back quite far and only found your question which didn't really answere my question because I can't figure out how to identify what year head, (more importantly)what year cylinders I bought.  The head really is inconsequential, I have a head off of a 77 that I will be using, but I don't know how to figure out if the the cylinders are interchangeable.  I really don't know what would be different?  It has to hold 4 cylinders and bolt up but if there are differences I should know so I can get another set of jugs bored for this 736 kit.??  Thanks for the reply though.  Any little bit of information helps 

[750]

Bump, Bump, Anyone??  Please???

[scondon]

The only oddball engine in the cb750 line, cb750 Automatic excluded, is the 77-78 750F motor, and this was painted black at the factory. All other cylinders and heads from different years can be mixed and matched. There are slight changes and modifications done throughout the years, but nothing that will make the parts you have incompatible with each other. Bores are the same and everything lines up and bolts together the same.

If you have questions as you put it together, ask 'em here.

[750]

The only oddball engine in the cb750 line, cb750 Automatic excluded, is the 77-78 750F motor, and this was painted black at the factory. All other cylinders and heads from different years can be mixed and matched. There are slight changes and modifications done throughout the years, but nothing that will make the parts you have incompatible with each other. Bores are the same and everything lines up and bolts together the same.

If you have questions as you put it together, ask 'em here.

Wow, thanks   That is such a help.  Time to build a motor. 
Thanks again

[HondaMan]

In the K0-K2 engines, the seals between the head and cylinders were different from the later engines. The cylinder on the early ones had shallow recesses around several of the long studs for O-rings to seal the oil passages that go to the head. Starting with the K3, these recesses were bored about 1/2" deep and long rubber tube seals were used around the dowel pins to improve the seal. If you use the later cylinders with the earlier heads, you just have to make sure the dowels are not too long, which would push the head away from the cylinder surface. Since the dowels came in 2 different lengths, depending on year, it's just something to watch for: you can trim the longer ones down, if need be. The shorter ones, if used in cylinders with a too-deep bored dowel hole, will not reach above the rubber seal. That's your clue that you need the longer dowels.

I have so many unidentified cylinders and heads now that I can't tell for dead sure which model introduced the extra-long dowels, except to say (like 750 above) that it happened on the cylinders with the square-ish inner fin bolsters (i.e., later models). I suspect it was the K5 or K6, which became the "F" cylinders shortly after. But, so long as both the cylinder deck and the head are flat, they can mate. Check them, or have an engine shop flat-surface them both for you: around here that costs about $20-$30.

[750]

In the K0-K2 engines, the seals between the head and cylinders were different from the later engines. The cylinder on the early ones had shallow recesses around several of the long studs for O-rings to seal the oil passages that go to the head. Starting with the K3, these recesses were bored about 1/2" deep and long rubber tube seals were used around the dowel pins to improve the seal. If you use the later cylinders with the earlier heads, you just have to make sure the dowels are not too long, which would push the head away from the cylinder surface. Since the dowels came in 2 different lengths, depending on year, it's just something to watch for: you can trim the longer ones down, if need be. The shorter ones, if used in cylinders with a too-deep bored dowel hole, will not reach above the rubber seal. That's your clue that you need the longer dowels.

I have so many unidentified cylinders and heads now that I can't tell for dead sure which model introduced the extra-long dowels, except to say (like 750 above) that it happened on the cylinders with the square-ish inner fin bolsters (i.e., later models). I suspect it was the K5 or K6, which became the "F" cylinders shortly after. But, so long as both the cylinder deck and the head are flat, they can mate. Check them, or have an engine shop flat-surface them both for you: around here that costs about $20-$30.

Thanks for the input.  From that I gather my 836 cylinder block is off an early model.  I think I'll counterbore the holes to mach the 78 cylinders even though I could use it just the way it is I have the ability and access to a cnc bridgeport  and I like the way it seals better.  Any thoughts??

[HondaMan]

In the K0-K2 engines, the seals between the head and cylinders were different from the later engines. The cylinder on the early ones had shallow recesses around several of the long studs for O-rings to seal the oil passages that go to the head. Starting with the K3, these recesses were bored about 1/2" deep and long rubber tube seals were used around the dowel pins to improve the seal. If you use the later cylinders with the earlier heads, you just have to make sure the dowels are not too long, which would push the head away from the cylinder surface. Since the dowels came in 2 different lengths, depending on year, it's just something to watch for: you can trim the longer ones down, if need be. The shorter ones, if used in cylinders with a too-deep bored dowel hole, will not reach above the rubber seal. That's your clue that you need the longer dowels.

I have so many unidentified cylinders and heads now that I can't tell for dead sure which model introduced the extra-long dowels, except to say (like 750 above) that it happened on the cylinders with the square-ish inner fin bolsters (i.e., later models). I suspect it was the K5 or K6, which became the "F" cylinders shortly after. But, so long as both the cylinder deck and the head are flat, they can mate. Check them, or have an engine shop flat-surface them both for you: around here that costs about $20-$30.

Thanks for the input.  From that I gather my 836 cylinder block is off an early model.  I think I'll counterbore the holes to mach the 78 cylinders even though I could use it just the way it is I have the ability and access to a cnc bridgeport  and I like the way it seals better.  Any thoughts??

I've read here where others have done that. I haven't, but it makes good sense. The O-rings on the early ones would often leak after about 40k miles, making a mess by the inner two carbs. Using 10w40 oil seemed to make them leak more, too, which usually indicates it is a minor gap doing the leaking. I prefer, when building the "older" engines, tu use O-rings that are 0.5mm thicker than the stock ones (I think those are 15x2.5mm, I use the 14 or 14.5x3.0mm instead, with the latter being the max before the seal gets pinched between the surfaces).