Sunday, February 13, 2011

Setting Pinion to Cam Gear Lash

This is one of those tech tips that I have considered writing several times, but each time I considered it, I decided to put it off until I could provide some pictures to go along with it. But, it seems that I never have an engine at that point when I think of doing this post, and never remember to take pictures when I do. So, we're all going to have to tough it out without pictures, as though we were adults.

Noisy motors are something that are a source of annoyance, and sometimes even embarrassment. The following is directly applicable to Big Twin from 1940 to 1999 as well as most S&S motors, and also can be applied to some extent to Flatheads and Sportsters. With the abundance of cams on the market, and the frequency with which they are changed, whether due to wear or for performance, this is always a timely subject.

First things first. Let's debunk an old wives tale having to do with "a matched gear set." While old wives are the best kind to have, particularly if you are an old husband, it has been my experience that they are an unreliable source for Harley technical advise. The "myth" of the matched gear set stems from the fact that the Factory did (maybe still does) sell a cam and pinion gear set. Trouble is, all that means is that the set comes with both gears in the middle of the size range. There are absolutely no guarantees that size combination will be correct for your engine. After all, if the factory could make a gear set that would fit all of their motors correctly, there would be no reason for them to make more than one size pinion gear and one size cam gear.

But they do, and they have since sometime back in the 1970's. The reason is to compensate for manufacturing tolerances in the center to center distance between the pinion shaft and the cam bearing in the crankcase as well as the pinion bushing and cam bushing in the cam cover. What did they do before different gear sizes were available you ask? Well, I guess you just had to live with a little extra noise.

Now, it is important to note that there are two separate types of bad fitment that will lead to noise: too tight and too loose. Too tight is actually a much bigger problem than its opposite. Too tight a fit between the pinion gear and the cam gear will result in a pronounced whine, and whining is never a good thing whether it emanates from your friends or your engine. In the latter case, it can lead to localized overheating and destruction of the gears. In the former cases it can lead to localized overheating of your temper. Neither is a good situation but the situation with your engine is easier to remedy.

Too much lash between the cam and pinion gear, on the other hand is generally harmless. Annoying but harmless. In fact, often times, a set of perfectly innocent lifters will be blamed for the "ticking" noise caused by pinion gear fitment. But lets get to the point of this post. Setting up proper cam to pinion gear fitment.

When installing a cam and pinion gear combination of unknown fitment, I have found that the best way is to test fit the combo, and be prepared to spend some time getting it right. If dealing with a rebuild where bushings have been replaced, it is worth installing the cam gear in the case without a pinion gear. This is particularly important on an early engine which uses a bushing in the crankcase rather than the late style Torrington. Install the cam with some lube on each end, and without a spacer or thrust washer. Once the cover (with gasket) is tightened, the cam should rotate freely with only light finger pressure. If the cam is binding in the two bushings you need to address that first so that you will be able to "feel" the fitment after you add the pinion gear.

Now that you know the cam is not binding, you can install the pinion gear, cam (again without thrust washer or spacer) and cover. Reaching in through the lifter block hole you should be able to slide the cam in and out easily. That is why you left the spacers out; so there would be plenty of end play to give a good feel. If you cannot slide the cam back and forth easily with just finger pressure, then it is too tight and it will whine.

So, what if by some stroke of luck the cam slides easily back and forth at this point? Are you done? Fat chance. This party is just getting started! If the cam does slide easily without bind, you need to check this at different points in its rotation. That means turning the engine over by hand. If the engine is in the chassis, jack the rear wheel up and with the plugs out and the trans in high gear, turn the wheel to rotate the engine. You will want to check the fitment at at least four places in the cam's rotation. If you find a place where the cam does not slide easily, it is too tight. If the cam will slide easily throughout its rotation, you have established that the fitment is not too tight.

The next step is to check to see if it too loose. Again, reach in through the lifter block hole but this time try to move the cam back and forth in its rotation. If you can feel, or hear a slight click as you move the cam back and forth, it is looser than you would like. Proceed as before and check this fitment in multiple locations in the cams rotation. Perfect fitment is when the cam can be easily slid in and out at any point in its rotation and likewise no lash can be felt or heard when attempting to move it back and forth.

Trouble is, you will rarely find a combination that is perfect. The culprit again is manufacturing tolerances. If the the cam gear and the pinion gear were each perfectly concentric and the crankshaft had zero runout, then there would be no need to check the fitment at more than one place in its rotation. But they aren't and so you do.

