High Accuracy Degree Wheel

[posplayr]

reddirtrider

When all else fails post credentials.

Now you are calling me a liar.

Your tactfulness goes hand in hand with your lack of understanding (to put it mildly).

[reddirtrider]

Now you are calling me a liar.

Your tactfulness goes hand in hand ignorance.

I called you a liar? Not at all. What I said was that credentails are irrelevant to this discussion. I could unzip and post mine too, but they simply do not matter.

Stick to the facts of the discussion and stop taking this personally. It's not.

[posplayr]

Red

That means I have a thorough understanding of measurement accuracy, positional accuracy, estimation uncertainly and certainly standard deviations.

The purpose of me elaborating on my background was to provide you with a context to understand the above statement. Unfortunately that context is meaningless and you apparently can't distinguish between these quantities and the relationship of these elements to the numbers I posted.

Let me be more clear for you.

1.) measurement accuracy

Even with a 9" degree wheel, this safety razor welded to a clutch cover bolt allowed for +/- 0.1 degree (+/- 1 sigma) accuracy readings.

2.) positional accuracy

It is hard to adjust the valve timing to less than 0.5 degree increments

3.) estimation uncertainly

measurement could be off by as much a 1 degree and cause you to chase your tail as you keep rotating the cams looking for open/close 0.050".

4.) standard deviations.

(+/- 1 sigma) accuracy


You made this statement

For instance, how accurately can you stop the crank? 0.1 of a degree? If not, then your accuracy cannot be within 0.1 of a degree.

The accuracy of the crank stop (either in piston stroke, or angular accuracy) has nothing to do with the ability to accurately sub divide the degree wheel hash marks.

Measurement accuracy using the degree wheel does have certain error sources, mostly flatness of the degree wheel, run out error in the mount and primarily the error in the ability to sub divide the 0.070" hash marks of an 8" wheel degree wheel. While I did not quantify the first two, I did quantify the largest.

OK Some numbers.

for a 8" degree there is 0.070" separation between 1 degree hash marks

If you have your pointer 0.5" off of the wheel and read the wheel from 3 foot away then

6 inches of lateral movement in your eyeball is 0.083" (1.2 degrees) error

If you have your pointer 0.5" off of the wheel and read the wheel from 2 foot away then

6 inches of lateral movement in your eyeball is 0.125" (1.8 degrees) error

So how well are you relocating your eyeball measurement to measurement?

If you have not figured it out by now, measurement accuracy with respect to a degree wheel is a relative accuracy or repeatability of successive measurements which result in a numeric reading. It is the variance in that numeric value that is being reduced. It is not absolute accuracy with respect to TDC. While TDC can be determined more accurately using an improved measurement repeatability that is not the subject. So your statement is relating lack of 0.1 degree accuracy on TDC causing an inability to read the degree wheel is not only incorrect it is 180 degrees out in terms of dependency.

It is the repeatability of the degree wheel measurement which largely impacts the ability to find TDC not the other way around. TDC accuracy goes beyond this but we would have to delve into the accuracy of the piston stop, the estimation error in successive measurements and how well the final adjustment of the degree wheel was validated.

No where did I suggest that positional accuracy of 0.1 degree was being sought. In fact the position measurement was suggested to have a total uncertainty band of +/-2 sigma = 0.4 degrees with a suggested position accuracy of 0.5 degree increments. As you must know the measurement uncertainty should be less than the desired positional accuracy by at least a factor of 2. Theoretically it doesn't have to be (e.g. Delta Sigma Modulations), but the only way to get around positional uncertainty is to insure it is random and one must make many successive measurements to rely on the Central Limit Theorm (I can be vague as well).

As I stated before, you have mis quoted me and have abused the standard terminology. In addition and you have quite INCORRECTLY stated that there is a diminishing return of the proposed method due to uncertainty of TDC. This is patently FALSE. The opposite is true ; the proposed method makes finding TDC easier.

Given that cams specifications are provided in whole degrees, it is entirely appropriate objective to degree a cam within +/- 0.5 degree (+/-2 sigma). With the calculations above for 0.083" (1.2 degrees) , 0.125" (1.8 degrees) it is entirely possible that using a wire pointer this can not be reliably achieved. I would further submit that since you use a wire pointer you have no idea how accurate you which is probably no better than +/- 1 or 2 degrees (2 sigma) is fine. It won't stop the bike from running

Ultimately the only use I can derive from your garbled use of terminology is that you don't think that 1-2 degrees of positional error matters. Depending on your purpose it might not. In point of fact measurement accuracy matters most in the repeatability of measurements which allows the cam timing to be established earlier due to the improved repeatability.

