Roller Cam and Lifters

[John]

http://wps.com/AMC/Navarro-turbo-motor/
http://wps.com/AMC/Navarro-Indy-motor/index.html
I have several more online references to Barney's build if you would like.
By the way, AMC advertised this as a reground factory camshaft and reports of the day claimed it running around 6000 RPM.
John

[SIXPAK]

Here are the pics of the cast roller cam, for reference approx 250-260 @.050 dur, .640 lift. Spring pressure was 160 on the seat 360 on the nose[open]

just an overall pic

exhaust #1 cyl closing side of ramp

lifter and #1 intake and exhaust

exhaust #4 and dist gear, shows original rough dia of cam,comparison to under cut of base circle

another view of #1 exhaust

The family heirloom


Body of cam beside basecircle of cam MUST be equal to or smaller than the basecircle of cam profile. You can see that most all lobes are off center from the wear pattern of the lifter. Since the roller lifter is wider than the width of the profile-and the contact area is off center- the roller lifter will collide with the body since it started at a larger dia than the base circle. Base circle is the part of the cam lobe that has no lift, or valve is closed.
Imagine an unground jeep cast cam core at any cam grinder. The nose is the point of max lift, to obtain higher lobe lift the base circle must get smaller since the nose is limited to the overall unground dia. The more lift you run, the smaller the base circle, the weaker the cam is. Just FYI

[1bolt]

vibration dampening to the camshaft. I think that might also raise the critical failure point rpm? Going to play with this some on down the road. I have thought too much about this ever since I read Lee"s thread about camshaft failure and the modifications to prevent this.
John

Yeah I think the fuel pump being on the cam has to play a significant damping role, I thought the same thing when I saw it. A mini harmonic dampener in front of the timing sprocket could maybe mitigate the harmonic. Wouldn't be too hard to make something either...

Like you were saying loading on the cam plays a roll just like muting a string with your palm or picking the string harder or softer. Question is, does the lower amount of stress from a roller lifter actually make for worse harmonic dampening? Or does it help by reducing the factors that lead to the harmonic in the first place?

In other words if flat tappet lifters are "plucking" the string, are roller lifters plucking harder or softer? We know the roller itself will put more localized force on the lobe face because the point of contact is tiny between two convex surfaces. Not spread out as much, like a flat lifter face on the lobe... spring pressures are lighter though...

There's food for thought here, but Cams are not my area of expertise I will be the first to admit.

[John]

1bolt, I am sure you would change the vibration characteristics by going to a roller cam set up, I would suspect the raising in RPM of the critical harmonic. If you look at the lobe profile in SIXPAK's photo's you will see gentler ramps, smoother transitions, than those on a flat tappet camshaft. Loading forces will be more constant, less harsh transitions as the valve train changes direction.
John

[John]

Flash, if you haven't read this link, that I posted elsewhere, it will help see some of my reasoning.
http://www.hesco.us/forum/forum_posts.a ... 00+rpm+fix
John

[1bolt]

I always see copper on roller cams, why is that?

[Flash]

Flash, if you haven't read this link, that I posted elsewhere, it will help see some of my reasoning.
http://www.hesco.us/forum/forum_posts.a ... 00+rpm+fix
John

Yeah thats the one i read.......but I went and read it again...........sure wish i could read between the lines better.

Don't know if this has any thing do with the problem(according to hesco, no) but when Joe at roto faze, and i was talked about the price of the blank, the Dist gear had to be sent out to be cut........and the AMC/chry 6 has an odd ball depth and an angle cut into the gear, then most other cams or manufacturers.


As far as whether the roller cam strokes the guitar string harder or softer.........I would thing that it would be a harder stroke

Flash

[Flash]

SIXPACK, since you have played with a roller cam and a flat tappet cams on the same vehicle........which would take more spring pressure, for the same lift? Flat tappet or Roller??????


Flash.

[John]

"Yeah thats the one i read.......but I went and read it again...........sure wish i could read between the lines better"
Yeah there was a recall on my clairvoyance, something about faulty vision.................
Well let's hope we get a chance to find out with certainty.
John

[SIXPAK]

Rollers are by nature are more aggressive so they run more pressure. Standard flat tappet lifters don't like much over 175 on the seat. I am running the same seat pressure on my flat tappet that I did on my roller.150 lbs. The roller lobe profile I ran was not that radical.

