Camshaft - hot, cold or otherwise?

[RupertB]

Happy festive season all. The time of year when what little money I have is spent on the unaffordable to give to the ungrateful, instead of investing it in motorcycle spares. But, one part which doesn't appear to need renewing is the camshaft on the K4 engine, but I wonder if anyone can give a definitive answer as to whether it is stock Honda or not. It has the characters R10 stamped on it which some say indicates a Yoshimura cam, and has what looks to me like a fairly steep drop on the cam lobe, but again others say is pretty normal.
I am not very bothered either way as long as it opens and closes the valves at the right moment when it is all together, but it might be worth knowing for carburettor purposes if nothing else.
So below is a sort of 'end on' pic to show the lobe profile as far as I can. All info and guesses gratefully received.

[Bryanj]

All honda cams have an "R" on them and it means sod all, if there are no other makings on the cam stamped or ground in it is almost certainly a standard Honda cam and there is not normally enough difference to separate them visually, you need to get the opening and closing points with a degree disc and the clearance set at a specific gap

[RupertB]

Thanks for that - just in case it helps with I.D. I will attach below photos of the only identifying marks on the cam. R10 looks to be stamped in and the others look cast.

As I say, it is more out of curiosity and I will find how it behaves whenever it gets reassembled. Just hope it won't take too long!

[Yoshi823]

If it was an F2 or Yoshi cam the extra lift could cause the valve springs so go coil bound if used in a K or F1 cylinder head. The slightly shorter valve guides & less densely wound valve springs specified for the F2 cam allowed this higher lift. If the full race Yoshi cam were to be used the cam carrier would need to be relieved of material for sufficient clearance.

Looking at the cam profile it does look as though the closing ramp of the cam is the rounded one so that it would gradually & gently close the valve against its seat, whereas the flat part of the lobe would be the opening ramp.

If you cannot get the cam degreed in to the correct lobe centres you may well have to elongate the cam mount bolt holes in order to get them in the ballpark. But if you were to advance or retard the cam too much in one direction, this would affect the phasing of the other lobe, the system being dictated by the single cam. I had this after I had my standard F2 cam reprofiled to faster road spec by increasing the lift slightly. When I degreed in the cam using the wheel & a dial gauge I plotted the ramps & lift onto graph paper so that I could make sure that top dead centre was wher it should be. I did buy myself a 750 K0 cam sprocket as this is solid on that bike, as against the F2 item which as can be seen from the pictures, has been Swiss-cheesed by Honda in an effort to reduce reciprocating weight. In this way the cam mount bolts could then be elongated without fear of collapse if I had tried to do this to the F2 sprocket. As it happens I didn't need the K0 item, so I still have this should you need one.

[RupertB]

The thot plickens as they say...
You must bear in mind that the CB750 I have was bought principally for the Foale frame, and the engine is a complete unknown. The guy I bought it off had no idea of its history, having been given it in return for money owed. The engine had (by repute and folklore only) got a Yoshimura big bore and a close ration gearbox. Neither the seller or I had any great faith in this. So, on stripdown, I found a set of 810cc pistons, but made by Henry Abe not Yoshi, and the wheels turned out to be Abe ones as well. I use the name Henry Abe in that rather casual way to sound like I know how famous he just has to be - in reality I'd never heard of him until I bought this bike, and my teenage years were spent slobbering over Honda 4s and other stuff of the 70s!
So whether it ha a close ratio gearbox or not has yet to be discovered. Frankly I'm not holding my breath, but you never know.
However any other info on the cam will be gratefully received - are you saying this is an F2 cam sprocket beyond any doubt? If so it adds intrigue to the setup, but once again it is all out of curiosity not vain hope. I'd be just as happy if it was all bog standard!

[the-chauffeur]

Looks to me like you've got a Honda camshaft and a late (F series) cam sprocket.

As Ash says, the later sprockets were drilled to reduce reciprocating weight, which is great so long as you don't want to advance/retard the valve timing.  The early models are solid, as per his other picture.  I've got a third type - an aftermarket adjustable from Cycle X.  If yours was aftermarket, it would almost certainly look like the Cycle X.  

It also seems a little unlikely you'd have a non-adjustable attached to an aftermarket camshaft.  As for the camshaft manufacture, the stamping certainly looks like it's a Honda.  In addition to the cam sprocket, I bought a Cycle X camshaft, and as well as different markings and heat treatment from Honda's, it doesn't have the timing alignment marks on the right hand end (like the ones in your photo).  Having said that, it's always possible the cam could have been reprofiled at some point, but unless you've got a detailed engine history, send it off to someone like Phil Joy or have one to do a side-by-side comparison, chances are you'll never know.

Does that help any?

[honda-san]

A cam shaft with an R-- number on it is 99% certain to be a standard Honda cam. They started at R1 in '69, and the R number tends to increase as the years / models roll by. Whether the number next to the R indicates the mold/ casting / forging, or in some way relates to the lift (though I have never measured a difference in lobe height which could be related to the R number) / angles, or date range / model range is certainly not dcoumented that I have found so far. Having stripped 30+ of these engines over the years I have only ever found ONE non Honda camshaft - and that DEFINATELY did not have an R number on it.

Cheers - Chris R.

[RupertB]

thanks folks - all uiseful and all gratefully received. I am being very patient at the moment and am just getting barrels and head (castings) properly checked and sorted to see if they are salvageable, and only then will I move on to valves, cams pistons etc. I could also do with an ambient temperature which doesn't threaten to freeze treasured bits of my anatomy off my body. I'm sure that applies to all of us who don't have heated garages.
So any more info will be received with interest, but updates and the like on progress will be a little slow in arriving. But have patience, they will get there.
Happy Christmas one and all by the way!