Rocker Arm bearings theory
Launching!
Joined: Feb 2004
Posts: 233
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From: STL, MO
Now that I have the YT's though, I would use them over stock rockers if there was room in the budget.
TECH Fanatic
Joined: Jun 2011
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From: Katy, TX
Has anyone had wear problems that you can trace directly to the comp cams bearing upgrade? Very interested to hear about it.
One thing that I feel is being overlooked the the rocker isn't loose as the valve opens. Once the pushrod starts moving the rocker to open the valve, there is upward force on the rocker bearings from the pushrod's movement. The friction between the rocker tip and valve would have to be so great that it would have enough sideways force to overcome the upward force applied by the pushrod. One would think that the rocker tip would scrub the valve before it moves that whole rocker body sideways...
Yes, I thought of that. As the title says, this is a theory of mine and needs to be proven with real measurement of the rocker arm, the valve tip scrub and how it changes with the Comp Cam trunion upgrade kit.
Another thing to think about is where where the actual fulcrum point ends up since there is slop in the bearings. I would believe the biggest gap between the little rollers will be at the very top or at the 12 o'clock position looking at the end of the bearing. So the true fulcrum is not exactly centered on the stock trunnion if the bearings were a tight fit.
After setting up my Yella Terra's on my .631" / .644" lift cam, I was able to get nice scrub pattern centered on the valve tip. And there is very little movement in the trunnion bearings.
The factory rockers when in your hand have more side to side slop then up and down. To explain if u bolt it in place without a pushrod u can rock the body in the way it was never intended. Kinda like a boat swaying on its short side. I think the force from the pushrod driving it up keeps it from doing this while its acting on it. The rocker has a radius on its tip to prevent as much side loading as possible there will be some scrub. I recently did the comp trunion upgrade and there is 0 side to side and up and down slop. There is some shaft end play on all some more then others. This depends on the rocker bodies. If u end up with one that has 0 shaft end play chances r it will not pivot smoothly. U will need to back the bearings out very little to make it pivot smooth. I think the comp upgrade is worth it.
Launching!
Joined: Jul 2010
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Iv been looking at Yella terra roller rockers for my .617/.624 lift comp Lsl cam with Lunati .660 dual valve springs and have been told by two places recently to run the factory rockers over the yt's. Would the factory rockers with trunion upgrade be better?
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TECH Regular
Joined: Jul 2011
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The Comp Cam trunnion & bearing kit will only reduce the axial play of the rocker arm if you set the bearings up right (ie, press them into the rockers enough to reduce the trunnion's axial play).
When I installed the Comp Cams trunnion/bearing kit in my LS6, I set the axial play to 0.010~0.012" on every rocker arm. This meant I had to tweak some of the bearings after the initial press in to achieve this clearance range. Stock axial play was around 0.020~0.022". The valve train "rattle" (what little there was/is) did not go away with the tighter rocker arm bearing setup.
Last edited by ZeeOSix; Feb 8, 2012 at 01:10 AM.
TECH Regular
Joined: Jul 2011
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The Comp Cams trunnion & bearing kit shouldn't change any geometry between the rocker arm and valve stem tip. If anything, the kit should reduce the amount of axial side play in the rocker arm, and keep the tip of the rocker more centered in the axial direction over the valve stem tip.
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From: Katy, TX
Staging Lane
Joined: Oct 2005
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First post My first post is not going to be a good one lol.
The roller tip on roller rockers dose not roll but slides across the valve stem.
Once the engine is running and everything is covered in oil it slides across the tip.
And givin that the factory rocker has a much bigger radius compared to a roller tip it probly slides across with less friction.
One good reason for the factory rockers having side to side play is that it allows the tip of the rocker to sit flat on the valve stem, not unlike factory pivit ball style rockers gm used for decades.
That being said the factory rockers were only designed for a given rpm and load rating (spring presure and cam lobe acceleration).
Once you excede these ratings go aftermarket ( prefer shaft rockers for various reasons)
I am by no means an expert and these are just my opions and findings.
But how does the saying go This aint my first rodeo.
