How to measure a Cam in the Hand

[JohnD]

Thanks, Alan!

Too many projects, me.

JOhn

[JohnD]

It's taken me at least three sessions, the first in the garage, where I just froze to death until I could hardly move my hand to grip the shaft to turn it, before I realised there was no harm in bringing the rig indoors!    Then I had to get my head around the orientation of the lobes, and taking readings from one, then  the other.      Too complicated to read two lobes at once!  Even though I have two DGIs and it would have been technically possible.  So this is what I've got:

37

It appears from the timing on the label, 47-73-83-37, that this may not be a classic 'symmetrical' cam, but I've aligned the cross over to TDC anyway, as that is how I would intend to time it (ELOO).   And I've added two lines to show the designated "Valve  Settings" by which I presume they mean gaps between rocker and valave stem, Inlet 28 and Exhaust 30 thou - big and its says "Hot"! 

 It may interest you, Alan, that the blurb includes advice on duration and timing at both 16 and 50 thou tappet gaps:

@ tappet lift 16 thou 47-73-83-37 duration 300

@tappet lift 50 thou 24-50-60-14 duration 254

Lift is 325 at the cam and they suggest 465 at the valave with a 1:1.44 rocker ratio.

It's a peaky stick!

JOhn

 

 

Edited February 1, 2019 by JohnD

[oldtuckunder]

Hi John

need to find half an hour to really look at that cause on face value the timing numbers and duration look?, however the lift is right .

I'll try and get back later

Alan

[oldtuckunder]

On 2/1/2019 at 1:45 PM, JohnD said:

It's taken me at least three sessions, the first in the garage, where I just froze to death until I could hardly move my hand to grip the shaft to turn it, before I realised there was no harm in bringing the rig indoors!    Then I had to get my head around the orientation of the lobes, and taking readings from one, then  the other.      Too complicated to read two lobes at once!  Even though I have two DGIs and it would have been technically possible.  So this is what I've got:

37

It appears from the timing on the label, 47-73-83-37, that this may not be a classic 'symmetrical' cam, but I've aligned the cross over to TDC anyway, as that is how I would intend to time it (ELOO).   And I've added two lines to show the designated "Valve  Settings" by which I presume they mean gaps between rocker and valave stem, Inlet 28 and Exhaust 30 thou - big and its says "Hot"! 

 It may interest you, Alan, that the blurb includes advice on duration and timing at both 16 and 50 thou tappet gaps:

@ tappet lift 16 thou 47-73-83-37 duration 300

@tappet lift 50 thou 24-50-60-14 duration 254

Lift is 325 at the cam and they suggest 465 at the valave with a 1:1.44 rocker ratio.

It's a peaky stick!

JOhn

 

 

OK taken a look at this and as always when I look at what is real and in the hand and what a Cam Manufacturer has published about it we seem to get into apples and pears territory.  I'm 99% certain that John will have measured the real cam correctly, its hardly rocket science and I'm fairly certain that a 12 year old once shown could rotate a cam, watch a DG and write down some readings.

About the only think I would question in the above is possibly John's choice to align the lift cross over with TDC, rather than possibly a timing number given by the manufacturer. However at worst all it does is slide the lobe values as a set left or right. The reason I might question that choice is that it means maximum lift on the Inlet Valve occurs at 40 deg (cam) ATDC or 80 deg (crank) ATDC which seems very very short to me and not in the 100-112 ATDC ball park I would expect. However as I said at worst all it does is slide everything left a bit, and as you can see from my following numbers even if you factored in that shift into my numbers it would make some even more abnormal.

So John has been given data on the cam that includes.

"Lift is 325 at the cam and they suggest 465 at the valve with a 1:1.44 rocker ratio."

Which given a RR of 1.44 at the highest lift point isn't far off the 0.440 there would actually be after deducting their recommended clearance of 0.028  But at least they have used a 1.44 RR rather than the much banded fictitious 1.5

However its really Timing and Duration we are really interested in and we are told

that the blurb includes advice on duration and timing at both 16 and 50 thou tappet gaps, so lets take

@tappet lift 50 thou 24-50-60-14 duration 254

Now there could be some dispute what they mean by "tappet lift" do they mean cam lift on the tappet or lift at the valve tip after factoring in RR and valve clearance. I didn't know so after looking at the numbers at 0.050 cam lift, I calculated the second and rapidly came to the conclusion that as the differences I was getting were so great the difference between either of these was so negligible that it didn't matter. i.e. Regards timing and duration the difference between taking the readings at 0.050 cam lift and (.050 + 0.028) / 1.44 = 0.054 is hardly here or there if you look at the above graph.

