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In the last few years there has been more interest in
quieter engines. Since cam gear noise can sound like bad lifters, the
following description should be helpfull. This explanation mostly applies to
H/D type four lobe cams.
Whenever the roller follower on a cam lobe passes the
maximum lift point, the forces on the cam drive gear teeth changes
direction. If more than .002 inches (.005mm) backlash is present between the
cam and pinion gear, the directional change of force will result in an
audible "click" as the backlash moves from the back side of each gear tooth
to the front side.
While some positive backlash is necessary to prevent
localized gear tooth overloads, excess backlash (and "clicking") may sound
annoying but won't hurt anything.
Tight fitting gears will cause very noticeable
whining which is definitely a more serious problem. Gear tooth and bearing
damage can result from running zero backlash. In this case, a smaller cam
gear or pinion gear would be required.
Different size gears permit custom fitting for a
specific engine. By choosing two gears which are compatible sizes for a
given engine, gear backlash can be minimized so that gears will not whine or
click but just run quietly.
If you need them, Andrews Products makes cam gears
one size larger than standard and one size smaller. H/D makes pinion gears
in a range of sizes.
If you are working with an engine that does not have
quiet running cam gears to use as a starting point, another method may be
used to size drive gears when installing new cams.
In this case it will be necessary to use either a
larger cam gear, a larger pinion gear, (or both) to correct noisy gears. If
the problem is excess whining, a smaller pinion or cam gear will be needed.
Measure pinion and cam gear sizes over pins. Look in H/D service manual for part numbers listed by pin sizes. A
decision must now be made regarding what size pinion or cam gear to choose.
Our recommendation would be to pick 2 sizes larger (to correct clicking) or
2 sizes smaller (to correct whining) as a starting point.
If both gears are sized properly for the engine, a
very slight whine is normal. Only a small percentage of engines are made
with larger size cam drive gears. The two largest sizes of cam drive gears
will be color coded green or black. If a particular engine has a stock cam
with one of these color codes, matching cam drive gears and pinions for
correct backlash can result in a quieter running engine whenever a new
camshaft is installed.
Engines having cam gears color coded red or blue
should not require any cam or pinion gear changes.
Another approach is to press the stock cam gear off your stock cam and
install it on the new camshaft. Assuming it ran quietly before, it should
also run quietly with a new cam. |
