Is the load on solid roller lifters really the highest at idle???
Drifting
Joined: May 2001
Posts: 1,651
Likes: 13
From: Holly MI
Rotation is promoted by offsetting the contact patch from center. That is done to spread the wear over a larger area of the components.
Ken
Team Owner
Joined: Nov 2005
Posts: 28,232
Likes: 2,872
From: Beach & High Desert Southern California
You bring up some good points to add to the discussion. Nice contribution 
A few comments though. I said myself in my earlier post about the root cause failure analysis I did on solid roller lifter failures, that larger lifters would indeed improve on the situation we now have by reducing the psi stress on the lifters, thus extending their metal fatigue life. Though to make them large enough to get us out of the woods is probably impractical. In any case, we are in full agreement there.
As for the friction forces involved, there is a static coefficient of friction given as mu s, and a kinetic coefficient of friction given as mu k. Mu s for static, is used to calculate the friction force that is holding something in place without slipping. Mu k for kinetic, is used to calculate the friction force trying to resist the movement of something that actually IS slipping. Once something is slipping, it is slipping, so there is no further significant change in the mu k value. So, the friction force will not appreciably change any further. That being the case, I believe you overstated your concerns about the friction as it relates to engine rpm.
I also have to disagree with your specific concerns about side loading friction. In theory, what you wrote, may have some value. But the problem with a perfectly good theory, is that it can be ruined be a simple real world test. If this were truly a real problem, it would show up on the lifter bodies and the lifter bores in the form of wear and/or wear marks. And in the real world, your side loading concerns don't appear to be the case at all. When I did that root cause analysis on the failed lifters. I got failed lifters from 3 different BBC's. I disassembled them and very carefully made a thorough inspection of every part. Two sets of the failed lifter were Crower HIPPO's, and one set was an Isky Redzone needle type. All had failed axles and needles, while some also had failed roller OD's. What they had suffered was metal faigure failure in the form of spalling or flaking/pitting. And generally the lifter bodies didn't exhibit any significant wear marks or patterns that you'd see if side loading and inadequate lubrication were a meaningful problem. I said "generally" because the Isky Redzones did show excessive wear at their very bottom lands below the large oil band. Their design here has insuffiecient bearing area, so it wasn't surprising to see that in this location. But no other area on the Redzone bodies, and no areas on the Crower bodies showed side loading or lubrication issues. So, while it did make for interesting discussion, I don't believe we could gain much in terms of lifter life, by trying to do something special here. My findings indicated that the .842 lifters are simply too small for the operational loads they see. As such they are overloaded and their fatigue life is simply reduced to unacceptable levels. I swithched to the Isky EZX bushing type roller lifter to escape the needle/axle issue, but I'm not out of the woods with regard to roller OD concerns. Maybe we should all go to DOHC motors
A few comments though. I said myself in my earlier post about the root cause failure analysis I did on solid roller lifter failures, that larger lifters would indeed improve on the situation we now have by reducing the psi stress on the lifters, thus extending their metal fatigue life. Though to make them large enough to get us out of the woods is probably impractical. In any case, we are in full agreement there.
As for the friction forces involved, there is a static coefficient of friction given as mu s, and a kinetic coefficient of friction given as mu k. Mu s for static, is used to calculate the friction force that is holding something in place without slipping. Mu k for kinetic, is used to calculate the friction force trying to resist the movement of something that actually IS slipping. Once something is slipping, it is slipping, so there is no further significant change in the mu k value. So, the friction force will not appreciably change any further. That being the case, I believe you overstated your concerns about the friction as it relates to engine rpm.
