[4zpeed]

Originally Posted by PAUL K

Not sure how to explain that chamfer is a bad idea. I once waisted time trying to explain millions of vehicles make it to work everyday with pressed in rocker studs and it went over the tops of a lot of folks heads, but I'll give it a try.

Flat tappet camshaft ramps are designed for a
specific diameter lifter. The opening side has to
open as fast as possible but is limited to the
diameter of the lifter. If a lifter has a large chamfer
you no longer have the same diameter lifter at the
liifter face than the cam is designed for. With a
larger chamfer the lifter jumps part (or all) of
opening ramp and wants to dig into to the part of
the ramp that raises the lifter, rather than glide over
it. This starts to chip away at the lobe itself and the
lifter wants to dig into the lobe rather rotate and
follow the lobe. On the closing side of the lobe the
lifter will drop off of the lobe and skip the trailing
end the closing ramp.

Other than floating out or unless mismatched or extensive wear, taking into consideration the profile of the lifter and cam, this shouldn't be a issue that far out should it?


Frank

[dataway]

Originally Posted by 4zpeed

Other than floating out or unless mismatched or extensive wear, taking into consideration the profile of the lifter and cam, this shouldn't be a issue that far out should it?

Frank

That's kinda what I was thinking. Do we know that the lifter diameter WITH the chamfer taken into consideration is not within the design limits of the lobe/lifter geometry?

Worn OEM lifters used with OEM cam often show no wear indications that would show the lifter contacting the lobe in the area where the chamfer is. I certainly understand Paul's explanation, but wouldn't it depend on if that area of the lifter face is actually in contact with the lobe? The smaller the base circle of the lobe, and the less steep the ramp, the less chance the lobe would ever encounter the very edge of the lifter face.

I can certainly see how on more radical profiles the diameter of the lifter face would be a major consideration, the larger the better.

[PAUL K]

Originally Posted by 4zpeed

Other than floating out or unless mismatched or extensive wear, taking into consideration the profile of the lifter and cam, this shouldn't be a issue that far out should it?


Frank

Originally Posted by dataway

That's kinda what I was thinking.I can certainly see how on more radical profiles the diameter of the lifter face would be a major consideration, the larger the better.

The main concern with using a lifter with a large chamfer is it will dig into the lobe (because it misses the opening ramp) and gouge into the lobe while not wanting to rotate. If you can some how manage to survive that situation you need to control the lifter as it closes because it's going to miss all or part of the closing ramp and want to

bounce off the seat.

A lifter shows most wear towards the center of the face because that is where it sees the most spring
pressure and has the least amount of contact.

A lazy lobe creates a worse case scenario because it has a smaller opening ramp.

I probably have thirty sets of lifters on the shelf here by various manufacturers. Most of them have no chamfer at all on the edge of the lifters. Some have a very small chamfer. There are none with a large chamfer.

[4zpeed]

So weak springs or higher RPM's and bouncing with higher spring rate? I can visualize what your saying I'm just trying to confirm the cause and appreciate the insight.


Frank

[PAUL K]

Originally Posted by 4zpeed

So weak springs or higher RPM's and bouncing with higher spring rate? I can visualize what your saying I'm just trying to confirm the cause and appreciate the insight.


Frank

Frank I'm not sure I'm following you.... If your asking for tips on how to avoid issues when you have a lifter with a large chamfer on them my best advice would be to throw them in the dumpster. Plan B
would be to contact the manufacturer of the lifter, then contact the manufacturer of the cam. If they are both one in the same and they say it will be fine and you trust them.... Run'em ..... IMHO your odds of getting a full life out of them are about as good as your favorite team winning the Super Bowl tomorrow if it's not the Chiefs or 49ers.

[4zpeed]

I feel you're narrowing my odds, shame they both can't lose. My lifters don't have that big of a chamfer. I guess what you're saying is, the chamfer is the problem, the entire bottom of the lifter is engaged, so actually the lifter is rolling off the lobe losing contact, good enough. Always trying to understand what I don't can be a lengthy process although worthwhile.


Frank

[PAUL K]

Originally Posted by 4zpeed

I feel you're narrowing my odds, shame they both can't lose. My lifters don't have that big of a chamfer. I guess what you're saying is, the chamfer is the problem, the entire bottom of the lifter is engaged, so actually the lifter is rolling off the lobe losing contact, good enough. Always trying to understand what I don't can be a lengthy process although worthwhile.


Frank

I agree ..... Maybe it'll be a zero-zero tie.... Yes the chamfer on the lifter is the issue. The larger the chamfer the worse the situation.

[Shiny]

Paul - Thank you for taking the time to explain.

It makes a LOT more sense now. Here's a couple snapshots I took off a Youtube video that illustrates how the cam profile can cause the contact point on the lifter face to cover a large radius. I'm sure this cam lobe is make-believe, but I think it illustrates at least some of what can go wrong.