[tirod]

Thanks for the pics. It looks like the rollers somehow were incompatible with the cam lobes, obviously. They are smaller than the width of the lobe, but a flat tappet has even less contact area because of the crowned surface and cam lobe taper. Perhaps the cam itself wasn't nitrided after grinding, or low ZDDP oil was used?

Most of those who would spring for a roller still won't turn them over 5200 rpm. Harmonics are not that significant in stock engine applications where the market dollars are, so I don't see a point in it other than over 6k rpms, which is what the Hesco link discusses - there are lots of other issues then. Rollers do allow a faster profile to open the valve sooner and get more power at lower rpm, which is why I think Detroit went that way, to overcome soft emissions tuning.

Roller cams are a good source of hp when the factory underwrites the research to do it - which in our case was a "year too late' for the 4.0's life cycle. Good ol' American hotrodding "enginuity" will just have to overcome this slight delay.

[1bolt]

I think the point of contact on a roller and lobe are much smaller than a flat tappet and lobe. Two convex surfaces touching versus one flat and one convex. Of course both are relatively small but in terms of distributing the bearing load at the point of contact (especially if it has higher spring pressure) the roller cam lobe must be harder than a flat tappet lobe. Also remember that the flat tappet is riding on a thin film of ZDDP that keeps the underlying iron from wearing too fast. The roller is metal on metal, and for all intents and purposes pushing most of the oil out of the way, like a snow plow.

I admit though I'm no expert, I'm still unsure why roller cams are usually copper coated. Copper is not hard.

The grooves in sixpac's cam are a result of him running a roller tappet on a normal cam. Even for a short time (as he said only a few high RPM runs) the roller grooved into the soft flat tappet cam material.

At least thats how I read it.

[John]

"I admit though I'm no expert, I'm still unsure why roller cams are usually copper coated. Copper is not hard.

The grooves in sixpac's cam are a result of him running a roller tappet on a normal cam. Even for a short time (as he said only a few high RPM runs) the roller grooved into the soft flat tappet cam material."

The copper you see on a steel, roller camshaft is a resist plated on then ground off where they want the cam to be hard. Under the copper flashing, it is still fairly malleable, but tough. The lobe surfaces get hardened to about to about RC40-45 for about.030 deep where the steel is exposed. The cams are also much more likely to warp during hardening without this process.

And yes the barrel shaped (big ass radius) roller bearing running on a iron cam was part of the above failure. A roller cam puts more stress loading than our iron camshafts are designed for, Without reheat treating or nitriding, the cam, some of the hardened surface may have been too thin.
John

[Flash]

"I admit though I'm no expert, I'm still unsure why roller cams are usually copper coated. Copper is not hard.

The grooves in sixpac's cam are a result of him running a roller tappet on a normal cam. Even for a short time (as he said only a few high RPM runs) the roller grooved into the soft flat tappet cam material."

The copper you see on a steel, roller camshaft is a resist plated on then ground off where they want the cam to be hard. Under the copper flashing, it is still fairly malleable, but tough. The lobe surfaces get hardened to about to about RC40-45 for about.030 deep where the steel is exposed. The cams are also much more likely to warp during hardening without this process.

And yes the barrel shaped (big ass radius) roller bearing running on a iron cam was part of the above failure. A roller cam puts more stress loading than our iron camshafts are designed for, Without reheat treating or nitriding, the cam, some of the hardened surface may have been too thin.
John

So why don't they just heat treat our flat tappet cam and then there wouldn't be a problem with cams going flat??????????

or would it just cause the lifter to ware faster do metal differences???????

And what if they were to heat treat or Nitriding SIXPAK cam, would it have last it longer????????

Flash

[John]

So why don't they just heat treat our flat tappet cam and then there wouldn't be a problem with cams going flat??????????

or would it just cause the lifter to ware faster do metal differences???????

And what if they were to heat treat or Nitriding SIXPAK cam, would it have last it longer????????

Flash

The proferal grey iron is flame hardened for "heat treat", then parco lubrite treated. Of course we will have to keep it properly lubricated. We do really high shear wear to oil films at low rpm's and worst at start up. Zinc/phosphorous and high shear oil film strength.
The SIXPACK camshaft failure seems due to several things, he pointed out collision points with the base circle, less than choice parent material to run on a 52-55 RC roller, modification of surface hardening depth with unknown to me, follow up surface treatment. I think the life could have been extended, but the outcome would have eventually occurred.
John