Frank/Rebop

Bristol, In ( by Elkhart) 

Dennis.  You’re right in that I’m correcting for the dynamic and not the static.  When doing a camshaft, I have a pair of upper supports that holds the camshaft in place on the trunions for the initial weight correction.  The camshaft itself is cradled on the end journals.  Once the majority of imbalance is taken out, then the clamps are no longer needed.  The clamps are only there for safety reasons as a camshaft can get up to speed in a hurry due to its lack of mass and in extreme cases, can try to leave the machine.  Imbalance at the drive end (front) is compensated for by drilling the timing gear at its outer edge.  The imbalance at the rear of the camshaft is taken care of by using Tungsten on the light side or opposite where the electronics says it’s heavy.

And you’re also right about the straigtness of the shaft.  It’s just another factor in which to take into account.

As far as the amount of unbalance in the camshafts, it varies depending upon the engine family.  The Fe camshafts are increasingly more out of balance at the rear of the camshafts versus the Y-Block which exhibits more imbalance at the drive end of the camshaft.  This is without fuel pump lobes in place.  Looking at my notes for the EMC Y engine I did last year, the initial amount of imbalance at the drive end of the camshaft with the fuel pump lobe and no counterweight was off the scale (in excess of 1 oz-in) while installing the counterweight reduced this imbalance to .44 oz-in.  I don’t recall the amount of imbalance for just the cam and the drive gear on the front but do remember it being slightly less than the values obtained using both the fuel pump lobe and the counterweight.  These numbers were obtained using an Isky camshaft ground on 107° lobe centers as a point of reference.  I normally don’t keep notes on this kind of thing but in this instance I documented just about everything that was done on this particular engine in the hopes that I’d be doing an indepth article on it.  I also converted all these numbers from the g-mm numbers that I typically use in lieu of oz-in values.

I have a theory on why the FE cams are worse at the back and the Y worse at the front.  Theoretically, every lobe on the cam should have a twin, 180 degrees apart, somewhere on the shaft, which would render it statically balanced, assuming a perfect casting.  With the Y firing #1 right after #2, the lobes for those cylinders would be bunched up on the front of the shaft.  With the FE firing #7 and #8 in succession, those lobes would be bunched at that end.  Therefore, they are dynamically out of balance.  Am I all wet?

By the way, in all my 50+ years of working on cars, I have NEVER thought about camshaft imbalance.  Never too old to learn.

John

John - "The Hoosier Hurricane"

    The amount of imbalance was 1 oz Static, what actual force (pick an RPM) does that equate to? I'm assuming for the discussion it's all in one place because I don't want to add a rocking couple to the answer.

Frank/Rebop

Bristol, In ( by Elkhart) 

Ditto on your last two sentences!

Paul,

Boonville,MO

Another factor is center of mass against the geometric center.  Typically on crankshafts, the center of mass is found using a balancing machine that determines the centers for the machining process.  This is done to minimize the amount of material removal required to balance a finished crankshaft.  Perhaps the imbalance of a camshaft is influenced that the machining centers are not the same as the center of mass.

The amount of centrifugal force generated at 3,000 rpm (camshaft speed) with 1 oz in of unbalance is 15.98 lbs.  With .44 oz-in of unbalance it is 7.03 lbs.  At crankshaft speed, 6,000 rpm, 1 oz-in = 63.93 lbs. and .44 = 28.23 lbs.  Incidently, the allowable amount of crankshaft imbalance is .5 oz-in, even on the 427 crank.  Obviously speed is a large factor on the amount of centrifugal force generated.  The fact the camshaft runs at half speed, centrifugal force is 1/4 and could be considered negligible.   

There is an SAE paper, #540266, from Jan 1954 on "The New Ford V8 Engine".  It is mainly an engineering comparison between the flathead and the 239 OHV.  Re the fuel pump eccentric, it states: 

"The fuel pump is driven by the hard chrome-plated eccentric which is bolted to the front of the camshaft sprocket.  As an indication of the extra attention that was paid to small details, you will note that the eccentric is provided with a counterbalance." 

I would assume the counterbalance was designed to neutralize the offset mass of the fuel pump eccentric.

OK, it's time to put my calculator away. 

Regards,

Dennis

          That makes the point, to me at least, that the total forces generated by camshaft imbalance are insignificant compared to the forces generated by the springs and inertia of the valve train. 15 or 16 lbs is not much. Now an aftermarket, Chinese, cam blank that is 6 or 8 oz out of balance would be a different issue.  

     Do you remember the factory tolerance on this?m 

Frank/Rebop

Bristol, In ( by Elkhart) 

Nope.  You’re right.  When you lay the camshafts down and look at the lobe layout, you can see where the firing orders that are together are also bunched up on the camshaft without any other lobes in close proximity in which to counteract the offset in weight.  In theory, each quadrant of the camshaft is expected to have equally spaced lobes for a perfectly balanced camshaft which in turn would require no modifications in the balancing department.  But mainly because of the firing orders, the camshafts will be out of balance by different amounts end for end.

As Dennis brings up, any balancing is a compromise simply because of the other forces that are in play around it.  Good analogy on the tappets as there are some forces taking place there that are beyond what just a plain balance will compensate for.

But blue sky thinking says if the camshaft rpm is cut in half again (runs at ¼ speed of the crankshaft) and the lobes are then made two sided or dual lobed, then the balance situation is solved.  This goes back to what you were saying in that each lobe should have a twin.  But with this camshaft, the distributor is also running at half speed as well as the oil pump.  Oil pump is solved with either a dry sump system or a high volume pump.  For the ignition, I’m thinking several different options with one being a distributor cap with sixteen contacts for the rotor and these sixteen contacts simply pair off to the outside of the cap for the individual wires going to the plugs.  Another being a belt driven distributor at the front of the engine that's either being reduced in speed because it’s being driven off of the crank or increased in speed because it’s being driven off of the camshaft through the timing cover.

Short term, I believe I’ll just keep balancing the camshafts with the hardware that’s being used bolted to the front of them.  But on other engineering that got dropped in 1956, what about the drip oiler or tray for the timing chain that bolted on the block just above the lower crank gear.  I would suspect this was also a cost cutting measure.  I put one of these back on the EMC engine just for the heck of it as it just made good sense to put some extra oil back on the chain.  I even made a transfer template so I could put the required ¼”X20 threaded hole back in the exact spot on any post 1956 block without a lot of measuring.

Lorena, Texas (South of Waco)

Do you remember the Shaller 1/4 speed camshafts of the '60s?  Dual lobe, as you depicted.  They were roller tappet cams, and gear driven.  They had to do that to keep the size of the top gear small enough to fit inside the timing cover.  Included was a distributor with a built in planetary gear setup to speed it and the oil pump back up to 1/2 crankshaft speed.  They were short-lived, either to expensive to produce competitively, or were never accepted by the rodders.

John

John - "The Hoosier Hurricane"