Originally Posted by dataway

That's kinda what I was thinking. Do we know that the lifter diameter WITH the chamfer taken into consideration is not within the design limits of the lobe/lifter geometry?

Worn OEM lifters used with OEM cam often show no wear indications that would show the lifter contacting the lobe in the area where the chamfer is. I certainly understand Paul's explanation, but wouldn't it depend on if that area of the lifter face is actually in contact with the lobe? The smaller the base circle of the lobe, and the less steep the ramp, the less chance the lobe would ever encounter the very edge of the lifter face.

I can certainly see how on more radical profiles the diameter of the lifter face would be a major consideration, the larger the better.

Originally Posted by 4zpeed

I feel you're narrowing my odds, shame they both can't lose. My lifters don't have that big of a chamfer. I guess what you're saying is, the chamfer is the problem, the entire bottom of the lifter is engaged, so actually the lifter is rolling off the lobe losing contact, good enough. Always trying to understand what I don't can be a lengthy process although worthwhile.


Frank

After having the risk explained, I conclude this is another situation that cannot be "generalized". Clearly, the risk for the contact zone reaching the chamfer is totally dependent on the cam geometry and lifter width.

I can only assume the factory geometries had more than enough design margin to tolerate larger chamfers. To Paul's point, put that same lifter on a different cam lobe and the margin may evaporate.

A comparison of "maximum contact radius" on the lifter for commercial cam lobes would enable some "informed" decisions... anyone ever publish this ?????

.................................................. ........

Warning noted and visual seed planted! To me, this is similar to adjusting a pushrod length by keeping the contact path centered on the valve stem face.

The people like Paul and all of you that share your thoughts and knowledge are why this forum is like The Force for me.

Mike

[VCho455]

Personally I feel the chamfer issue is overblown. GM designed them to work with GM camshafts. They most certainly knew what they were doing. Once you step outside that realm you're on your own hence why you take the time to verify your parts by doing what is known as "Blueprinting".

Personally I believe that time spent with your choice of cam and lifter installed with some gear marking grease would answer the question if the lifter chamfer was touching the lobe.

My guess is that GM had its own reason(s) for adding the chamfer as GM never does something that adds cost without recouping that cost somehow. Maybe GM had problems with nicks on the edges from being dropped during assembly or shiping. Maybe GM decided assembly time was reduced when the lifter had a chamfer. This is one of those never to be known answers.

[4zpeed]

Well I thought it was a great topic for discussion, I'm sure there's folks out there that's never considered it. Many actually source OEM lifters with quality at the forefront of their thoughts, possibly to their detriment. Could be a issue with trying to use OEM lifters and aftermarket Cams. To get the right answer you must ask the right question.

Many Thanks Paul! I took some notes for future reference...




Frank

[PAUL K]

Originally Posted by VCho455

Personally I feel the chamfer issue is overblown. GM designed them to work with GM camshafts. They most certainly knew what they were doing. Once you step outside that realm you're on your own hence why you take the time to verify your parts by doing what is known as "Blueprinting"

Personally I believe that time spent with your choice of cam and lifter installed with some gear marking grease would answer the question if the lifter chamfer was touching the lobe.

My guess is that GM had its own reason(s) for
adding the chamfer as GM never does something that adds cost without recouping that cost somehow. Maybe GM had problems with nicks on the edges from being dropped during assembly or shiping. Maybe GM decided assembly time was
reduced when the lifter had a chamfer. This is one of those never to be known answers.

While you are certainly entitled to your opinion, an excessively large chamfer is a major concern unless one is looking to practice changing camshaft.

The chamfer on the GM lifter posted earlier is not good. If you compare it to the other GM lifter it's noticeably bigger. GM had an issue with cams going flat in the late 70's early 80's. That chamfer may have exposed the reason. I'm sure Pontiac did not intentially design their cams to work with a large chamfer lifter. If they did, they had millions of defective lifters that missed receiving a "large" chamfer.

[dataway]

I was looking through the 68 service manual and noticed all the lifters they show in their photos have the "cap" on them.

The set of 70's era NOS GM lifters I have do not have that cap ... so, sometime between 68 and the 70's evidently their lifter design changed, perhaps not for the better in my case. Or perhaps they just reused photos from previous years manuals.

Lots of info to process on this subject.

[P@blo]

The hard faced or capped lifter is also called iron chilled. I posted a link from Truman Fields aka Hard-timess.

From Isky website:
"Isky Chilled Iron Solid lifters are compatible with our hard face overlay series cams only (not for cast billet type cams). Hardened by the chill-plate method which produces ideal surface grain structure, they are the only flat tappets that will survive in the grueling environment of today's funny car, fuel-dragster and competition engines."

https://forums.maxperformanceinc.com...t=Iron+chilled