R&D platform

[bobcat]

We're here for you Bob. Holler if you need something, within reason.....

Rick, there is something that I could use for a motivational boost !
A couple of CBX posters for these otherwise barren walls would be
very inspirational. This place and staff are wearing my spirit thin.
I hope to try to get out of this bed next week after laying on my
back for nearly a year now. Maybe a bike seat for physical therapy
soon just to get my legs apart from each other.
Never take riding for granted !!!

[bobcat]

Excited ! After nearly 6 months of laying on my back, only rolling side to side
occasionally, I sat upright on the side of the bed today with minimal help from
the physical therapy team. None of us really knew what to expect. I was sure
I would feel agonizing pain or at least throbbing legs and feet but after a few
minutes of minor dizziness and stiff back I was able to sit upright with no assist.
They asked me if I was ready to lay back down, I said no, this feels pretty damn
good ! Tomorrow maybe try to put some weight on my feet and then it's time to
get back to work.
I hope to drag out the platform motor (parts) and resume research* and start adding
some of the findings to this thread including pictures. I can hardly wait to get
started working on my project and teaching my grandson as much as his attention
span will allow.

*hint; CB1100F A chain tensioner to begin with.

[Rick Pope]

Woo Hoo!!!! Good news!!

[steve murdoch icoa #5322]

Great to hear, Bob.
Minor dizziness and stiff back? Sounds like my daily routine.

[bobcat]

Hi Forrest !

[bobcat]

Great to hear, Bob.
Minor dizziness and stiff back? Sounds like my daily routine.

Hi Steve, I don't know what my daily routine is anymore except toleration.
I look forward to being a slave to the shop, maybe sleep a little here and there.
Now I really wish I had built the shop in my back yard while I had the chance.
I could just move in there and leave the house to my wife and grandson.
I can see 4 projects going at once.

I was going to save project pics for when I can finally get underway and start
a project thread but here's a hint of things to do; not as easy as it looks but
I've at least developed a method and got enough covers to experiment with.
Preparing for a transplant :

[Syscrush]

This is the best news you've had for us in a long time, Bob. I hope that all goes according to plan. I would love to switch from being jealous of your collector to being jealous of your whole exhaust system.

[NobleHops]

Wonderful news!!!

[bobcat]

Wonderful news!!!

Nils, it just got a whole lot more wonderful (from my perspective) this morning!
They got me out of the bed and into this recliner/wheelchair contraption and
rolled me out of the room. The therapist asked me if I wanted to go outside
"ARE YOU KIDDING ME"??? Where's the door ?!!!
It's a beautiful day here, a bit windy but sunny 75f. It's the first time I've been out in
the direct sun in about 6 yrs. and it felt SOOOO good... but the wheels were in the wrong
place and no handlebars. With the wind it felt like riding without a helmet. All I could
think about was the two CBXs in my garage.
They're sending me home tomorrow and it's complicated but I'll make it work somehow.
See you there !

[Jeff Bennetts]

Sending you home or kicking you out? LOL
Glad you’re out of that atmosphere and heading home, get back to some familiar surroundings and feel better!

[bobcat]

Sending you home or kicking you out? LOL (quote)


Thanks Jeff, both actually. Now I get to go face my Wife's wrath.

Once I get over the initial disorganizational chaos I want to write about some
conclusions I've reached about valve size, exh. in particular. Maybe get some
feedback for a change.


Why did what I just wrote get into the quote block ?

[Jeff Bennetts]

You posted within the quotes of my post on your reply.

[bobcat]

The case for small EXH. valves...

Quite some time ago I had bought an assortment CR750 (SOHC) race kit parts
with the intention of using some of them in my 76 CB750/900F rebuild. There's
a story behind how the CR750 race kit came to be, but essentially it replaces
everything but the crankcases and the frame.
The cyl. head came with oversize stainless IN. valves but I was surprised to find
that the EXH. valves were smaller than the original stock valves. I thought that
it must have something to do with the long duration Daytona grind cam and valve
interference issues but I don't think that was the issue after some later observations
about EXH port configuration and porting.
I had read an article about EXH ports not needing much attention because they were
overly efficient in stock form other than needing little more than polishing. Later on
I got in a discussion with a friend about valve clearances. He was into drag racing and
he said they would set EXH clearances looser than stock specs to help build torque.
Then when you consider that smaller dia. header tubes make more torque the conclusion
is that all of these things build back pressure which speeds up the flow of the EXH gasses
by diminishing EXH volumetric efficiency.*
All of these clues lead me to believe that oversize EXH valves aren't preferable to the
stock valves. More on this later......

*see "venturi" effect theory.

[bobcat]

.....The reasoning behind larger IN. valves is that it creates more area for the incoming
charge to collect before the valve opens. The sooner more fuel/air enters the cyl.,
the more complete the cyl. filling is. Consider that the IN. flow is the opposite direction
of the EXH. flow and that the EXH gasses don't need more area to collect before exiting
the combustion chamber and the question is why have a larger EXH valve ? It would seem
that the larger valve would be an obstacle to EXH flow. Ideally you want the least obstruction
to EXH flow to get the heat out of the cyl. as quickly as possible. With a larger EXH valve
the gases have to go farther around the valve to enter the port restricting flow.

This could be one of the reasons behind the CR750 EXH valves being smaller than the stock
CB750(SOHC) valves. In a way it seems contradictory to the increased backpressure idea but
speeding up the EXH flow at the valve seat into a smaller dia. header tube would make sense.

(maybe). These are the speculations of a bedbound mechanic with too much time to think.
When/if I get the chance to build my project motor (1150) I intend to use CB1100F IN. valves
and the stock CBX EXH valves.

[Rick Pope]

Bob, wouldn't a small intake valve also tend to run cooler? The ratio of surface area/seat area would be better with the smaller valve. Or so it seems. to this unschooled farm boy.