The roller tip on roller rockers dose not roll but slides across the valve stem.
Once the engine is running and everything is covered in oil it slides across the tip.
And givin that the factory rocker has a much bigger radius compared to a roller tip it probly slides across with less friction.
One good reason for the factory rockers having side to side play is that it allows the tip of the rocker to sit flat on the valve stem, not unlike factory pivit ball style rockers gm used for decades.
That being said the factory rockers were only designed for a given rpm and load rating (spring presure and cam lobe acceleration).
Once you excede these ratings go aftermarket ( prefer shaft rockers for various reasons)
I am by no means an expert and these are just my opions and findings.
But how does the saying go This aint my first rodeo.
Last edited by john stewart; Feb 9, 2012 at 11:13 AM.
When I had the stock rocker arms running on my LS2 with a cam with .631" / .644" lift, the rocker tip wipe went over the edge of the valve and wore a nice groove in the rocker arm. With the Yella Terras, the wipe pattern is stays right in the center.
I've about 10 Comp Cam trunnion swaps so I know the stock bearing are sloppy in all directions. I don't disagree with the roller tip sliding over the valve tip but that is not the point of this thread.
But I want to bring this thread back on point to discuss if the stock bearings were designed on purpose to be sloppy to allow the rocker to move thus keep the rocker tip closer to the center of the valve tip on a STOCK lift cam.
I've about 10 Comp Cam trunnion swaps so I know the stock bearing are sloppy in all directions. I don't disagree with the roller tip sliding over the valve tip but that is not the point of this thread.
But I want to bring this thread back on point to discuss if the stock bearings were designed on purpose to be sloppy to allow the rocker to move thus keep the rocker tip closer to the center of the valve tip on a STOCK lift cam.
if they were designed like that for that reason they also lose effective lift as the pivot point rises slightly. That wipe on the big lift is interesting im at .600 but havent installed everything yet to see the geometry. I will be pretty soon though.
My theory says as the cam lifts, because the stock bearings are loose, the pivot point shifts slightly thus allowing the rocker tip to stay centered on the valve tip effectively reducing valve guide wear. Of course, it depends on the angle of the pushrod.
This geometry works well with a stock cam but not with a high lift/fast ramp cam. Its exceeds the stock design limits and you hear lots of noise as the bearings rattle around.
Then when the Comp Cam trunnion bearing kit is installed, it eliminates the rattling and noise so you think its better and in a way it is. But with a high lift cam, the geometry is worse than it would be with the stock bearing on stock rocker arms. This is why (I've heard) Trick Flow does not like the Comp Cam trunnion kit.
As for the roller rocker tips, you have to visualize the contact point of the roller tip as the valve moves up and down. Because of the smaller radius of the roller tip compared to the stock rocker tip, the contact point remains more centered on the valve tip than the stock rocker arm. Hard to explain here but if you visualize how it, you will understand. Yes, I've read about how the roller tip does not really roll but not sure if that's the case or really makes a difference.
Last edited by Mez; Feb 11, 2012 at 01:29 PM.
I have a theory why GM's stock rocker arm bearings are so loose and rattle at idle.
If you have removed the stock rocker arms, you will notice there is a lot of movement of the bearings. Some say sloppy. Like me, I thought it was terrible quality or cheap design.
Here is my theory. GM designed them to be like this intentionally. As the cam lifts the pushrod which in turn pushes on the rocker arms, the rocker tip pushes down on the valve tip. The least about of wear on the valve guides is when the rocker arm tip stays centered on the valve tip through it whole cycle. Below is a picture of the rocker arm to valve tip geometry that assumes the bearings are tight:
From this illustration, the rocker arm tip does not go straight up and down centered on the valve tip. It goes through an arc so you would assume it would scrubs across the tip of the valve. Now, since the bearings are sloppy, my theory is the tip of the rocker arm actually remains centered on the valve tip. Pretty ingenious design if you ask me.