I also have to disagree with your specific concerns about side loading friction. In theory, what you wrote, may have some value. But the problem with a perfectly good theory, is that it can be ruined be a simple real world test. If this were truly a real problem, it would show up on the lifter bodies and the lifter bores in the form of wear and/or wear marks. And in the real world, your side loading concerns don't appear to be the case at all. When I did that root cause analysis on the failed lifters. I got failed lifters from 3 different BBC's. I disassembled them and very carefully made a thorough inspection of every part. Two sets of the failed lifter were Crower HIPPO's, and one set was an Isky Redzone needle type. All had failed axles and needles, while some also had failed roller OD's. What they had suffered was metal faigure failure in the form of spalling or flaking/pitting. And generally the lifter bodies didn't exhibit any significant wear marks or patterns that you'd see if side loading and inadequate lubrication were a meaningful problem. I said "generally" because the Isky Redzones did show excessive wear at their very bottom lands below the large oil band. Their design here has insuffiecient bearing area, so it wasn't surprising to see that in this location. But no other area on the Redzone bodies, and no areas on the Crower bodies showed side loading or lubrication issues. So, while it did make for interesting discussion, I don't believe we could gain much in terms of lifter life, by trying to do something special here. My findings indicated that the .842 lifters are simply too small for the operational loads they see. As such they are overloaded and their fatigue life is simply reduced to unacceptable levels. I swithched to the Isky EZX bushing type roller lifter to escape the needle/axle issue, but I'm not out of the woods with regard to roller OD concerns. Maybe we should all go to DOHC motors
The side loads are real, a simple free body diagram of the lifter & roller assembly will reflect the moment applied on the roller end of the lifter assembly. The unknown is if the friction reaction to the side loads misalignment in the lifter bore is significant (?). Your failure inspection reflects no wear of the lifter or bore, so the side loads may not be an issue in the lifter bore, but side loads are an additive load on the roller & roller bearing. With a big block the misalignment of the pushrod angle may also play a combined factor in an additive friction reaction load placed on the roller bearings, but without looking at a sample of failures and identifying a lifter bore that experiences the most failures any answer is a SWAG.
Your comments on the inspection of the roller axle & needles reveals the design limitation of the roller bearing size compared to the required load carrying capacity. The problem is similar to the failure problem with high loads on misalignment universal joints running at low speeds (front axles in 4x4 competition, an application where the bushing style bearings have replaced needle bearings if the u-joints have the benefit of a frequent inspection and maintenance program). The EZX lifter design may be the best that can be accomplished (with a few material improvements to tune the product).
The surface fatigue identified on the roller reflects the roller design is just too small in diameter and narrow to resist the load. Do the larger diameter Chrysler roller lifters have similar problems? This comparison would tell us if the limit is the 0.842" lifter bore constraint.
A reliable DOHC 632 would be fun, but then everyone would have one.
Good Luck.
Racer
Joined: Oct 2006
Posts: 435
Likes: 18
From: Florida
BB69 please explain to me and everyone else how crowning a flat tappet cam and lifters makes the contact area larger? Maybe a picture would suffice, how two opposing curved surfaces have more contact than two flat surfaces.........
http://www.cranecams.com/images/down...PN1053516).jpg
I KNOW THAT THOSE ROLLERS LOOK VERY FLAT..........
http://www.cranecams.com/images/down...All%20PNs).jpg
I KNOW THAT THOSE LOBES LOOK VERY FLAT.........
http://www.cranecams.com/images/down...PN1053516).jpg
I KNOW THAT THOSE ROLLERS LOOK VERY FLAT..........
http://www.cranecams.com/images/down...All%20PNs).jpg
I KNOW THAT THOSE LOBES LOOK VERY FLAT.........
Last edited by tt 383; Oct 11, 2008 at 12:29 AM.
Melting Slicks
Joined: Mar 2002
Posts: 2,164
Likes: 7
From: Beringen
540rat, what kind of spring loads and lifts are you using ?
I have a small block with 220 on the seat and 500 over the nose. I also use a revkit wich adds another 100 over the nose.
The cam is pretty agressive with a may or intensity of 32°. Open duration at .050 is 246-256°. Lift is .63
I have a small block with 220 on the seat and 500 over the nose. I also use a revkit wich adds another 100 over the nose.
The cam is pretty agressive with a may or intensity of 32°. Open duration at .050 is 246-256°. Lift is .63
Drifting
Joined: May 2001
Posts: 1,651
Likes: 13
From: Holly MI
BB69 please explain to me and everyone else how crowning a flat tappet cam and lifters makes the contact area larger? Maybe a picture would suffice, how two opposing curved surfaces have more contact than two flat surfaces.........
http://www.cranecams.com/images/down...PN1053516).jpg
I KNOW THAT THOSE ROLLERS LOOK VERY FLAT..........
http://www.cranecams.com/images/down...All%20PNs).jpg
I KNOW THAT THOSE LOBES LOOK VERY FLAT.........
http://www.cranecams.com/images/down...PN1053516).jpg
I KNOW THAT THOSE ROLLERS LOOK VERY FLAT..........
http://www.cranecams.com/images/down...All%20PNs).jpg
I KNOW THAT THOSE LOBES LOOK VERY FLAT.........
