Camshaft Balancing

I’ve always said, “If it spins, then it likely needs balancing”.  When going for that last bit of detail in blueprinting an engine, then camshaft balancing comes into play.  How much is it worth you ask? That’s difficult to say as I’ve simply not tested this scenario by itself but suffice to say, it sure can’t hurt.  The camshaft itself runs at half the speed of the crankshaft so any amount of centrifugal imbalance is already reduced to one fourth of the significance of any crankshaft imbalance.   And because the camshaft is somewhat isolated from the crankshaft by lieu of the timing chain, then transmitted harmonics will be minimal to or from the crankshaft.  But any imbalance at this point can still be an issue in regards to camshaft bearing wear and/or valve train related breakage.  And any harmonics transmitted to the distributor as a result of these imbalances can also produce havoc within the ignition and can go so far as reaching the oil pump.

On a solid lifter engine such as the Ford Y-Block (239,256,272,292,312), there is the remote possibility of lifters being deflected from the lobes as a result of imbalance.  To compound the potential for problems, the mushroom tappet design of the Ford Y-Block lifter makes the lifters more susceptible to damage than the more traditional lifter designs.  Even if lifter issues are not at the forefront with camshaft imbalance, then cam bearing wearing would be.  Summarized, the higher the rpm, then the greater the potential for issues that arise from camshaft imbalance.  For a stock engine, problems that could arise as a result of camshaft imbalance are minimal if not non-existent.  But for an engine running in excess of 6000 rpms, then this becomes an area worth exploring.

Balancing the camshaft is similar to balancing a crankshaft in that dynamic balancing is incorporated which has any imbalance corrections being performed at the ends of the camshaft.  At this point, the balancing operation becomes specialized as it requires a machine capable of dynamic balancing.  But a fair number of shops with dynamic or crankshaft balancing capabilities do not balance camshafts as it’s an area that’s simply just overlooked.  This is just something that a machine shop will need to be approached about and decide if this is an area that they would want to tackle.

Any production camshaft is inherently out of balance due to engine cylinders being directly across from each other that fire or ignite consecutively in the firing order.  This means the camshaft lobes for those cylinders are bundled up on the same side of the camshaft and subsequently makes the camshaft predominantly heavy sided on that side of the camshaft.  For the Ford Y-Block, the camshaft is lopsided on the drive end of the camshaft while on other engine families (ie. the Ford FE & MEL big blocks) the camshaft may present greater levels of imbalance on the back or rear end of the shaft.  Engine design and/or firing orders will dictate where the imbalances will be most heavily concentrated on the camshaft.

The drive end imbalances on most camshafts are more easily compensated for in that they can be corrected at the timing gear itself whereas any correction that must be done at the back end or rear of the camshaft is typically performed in the rear journal.  The larger diameter of the timing gear simply allows for much easier imbalance correction with less material removal.  If offset keys or bushings are being used with the cam gear at the camshaft snout to degree in the camshaft, then these must be also in place at the time of camshaft balancing.  If the cam is being degreed in at the crankshaft gear, then the cam gear position will not be a consideration at this point.

For the Ford Y-Block, there are at least three different balancing scenarios that can take place with the camshaft installation depending upon what parts are available.

These scenarios can be listed as:

(1) the timing gear being installed with only the fuel pump lobe on the front.

(2) the timing gear being installed with both the fuel pump lobe and the early model counterweight.

(3) the timing gear having the fuel pump lobe removed altogether as would be in the instance where an electric fuel pump is being used.

All of these result in a different amount of imbalance at the drive end of the camshaft.  When balancing the camshaft, it will be important to have the hardware on the front of the camshaft that is actually going to be used.



Click image for a larger picture

For a Y camshaft that was custom ground on 107° lobe centers, the amount of imbalance on the drive end with the fuel pump lobe installed and not including the early model fuel pump counterweight was in excess of one oz-inch.  In balancing terminology, this amounts to a large amount of imbalance.  Installing the fuel pump counterweight reduced this imbalance to 0.44 oz-in which is a significant reduction in balancing terms.  In an irrigation pump or industrial engine, this is likely not enough to worry about but in a peformance application, even the smaller amount of imbalance that’s evident with the fuel pump counterweight in place is enough to warrant some additional attention and correction in a serious effort blueprint or performance application.

As already stated, imbalance corrections on the drive end of the camshaft are performed on the timing gear and more specifically on the outer edges of the gear where centrifugal forces work to our advantage.  Rather than adding weight as in the case of a counterweight, the gear is simply lightened on the indicated heavy side.  The imbalances in the rear or distributor drive end of the camshaft are not as easily compensated for due to the small working diameter of the rear journal.  The rear journal is either lightened in the appropriate location with holes or heavy metal being added and in some instances, both heavy metal and lightening holes are employed simultaneously as imbalance correction methods.  On the Y camshaft, the oiling holes present in the outer edge of the rear journal must be also taken into account; any modifications to the rear journal in regards to balance must still maintain the oil path for the oil to travel to the distributor pilot hole.  A vent hole in the rear cam journal must also remain so that oil pressure within the cam plug area does not unseat the plug thus becoming an external oil leak at the rear of the engine.

Don’t take this article as saying your camshaft has to be balanced.  Balancing the camshaft is just that extra level of detail that can be performed when doing a serious blueprint to an engine.  I simply do it just for that extra bit of performance and engine durability it can provide.

Until next time, Ted Eaton

Originally published in Y-Block Magazine, Issue #96, Jan-Feb 2010, Vol. 17, No.1