Camshafts and Compression

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Bewy said:
Wrong,
They do act the same. What differs is the percentage difference. Bob Bolles, the Technical Editor of Circle Track magazine did an in-depth article on Crane's quick lift rockers & rockers in general.
[1] Crane does not believe in the minimum width pattern on the valve tip at the mid lift point. Many others do not believe in it either. See the first pic. Crane goes for the rocker tip centered at full lift, which minimises side loading of the valve stem/valve guide.
[2] The next two pics show how the ratio changes during operation. To claim that the ratio remains constant as a bold statement in post #205 is just wrong & can only be interpreted in one way: the words say it all.
[3] And the prod side of the rocker? Everybody worries about the roller centered on the valve tip but in Post #178 you can see the valve lift changed by 0.029" by changing prods.

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Crane not believing in something doesn’t make it true. That whole article you posted sounds like a sales brochure trying to sell rocker arms. Never once do they talk about the most important aspect of proper valve side geometry, the fulcrum location. And that comes from someone who runs Crane rockers, Me.
 
TT5.9mag said:
Crane not believing in something doesn’t make it true. That whole article you posted sounds like a sales brochure trying to sell rocker arms. Never once do they talk about the most important aspect of proper valve side geometry, the fulcrum location. And that comes from someone who runs Crane rockers, Me.
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I'm not saying who is right or wrong. Mike seems to consider the load comes only from the spring. So higher lift equals more load.
I don't know how much the inertial forces are compared to the load from the spring but they must count for something.
These forces would come at the moment of highest acceleration (at or near valve opening) and are influenced by the mass of the objects being accelerated (weight of the valve assembly). Conversely, as the valve reaches the point on the cam lobe where the acceleration starts to slow, the inertia of the already acccelerated mass starts to take load away from the rocker tip negating spring pressure felt at the tip. This counter force would be greatest at or near the end of opening and the begining of closing or the point that the spring pressure is at it's highest. Again I don't know the quantity of that force (dependent on the mass and acceleration rate) and how it compares to the force from spring pressure.
But what if for arguments sake it is more than the spring pressure at the seat. This could mean that the load on the rocker is higher at beginning lift and lower at max lift.
 
92b said:
I'm not saying who is right or wrong. Mike seems to consider the load comes only from the spring. So higher lift equals more load.
I don't know how much the inertial forces are compared to the load from the spring but they must count for something.
These forces would come at the moment of highest acceleration (at or near valve opening) and are influenced by the mass of the objects being accelerated (weight of the valve assembly). Conversely, as the valve reaches the point on the cam lobe where the acceleration starts to slow, the inertia of the already acccelerated mass starts to take load away from the rocker tip negating spring pressure felt at the tip. This counter force would be greatest at or near the end of opening and the begining of closing or the point that the spring pressure is at it's highest. Again I don't know the quantity of that force (dependent on the mass and acceleration rate) and how it compares to the force from spring pressure.
But what if for arguments sake it is more than the spring pressure at the seat. This could mean that the load on the rocker is higher at beginning lift and lower at max lift.
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It’s possible the valve speed can outrun the spring off the seat.

Another reason to detest flat tappet cams.

Once you hit the 180 on the seat and (going from my memory) 485 over the nose you are at the limit. And that’s pushing it. I put 200 runs on that cam before it had to come out and go back to Isky to get touched up.

At that point you are now going to Ti intakes, the lightest retainers you can and maybe you can’t control the valve.

Hydraulic rollers are the same. You can only put so much load on the hydraulics and the .750 wheel will only tolerate 7500 rpm on a Chrysler sized cam bearing. If you can get it that tight.

If you have to slow down valve speed to control the valve train it’s time to go to a roller lifter with a minimum .800 wheel.

Valve speed is king until you can’t control it.

Getting the valve off the seat and the hell out of the way at low lifts is the best thing you can do.
 
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92b said:
I'm not saying who is right or wrong. Mike seems to consider the load comes only from the spring. So higher lift equals more load.
I don't know how much the inertial forces are compared to the load from the spring but they must count for something.
These forces would come at the moment of highest acceleration (at or near valve opening) and are influenced by the mass of the objects being accelerated (weight of the valve assembly). Conversely, as the valve reaches the point on the cam lobe where the acceleration starts to slow, the inertia of the already acccelerated mass starts to take load away from the rocker tip negating spring pressure felt at the tip. This counter force would be greatest at or near the end of opening and the begining of closing or the point that the spring pressure is at it's highest. Again I don't know the quantity of that force (dependent on the mass and acceleration rate) and how it compares to the force from spring pressure.
But what if for arguments sake it is more than the spring pressure at the seat. This could mean that the load on the rocker is higher at beginning lift and lower at max lift.
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I tend to think similarly and have never sat down to calculate the loads at different points but I think it’s really unnecessary (unless you’re building valvetrain components). What Mike is doing (and saying) is place the shaft at a location that eliminates sweep on the valve side, puts it on the pushrod side, run the longest pushrod you can to make the sweep minimal and then the loads (and ratio change, effective length) at the valve, as well as acceleration/deceleration of the valve at different lift points will all be as good as they can be and work in your favor.
 
Pic of the checking pushrod set to 7.600’’. Adjuster protrusion is at 0.310’’.

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Newbomb Turk said:
PERFECT. If that’s at zero lash it’s even better!
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That setting is with 0.012’’lash on the Rhoads v-max lifter. Looks good to me.

A 0.020’’ setting would bring the adjuster protrusion back to around 0.300’’.
 
I got the intake manifold back from being ceramic coated, very nice. Pushrods on the other hand, no one’s getting back to me…:rolleyes:

Tried a comp test, no intake on and stone cold. Only did three pumps, don’t want to burn the starter bushes. ( done that in the past ) - 155-160psi. Looking good.

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Valman said:
I got the intake manifold back from being ceramic coated, very nice. Pushrods on the other hand, no one’s getting back to me…:rolleyes:

Tried a comp test, no intake on and stone cold. Only did three pumps, don’t want to burn the starter bushes. ( done that in the past ) - 155-160psi. Looking good.

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So from 210 - 220 psi to 155 - 160 psi as a result setting the lifters properly. Looks like in your case hydraulic lifter bleed down can significantly affect cranking compression.
 
Valman said:
I got the intake manifold back from being ceramic coated, very nice. Pushrods on the other hand, no one’s getting back to me…:rolleyes:

Tried a comp test, no intake on and stone cold. Only did three pumps, don’t want to burn the starter bushes. ( done that in the past ) - 155-160psi. Looking good.

View attachment 1716372154
Click to expand...
Should re-title this thread from " Camshafts and compression " to " hydraulic camshafts and cranking compression" lol
 
It’s not surprising to me that with a fast bleed type lifter(which the Rhodes are), that there would be a noticeable difference in cranking pressure between having the lifter preload set near the top of the plunger travel vs set near the bottom of the travel.

I can see where it could be a difference of 15-20* of valve seat timing at the valve, at low engine speeds.
 
You're supposed to spin the engine until the cranking pressure stops rising. That normally takes 5 or 6 turns. If it hurts the starter, then the starter was already a piece of chit to begin with. Any good starter will take everything you can throw at it.
 
PRH said:
I can see where it could be a difference of 15-20* of valve seat timing at the valve, at low engine speeds.
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Where I have the lifters set, it should reduce the duration by about 7-8 degrees. - 0.012’’ off the bottom of the lifter.
 
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