R&D platform

[bobcat]

....What does the stagger (ie. 103-105) represent ?
By the time I realized that adding the two numbers and dividing by 2 gave me
the starting point no., I was referring to the chart frequently with the numbers
that I was given by Yoshimura many years back still in the back of my mind.
Somewhere early on I realized that 103-105 represented 104 advanced 1 degree.
Remember that as the IN. is advanced, the LC no. falls, as the EX. is advanced
the LC no. rises. But advanced from what, or what is the "constant" in the
starting no. ? It is TDC of the EX. stroke of that cyl.! (pardon all the abbrev.).
It is that point where the max. overlap occurs in relation to the crank/piston
position. If you use the start. point no. for both IN. and EX., max. overlap will
occur at TDC.

For some (most) motors the max. overlap works best when it happens before
the piston reaches the top of the EX. stroke and begins the downward IN. stroke,
thus the advanced 1 degree 103-105. Note the CB900F likes that event (max. overlap)
to occur way in advance at 102.5-107.5 from its start. point of 105. If I can remember
to, I'll come back to why later.

Break time...and I need to read this to see if it's too confusing.

Ah! I can see where there might be some confusion; when I use the numbers 103-105
it is from the start. point of 104. Everywhere else I have included the start. point. no.
like for the 900F 105.

Also, the "constant" I substituted for "stationary" and another edit about TDC that should
be more clear.

[bobcat]

As the pieces of the LC chart puzzle started falling into place it was like a light
came on in my mind, what the LC chart is all about !

Advance or retard from the LC chart start. point number, the stagger, or relationship
of the IN. cam to the EX. cam remains the same. The LC start number represents the ideal
amount of valve overlap for a given stroke radius and rod length at TDC. Advance or retard
the cams determines the point at which the max. overlap point happens in relation to the
piston/crank at TDC of the EX. stroke (end of EX. stroke, beginning of IN. stroke).

This is the part of chart that I believed to be the sole domain of the engineers and dyno research.

Now I believe it is as simple as a math formula (that I don't have or know). How is this calculated ?
Or is it a calculated formula ?

Either way the chart is a tool, not the rule and all the variations of bore to stroke ratio
(oversquare, undersquare or square) come into play but it's hard to go wrong if you
just use the ideal LC number on the chart. For most motors a good rule of thumb is
the LC hart no. advanced 1 degree. 103-105 is advanced 1 degree from 104.

A bit repetitious but I hope the idea is clear. I know I'm missing something but onward
to the idea of remote cam degreeing and how the idea can be used in making it into
a simple adjustment even if you don't do the initial degreeing remotely (mock up motor)..

[bobcat]

The goal of degreeing the cams to the optimum specs is to maximize the velocity
of the IN. charge and EX. gasses to where one helps the other and the piston doesn't
do all the work. I guess a way to put it is it reduces the drag on the piston allowing
the crank to turn more freely and filling the cyl. as full of fresh charge as possible.

The issue for all motors with cam timing chains is chain stretch. Most chain stretch
occurs in the first few thousand miles and levels off after that. Stretch doesn't mean
the chain(s) is worn out although wear is responsible for most stretch after the initial
stretch from break in.

The problem is as the chain stretches, the timing of the cams retards from the initial
settings, either factory or degreed with a new chain. I read a magazine tech. article
many years ago about this issue which suggested that rather than replacing the chain
to restore initial cam timing, re degree the cams because replacing the chain will only
put you right back where you were after a few thousand miles as the new chain stretches.
And no, the timing doesn't change every time the chain is adjusted after initial stretch
as suggested earlier in this thread. The change in timing is so minimal that it takes many
more miles to show up as compared to the initial stretch which will retard the cams on
average about 2 degrees. That throws off the max. port velocity achieved by optimum settings
enough to feel a noticeable loss of power and responsiveness. Even if you just restore the
timing to the original factory LCs you will notice an improvement.

Back after a chair break...

[bobcat]

Most every CBX on the road today has retarded cam timing from chain stretch
unless it has brand new cam chains or the cams have been degreed or in the
rare cases very low mileage.

I had a guy drop off a very nice red 79 at my shop back in the late 80s. He brought
it in on a trailer and said it needed the carbs and tank cleaned and handed me the
key. I old him and his friend to pull around to the back and unload it and I would
roll it in shortly. When I went to fill out the bike info on the service ticket and record
the mileage ...shock! It had 3.6 miles on it. I wondered where has this thing been all
this time ? I very carefully went about cleaning the fuel sys. and giving a good once over,
adjusting things like the clutch free play etc.
Time for a test ride to be sure all was working properly A quick roll on in 1st gear
and it easily lofted the front wheel. Compared to others I had ridden with more miles
(and cam chain stretch), this one was very responsive and crisp. I nearly doubled the mileage
on the test ride but the customer was quite pleased. I wondered if it was taken home and
parked again.
The story is about the difference correct cam timing can make and I'm sure someone will chime
in about all the other factors and variables that could be responsible for the difference but
I would invite them to go back and read Jonesbear's testimonial where I set the cam timing at
103-105. I did two other Pro Link models using the same no.s with the same results. All were in
the 25k to 30k miles range and had been well maintained prior to degreeing the cams.

