Valve face diameter?

thanks for the advice guys.

Like the maintenance and operators where I work, always blaming engineers for making things more difficult than what they need to be .

I don't have a leak down tester and I don't know anyone that does. I'll try the oil in the cylinder trick though.

Larry, I'm going from memory, but I thought I had a 3.5 mm shim. When I got the bike a few years back the shims were never checked. Two hooligan brothers that spent more time in the taverns and beating the poor bike than maintaining it owned it before me. I got it for free. A family friend who works on kaw's did the initial shim changeout. They've been in spec since then, until the fateful day when I blew it. I'll check my manual tonight and report back.

turboguzzi wrote: BTW, have no idea why you are digging so deep into thermodynamics,

Chemical Engineers tend to end up dealing with thermodynamics. It's where all the interesting stuff happens... everything from simply compressing a cylinder to the probablility that we even exist. :laugh:

Makes more sense to me than eletrical. That stuff is black magic

apbling wrote: Lou- What the heck? I thought you were an EE? .

apbling wrote: I figured adiabatic compression because I figured any temperature increase from the compression would be neglegible compared to the heat generated by the combustion..

Yes, that may be, but no combustion in a compression test, so probably have to consider T in the equation. But that's too many variables in too few equations. You'd have to measure it, which is damn near impossible to do fast enough.

apbling wrote: As for calculating volume of the cylinder, I just used the bore and stroke, but if I did that it would neglect the domed head space, correct?

Yes. That domed head space, ... and piston shape if it is not perfectly flat, and really, even the space around the piston down to the first ring, etc.

apbling wrote: Now, correct me if I'm misunderstanding Lou, but you telling me since the compression ratio is 9.5 to 1, that means that the best my bike can do at a given atmospheric pressure is 9.5*that pressure?

Assuming perfect seals, perfect volumetric displacement (which is not possible since valves are open while the piston is rising), and assuming adiabatic (which is impossible since the reading is happening pretty quickly.

apbling wrote: I could have sworn in my clymer manual it showed compressions as high as 170 psi.

Every normal gpz 550 motor I've compression tested, using many different gauges, ended up maxing out right around 180 to 185 psi. (Choke open, throttle open, hot motor.) They are all rated 10:1. Even a ZX550 (which has a bit more cam duration) ended up in that range. But if we take the above assumptions, it should only be 147 psi. (Assuming STP, 14.7psi.)

At 9.5:1, we'd expect the KZ550 C to be 140 with the same assumptions. (But it also has less duration and lift on the cams.)

So a quick and dirty ratio would be: real number / theoretical expectation.
For the gpz, it's 180/147.
Using that ratio, at 14.7 atmospheric, the real compression number for a KZ550 C would be expected to be right around 170 psi.

The FSM I have says the acceptable range is 155 to 235 psi. That's a big range.
My Clymer, page 65, says 125psi or higher is acceptable. :huh:
Gotta go with the FSM.
Also, just to be sure, when you do the test, the motor is hot, all 4 plugs are out, and the main thing is that the compression tester has to have a check valve as close to the tip as possible. Without that, the compression ratio drops a lot.

hmmmm, well I honestly can't remember if my motor was that hot when I did it... It all melts back together because when we lived in IA the bike was in WI at my parents, and I would work on it on the weekends I was back home.

A guy that builds drag cars here told me that it needs to get some miles on it and get up to operating temperature a few times before I can make an accurate measurement.

I'm not racing around with it...it's more of a commuter and sentimental bike, so if I'm not laying rubber everyhwere I go it won't make me sad.


Worse comes to worst I'll just find a good motor off a junker and go that route.

apbling wrote: thanks for the advice guys.

Like the maintenance and operators where I work, always blaming engineers for making things more difficult than what they need to be .

I don't have a leak down tester and I don't know anyone that does. I'll try the oil in the cylinder trick though.

Larry, I'm going from memory, but I thought I had a 3.5 mm shim. When I got the bike a few years back the shims were never checked. Two hooligan brothers that spent more time in the taverns and beating the poor bike than maintaining it owned it before me. I got it for free. A family friend who works on kaw's did the initial shim changeout. They've been in spec since then, until the fateful day when I blew it. I'll check my manual tonight and report back.

2.00 - 3.00 is the OEM shim range. There are some thinner than .200 available aftermarket but I've never seen, nor could I conceive ever needing one thicker than 320. Pre-valve job, normal shim ranges tend to run 235 - 285 range, depending on the condition of the engine.



Anyway, that's all neither here nor there at this point. What warrants consideration is if the valve job or the rings are holding the compression down. Like I said, the poor man's, teaspoon of oil in the cylinder test will tell you that answer Enjoy the riding season

Regular oil sufficient?

LarryC wrote:
Serdi, Sunnen, etc. etc. etc.... don't mean the seat is straight just because the machine cost a pile of money. It only means you can cut seats faster.

And they are all exactly the same, and the same depth.

apbling wrote: Regular oil sufficient?

Yep

APE Jay wrote:

LarryC wrote:
Serdi, Sunnen, etc. etc. etc.... don't mean the seat is straight just because the machine cost a pile of money. It only means you can cut seats faster.

And they are all exactly the same, and the same depth.

Yep....and still, to this day, many pros will dust the seat with a stone after the blade cut I can name several that might shock you

we do that if necessary

APE Jay wrote:

LarryC wrote:
Serdi, Sunnen, etc. etc. etc.... don't mean the seat is straight just because the machine cost a pile of money. It only means you can cut seats faster.

And they are all exactly the same, and the same depth.

Yep....if only the port gave a damn life would be easy hey Unfortunately, many times, the width of the bottom angle that serves the long side well does not server the short side well at all. Adjustments still need to be made by hand after a valve job, no matter how expensive the valve seat cutting equipment may be or how fast it will rip multiple angles, all nice and neat :lol: