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E: Engine Camshaft


Flo

Active Website User
VOC Member
Bruce, your reference to constant accelleration should have been answered in my previous post. Attached is a graphic to illustrate four traces, lift, velocity, accelleration and jerk. This clearly shows a fairly long duration where accelleration is constant, and because accelleration is constant, so is jerk.
The data is design data, not measured, and John Andrews original design data would have been similarly smooth
Hi All,

this Forum seems to concern primarily the analysis of cam profiles by measuring. The methods reported so far will always stuggle with the quality of the measuring apparatus (exemplified by the Grey One's data of a professional rig) and the method of interpolation (although at 21600 P/r this is obviated by the data density) all splines have a tendency to oscillate (usually smotheness is defined as continuity and differentiability for 2 derivatives. Whether applying a low pass filter might be helpful is outside my personal experience (I have always insited to see 'raw' data i.e. what comes out of the sensing element).
It is obvious though that the precision requirements are much less for design data, where one would put the profile together from known functions (always making sure that at the transitional points the 3d derivative (jerk) is continuous and differentiable) so the relation of successive surface points is obeying the maths and not the absolute value. I am sure that Mr. (Dr. ?) Hubbard has something to say about this in his Handbook.

For a basic understanding of valve trains I always recommend Wolf Bensinger's classic text Die Steuerung des Gaswechsels in schnelllaufenden Verbrennungsmotoren (unfortunately in German). Hence the quieting ramp is really important for the opening flank (when the effective clearance is reached on the closing flank valve and spring have come to rest and do not contribute to valvetrain inertia and forces. And of course when acceleration is constant jerk is zero (which I am sure has contributed to the German misconcepton of Ruckfreier Nocken). While a world free of jerks is certainly not achievable a cam profile free of jerk is not even desirable.

F
 

roy the mechanic

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VOC Member
Ever since the industrial revolution there have been prototype engineers and toolmakers who take pride in making the most accurate and best finished parts possible. In the real world for an air cooled motor around .001" will give good service. But you must not tell the guys making your parts, they get upset. On a personal level it's nice to do a build with the best quality parts.
 

vibrac

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VOC Member
I dont know about Maughan & Sons but I bet Roger Moss could give it a good go I visited his place a year or so ago when |I wanted some advice on a Scott engine I was building. He has certainly has a lot of fancy machine tools and measuring equipment.
 

Bill Thomas

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VOC Member
Hands up, All the Vincent owners that have seen an 1/8" tappet clearance at some time in there life !!.
Even if you got it spot on , It would not stay like it long. Cheers Bill.
 

Grey One

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Non-VOC Member
MK 2 cam profiles meaured from a new cam in 2012. The intake only is shown, with velocity and accelleration traces overlaid.
Unfortunately the manufacturer is unknown as the cams carried no identification. This is data measured at the cam, not via the follower. This data would be the basis for constructing a manufacturing file to have copies ground up.
Attached is a strip of closing data to 8 places of decimals, measured at 1 degree increments. With such data it is possible to determine the roughness of the profile being measured. Less accurate data at greater degree increments makes it difficult if not impossible to determine whether roughness is the resjult of the data format, or the cam surface. Rough data can be used to check the cam installation, but is worthless for any meaningful comparison purposes.
 

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timetraveller

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VOC Member
It is always interesting to communicate with an expert and someone who has designed cams which won TT races etc. is certainly an expert. However, referring to the above graph from Grey One which is taken from the face of the cam with no cam follower and no allowance for Vincent timing gear geometry, then it seems to this untutored producer of 'worthless data' that although this might be the correct way forwards to manufacture cams, it lacks something vital when it comes to valve movement etc. And before Grey One asks, yes I have designed cams and had them manufactured and, as an aside, I found it difficult to get people to work to one tenth of a thou (fourth decimal place) never mind an eighth decimal place. My worry about the relevance of the above graph to the behaviour of the valves in an engine is the geometry of the Vincent valve gear. The flat based lever follower imparts a variable lever ratio between the cam face and the valve movement. Once again, writing as a non professional cam person, it seems to me that it is the movement of the valve which is of importance, not just the cam profile. I have taken the liberty of tracing the profile above on to tracing paper, inverting it and then putting it on top of the original to see just how asymmetrical this displacement curve is. The answer is ' not very'. This seems strange to me as Vincent cams are clearly very different from one side to the other.
Below I am going to show a graph of the valve motion and the cam displacement for a Vincent cam.
26283
The blue points are the valve motion and the red the cam displacement. One can clearly see the differences in the ratios as the cam surface moves along the flat lever follower, giving a variable leverage ratio. The horizontal scale is cam degrees and the vertical scale is inches.
The next graph shows the way in which this ratio varies Between about 1:1 and 2.8:1.

26282
Please note that the shape of this graph would change if one were to index the lift profiles at a different point. Moving the point at which the two maxima coincide makes a big difference to the ratio values but they always vary considerably. Consider that the inlet valve starts to lift when the cam is contacting the lever follower towards its pivot, high ratio, and the exhaust starts to lift when the cam starts to contact the lever follower away from the pivot, low ratio.
What I do not understand and which it would be a pleasure to be educated about, is why the velocity and acceleration curves from the cam surface look sensible when the above ratios need to be allowed for when it comes to valve movement, which also has to look sensible.
 

roy the mechanic

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Having spent 30+years building race car engines (a lot of them winners) cams are still a black art. I have worked with two well known cam makers. To the best of my experience, they are all full of "bull cookies". It is no importance what it looks like on paper. The only parameter is the numbers on the dyno, and the numbers on the stopwatch. that's the only way forward. Or go back and spend more money!
 

greg brillus

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Yep.......Look at modern engines and the trouble manufacturers have gone through to get engine performance and tractability. Variable valve timing, exhaust port/ pipe valves to vary back pressure, variable length inlet trumpets............ All the stuff we are playing with is stone age.
 

Grey One

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Having spent 30+years building race car engines (a lot of them winners) cams are still a black art. I have worked with two well known cam makers. To the best of my experience, they are all full of "bull cookies". It is no importance what it looks like on paper. The only parameter is the numbers on the dyno, and the numbers on the stopwatch. that's the only way forward. Or go back and spend more money!
Roy,
The Americans found this out some years back when they devised the Spintron equipment and discovered there could be a big variation between static and dynamic valve actuation. Originally designed to observe the flex of pushrods, it was quickly expanded to cover all components of the valve train, and the variations that were found to occur between the static and the dynamic valve actuation were a big eye opener.

TT
I attach a graphic to show overlaid traces of measured cam data, the MK 2 profiles and those of the 105.
The intake lobes are both aligned exactly one on top of the other, and in addition to the cam lift, the graphic also includes the velocity traces. You just cannot get this kind of graphic from rough data. The traces show where discrepancies occur between the two cams, even though the 105 was said to be a copy of the MK 2 but with the lobe separation increased. If required a section from anywhere on the graph may be enlarged (zoomed), by four times if needed. All the top cam grinding companies now have CNC grinders although the older Churchill and Berco machines still handle a lot of the run of the mill grinds The CNC machines run from data files which contain data to 8 decimal places.

Greg
I agree with your 'stone age' comment, but it doesn't need to stay that way. I guarantee the Horner brothers didn't operate that way when deloping their Vincent racers.

Anyone sufficiently interested in this subject would do well to obtain a copy of Jeff Williams book "Introduction to the Analytical Methods for Internal Combustion Engine Cam Mechanisms".
Jeff designed the cams for the ILMOR 265E engine (V8 pushrod) that won the INDY 500 in 1994
 

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Robert Watson

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VOC Member
I have just had a recall on a 2012 Subaru 2.0L because they are breaking valve springs. They don't have the tooling or the parts yet at the dealers to do the repair. If one breaks you may feel a vibration or hear abnormal engine noise and the engine may stall and be unable to restart. If this should occur please pull over and call your nearest Subaru dealer.

It amazes me that things like this still occur, and why they still are unable to make many disk brakes that will not warp in normal driving conditions.........

Never mind cam design!
 

Cyborg

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VOC Member
Spintron....

A fairly large percentage of the warped brake rotors that I came across were caused by folks jamming the wheel nuts on with an air impact driver. Grossly over torqued they would distort the hub and that in turn would distort the rotor.
 

