unusual modded engine SOHC?

[K2-K6]

Have a close look at the bottom, then the top.

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See what's been done?

[Bryanj]

Shame there are no internals

[Laverda Dave]

Interesting. Did I read somewhere in the distant past that Honda used the sohc bottom end but with a dohc top end for the 850(?) RSC racer in the late 70's and early 80's? Is this one of those bikes.
Or just maybe I've been soaking in Christmas brandy for too long today 🎄🤕

[K2-K6]

Yes Dave,  the RCB was built on CB750 bottom end but had bespoke barrels and twin cam head that made the first iteration 16valve endurance racer.

That one had cams really close together as in this photo

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Then came the later RSC1000? (think that was it's designation) which was development of production 900 twin cam road engine that was the CB900 but a completely different engine to the SOHC.

That first post here seems to have grafted on the CB900 type head onto CB750 SOHC cases, which I've not seen before. So they appear to have made a hybrid out of production motors. 

The brandy is not playing tricks 

[Laverda Dave]

Thanks for update Nigel (you really should think about writing a book with all your knowledge).
Looking at the original photo again I can now see what you mean. Whoever is building the bike is spending some ti. E and money and hopefully the internals will be added soon as Brian mentions.
Where did the photo surface from and how old is it, it may actually be running by now?

[K2-K6]

I think it maybe my geeky fascination of the RCB bikes but they don't appear to generate much interest.

They are kind of the missing link in Honda development as they are all built on original CB750 bottom end but point the way to twin cam 16valve development as it was racing in 1976.  Probably the last iteration of Honda's original four I suppose. 

Also first factory involvement after the pull out of GP bikes in the sixties and subsequently of the CB750 racers being curtailed after that Daytona win.

It also put the alternator above the gearbox,  and they converted into gear primary drive,  so there was all sort of experimentation going into it without big publicity.  Very successful in endurance racing,  more well known in France, both class of racing and these RCB bikes.

[philward]

Interesting post! And based on the previous info, could it be that the builder is trying to build a replica of the pre RCB1000 engine (and bike?) as otherwise why go to the trouble of grafting the 900/750 DOHC top end to the SOHC - easier to just to use the whole DOHC motor. It would be good to hear the builders design criteria. Lot of clever engineers still about!

[neilg]

Yes Dave,  the RCB was built on CB750 bottom end but had bespoke barrels and twin cam head that made the first iteration 16valve endurance racer.

That one had cams really close together as in this photo

(Attachment Link)

Then came the later RSC1000? (think that was it's designation) which was development of production 900 twin cam road engine that was the CB900 but a completely different engine to the SOHC.

That first post here seems to have grafted on the CB900 type head onto CB750 SOHC cases, which I've not seen before. So they appear to have made a hybrid out of production motors. 

The brandy is not playing tricks 

I seem to recall a magazine article with the cases split and I'm sure it was a gear primary drive.  anyone know for sure?