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camshaft balancing


MONZTER

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I think 1 fast Z did some work on this idea.

 

Anyways I am not a crankshaft guy to know what is considered "In" balance, but the "out of" balance they found in the article seems to be alot even though it is a cam and not a crank.

 

In this example the camshaft is running at 4,000 rpm (half of the 8,000 rpm crankshaft speed). The left side of the camshaft is generating a force of 34.3 pounds and the right side is 47.6 pounds, and both are ­hammering at 66+ times per second. This may be enough to cause the camshaft to ­become excited and set up a vibration pattern that will motivate the roller lifter to bounce on the surface of the lobe. Ultimately, the valve will respond to all of this activity and most likely this will cause the valve to follow a path that is not equal to the designed cam lobe profile. This may also cause the valve spring to become excited, generating an inconsistent travel pattern ­commonly known as valve spring float.

 

Some of the castings on our z cams are really rough and makes me wonder.

 

I wonder if a crank shaft guy could balance a camshaft?

 

MonZter

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I hate to be a curmudgeon, but to me, that article contained a whole lot of not much, and my BS meter was beginning to move off its peg.

 

I guess it would have helped if I'd read Part 2 of the article.

 

I am still suspicious though, because they seem only to have thrown a cam on a balancing machine and found it to be out of balance, and the rest is just theory. There are a lot of "may cause valve float," or "may cause excitation", "May do X" comments with no data to back it up.

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A couple points. A cam has a very small PMOI, so that effect of being out of balance wouldn't be nearly as strong as a crank or a wheel or something larger. The cam is captured and that means that even if it is out of balance it's not going to start a big oscillation like a wheel would because it can't move outside of the bearings. So it seems that the limit of the effect would be confined to the clearance in the bearings, and perhaps some bending in the cam as it rotates. A cam is very long, so if you balanced it by adding weights to the gear, I think you'd have what could be compared to a static wheel balance and there might still be a dynamic balance that is out. IME it's been pretty obvious when valve float happens. It is possible that there might be some less dramatic version of valve float going on because of cam vibrations, but if it was a real problem I suspect you would be able to see it on a dyno graph. If you can't, then is the problem worth worrying about? I don't doubt that balancing the cam has the potential to make the engine run smoother, and I wouldn't rule out the possibly of cam balance have a small effect on valve timing events, but I do question the ROI of going through the trouble to fix it. I don't think it will hurt anything more than your pocketbook to do it though...

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I think 1 Fast Z was being facetious...

 

But anybody with a balancing machine should be able to set up just about anything that is round and can be spun, and get a vector and imbalance reading on the machine.

 

From there you can correct for it.

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Rifle drilled Titanium cams.

 

Titanium Tubing with shrunk on rollercam-lobes and shrunk-on journal bearing surfaces...just like large industrial engines have been using for years!

 

Maybe an aluminum/titanium lobe drilled for lightness and with a hardfaced skin coating or surface treatment.

 

Then you have the ultimate in low-weight for best acceleration as well!

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