Nov 272012

While the Blue Knight article is correct on many fronts and I personally know about and have seen the results of the Harley Davidson Cam Chain failures issues there is a very important piece of the puzzle I wanted to let everyone know of. So getting to the basic of why HD has Cam Chain tensioners in the first place: They are designed to keep the proper tension on the Cam Chain for not only driving the Cams and keeping them in time, they also drive the HD oil pump and both chains are driven off the HD crankshaft. And herein lies the problem with simply switching to Gear drive cams as expressed is that HD allows up to 12,000 run out which is like watching an egg roll around so they have to have the chains and respective tensioners to allow for such a wide variance of run out as HD does not balance their crankshaft assemblies. Now one would wonder why they do not true and balance their crankshaft assemblies and it is simply a costly procedure. here you see an HD with the run out as shipped from the factory and this run out is what causes so much Cam tension wear and invariably motor failure on the HD’s here it shows the run out test and this motor is around 3,000ths run out or at the limit it can be for gear drive cams and we all know when a part is placed in a motor and is considered at the serviceable limit that does not always compute to reliability.

So while adding Gear Drive Cams to your HD may help save the motor from the effects of the Cam shoes wearing it is important to note that having too much run out and installing the Gear Drive Cams will only result in a catastrophic engine failure and the only thing you won’t hear is that it was caused by the Cam Shoe tensioners but the change to the Gear Drives is probably the cause if you have excessive run out and HD allows up to 12,000ths run out or 4-5 times of the allowance by the Gear Drive manufactures.

The physics of the Harley 45 degree V-Twin with its  Siamese crank and 405/315 degree firing order are well known. Primary and secondary shaking forces conspire to loosen bolts, break brackets and kill sensitive components. Some manufacturers put in heavier cranks, 45 pounds or more to hold the fort down. Heavier wheels store energy in low output engines but kill the “rpm gain per second/per second” game. Add a balance shaft and you limit the rpm and add in components that fail this video speaks to the trueing of the HD crankshaft and begs to question why HD itself does not do this for its customers, he hits it on the head, it’s the money stupid.


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