So my calculations:  Oh first of all lets restate what we think we are measuring ( again someone else's words not mine)

Valve Opening and Closing Angles – the angles (usually measured in crankshaft degrees) when the valves first leave and then return to their seats.  The opening and closing angles may also refer to a specified nominal lift, e.g. at 0.050 in cam lift.  For example, a cam's timing may be stated as 25-65-65-25.  These numbers are (1) intake opening BTDC, (2) intake closing ABDC, (3) exhaust opening BBDC and (4) exhaust closing ATDC.  For these numbers to have meaning, the lift at which the numbers are taken must be specified.

Duration - the difference between the closing and opening angles. This is the number of degrees the valves are "off their seats". Duration is usually expressed in crankshaft degrees. Duration may also refer to the number of degrees that the lift is greater than a specified value, e.g. duration at 0.050 lift.  For a cam with timing 25-65-65-25, the intake and exhaust duration are both (25 + 65 + 180) = 270 degrees.

Advertised Duration - a duration which is advertised without specifying the lift at which it was measured.  These numbers are worthless.

So at 0.050

Inlet Opens 18 (cam) BTDC or 36 (crank) BTDC
Inlet Closes 0 (cam) ABDC or 0 (crank) ABDC   (note this is actually at BDC not "n" ABDC)

Exhaust Opens 5 (cam) ABDC or 10 (crank) ABDC (again note this is ABDC not "n" BBDC we might expect)
Exhaust Closes 18 (cam) ATDC or 36 (crank) ATDC

So the above at 0.050 gives us cam timing in crank degrees of 36-0, minus10-36 which means we have durations of Inlet 36+0+180 = 216 and Exhaust 36-10+180 =206.

So none of this ties up with "@tappet lift 50 thou 24-50-60-14 duration 254"

So as I said earlier this is based on the Inlet Valve reaching full lift at 80 deg (crank) ATDC, what happens if we slide that full lift point to a conventional 110 ATDC? bearing in mind if we do that everything moves 30 deg together as its ground in the cam! we cant move Exhaust one way and Inlet another!

So at 0.050

Inlet Opens 3 (cam) BTDC or 6 (crank) BTDC
Inlet Closes 15 (cam) ABDC or 30 (crank) ABDC 

Exhaust Opens 20 (cam) ABDC or 40 (crank) ABDC (again note this is ABDC not "n" BBDC we might expect)
Exhaust Closes 33 (cam) ATDC or 66 (crank) ATDC

So the above at 0.050 gives us cam timing in crank degrees of 6-30, minus40-66 which means we have durations of Inlet 6+30+180 = 216 and Exhaust 66-40+180 =206.

So again none of this ties up with "@tappet lift 50 thou 24-50-60-14 duration 254"

In fact at no cam lift or adjusting max inlet timing anywhere can I find any point where the quoted numbers make any sense at all to me?

Alan

 

[JohnD]

Just to remove all doubt, or at least as far as possible, below is a scan of the Spec sheet that came with the cam.      It doesn't include a magic timing number, as far as I can see, but I fully recognise Alan's point that to align the cross over to TDC is arbitrary and possibly incorrect, or more strictly  a disadvantage given the cam grind.

And here are the same data, without being manipulated to place the cross-over at TDC.   I used the peak of the exhaust valve as my reference as I had no idea where TDC should be.   If that is TDC, then the peak of the intake cam is at 70 degrees ATDC, which is no better in terms of your criteria, Alan.  But I don't understand those, as you own cam trace shows the inlet peaking at 50 ATDC.   ("maximum lift on the Inlet Valve occurs at 40 deg (cam) ATDC or 80 deg (crank) ATDC which seems very very short to me and not in the 100-112 ATDC ball park I would expect")   Am I confusing cam and crank rotation, so that the last figure (100-112 ATDC) applies, but then mine would be 140 ATDC!

