Discussion in 'General Ranchero Help' started by john777, Aug 18, 2016.
There's plausibility in what you're saying, but sure sounds like a secondary effect to me.
Smooth running oiled gears suffer significantly less wear than ones subjected to vibration. If you work around machines for a while you will find that as vibration goes up, reliability goes down.
The first time you try to turn over (by hand) an engine with a fairly radical solid roller cam with only two lifters in it you will see exactly what Ribald is talking about. The cam will actually "snap" back and forth from the load of the springs. Now imagine it with 16 lifters.
Yes, I've cranked enough cams to know what is being referred to... which is why i consider it plausible. Velocity will alter the dynamics of what's happening at the timing chain. As velocity increases, the forces that would tend to accelerate the cam (the downhill side of a lobe) will be significantly reduced. There can be these "snapping" motions, but when you rev up to x,000 RPM's, the torque will become positive and dampen out a significant portion of the vibration.
This idea that vibration due to high spring pressure vs slack in a timing chain is the cause of a distributor gear wearing out would seem to indicate that a gear driven cam would have significant reduction in the "slack"/vibration issue. Is this the case? I've never heard that running a gear driven cam will save your distributor gear....but certainly, I haven't heard it all. The same vibration would occur on said cam gear drive and, purportedly, cause an accelerated wear condition.
I also have never heard of a gear drive reducing this issue. I imagine that the opposite is true as a chain would act as a spring, and a flywheel, and damp the activity. I think that is why belt drives improve timing accuracy.
As to RPM increase resolving it, the inertia of all the parts increases equally as velocity rises, so the actual force against the cam increases also. So RPM only increases the frequency of the vibration, not it's amplitude. In fact, as the forces rise the cam will start twisting and untwisting adding another element to the mix.
The solution is a front driven oil pump to remove load from the gear, of better yet, a front driven oil pump and distributor less ignition. That is why you see production car companies going in that direction with their performance vehicles.
That's why I refuse to put gear drives in engines I build - the direct gear-to-gear contact has shown(in the past) a detrimental effect on valve train parts, increased spring breakage, rocker issues, and yes, distributor issues.
Inertial effects only apply during velocity changes (such as when a lifter reverses direction). This is why a flywheel makes for a good way to store energy...it takes very little torque to keep it spinning, once it reaches whatever velocity you want it to run.
In the case of springs and lifters, these items will produce less force on the trailing end of the cam lobe as RPM's increase (due to inertial effects. Think valve float...zero or near zero force on trailing end of cam lobe in this situation). This will tend to reduce the level of positive torque on the cam. As speed increases, torque on the cam will also increase. The proportion of positive torque due to the trailing end of cam lobe will become less and less as speed increases. How much less, I don't know...would have to perform the calcs to see the result. The first order effects on increased torque-load on cam vs RPM will be due to inertial effects on the leading side of cam lobe and friction.
We agree that velocity will increase the frequency of vibration, but will most certainly impact the amplitude and the overall shape of the vibration wave form. ...and, as you stated, cam wind-up will also have an effect. The magnitude of wind-up will be a function of cam's torsional stiffness vs load from valvetrain.
Is this effect you describe primarily an effect due to spring pressure, or do lift and lobe profile play into it significantly as well? Are there guidelines for pressure/lift/ramp rate to avoid this situation? I did some limited interweb research and didn't come up with anything.
Interesting info Phil. It would be an interesting simulation to run and observe the effects of different drive systems on valvetrain components.
Inertia plays a significant role as RPMs increase as the load on the cam increases during the lift phase even though the pushing effect is diminished during the return phase. That increased load is the source of cam twisting and whip. Even without the push, the load/unload cycle of the lift portion will induce stretching and associated spring action in the cam drive chain. (chain as in group of components)
There is no doubt that the nature and waveform of the vibration becomes more complicated as RPMs increase all evidence points to the energy component of the vibration increasing with RPM. Don't forget that energy goes up with a rise in frequency even if amplitude is the same.
That the forces rise with RPM becomes painfully obvious at exactly the RPM where a part says "I'm outta here!".
Unfortunately, it was not a simulation, it was real life. A long time customer wanted me to install a gear drive at freshen-up time, which I did. This is on a drag SBC that logs approx. 200-250 passes per year. We freshen said engine every 2 seasons. Same brand of springs, lifters, and retainers, no cam (or other) changes. The result was 3 broken valve springs (the rest checked down in pressure) after only 63 passes. Fresh set of springs/retainers and a return to a chain, and things went back to normal.
Possible bad batch of springs? Maybe, but PAC has probably the best process in the industry, I could believe 1, but not a set. This is a solid roller 7,400 RPM piece.
The breakage combined lowered pressure across the board sounds more like spring bind than anything else.
Nope, same combo for 7 years, same spring height, same rocker ratio, installed at the same pressure (245 lbs.), heck, even the same part number spring.
I once received a brand new lunati cam. It was not what the box described it as. Had I not verified it could have been a significant issue.
AFR had a period where heads got shipped out with faulty studs. I was lucky enough to get a pair of them. I won't even get into TCI.
Mistakes get made, there is no way around it.
Yup, just got a Crane cam last month - was supposed to be small base circle, even marked that way on the cam and card, but, no, it was standard size. It went back. And you are SO right about the AFR studs - the 3/8 studs were JUNK. After 2 broken ones (on 2 different sets of heads) I either order them with 7/16, or installed ARP when they came in.
Measure, check, then check again. Then fix .
The machinist looked at the motor and determined that there is not enough material in the motor to substantiate a bearing issue. After some other investigation determined that there was nothing out of the ordinary with the motor. HOWEVER he did determine that half of the flexplate bolts were extremely loose, which he thinks is what caused the knocking.
Note: the flexplate was powder coated around the area where the bolts went in and when the powder coating wore down under the stress, the bolts came free. We even had locktite on the bolts.... going to sand down the area of the flexplate to avoid this happening again.
For my insurance purposes to avoid several more ins and outs with the motor, the machinist is going to dyno the motor.
Hopefully all is going to be ok and there is not any damage to the engine and only my ego...
I'm going to leave the existing cam in the motor, but change the dizzy gear from a bronze one to a composite one:
Happy Thankgiving to all.
Something to be truly thankful for.
I'm not going to ask why it was powder coated. Just make sure none of that crap is on the other side where it mates with the crankshaft also. Powder coat is plastic and becomes rather soft at 200 degrees.
The flex plate was the problem. Powder Coating under some bolts and they worked loose causing the "bearing failure" sound.
Motor was on the dyno yesterday. Mild Street cam...
Peak HP: 552 @5200rpm
Torque: Flat curve all the way across
556 Ft lb @ 2500 rpm
Peak of 613 @ 4000
I went back and watched your videos...sounds sweet! Nice numbers on the engine, too. What are the cam specs and what heads are you running, if you don't mind my asking?
That should be enough to keep a prius from passing you!
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