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CB750F3

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Rozabikes Tim:

--- Quote from: royhall on October 03, 2017, 10:08:57 AM ---Rushed updates to keep the 750 current against newer competition. Not enough testing time initially as the 'delta' part later fixed the problem.

--- End quote ---
What's a "delta" part Roy?

K2-K6:
I went to have a look at an F2 which a friend has got parked next to a K6 to see if there's anything obvious (it's fine to point out that I should get out more).

What they seem to have done is kind of a combination of quite a few bits in the posts above,  I'll say "seem" as I can only look at them in situ and take valve caps off.
To create space in the combustion chamber along with the volume it looks like they've just moved the valves,  and seats, back into the head but with no change in angle. As they are splayed from bore axis this moves them apart, didn't think of it like that before. This appears to move the valve top up but still under the same rockers so that this interface is in a different position where it intersects the rocker arc. It's not by much, but is there.
I'm wrong about the K7 cam as it seems to have the same lift as the F2 example,  they just changed the timing,  duration and overlap to get the engine to rev and not go flat at about 9000 rpm. This shifted peak power from 8500 to 9500.
They say it's safe up to 10500 rpm and to get this they've changed the spring rates from 154 to 202lb. That's a massive jump and must be one of the biggest contributors to imposing a sideways load on the valve. If they've taken the tappet to valve angle away from optimal and wacked that much extra spring rate on it, then it's not surprising that the tappet screw it reluctant to slide across the top of the valve.
They appear to try and contain this by pairing the oil pockets (which are separated on non F2 heads) around the valve springs and then reducing the exit route, it looks like an attempt to get that valve top covered in oil to try and keep the tappet joint covered.
On American V8s when they get into this realm of revs and valve gear loading they use roller tipped rockers to stop the valves pushing sideways. Looks like they're at those margins here.
As has already been said,  the original was fairly close to perfect and trying to push some areas like this illustrate why it was replaced.

It's funny that it's also a bit of an illusion regarding power also. BHP is kind of slightly fictional (I know it makes comparison easier) as it takes real torque and uses rpm as a gain factor in it's calculation. So, if you get the same torque just moved up the rpm scale, it just makes the BHP look higher. This makes more difference certainly at the gain seen in this engine for marketing purposes really.
As I think Roy said, it just shows its a stop gap to try and hold market position by making it look newer.

I still like them though.

neilg:
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.

royhall:

--- 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.

Woodside:
well i never knew that

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