Experience With "Balanced Cams?"

[SchmidtMotorWorks]

I didn't know what else could do it. Changing the cam made the problem disappear on each of the motors.

Were the cams straight? Were journal fit and finish OK? Drive tension too high?

[Jerry ARNOLD]

I have balanced my camshafts for some time now,and when you spin it up you will see why it out of balance.
You can see the heavy side has the lobes favoring that side.
lobe centers and design change move the lobes around.
If your using a 55 or 60 mm core, we just stood the cam on end and drilled into the bearing dia.
We had one cam that was 20 grams out on each end.
Even though the cam only spins 1/2 engine rpm, would you want something in a race engine 20 grams out?
I don't!

[J.C.]

What is the typical cost of having this procedure done? Is there special equipment that is needed for a cam balance job?

[BRENT FAY]

I didn't know what else could do it. Changing the cam made the problem disappear on each of the motors.

Were the cams straight? Were journal fit and finish OK? Drive tension too high?

Was the base circles the same? Was the lash adjusters changed? How about overall valve stem height inc. the lash caps changed? How was the pattern on the wear pad? Possible coil bind? Was the cam brgs. change to a different material? Any changes in oil to the cam brgs. There are others on this forum that can give you more insight to your problem, like Bill Jones. .....................Jerry, at that cam small radius how much material did you have to remove? How many holes? I'm having trouble imaging that? i would think heavy metal would have been better,along with some holes. I havent tried taking that much out at such a small correction radius. I dont know. I'll spin a B/B cam next week for my own giggles. Brent

[SchmidtMotorWorks]

Even though the cam only spins 1/2 engine rpm, would you want something in a race engine 20 grams out?
I don't!

It won't make any difference becuase the lifters move with the cam amking the moving assembly out of balance.

Balancing a cam is like balancing a crank without bob weights. Pointless.

[headman]

Any rotating part whose center of mass is not collinear with its center of rotation should be balanced.
If you ever watched an out of balance camshaft spin on a soft bearing machine, then compared the ampitude to a cam with a much lower oz/in of imbalance, it would be easy to understand the load the imbalance applies to the bearings. (Typically, crankshafts and camshafts alike, have a dynamic tendency to flip end over end, directly proportional to the oz/in of out of balance).


Inline crankshafts are balanced without bobweights.
We simply match the weights of the reciprocating components and match the weight of the rotating components that will be attached to the crank.
The crankshaft, balancer, flywheel, and so on are dynamically balanced without bobweights.

As far as the lifters are concerned, their reciprocating motion applies a force toward both the cam and pushrod. As with any other reciprocating part, reduce the mass, and reduce unwanted displacement (vibration).
Ideally, adjacent lifters would have opposing motion.

[Nwguy]

If the forces on a cam are sufficiently strong to break the cam towers on a 2.3 ford, I can't see where a relatively minor imbalance in the rotational balance is going to have any real effect. JMHO

[SchmidtMotorWorks]

Any rotating part whose center of mass is not collinear with its center of rotation should be balanced.

Nope, not always, it depends on the source of imbalance and how you plan to correct it.

If the object being balanced is flexible (like a cam is) and you are balancing it with modifications to the ends of the cam you have no reason to believe that you are reducing bearing loads and plenty of reason to believe that you are increasing them where you have added or removed metal to compensate for imbalance in a region of the body that will not be effected by change in balance to a timing gear.

I think the part of this that everyone is missing is that dynamic balancing of the entire body doesn't mean anything to the local balance of sections of the body. This is of critical importance when the body is flexible (as a cam is). The cam already bends more from loads from the lifter than it ever will from out of balance loads.

If you really wanted to do this right, you would have to cut the cam into pieces, balance those pieces then duplicate the changes on an intact cam.

I've done this on crankshafts until I figured out a way to determine the internal imbalance with other measurements.

[SchmidtMotorWorks]

Maybe this image will help explain.

Imagine you had a body where there was an imbalance caused by a eccentric like the green lobe. because the shaft is flexible, this would put loads mostly on bearings 2 and 3, a very little on 1 and 2.