Grey One

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TT
sorry I didn't reply to your query re the difference between cam profile data and how it can be related to lift at the valve. I must stress the graphics are cam lift data only.
I would not start to work from the cam, but would start from the valve lift design that all my calculations and simulations (both static and dynamic) indicate would be capable of meeting the design performance target. This valve lift design is then processed through the valve train of the engine in question to arrive at the cam, where a profile will be calculated.
It is of course necessary to have complete data for the valve train, dimensionally and with X and Y co ordinates where appropriate, together with all weights and inertia and stiffness values for the moving components, which will also include full valve spring data , and this can take some considerable time to collect if the data is to be accurate. which it must be.
With some engines I have to build in a provision to cover an over rev through a missed gearchange or similar, and it often involves a number of detail changes in order to arrive finally at a satisfactory outcome.
Cyborg
a great little Spintron movie, but the end comments re valve seating bounce where poor springs are blamed, is not strictly correct. Bounce can be the result of a badly designed closing side of the cam, and with a better design the springs would be OK. No matter, the spring oscillations are shown in the output graphics of my dynamic simulation, and when I get it wrong I see the bounce , just as the Spintron shows it.
 
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Cyborg

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VOC Member
I wondered about the spring comment. This is all way above my pay grade, but after fiddling around with some of Honda's smaller multi cylinder engines, it becomes apparent that they don't achieve that high RPM, by throwing stronger valve springs at them. It seems to me that stronger springs are often used to try and correct a problem elsewhere..... Like my neighbor with the drag boat that changed cams as frequently as oil.
I always thought that if the opening and closing velocity was pretty much equal, that would create a more fluid/harmonic situation with less bouncing around. Now I'll exit stage right, before I dig myself in any deeper.
 

greg brillus

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VOC Member
I have spoken to Ken Horner several times about the valve train in a Vincent, and there is always an expression of despair on his face. The biggest limitation is available room, the cams/followers are too small to take any real heavy loading. They try and get around this using the same pivoting cam followers but with a roller mounted at or near the tip and symmetrical cams. They then use rocker arms with a much larger ratio than the stock 1 : 1 and I'm guessing they must get at least 600 lift at the inlet valves. The rework on a standard head type Vincent engine to get that kind of lift is very difficult, along with everything else, this is a major limiting factor for most owners even if they want to build an all out race engine. These engines were designed to be large valve low lift valve train with pretty low valve spring rates. The cost of trying to achieve any of this is quite high and the numbers interested in doing so are small, given there are very few Vincent racers out there anymore.
 

oexing

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VOC Member
Publishing one´s measuring machine´s accuracies may be veeery impressive but at these numbers all this does to me is rolling my eyes . . . . I have limited resolutions on my test stand for cams to 1 micron (1/25 of one thou) and 1/4 of one degree on the rotary encoder. I am not interested in anything better as I know from my professional life being retired toolmaker , accuracies in REAL life are quite different from what academic people believe in their imagination. All these numbers may have some meaning for computer calculations to arrive at some result in the CAD exercise but in the toolroom you are happy to see one thou or half of it close to the desired size, no way near 8 decimal places in existence. In fact, when you get a new cam from any company, you are lucky to see a base circle with less than two thou runout, all other base circles with runouts all over the place.
Anyway, this is not our concern, we just had a look at cam lobe shapes for comparison and evaluation from other cam data bases in order to be able to assist buyers in finding suitable camshafts. I do have a few programs from Perfrmance Trend, cam analyser and cam grinder. BUT, big question is,how do you arrive at the cam shapes ?? And right here all postings are veeery hazy, it is quite obvious that the start has to be the valve lift diagramm. I can provide 40 different computer calculated files , different in lift numbers, acceleration , and duration, three decimal places - in millimeters, one micron that is.
Now the REAL hard work is to model all levers, rocker finger shapes, cam follower details, into a CAD program that handles these kinematics to transform in the end valve lift numbers into cam lobe shapes !! I was toolmaker in life , with all traditional skills, but CAD was not one of these. So is there a chance to get any info here on suitable programs for such calculations , Fusion 360 , not so much ?? I believe Performance Trend can analyse dynamics in the valve train by simulation but only AFTER a cam was fabricated, it does nothing for designing a cam.
So the procedure to arrive at a particular cam shape , starting with valve lift numbers , is definitely my big question but I guess that haziness about details will continue . . .
Valve bounce and other adverse effects are seen mainly in race type engines and I believe there is no universal solution in all cases and has to be dealt with individually. Most Vincenteers will be more interested in smooth operation by mild acceleration and quieting ramps so no radical fast wearing shapes acceptable.