I know that tuners will vary the position of the maximum power band by moving the cam shaft in relation to the carnk a few degrees either way, but not the tens of degrees that you refer to, Alan.  And to install it as above would seem extreme.     

John

PS I tried to learn about varying the position of the cam reference the crank by searching online for "swinging the cam" .    Thank you, deviants in Cambridgshire - I didn't want to know!

 

Crane cam specs.pdf

Edited February 3, 2019 by JohnD

[oldtuckunder]

Hi John

Just hidden in the small print is that they think the cam should be timed with max inlet lift at 103 ATDC  which from looking at the graph alone (as I don't have the numbers) means that you need to slide all your cam lift numbers approx 10 deg (cam) to the right (if you see what I mean) or rather calculate the difference between max inlet lift you have and 103, and add the respective cam deg difference to all your readings.

Still not sure what sense it makes of their quoted cam timing numbers, but its way quicker to adjust the data and then look again rather than trying to recalculate.

Alan

[oldtuckunder]

Hi John

Missed your edit whilst looking and replying, OK I Think I know what we need to do with your data.

Crank TDC is always at 0 (cam) deg right in the centre.

Slide your data so that peek lift Inlet is at 51.5 deg (cam) ATDC, this equates to the 103 deg (crank) that Crane recommend.

The graph is always 360 cam rotation, every cam deg = two crank degrees, so easy to convert from one to the other.

Alan

[JohnD]

Thank you, Alan!  Here's the result, peak Inlet at 51.5 ATDC.

This is annoying - my PC must be suffering from the cold - it will NOT copy 'n' paste the chart here, so I've posted a Word image of it.

That puts the cross over at about 3.15mm (124thou)(sorry, I have metric DGIs!) at an angle of 15.5 ATDC.

That gives me two corresponding targets for cam timing, ELoO at 31 ATDC crank and peak inlet at 103 ATDC crank, but what made you choose that point, Alan?   

I can see " MAX Lift 103degrees ATDC" on the spec, but that's in the section labelled "Cam timing at .050 TAPPET" and referred to "INTAKE".       Next to it is "Max Lift 113 degrees BTDC" referred to Exhaust, but this orientation of the cam would place that point at 18 degrees BTDC.    That particular section of the spec chart is most mysterious!

JOhn

 

crane cam profile adjusted to inlet peak at 51.5 ATDC.docx

Edited February 3, 2019 by JohnD

[oldtuckunder]

2 hours ago, JohnD said:

That gives me two corresponding targets for cam timing, ELoO at 31 ATDC crank and peak inlet at 103 ATDC crank, but what made you choose that point, Alan?   

I can see " MAX Lift 103degrees ATDC" on the spec, but that's in the section labelled "Cam timing at .050 TAPPET" and referred to "INTAKE".       Next to it is "Max Lift 113 degrees BTDC" referred to Exhaust, but this orientation of the cam would place that point at 18 degrees BTDC.    That particular section of the spec chart is most mysterious!

JOhn

I chose 103 ATDC as that's what they said, NB regardless of what cam timing lift or valve clearance the max lift point won't change unless you move it by re-timng the cam. The max lift point seems to be a value that most cam manufacturers (even the english ones who seem reluctant to almost admit they ground it let alone give any meaningful data) all seem to supply, and 103 ATDC does fall into an expected ball park. However as you comment it makes the Exhaust number seem way odd. Also assuming your measurement data is good its very hard (like impossible) to actually tie the cam timing data they supply to anything that is measurable.

PM your data and I'll do a sensibility check.

NB.  I'm starting to have a sneaking suspicion that some cam manufacturers grind  a cam and then just make up a bunch of numbers that they think look good, on the assumption that nobody will check, and that if anyone used them to try and copy the cam they would end up with a pile of scrap 

NB whilst not quite sufficient granularity on the chart to accurately read, and it doesn't agree with the figures that Crane have given you, looking at your measurement of the inlet valve its duration at .050" seems to be around 220-230 deg (crank) which would slot it into the "3/4 Race" ball park description according some sources.

Alan