You could "balance" the shaft by adding the red counterweights, but all you would accomplish is adding loads to bearings 1 and 2 and having little, if any, improvement to bearings 2 and 3 (in fact you are just as likely to make them worse).

Dynamic balancing does a lot less than most people think it does when you consider that the body is flexible.

[ChrisU]

HHHmmmmmmmmm didn't think about that one.

If the cam is twisting in the rear in the field, how can it hold a balance, after it's been balanced in what I would call a non-dymanic condition for lack of better terms...


???????????

[bobqzzi]

Any rotating part whose center of mass is not collinear with its center of rotation should be balanced.

Nope, not always, it depends on the source of imbalance and how you plan to correct it.

If the object being balanced is flexible (like a cam is) and you are balancing it with modifications to the ends of the cam you have no reason to believe that you are reducing bearing loads and plenty of reason to believe that you are increasing them where you have added or removed metal to compensate for imbalance in a region of the body that will not be effected by change in balance to a timing gear.

I think the part of this that everyone is missing is that dynamic balancing of the entire body doesn't mean anything to the local balance of sections of the body. This is of critical importance when the body is flexible (as a cam is). The cam already bends more from loads from the lifter than it ever will from out of balance loads.

If you really wanted to do this right, you would have to cut the cam into pieces, balance those pieces then duplicate the changes on an intact cam.

I've done this on crankshafts until I figured out a way to determine the internal imbalance with other measurements.

Nice explanation.
So, to balance a cam, you'd need to insert heavy metal on the heel opposite each lobe. Sounds like a niche industry for someone.

How is that bespoke V12 coming?

[MadBill]

I think there's merit to this argument, as illustrated by the preference shown by most high end race engine builders for locating counterweights close to the source of the imbalance. However, I don't see the situation as being all that different from that of an externally balanced crankshaft. It too is flexible (although how flexible relative to the forces in play is open to debate) and yet millions of engines are balanced this way, just as proposed for the cam situation.
The bobweight argument, as has been mentioned previously, is irrelevant since inline engines which don't use them for balancing also often locate counterweights (if they use them at all!) where convenient rather than disposed symmetrically at each crank throw.

[SchmidtMotorWorks]

However, I don't see the situation as being all that different from that of an externally balanced crankshaft. It too is flexible (although how flexible relative to the forces in play is open to debate) and yet millions of engines are balanced this way, just as proposed for the cam situation.

And the effect of external balancing on bearing loads is already known, an externally balanced engine has much higher bearing loads on the 1st and last journal, in fact the bearing loads can be reduced by removing the external balancing objects. Yes the vibration will be higher but the bearing loads will be lower.

To get a good understanding of the effect or lack of effect of dynamic balancing on a crankshaft you only have to look at where the wear is on the 2nd main journal, the wear is near the point opposite the angle between the rod pins for cylinders 3&4. This is because there isn't enough room in a block to make the CWs thick enough.

You can cut the 3rd and 4th CWs off the crank completely and compensate for it by adding weight to the first CW, does that mean that you have corrected the loads on the 2nd main? Of course not, it only keeps it from vibrating the entire engine. There was a time when it was popular to put center CWs on cranks that had similar orientation to the end CWs, some people mistakenly thought that because they were easy to balance that they must be better or bearing loads; the opposite is well know to be true now.

When balancing a high speed, high load part it is best to think of it being very flexible.

[machine shop tom]

You guys are tempting me to put a cam on the balancer ane start fooling with it!!



tom

[BRENT FAY]

How about a round 2"x24" solid steel or cast iron shaft spinnining at 5000 rpms supported at 5 places would it be needed to be balanced? Think turbine engines (there is someone on this forum that has dealt with these,from AZ ? if i remember)granted were not spinnining them at those at turbine speeds. Now if you add some lumps,lobes or bumps to this shaft would it be needed to balanced? ..........I would think so...... Jon's graphics shows insight. ................but with a shaft that is balanced you have eliminated one source of imbalance/ harmonics?............with the rest of harmonics coming from the rest of the valve train above the cam.......... So how about a hollow cam that was splined to the center shaft that was also splined to have elastomer rubber splines to dampen harmonics. Just food for thought for you wolves! Brent