Vic26313
 

Grey One

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Non-VOC Member
Cyborg
valve springs all possess a natural frequency of vibration. it's essential that this does not co incide with that coming from the cam design anywhere within the engines normal operating speed range. In olden days this was not well understood at all, but now it's part of the overall design process, and most usually this frequency clash is arranged to be outside of the engines main operating speed range. If you now add a pushrod into the mix, you really do get problems, for the last thing you ever want it for the natural frequencies of the pushrod and the valve spring(s) to clash. It is all so easy to get into what amounts to a can of worms, and the more one tries to push the limits, the deeper into the can one gets. I've been deep among the worms plenty of times !

Greg
you describe exactly the problem that anyone wishing to seriously boost the performance of a Vincent engine faces. Do you stay within the original outward design envelope, and try to make all modifications within the engine cases, or throw away these concerns and modify as and how necessity determines? Obviously it's for the individual to decide, but Classic Racing rules usually require the outward appearance to be consistent with the original engine, so one ends up being as it were, stuck between a rock and a hard place !

Oexing
your measuring jig appears to have all the essentials for you to obtain meaningfull data.
The value of data to 8 places of decimals is certainly not necessary if only the profile of the cam is the sole interest, but it's when the second and third derivatives are to be investigated that the more detailed data becomes a necessity. The standard for measuring cam data is the Adcole system, very expensive but used throughout industry, and can be tailored to suit each individual users requirements. Almost as good, and certainly far less expensive are Performance Trends Cam Analyser, and Audie Technologies Cam Pro Plus. For either of these you would need their monitor and software program, you have apparently the requisite encoders.
John Andrews also had design software, but since he's been taken over I don't know whether this is still available. He marketed EZcam, a software program designed for measuring and analysis of cam data.

For an understanding of the calculations of the pushrod system, you will find very detailed explanations with all relevant diagrams and mathematics in Jeff Williams previously mentioned book
 

Flo

Active Website User
VOC Member
Grey One, can you please qualify thr 8 decimal places in your data e.g the dimension inch or mm. So do you think that you need a precision of +or - 0,00000001 mm or 0.00000005 inch?

Let me make clear that the analysis of an existing cam profile surely will present challenges bordering on the impossible.
 

greg brillus

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The only other thing I would say about having a performance cam in a Vincent, especially if the closing point of the inlet valve is very late, is that the engines can a be very difficult to start. I'm guessing this is because so much dynamic compression is lost. Hence the need for high comp pistons when big cams are used. I had 2 fully restored shadows with new Mk 2 cams from a known source that were not only very difficult to start but would not idle very well at all, no matter what you did.
 

Grey One

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Non-VOC Member
Flo
both, metric or imperial. The full 8 places are not always used, but are available and can be used as and how the linear encoder detects. If you look at the short data list I posted earlier you will see that not all entries were to 8 places, many were 7, and further into the list (not shown) some were 6 and 5 places.

The measuring equipment I use is Audie Technologies Cam Pro Plus, and for some designers who wish to work to the fourth derivative, Snap, such detailed data is essential, (Cam Pro Plus has lift, velocity, accelleration and jerk, no snap, so if I wanted snap it would have to be derived from a separate computation).

Design may be extremely detailed, where necessary to the 8 th decimal place, and when verifying the accuracy of the manufactured cam it's generally accepted that the measuring accuracy should match the design accuracy for depth of data, this for ultra high performance high speed use, where any slight deviation from design could well end up in a mechanical disaster.
Because I have always designed this way, I use the same methods for whatever work I am involved with, be it an ultra high revving multi cylinder race engine, of a much lower revving single cylinder Classic racer.
 
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