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Roller cams and max open degree's #3005274
01/14/22 02:08 PM
01/14/22 02:08 PM
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Mt Morris Michigan
mopar dave Offline OP
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I just installed and degree'd the new Bullet roller (269/275@50) in my 511. Just matching the dots up gave 103* centerline and the cam is on a 108* LSA. My question, i noticed the lifter stayed at max lift with indicator reading 0 for a total of 10*. Is this normal for a roller cam to keep the valve at max lift for 10* of rotation? Just curious.

Re: Roller cams and max open degree's [Re: mopar dave] #3005324
01/14/22 05:40 PM
01/14/22 05:40 PM
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My CompCams hydraulic roller shows the following:

1) INTAKE - max lift is 0.365

DEG - LOBE LIFT
225 - .358
230 - .363
235 - .363
240 - .359

2) EXHAUST- max lift is 0.362

DEG - LOBE LIFT
115 - .358
120 - .362
125 - .362
130 - .357

So I think that basically matches what you see I think, or close enough maybe?

Re: Roller cams and max open degree's [Re: mopar dave] #3005374
01/14/22 08:53 PM
01/14/22 08:53 PM
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It doesn't actually hold max lift for 10 degrees but it might look like that on your dial indicator, especially if you don't have the full spring load hooked up.

Re: Roller cams and max open degree's [Re: AndyF] #3005399
01/14/22 09:53 PM
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Originally Posted by AndyF
It doesn't actually hold max lift for 10 degrees but it might look like that on your dial indicator, especially if you don't have the full spring load hooked up.
iagree scope
The only way the roller should stay still on the top of the lobes is it is flat on the nose, which I have never seened shruggy


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Re: Roller cams and max open degree's [Re: Cab_Burge] #3005405
01/14/22 10:19 PM
01/14/22 10:19 PM
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I'm sure it's not flat on the nose, but i have never noticed this before with any other cam i had. May not be flat, but pretty close to it as the indicator stays right on 0 for atleast 10* as i stated. Just curious if this was normal and i never noticed before. Thanks

Re: Roller cams and max open degree's [Re: mopar dave] #3005406
01/14/22 10:20 PM
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The lobe's peak is then (briefly) a perfect radius concentric and equal to the base circle plus lobe height


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Re: Roller cams and max open degree's [Re: polyspheric] #3005408
01/14/22 10:39 PM
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Originally Posted by polyspheric
The lobe's peak is then (briefly) a perfect radius concentric and equal to the base circle plus lobe height

Yup...and plugging in a little math here could literally convert the length of that perfect radius and it's proportion to the size of the roller lifter's roller wheel diameter to crankshaft degrees duration. Effectively at the very peak (nose) of the lobe you have a phase where the roller wheel begins traversing that radius and eventually "comes around" to the other side of the nose, while all along the lobe nose hasn't really moved away all that far.

I think this is the "hang" time you're seeing. Math should prove out this perception and for my purposes I literally took a measurement of the lobe lift every 5 deg and as you can tell that "hang" time is there.

Disclaimer: that math I referenced above is a bit beyond my feeble know-how as it took me a couple of hours to build a spreadsheet calculation to show and compare the piston bore movement per each crank deg rotation of a stock 3.58" vs stroker 4" crank. Interesting results though, especially as you try to compare that to the lobe open and closing events and try to understand how the combustion pressure dissipates on the piston's downward push on the power stroke. (sorry, tangent thought right there...)

Re: Roller cams and max open degree's [Re: Diplomat360] #3005410
01/14/22 10:48 PM
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No problem, my lifters are BAM solids and i assume .750 wheel, but not positive on that, will have to check.

Re: Roller cams and max open degree's [Re: mopar dave] #3005429
01/15/22 12:14 AM
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Originally Posted by mopar dave
I'm sure it's not flat on the nose, but i have never noticed this before with any other cam i had. May not be flat, but pretty close to it as the indicator stays right on 0 for atleast 10* as i stated. Just curious if this was normal and i never noticed before. Thanks


That is just what you are seeing, it isn't what is actually happening. The tappet is moving up and then back down but you can't see it because the tools you are using aren't good enough. If you used a yard stick to measure bearing clearance you would say the clearance is zero because you wouldn't be able to see it with the yard stick.

Re: Roller cams and max open degree's [Re: AndyF] #3005466
01/15/22 08:42 AM
01/15/22 08:42 AM
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I understand Andy, but the tools i'm using are the same tools i used to install about a dozen or so other cams and i have not ever notice the indicator stall on the nose of the cam for this long of a duration of time. Not a big deal, just thought i might have a better ground lobe than what was on my other roller cams in the past. Adding duration on the nose of the cam, allowing the valve to stay open a bit longer at max lift would be cool or am i wrong in thinking that.

