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CB750F3

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Bryanj:
The only one I did many years ago came in as a part ex for something and was in a poor cosmetic state but cheap in order to put right with new genuine bits, should have guessed mechanics would be as bad!. I borrowed it to go to the TT as is and noticed in Liverpool it had used some oil, about 350mpp but came home early having gassed an IOM plod on mad Sunday (Max 99mph and 150mpp oil). I stripped it expecting bad pistons and rings but, eventually, found very bad exhaust guides and 2 stem seals broken with lots of oil in exhaust ports(inlet OK) ordered and fitted Honda parts from Fowlers(no idea if same or delta) borrowed a reamer from the local dealer, grinding paste on valves(lucky they came out OK) after re building, along with many cycle parts put on showroom floor sold quickly and never seen again.

neilg:

--- Quote from: royhall on October 04, 2017, 06:11:37 PM ---
--- Quote from: neilg on October 04, 2017, 05:17:50 PM ---For info, a Delta Part is one that is an updated modified part but still carries the original part number. Or in other words it's a modification done quietly by the manufacturer. So in reality if you buy a NOS part unless it's an obvious mod you might get either an updated piece or an old inferior piece with no way of telling just by the part number.

--- End quote ---
Thats correct. When I did my guides I had to get them one at a time from all over the place. I ended up with three the same and an odd one all in sealed Honda bags with the same number. The odd one was an original part so I had to source one more Delta item to do the job. Sneeky way of avoiding warranty claims.

--- End quote ---

Can I ask what was the difference and how were you able to distinguish which is which?

royhall:
Nothing you can really tell visually. I could fit the valve stem through the later ones (tight), but not on the older ones. They still required reaming after fitting but virtually nothing was removed (I think they were made tighter tolerance as the material was harder and therefore tougher to ream). Looked like the only difference to me. It all went back together nicely.

Yoshi823:
I fitted S&W valve springs & machined up some new valve guides out of aluminium bronze for my 1978 CB750F2 back in '82. I had a custom reamer made for me by a local place. 6.6mm from memory & I still have it somewhere.
Hadleigh Custom down in south east Essex used to have a page in their catalogue about the differences between the F2 & the other 750 engines & how it was suggested that the valve collets should be replaced whenever they were removed. The catalogue also showed the difference in piston crown height with the F2 piston showing the substantial increase as the combustion chamber was increased in size to accomodate the bigger valves. The OEM head gasket showed that the combustion chamber was also elongated to a degree to get the bigger valves in.
I never had a problem with oil consumption except for when the bores were increased to take the bigger Yoshi 823 pistons which were 65mm if my memory serves me correctly. But when the barrels were bored out the operator of the boring bar didn't hone the bores to clearance, so the rough bores chewed the new piston rings up. Once home from Assen after attending the Dutch TT in '82 then I took the head & barrels off & had the bores honed correctly & installed new piston rings (I could do this easily as i'd modified the frame so that I could remove the top end of the engine without having to take the whole engine out).
I had played with fitting a Yoshi Road/Track cam but I also needed to change the carbs to more race ready items, which effectively held the development of more power back quite a bit. So I found a good condition standard F2 cam & had that ground to my own specification (one mm off the base circle, which increased lift & duration). The exhaust was more easily modified for better flow.
I installed Andrews high output coils, Boyer Bransden electronic ignition, NGK Gold paladium plugs. I also installed a Derale oil cooler, a Lockhart/Phillips oil cooler thermostat, an increased poundage oil pressure relief valve spring, a GL1000 oil filter housing, main jets from a CB750K7 & K&N individual air filters.

With modified gearing (one tooth less off each sprocket) it was faster than my brothers GS1000S, not only because of an increase in power but also because I modified the bike with parts that were a lot lighter than standard.

K2-K6:
https://ls1tech.com/forums/generation-iv-internal-engine/1506256-rocker-arm-bearings-theory.html

Some good illustrations that shows what I think is the effect of rocker geometry on valve guides if it gets outside realistic limits,  relevant to previous discussion.

It's that rocker tip moving across the valve stem that loads the valve sideways.

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