The internal needles are crowned, as are the actual roller wheels. Flat tappet lifters are also crowned.
I searched all over for a picture, and couldn't find one. I would copy the page of the book, but that would surely violate some copywright laws.
EDIT: If you go to this link, it is a preview of one of Tedric's books. On page 23, he talks about crowning the rollers. On page 25, he has an illustration.
http://books.google.com/books?id=HrJ...esult#PPA23,M1
Last edited by bb69; Oct 11, 2008 at 08:29 AM.
Melting Slicks
Joined: Dec 2005
Posts: 2,441
Likes: 0
A flat tappet lifter body experiences minimal side loads, as the point of force from the cam & pushrod is always parallel to the lifter bore. The lifter body is pushed up and down, force applied at zero degrees to the bore, with minimal side load (only the very minimal sliding friction load of the smooth cam to flat lifter face).
The resulting forces the lifter will see do not originate from their centers and do in-fact experience side loading.
This is according to a manufactures explanation of cam grinding and break-in procedures, and if you look at a good flat tappet cam lobe pulled from an engine you'll see the wear pattern favors one side.
Last edited by shafrs3; Oct 11, 2008 at 10:26 AM.
Team Owner
Joined: Nov 2005
Posts: 28,232
Likes: 2,872
From: Beach & High Desert Southern California
The flat tappet cam is ground at a slight angle, a few degree off parallel from cam centerline, so that the edge of the lobe is contacting the edge of the lifter to facilitate lifter rotation.
The resulting forces the lifter will see do not originate from their centers and do in-fact experience side loading.
This is according to a manufactures explanation of cam grinding and break-in procedures, and if you look at a good flat tappet cam lobe pulled from an engine you'll see the wear pattern favors one side.
The resulting forces the lifter will see do not originate from their centers and do in-fact experience side loading.
This is according to a manufactures explanation of cam grinding and break-in procedures, and if you look at a good flat tappet cam lobe pulled from an engine you'll see the wear pattern favors one side.
The load direction of applied force (from the cam contact & pushrod) however is in-line with the lifter bore. The point of cam to lifter contact may not be centered on the lifter face, but the direction of force is always perpendicular to the point of contact (perpendicular to the lifter face, with the very slight convex face misalignment).
This point of contact force effect (force perpendicular to the contact point) highlights the difference between the forces on a roller lifter to the flat tappet. The force applied to a flat tappet is always perpendicular to the face & parallel to the lifter bore. The contact point with the roller on the cam is designed to be a few degrees off of flat everywhere but the base circle and lobe peak. The roller lifter will always have a vertical force component (in-line with the lifter bore, like the flat tappet) and an offset or angled force component (the designed-in contact angle that allows for a more aggressive intensity). The forces superimpose (add up) to increase the surface load on the contact point of the lifter to the cam (the roller will always see more surface load and fatigue load, even with the same rate & force from the springs).
I understand that many people believe a roller has more contact surface area than a flat tappet (it contacts the cam across the wide roller, not just the crowned point of the lifter face) but when you add the oil film between the two parts the flat tappet lifter face surface under hydraulic pressure of the oil film is equal (the common constraint is the cam lobe width).
I hope this helps.
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Melting Slicks
Joined: Dec 2005
Posts: 2,441
Likes: 0
The load direction of applied force (from the cam contact & pushrod) however is in-line with the lifter bore. The point of cam to lifter contact may not be centered on the lifter face, but the direction of force is always perpendicular to the point of contact (perpendicular to the lifter face, with the very slight convex face misalignment).
Yes it does, I see your point.
On a BBC the valves are splayed, so the top of the lifters are pushed off center to the bore, adding considerable side loading in this application, I would think. I failed to add this point in the first post.
Last edited by shafrs3; Oct 13, 2008 at 09:06 AM.