I think I have wasted enough time explaining this. I have just about lost my patience and will have little left to post on the high accuracy engine stop.

Pos

[reddirtrider]

Ultimately the only use I can derive from your garbled use of terminology is that you don't think that 1-2 degrees of positional error matters.

I'll leave out everything but this.

That's what you derive from my comments? For someone who likes to claim I'm not taking the time to understand (or possibly can't) what you're saying, that's quite an eye opener.

My point, and it's quite simple - until you take in all of the sources of error and quantify them, what you've given us is nothing but fluff.

I do find it telling that you must resort to insulting me to attempt to prove your point. That's something I never did in any of your threads, including the one on 'sneak paths' for the R/R. You were way off base in that thread and I let it slide. Apparently you like to post and have everyone bow down. I'll keep that in mind.

[posplayr]

Red

My point, and it's quite simple - until you take in all of the sources of error and quantify them, what you've given us is nothing but fluff.

This is patently false statement. Anybody that has had any experience at performing an error analysis knows that the first step in an error analysis is to a.) identify the relationships between parameters and performance and b.) Identify the dominate error sources and uncertainties involved.

NOONE with any experience would attempt to quantify all error sources ( I assume when you say quantify you mean quantitative that means to apply a number to the parameter ).

Some errors sources are inconsequential and are not "quantified" or are not easily quantified. For example I did not attempt to quantify the change in angle associated with the gravitational pull of the moon on the piston as I went through successive TDC measurements. Why??? because it does not matter. How do I know this? Call it engineering judgment. Could I calculate it ? Sure I could. Is it going to be accurate? Maybe maybe not. But what ever it is it will be so small as to be inconsequential.

Nobody quantifies all error sources, so maybe you mean that there is a significant error source I have missed? Don't say TDC .

I do find it telling that you must resort to insulting me to attempt to prove your point. That's something I never did in any of your threads,

I do not need to denigrate you to make a technical point, I can make a more than adequate technical argument.

Apparently you like to post and have everyone bow down. I'll keep that in mind.

You may choose to bow or not, you may choose to participate in a technical conversation or not, but if you try and push uneducated statements like the above statement I will respond.

Since you have said you are an engineer, I guess I have less tolerance for inaccuracy in your statements. Even further it is insulting me for someone that has supposedly been educated in such to reject albeit informal, a disciplined engineering analysis as fluff when you don't seem to understand the first principles of the process.

I'm still challenging you to make a technical statement that has any validity in conflict with my statements. If you think that is denigrating then as then say "...stay out of the kitchen".

oh yea the sneak paths don't have much bearing on deck height, so I did not quantify that either.

[rapidray]

I have a High School diploma & build faster engines than either one of you! Ray!

[reddirtrider]

This is patently false statement. Anybody that has had any experience at performing an error analysis knows that the first step in an error analysis is to a.) identify the relationships between parameters and performance and b.) Identify the dominate error sources and uncertainties involved.

NOONE with any experience would attempt to quantify all error sources ( I assume when you say quantify you mean quantitative that means to apply a number to the parameter ).

That is exactly what I'm saying and it's something you didn't do.

For instance, what are the manufacturing tolerances associated with the camshafts? How close can you physically get the crank to the intended mark on the degree wheel given the stiction and friction associated with moving this part? I asked those questions early on, and what do I get in response?

For example I did not attempt to quantify the change in angle associated with the gravitational pull of the moon on the piston as I went through successive TDC measurements.

Exactly, more bull****.

Nobody quantifies all error sources, so maybe you mean that there is a significant error source I have missed? Don't say TDC .

I mentioned 2, and yes TDC would be another.

I do not need to denigrate you to make a technical point, I can make a more than adequate technical argument.

I'm sure you can, I just haven't seen it in it's entirety.

You may choose to bow or not, you may choose to participate in a technical conversation or not, but if you try and push uneducated statements like the above statement I will respond.

By saying my comments are uneducated? I thought you didn't need to denigrate me? That didn't last long.

Since you have said you are an engineer, I guess I have less tolerance for inaccuracy in your statements. Even further it is insulting me for someone that has supposedly been educated in such to reject albeit informal, a disciplined engineering analysis as fluff when you don't seem to understand the first principles of the process.

More denigration.

I'm still challenging you to make a technical statement that has any validity in conflict with my statements. If you think that is denigrating then as then say "...stay out of the kitchen".

I like technical discussions, particularly if you can address the points I made.

oh yea the sneak paths don't have much bearing on deck height, so I did not quantify that either.