But the OEM rocker arm bearings still have design issues. First, because of the sloppy bearings, they rattle quite a bit at idle. At higher RPM, the exhaust noise drowns them out. Second, the roller bearings are not caged which is fine for stock lift cams. However, if a high lift cam is installed with higher pressure springs, it creates more stress on the bearings and the tiny rollers may escape and find there way down to the oil pan. Also, the bearing races and caps are stamped sheet metal, which are not as precise as components that are machined.
Comp Cam came out a few years ago with a very high quality caged bearing replacement kit. Great, they eliminated the slop so the valve train rattle at idle is gone. The caps and races are machined and snap rings are used to keep the bearings positioned correctly in the rocker arm. Its a great bearing. Unfortunately, this eliminates the design feature I outlined above so the rocker arm scrubs across the valve tip which results in increased side load on the valve which results in accelerated valve guide wear. Its not too extreme with stock cams lift, but as cam lift increases, the problem is much worse.
One aftermarket head manufacturer (Trick Flow) apparently recognized this problem and require full roller rocker arms such as the Yella Terra. Because Yella Terras have a roller tip, the valve to rocker geometry is much improved. See the illustration below:
Conclusion: In my opinion, with a stock cam, stick with the OEM bearings if they are in good condition and just accept the rattle at idle. With an aftermarket cam with lift below .550" the stock rocker arm and OEM bearings are still OK. Over .550" lift, consider upgrading to a full roller rocker arm. For really big lift cams, look at shaft mounted full roller rockers such as Jesel or T&D. These are expensive, so they are not for everyone.
If you have removed the stock rocker arms, you will notice there is a lot of movement of the bearings. Some say sloppy. Like me, I thought it was terrible quality or cheap design.
Here is my theory. GM designed them to be like this intentionally. As the cam lifts the pushrod which in turn pushes on the rocker arms, the rocker tip pushes down on the valve tip. The least about of wear on the valve guides is when the rocker arm tip stays centered on the valve tip through it whole cycle. Below is a picture of the rocker arm to valve tip geometry that assumes the bearings are tight:
From this illustration, the rocker arm tip does not go straight up and down centered on the valve tip. It goes through an arc so you would assume it would scrubs across the tip of the valve. Now, since the bearings are sloppy, my theory is the tip of the rocker arm actually remains centered on the valve tip. Pretty ingenious design if you ask me.
But the OEM rocker arm bearings still have design issues. First, because of the sloppy bearings, they rattle quite a bit at idle. At higher RPM, the exhaust noise drowns them out. Second, the roller bearings are not caged which is fine for stock lift cams. However, if a high lift cam is installed with higher pressure springs, it creates more stress on the bearings and the tiny rollers may escape and find there way down to the oil pan. Also, the bearing races and caps are stamped sheet metal, which are not as precise as components that are machined.
Comp Cam came out a few years ago with a very high quality caged bearing replacement kit. Great, they eliminated the slop so the valve train rattle at idle is gone. The caps and races are machined and snap rings are used to keep the bearings positioned correctly in the rocker arm. Its a great bearing. Unfortunately, this eliminates the design feature I outlined above so the rocker arm scrubs across the valve tip which results in increased side load on the valve which results in accelerated valve guide wear. Its not too extreme with stock cams lift, but as cam lift increases, the problem is much worse.
One aftermarket head manufacturer (Trick Flow) apparently recognized this problem and require full roller rocker arms such as the Yella Terra. Because Yella Terras have a roller tip, the valve to rocker geometry is much improved. See the illustration below:
Conclusion: In my opinion, with a stock cam, stick with the OEM bearings if they are in good condition and just accept the rattle at idle. With an aftermarket cam with lift below .550" the stock rocker arm and OEM bearings are still OK. Over .550" lift, consider upgrading to a full roller rocker arm. For really big lift cams, look at shaft mounted full roller rockers such as Jesel or T&D. These are expensive, so they are not for everyone.
A. OEM configuration - If the two set of bearings on both ends of the trunion are sloppy and causing noise during operation, wouldn't that suggest the tip of the rocker is (exaggerated) moving/chattering inconsistently over the tip of the valve stem? Wouldn't this inconsistent movement of the rocker tip transulated to adverse wear (elongation in ID due to wanton movement/pressure) in the valve stem seal?