Re: Roller cams and max open degree's [Re: mopar dave] #3005472
01/15/22 09:13 AM
01/15/22 09:13 AM
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Rough math ...

cam bore of approx. 2.5" (I think I'm overestimating big time here)
assume max lobe size so radius from cam center to tip of lobe = 1.25"
pi x R squared = 5" dia.
5" / 360 degrees = .014" per degree
cam turns at 1/2 crank speed so 10 crank degrees = 5 cam degrees
5 x .014 = .070"

I don't think you would see much movement on the dial indicator for less than .070" of rotation at max lift - particularly on a roller cam.

Re: Roller cams and max open degree's [Re: Stanton] #3005481
01/15/22 09:36 AM
01/15/22 09:36 AM
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Ok, so this is normal for a roller cam then. I'm good with that, just never paid attention to this in the past. Thanks

Re: Roller cams and max open degree's [Re: Stanton] #3005486
01/15/22 09:43 AM
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Originally Posted by Stanton
Rough math ...

cam bore of approx. 2.5" (I think I'm overestimating big time here)
assume max lobe size so radius from cam center to tip of lobe = 1.25"
pi x R squared = 5" dia.
5" / 360 degrees = .014" per degree
cam turns at 1/2 crank speed so 10 crank degrees = 5 cam degrees
5 x .014 = .070"

I don't think you would see much movement on the dial indicator for less than .070" of rotation at max lift - particularly on a roller cam.

Nice, that's what I'm talking about! stirthepot

To get the real nose measurement you could take the cam lobe base circle diameter, divide by 2 and add the lobe lift, this would give actual R value I think. Once plugged into the remainder of the calculation you provided that would give you a precise measurement of the distance covered at the nose for each crank degree rotation.

Re: Roller cams and max open degree's [Re: mopar dave] #3005493
01/15/22 09:58 AM
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Originally Posted by mopar dave
I understand Andy, but the tools i'm using are the same tools i used to install about a dozen or so other cams and i have not ever notice the indicator stall on the nose of the cam for this long of a duration of time. Not a big deal, just thought i might have a better ground lobe than what was on my other roller cams in the past. Adding duration on the nose of the cam, allowing the valve to stay open a bit longer at max lift would be cool or am i wrong in thinking that.


You aren't wrong about the duration. I always measure the duration at 050 and then at 200 and sometimes at even higher lift. The more aggressive lobes will have more duration at higher lift. Measure the duration at 300 or 400 sometimes and compare that between lobes and you'll see. Of course the downside is that lobes with lots of duration at higher lifts are usually much harder on the valvetrain since everything is just getting beat to heck.

Re: Roller cams and max open degree's [Re: Diplomat360] #3005501
01/15/22 10:26 AM
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Yeah, not gonna pull the cam back out to measure, but the lobe lift is .4300/.4300. Got lucky and didn't have to re degree this cam as i think it's close enough to 104* with a 103* actual install.

Re: Roller cams and max open degree's [Re: AndyF] #3005503
01/15/22 10:28 AM
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I will measure at those other points as you suggested. Would be nice to know. Thanks Andy.

Re: Roller cams and max open degree's [Re: mopar dave] #3005517
01/15/22 11:14 AM
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Quote
To get the real nose measurement you could take the cam lobe base circle diameter, divide by 2 and add the lobe lift, this would give actual R value I think. Once plugged into the remainder of the calculation you provided that would give you a precise measurement of the distance covered at the nose for each crank degree rotation.


You could do all that but I overestimated so much on the numbers that the end result would be significantly less than .070. Just not worth the hassle IMHO. i.e. if you have a 1" dia. base circle and a .750 lift cam (1/2" lobe height) you end up with .043" travel for 5 degrees of cam travel. You won't see any movement on a dial indicator at max lift. And the smaller the cam the less travel.

Re: Roller cams and max open degree's [Re: Stanton] #3005525
01/15/22 11:32 AM
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No problem. I have a half dozen dial indicators, i'll try my best one and see if there is any difference, in fact, i will see if i can find a new digital one and compare. Thanks guys.
What is a good brand name digital to look for? A bunch over on ebay from $26-$299.

Last edited by mopar dave; 01/15/22 11:38 AM.
Re: Roller cams and max open degree's [Re: mopar dave] #3005529
01/15/22 11:44 AM
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Originally Posted by mopar dave
No problem. I have a half dozen dial indicators, i'll try my best one and see if there is any difference, in fact, i will see if i can find a new digital one and compare. Thanks guys.
What is a good brand name digital to look for? A bunch over on ebay from $26-$299.


Mahr or Mitutoyo

Re: Roller cams and max open degree's [Re: mopar dave] #3005574
01/15/22 01:22 PM
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For some of the lobe contour, roller diameter is very important, but of course not at all for max lift and base circle.
If the roller diameter changes, the effects are not continuous or linear.
Harley-Davidson, running out of money 50 years ago, used Chet Herbert V8 roller lobe profiles in their Sportster-based race engine. Dick O'Brien (the boss) said "I know there are weird vibrations and loss of control, but it's all we could do for this season".
Reason: Herbert SBC .750" roller, H-D .855" roller.


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