You got one right.

[reddirtrider]

Let me try to lay out my concerns.

Yes, you've improved the accuracy of the reading by an uncertain amount. That would be the accuracy of reading with a pointer vs. using your razor blade. That isn't in contention. What you haven't done is given any figure for this improvement taking all relevant tolerances into consideration.

Next, unless this is the only parameter in this system that has tolerances and whose deviation might affect the performance parameter of interest (the relationship between the crank and cams) then we must take into consideration these other factors to determine what role they play.

To sum it up, you can continue to improve the measurement accuracy, but there will come a time when no matter how much that parameter is improved it has no effect on the overall performace of the system. That is what I'm trying to find out. Have we reached that point? Where is that point?

[rapidray]

Let me clue you 2 sixth graders in on something, even being an entire DEGREE off on where you are trying to set the cams will have LITTLE affect on the engine's power!!! Hello?!!! do you 2 GET it?!!! LOL!!!!
Measure with a micrometer, mark it with a piece of chalk, and cut it with a chainsaw! Ray.

[reddirtrider]

Let me clue you 2 sixth graders in on something, even being an entire DEGREE off on where you are trying to set the cams will have LITTLE affect on the engine's power!!! Hello?!!! do you 2 GET it?!!! LOL!!!!
Measure with a micrometer, mark it with a piece of chalk, and cut it with a chainsaw! Ray.

Which reminds me, we need a target for our performance parameter. This sixth grader and his pointer is capable of that.

[Billy Ricks]

...even being an entire DEGREE off on where you are trying to set the cams will have LITTLE affect on the engine's power...

1 degree out of 360 is just a little over .25%, not much and probably far less than tolerances from the factory. Probably wouldn't make but about 1 hp of difference if that.

[hp1000s]

Measure with a micrometer, mark it with a piece of chalk, and cut it with a chainsaw! Ray.[/QUOTE]

Ha! Nice one...*That's all well-and-good, as long as the chalk has been sharpened to a suitably accurate point.* "I've told you a million times to not exaggerate"
Hugh

[posplayr]

Wheel of Fortune

Measure with a micrometer, mark it with a piece of chalk, and cut it with a chainsaw! Ray.

I know your are a funny guy. However, you are also the main reason that I pursued this crusade to improve degree wheel read out accuracy.

There has been numerous times that you have posted here at GS resources to use an 18" degree wheel v.s. the smaller ones. You have told it to me personally at least three times and the last time you urged me was prior to buying those new 0.340 webcams (last week was it?). I had to debate about spending another $60 to get a larger degree wheel and having to pull my case savers off the engine in order to mount such a large wheel.

In addition, when I was at your house (last year) and you were degreeing my cams using the big 18" wheel , you asked me to read off an angle. I gave you my reading, and apparently not trusting me you came to my side of the engine to read it yourself. You said "no it's not you are 1 degree off". I did not argue as it is clear that depending upon where you stand you can get significant variation in readout.

So if I can be a degree off on an 18" wheel , all things being equal, I would be 2 degrees off with an 8" wheel.

Truth be told, the above was the deciding factor in my pursuit of better readout accuracy. To summaries:

a.) Rapid Rays insistence that 18" degree wheels are better than smaller ones "I don't mess around" to quote him. I'm not in anyway challenging his experience with respect to this benefits of the 18" wheel.

b.) The first hand experience at RapidRay's where he and I were reading the same wheel at the same setting and getting an answer that was a full 1 degree different.

What may not be obvious here and the reason I separated these two reasons, is that while b.) above is directly related to readout accuracy alone, a.) above relates to how the degreeing process improves due to improved accuracy. The first relates more to how the reduction in read out errors, improves measurement repeatability and insures that the final cam settings are within acceptable tolerances with fewer trials.

As I recall that day, we were within about 0.25 degrees on intake and about 0.75 degrees on the exhaust. As should be obvious there are measured quantities.

Pos

[Billy Ricks]

You can get different readings by using one eye versus the other. Most people have a dominant eye, it's what makes shooters and baseball hitters be a lefty or a righty.

[posplayr]

Red

Let me try to lay out my concerns.

Yes, you've improved the accuracy of the reading by an uncertain amount. That would be the accuracy of reading with a pointer vs. using your razor blade. That isn't in contention. What you haven't done is given any figure for this improvement taking all relevant tolerances into consideration.

Next, unless this is the only parameter in this system that has tolerances and whose deviation might affect the performance parameter of interest (the relationship between the crank and cams) then we must take into consideration these other factors to determine what role they play.