B. OEM configuration - Retro-fitted with Trunion upgrade, with the rest of the valve trains untouched - Given the inherent precision nature of the caged bearings supporting the trunion and the resulted decrease in valve train noise, would't that be the indication that the scrub between rocker/valve stem is consistent, excessive/undesirable movement is lessen, resulted in less friction, wear and ID of valve stem guide has less of the elongation effect?
So if the forgoing are true, than wouldn't it be better in oem trim to make the upgrade for the benefits of eliminating the inferior cage less bearing, improve/consistent contact, cutting down noise and friction?
11 Second Club
Joined: Nov 2005
Posts: 606
Likes: 1
From: NY
Hi Mez, couple of questions regarding oem set up:
A. OEM configuration - If the two set of bearings on both ends of the trunion are sloppy and causing noise during operation, wouldn't that suggest the tip of the rocker is (exaggerated) moving/chattering inconsistently over the tip of the valve stem? Wouldn't this inconsistent movement of the rocker tip transulated to adverse wear (elongation in ID due to wanton movement/pressure) in the valve stem seal?
B. OEM configuration - Retro-fitted with Trunion upgrade, with the rest of the valve trains untouched - Given the inherent precision nature of the caged bearings supporting the trunion and the resulted decrease in valve train noise, would't that be the indication that the scrub between rocker/valve stem is consistent, excessive/undesirable movement is lessen, resulted in less friction, wear and ID of valve stem guide has less of the elongation effect?
So if the forgoing are true, than wouldn't it be better in oem trim to make the upgrade for the benefits of eliminating the inferior cage less bearing, improve/consistent contact, cutting down noise and friction?
A. OEM configuration - If the two set of bearings on both ends of the trunion are sloppy and causing noise during operation, wouldn't that suggest the tip of the rocker is (exaggerated) moving/chattering inconsistently over the tip of the valve stem? Wouldn't this inconsistent movement of the rocker tip transulated to adverse wear (elongation in ID due to wanton movement/pressure) in the valve stem seal?
B. OEM configuration - Retro-fitted with Trunion upgrade, with the rest of the valve trains untouched - Given the inherent precision nature of the caged bearings supporting the trunion and the resulted decrease in valve train noise, would't that be the indication that the scrub between rocker/valve stem is consistent, excessive/undesirable movement is lessen, resulted in less friction, wear and ID of valve stem guide has less of the elongation effect?
So if the forgoing are true, than wouldn't it be better in oem trim to make the upgrade for the benefits of eliminating the inferior cage less bearing, improve/consistent contact, cutting down noise and friction?
Any responses? I am having the comp cam trunion upgrade done to my engine tomorrow (it's in the final assembly stage). It was recommended tome by my engine builder for the fact that at high rpm is where the stock bearings sometimes fail (more on race applications) but this is the last piece of the puzzle to have "every bell and whistle" figured what the hell? lol
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But here is my take FWIW, if you take the stock rockers apart, you will see that oem bearing actually have heat treated inner and outer race (CompCam bearing has only outer race and inner race is trunion shaft), bearing has sloppy axle fit between inner and outer race, outer race contact area on stock trunion shaft revealed uneven and small wear pattern on all 16 of my rocker trunion shafts. The noisy oem valve train at idle is the direct result of the poor and sloppy fitment of the complete assembly. To compound the poor fit, trunion shaft has no real captivation other than the shoulders within the press in needle bearing's outer race! So, in the case where either side bearing outer race press fit failed (unlike CompCam, their trunion shaft used two "C" clips for captivation), since there is no positive retention, then needle bearing will be everywhere!
Standard of precision bearing design stringent clearance necessitate for functional support and longevity! So, in simple term, trend of oem sloppy rocker bearing = sloppy fit = excessive noise = excessive friction = excessive heat = abnormal wear and all contribute to eventual failure with repeated high rpm demands!
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I have found after trunion upgrade, the previous "Sewing Machine" valve train noise at idle is all but gone! Now, you can only hear the fuel injection pulsating.
I hope this is helpful to you!