Am I right to say that if you have a gearbox with43 teeth on input gear and 99 on output gear theres no need to match mark.However if you have a gearbox with ( God forbid ) 20 teeth on the input and 60 on the output you would need to match mark if youre tearing down to do a bearing change.

Thanks

Mike,
I agree with you, but I suggest that gears should always match-marked as a common practice.

Walt

I agree with Walt.

I have been involved in a case where two gear sets, one helical and one beveled, were removed. The nameplate data indicated an assembly phase in the beveled set, but not in the helical. As it turned out, there was an assembly phase in both sets and the results were not good.

So, even when data is provided with the tooth counts and it indicates no assembly phase problems, I recommend that you mark the gears.

As Dan H. has pointed out that is why I always recommend match marking; you can never trust the nameplate.

Bevels by the way should usually be match marked at the factory as this is how various dimensional parameters are set when building the gear box. Look for two "X's" on one member and an "O" on the other.

John

Mike,
You are right about your gearbox. 43 is a prime number (http://www.math.utah.edu/~pa/math/primelist.html)and the common factor for your gearbox is 1. You can match mark them if you like, but the mark on gear A is going to touch every tooth on gear B before it gets back to the match mark on gear B.

David Eason

Some turbo manufacturers do not allow match marking. The resoning is that it's not needed but in case there is a failure for some reason people don't understand it and say it failed because the gears are not matching.

The attached shows why you should always mark teeth to get back to the same indexing. In this case the situation was aggravated by end thrust on the pinion, i. e., axial spacing is very critical on double helical gearing.

John

GCD_5.pdf (172 Kb, 31 downloads)