To sum it up, you can continue to improve the measurement accuracy, but there will come a time when no matter how much that parameter is improved it has no effect on the overall performance of the system. That is what I'm trying to find out. Have we reached that point? Where is that point?

I appreciate your improved tone, so I will try and answer in like kind.

From the above you have expressed a general concern for the diminishing return on "performance" improvement as a function of degree wheel accuracy. Well yes it should go without saying that my top speed of my GS will not keep increasing to the speed of light if I make my degree wheel ever more accurate. This is an absurd example to illustrate the point. This may sound sarcastic but should serve to reinforce your point and which should be pretty obvious.

So to if I might refine your question into something more specific, the main questions are :

1.) How accurately should your cams be set (physical accuracy relative to the pistons)

2.) How accurate (with respect to the dial indicator) does your dial indicator readout out need to be to achieve the accuracy in 1.).

3.) Are there any other relevant factors that effect the accuracy in 1.)?

The answer to 1.) is a "it depends" answer so there is no single answer. If you are happy with stock then live with stock tolerances which are probably +/-3 degrees of nominal (say 106/106 degrees for example). No other action requried.

If you are a drag racer, you probably want to get within 0.5 degrees (my guess). Hey Ray how accurate do you try and get on a built motor?

If you ride on the street and just spent $1500 for a top end rebuild on a $2000 bike then you probably want to at least follow the cam manufacturer's recommendations for degreeing the cams (somebody call my name?).

Since for my Web cams that is 105/107 degrees as opposed to Bill's bike which is 110/110 I'm figuring close to 0.5 degrees off is good enough for me, 0.75 will not kill anything. If it comes up 108 and the spec is 107 I will try harder and get closer.

As to the answer for question #2, if you want to be able to determine where your cam is set with respect to your TDC reference in one pass to within +/- 0.25 degrees then you are going to have to measure to within +/-0.18 = (0.25/1.41) . That is because you need two measurements to measure a lobe center and have two errors associated with each.

Determining Physical accuracy (with respect to measured TDC) of +/- 0.5 degrees requires:

an estimate (average of two points) with uncertainty of about +/-0.25
which requires individual measurement accuracy of approximately +/-0.18 degrees.

If your TDC is also in error it will only serve to increase the absolute error of the cam lobe timing with respect to the physical TDC. Of course this is only the TDC of cylinder #1 only and if you have a twisted crank then cam timing of the other cylinder will be off even further.

A crank from a 3" stroke motor will be out by about 0.026" from nominal with a 1 degree twist.

I don't know how tightly cams are ground but a 0.002" error at 1.5" radius is .15 degrees on the crank.

One might be well advised when degreeing your cam to check for crank twist by degreeing #1 cylinder and insuring that #4 is the same. As per the calculation above, if it is not you can likely attribute that to crank twist.

Finally the question #3, what else effects the overall accuracy of cam timing with respect to TDC.

First let me dismiss two of the sources you referred to namely stiction and friction. Stiction is a type of friction so I'll assume you mean dynamic friction; friction involving forces that oppose dynamic or actual movement. Since all measurements are performed statically, no dynamic friction is even present during the measurements. If you are talking about differential friction on main bearings causing differential loads which twist the crank when in operation than let me refer you to the section on "the price of cheese in Denmark" .

Realistically the best that can be done is to statically degree the cams. For that purpose dynamic friction has no bearing because the measurement is performed statically. As far as stiction is concerned, if anything this actually might help the measurement process. As the crank is set to a position it would tend to cause the engine to "set" and not move once the force from the wrench turning the engine was released. In a recent session I noticed that a movement of 0.5 degree (Bill at the wrench) ,would retrace to about 0.25 degrees. With the raser blade accuracy this was easy to see and what helped insure repeatability of what was going on.

Getting back to relevant topics, the only primary factor effecting the ability to degree the cam relative to TDC is in fact the determination of TDC itself. The angular accuracy of the TDC determination is based on two primary factors alone.

3.) How accurately the TDC can be measured by the degree wheel, and
4.) How accurately the piston height translates into a fixed TDC rotation.

For the answer to #3 see the answer to #2.

The answer to #4 is the subject of the "High Accuracy Piston Stop" how to.


Red,
I will not be the least bit surprised if you will be unsatisfied with the above explanation. I don't know if it will be simply to reinforce an argument that cam timing accuracy is irrelevant or if your objections will derive from an inability to limit the sope of the discussion to questions that can be answered v.s. those that can't. Regardless of which, I've done about all of the foundational work I care to to justify the pursuit of increasing degree wheel accuracy.

Pos