The next step, as you have likely already guessed, is to try another size pinion gear, but before you do, it might be helpful to make some notes of what you just found with the present combination. Personally, I always check the fitment every 90 degrees (4 places) in the cams rotation. My note might look like this: blue gear very loose 3 of 4/ slightly loose 1 of 4. The logical next step would be to try the next size larger pinion gear.

Conveniently both S&S and Jim's Machining offer a full range of color coded pinion gears. Though there are pins available which enable you to measure the gears, I find that they are really only of much use when dealing with a gear whose color code is no longer legible. Other than that, simply consult the color code chart from the appropriate catalog to guide you in selecting the next gear to try.

From there the process is repeated with your next selection of pinion gear. Use some common sense here. If the fitment was either extremely loose or tight, you might want to skip one color size to speed the process up. Remember, you will seldom get a "perfect" fitment between the gears, but you will always be able to get a "best possible" fitment - even if you wind up trying every pinion gear available. That is where those notes can come in very handy. Don't be surprised if you wind up going back to a size you already checked as the best possible combo.

One thing you want avoid is a situation where the the fitment is tight at any point in its rotation. Say for instance the fitment feels good 3 of 4 spots in the cams rotation, but is tight enough in one spot that you cannot slide it back and forth with just finger pressure; that combination will whine! I once had a cam that felt good in every place in its rotation with the exception of a short span of one or two teeth, where it took a screwdriver to pry the cam back and forth. I decided to try it, and surprisingly, it was a real whiner! The best coarse of action in such a (rare) case is to replace either the cam or cam gear. Hint: If a combination is tight in two spots in the cams rotation,180 degrees apart, the discrepancy is in the pinion gear or crank runout (since the pinion gear rotates twice for each rotation of the cam). Conversely, if there is only one tight spot, the out of round issue lies with the cam gear.

The best possible fit will be the largest pinion gear that has no bind. Don't be surprised if it checks something like this: good 1 of 4/slight lash 2 of 4/lash 1 of 4.

I guess by now it has become clear that it is beyond the reach of most guys installing their own cam to obtain the "best possible" cam to pinion gear fitment, what with 8 different sizes of pinion gear available, and each of them retailing for over $80. If you then multiply that by the four different styles of pinion gear (splined for Knuckles and early Pans, full length tapered for late Pans and early Shovels, stepped tapered for late Shovels and early Evos, and then of coarse late Evos) at least you can see why your local shop doesn't work for free.

So what are you to do? Well, the cam manufacturers know the danger of fitment that is too tight. That means that they provide cam gears that are on the small side of medium so you are much less likely to have a tight fitment than a loose one. A little ticking caused by gear lash won't hurt anyone, but the whining.... that's got to be fixed, unless of course it is coming from your friends, in which case there may be no cure.

4 comments:

Noot said...

Good job. You never touched on watered down compound tricks or measuring with pins(really the best way).

Noot said...

Hey, You wouldn't have a 1/4 speed gear to go with my 1/4 speed breather gear for XLR?

St.Lee said...

Hi Noot, thanks for taking the time to leave a comment. Sorry I can't help you with the breather parts, or even give you any good leads.

When I first read "watered down compound tricks" I did not have a clue what you were referring to. Are you talking about using lapping compound to "fit" the gears? If so, that kind of falls outside the scope of this post, since Big Twin single cam engines have undersized gears available which would be a quicker and cleaner way to remedy a tight fit. I can see where it might be a useful trick on a 4 cam engine though.

As for measuring with pins, like I said in the post, that is useful when you don't know the size of a gear. What I forgot to mention is that measuring over pins is a good way to be sure you are not throwing the lash off when replacing a gear in a known quiet motor.
Thanks!

Anonymous said...

Thank you Sir. for the facts on cam/pinion gear fitment. I find too often we rely on some magic indicator from manufacturing that leads us to a fix that may be less than desirable for our motors. I like the real way of using true fitment guidelines/indicators for better operation of interacting parts. This kind of knowledge is slowly disappearing. Thanks for sharing. Off to the garage to fit my cam/pinion on my beloved Shovel. What I was running was definitely too tight. Experienced a loose pinion gear recently. Localized heating? Thanks again. Arizona 365 daily rider.