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Experience With "Balanced Cams?"

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Experience With "Balanced Cams?"

Postby Cobra » Tue Feb 28, 2006 10:39 am

Balanced cams are used by racers with strict cam restrictions to increase RPM limit by about 500 RPM. Anyone have results to share?
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Postby machine shop tom » Tue Feb 28, 2006 10:57 am

I read that article too (latest Engine Rebuilder mag). I was wondering where the weight is removed to balance the cam.

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Postby MadBill » Tue Feb 28, 2006 10:58 am

I just finished e-mailing my shop re balance results on a custom ground SBC CC roller I left with him a week or so ago!
Will post findings, hopefully before the weekend.
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Postby MadBill » Tue Feb 28, 2006 11:06 am

Our plan is to take any weight off the sprocket up front and hope we can drill the rear journal as needed. Plan 'B' is to also add heavy metal in the rear journal. Plan 'C' is drilling & tapping the journal to attach a bob weight and hoping we can install the Welch plug backwards to get enough clearance...
My machinist/guru has a new top of the line CWT balancer that will calculate the forces created by the imbalance at any speed. This engine will see a max of just under 4,500 cam RPM, but I'll get results up to 5,000.
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Postby Dave Koehler » Tue Feb 28, 2006 12:56 pm

I have been balancing rollers for a few years now, mostly Chebbies. There is a substantial improvement that can be made.

On the BB at least, the pump cam can be removed or a wing thing made. At the rear you may not be able to achieve nirvana but do the best you can with what you have to work with. I use 3/8 and 7/16 HM to get it the best I can. Working around the oil relief holes is the troublesome part.
Any reduction of imbalance is a big improvement.

The funny thing is that I wrote an article on this issue showing what I found originally and how I went about the mods. I originally gave it to DRO back in their early days but no one thought anyone cared about this. After all, it's such a little thing, right? :wink:
I will see if he still has it on file, update it and get him to print it. Maybe something there will be of use.

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Postby Robert Kane » Tue Feb 28, 2006 7:52 pm

I wonder if anyone here has had a chance to spintron a balanced vs. unbalanced camshaft and how much "noise' was eliminated with the balanced cam?
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Postby Team Owner » Tue Feb 28, 2006 9:00 pm

I believe that someone told me that there is no difference between a balanced camshaft and a unbalanced camshaft.

Someone also told me that they attach weights to the cam to balance it .

You really cannot remove material from the camshaft.

Spintron tests are not going to show anything below 8000 rpm's due to the fact that the cam spins on bearing journals when it is in the motor.
There isn't anyplace for the camshaft to go. If it wobbled when it spins - it would take out the bearing and that would be it.

Now if you were talking Formula 1 Motors that spin in the high RPM range - say 18,000 rpms and Idle at 4,000 rpms = you could see a dramatic difference. Not a Single Cam Small Block Chevrolet.

You would be better off to spend your money on Brass Bumper Bolts or some new Muffler Bearings.
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Postby MadBill » Tue Feb 28, 2006 9:37 pm

Team Owner wrote:...the cam spins on bearing journals when it is in the motor.
There isn't anyplace for the camshaft to go. If it wobbled when it spins - it would take out the bearing and that would be it.
....


But isn't that statement a junior version of the case for balancing a crankshaft? Maybe balancing reduces cam bearing loading and friction?
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Postby BRENT FAY » Tue Feb 28, 2006 9:54 pm

The march 2006 issue of Circle Track has an article on balancing camshafts by Mike Jones of Jones Cam Designs. He has been doing it since the 80'sfor Indy cars and now Nascar (has seen 3 hp increase) They balance the cam at 400 rpm. Bolt a counter weight to the front and what you can see in the pic it looks like the machine a counterweight into the rear. On back to back test with same grind cam the balanced one,at max lift it didnt loft the valve as much and cut down on valve bounce. 4/7 swap takes a different counterweight. Balancing adds $100 to cost of cam. If I could fiquire out how to scan this article and post it I would. Brent
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Postby ChrisU » Tue Feb 28, 2006 10:46 pm

I would think a situation like an unbalance in a needle roller bearing could cause noise......?? There is clearance and there is room for the cam to move around... relatively speaking. Noise is created by high frequency movement, not some dramatic wobble....??????

I'd think on a max effort deal it would be wise to balance the cam??
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Postby headman » Tue Feb 28, 2006 10:50 pm

the older Sewart Warner and Bear "soft bearing" balancers actually showed ampitude from out of balance as the part rotates.

All you would need, is to see an FE ford cam, (or other cam with an encentric), jumping up and down to realize the need for balancing.

Sure, balancing the cam should be a considerable ways down the list of priorities.

I balanced the cam for my shop truck nearly 20 years ago, and everytime I haul off the trash, I have complete confidence the engine is well balanced. :wink:
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Postby SchmidtMotorWorks » Wed Mar 01, 2006 3:41 am

But isn't that statement a junior version of the case for balancing a crankshaft? Maybe balancing reduces cam bearing loading and friction?


I think that is the point, balancing a V8 crankshaft has no significant influence on bearing loads unless you make all the CWs exactly the same.

I spun-up a few cams to see how far they were out, if I remember correctly it was rather small amount. But balancing the cam alone is pointless, you would have to balance the entire valvtrain dynamically to know that you were changing anything let alone in the right direction.
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Postby ChrisU » Wed Mar 01, 2006 7:59 am

well I'm going to stick a 55mm camshaft on a balancer Friday and I'll report how out of balance it is....
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Postby MadBill » Wed Mar 01, 2006 10:51 am

Seems like if we're prepared to fixate on balancing our crank assemblies to ½ or ¼ of a gram instead of say 5 or 10, we should pay at least some attention to cam balance... :-k
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Postby Cobra » Wed Mar 01, 2006 11:14 am

I contacted Mike Jones of Jones Cam Designs and this is what he said: "Balancing a cam is not much different then balancing a crank.
We balance the cam along with the gear and anything else that is bolted
to the cam.
There was a article on our "Cam-Wave" cam balancing system in the March
issue of Circle Track Magizine.
We have done a lot of testing, both on the spin-tron, and on the dyno.
By balancing the cams, we are reducing the harmonics in the
valve-train.
In some applications, the valvetrain system dampens the harmonics
better then other systems.
Sometimes we see small power gains, sometimes we see the engine gain as
much as 500rpm before we hit valve float.
As far as your application, I'd have to know more about what you're
working with, and what it needs to do.

If you have any more questions, please give me a call."

Thanks,
Mike Jones (704)489-2449
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