Consider that 2 degrees of chain stretch on a 79 model will result in LC numbers of IN. 109.5 and
EX. 105.5 when it was (new) 107.5 IN. and EX. Although the EX. is very close to the LC chart ideal
start point, the IN. is far out of balance retarded which significantly reduces the scavenging effect
of the exiting EX. flow. Sure, the motor will perform quite (amazingly) well but there's more to be
had by having the cam timing corrected. The IN. cam can/should be advanced 6.5 degrees to 103.
Much attention and money is spent on other "high performance" items while the foundation of
performance tuning, cam timing, gets ignored. When that is corrected all the other items are far
more effective. JMHO.

The actual "foundation" of performance is a well sealed cylinder and combustion chamber, piston
rings and valves but that's another subject that comes before all else and requires considerable
work if the motor fails a compression test or better yet, a leak down test.

Note: Performance and performance tuning are separate issues.

[bobcat]

Too "over the top" ...crazy ?

[bobcat]

I will get to the adjustability subject as soon as I can tolerate this chair long enough
to write. I was also waiting for a cleaned up version of the lobe center chart but I can
proceed without it.

[Syscrush]

I was also waiting for a cleaned up version of the lobe center chart but I can proceed without it.

Hey Bob. Thanks again for your continued effort on this. What I'm working on now is coming up with an algebraic model that fits the numbers in the chart. I'm playing with it in Excel, and it looks like we should be able to make that work. Hopefully I'll have something to share in the next few days.

[bobcat]

I was also waiting for a cleaned up version of the lobe center chart but I can proceed without it.

Hey Bob. Thanks again for your continued effort on this. What I'm working on now is coming up with an algebraic model that fits the numbers in the chart. I'm playing with it in Excel, and it looks like we should be able to make that work. Hopefully I'll have something to share in the next few days.

Cool Phil ! That should be interesting.

Meanwhile until I can get going again, ponder this; adjustability without having to go through
the entire degree wheel/dial indicator process boils down to cam position in the cyl. head and
accurately marking it so that it can be easily checked and realigned if necessary. Once the
position is marked via the side thrust cam holder, the timing can be checked for chain
stretch at valve adjustment intervals. If adjustment is needed, loosen the sprocket bolts and
reset. Accurate cam location eliminates all variables except cam holder dowel location which is
not enough to worry about. Dowel location applies only to remote degreed cams on the mock up
motor or switching cams from one head to another.

[bobcat]

Off the subject briefly, does anyone have a set of 79 VB60A carbs off the bike
or just the OEM slide needles laying around ? I need to know what the needle number
is, stamped just below the head of the needle. More R&D.

Thanks.

[steve murdoch icoa #5322]

Bob, i just pulled one and it shows 05F.

[daves79x]

Correct and 55A are '80-'82 needles.

Dave

[bobcat]

Much thanks gentlemen. I might have a set here in my collection.
Usually the difference in numbers is the taper and/or root dia.

[bobcat]

My guess is that the 55A needles are a thinner taper (richer) in the absence
of the primary main jet. The same reason with the larger secondary main jets
in the carbs after 79.
I'm almost sure I have a set of 05F needles but I can't get to them or pull a needle
from my 81 to profile them without putting myself in agonizing pain.
As usual there's a story behind "profiling" needles but I'll save it for when I can
write more.

[bobcat]

Waiting for something new to read ? OK, back to the topic of adjustability
without having to set up a dial indicator, degree wheel etc.

Once again going back to the Yamaha FJ1200 motors, using the timing marks on
the cam sprockets, like most all OHC motors, is the method for timing the cam(s)
with the piston at TDC. However, there is a secondary check point on the FJs
in the side thrust cam holder cap. It is a hole in the cap directly above the flange
on the cam. When you have the cams properly installed there is a dot mark on the
flange that appears in the hole. The hole is larger than the dot mark but as long
as the dot mark appears in the hole, the cam is properly timed. As the cam chain
stretches the dot will appear farther to the rear of the hole. If you degree the cam
(advanced), the dot will appear either centered or toward the front of the hole.
This is the reason I mentioned the thrust flange cam cap on the CBX.....

[bobcat]

.... The same basic procedure is used on my vintage (89) Acura when installing
a new cam timing belt, only when the piston is at TDC 1&4 there is a hole in the
end cam holder as well as the cam where you install dowel pin or a punch to hold
the cam in place while installing the belt.

It occurred to me that a combination of these two procedures could be used on the
CBX (as well as DOHC fours) for accurate cam location in the cyl. head. There isn't
much room or material to work with on the CBX cam flange but it can be done by
first removing the cam holder and drilling a small hole through the groove for the side
thrust flange on the cam.
Reinstall the cam holder and degree the cam to whatever LC numbers you want. Then, using
a center punch or the same drill bit, mark the flange on the cam (through hole in the holder).
Remove the cam holder and, using the same bit used for the holder hole, drill a shallow hole
in the marked flange. You remove the holder so as not to wallow out the hole. You can then
use the blunt end of the bit as a dowel to accurately position the cam.

Once this task is done, when you have the piston at TDC 1 & 6, the bit/dowel should drop snugly
into the hole and flange. If it doesn't fit you can loosen the sprocket bolts, align the holes using
the bit and retorque the bolts and you have adjusted/restored the cam timing to your original
settings.
Note; you then remove the bit/dowel pin. There seemed to be some confusion about whether it
remained as a lock to prevent the cam from slipping. Pin or dowl is only an alignment tool.

More details after a chair break....