Measuring backlash

[redbloke1956]

Hi guys, I am unsure about backlash in the timing gear on my Comet, the general consensus seems to be around zero to 1 thou, but how is it measured? do I simply position a DTI at 90 deg to any tooth on a gear and measure it so? Or am I missing something?

Any input appreciated
Kevin

 

[ogrilp400]

HT Pinions

G'day Mate,
Measuring the amount of backlash does correspond to the increase in over size of the HT pinion. Essentially you are supposed to have a set of HT pinions at hand and you keep substituting them until you get one that shows little or no backlash.

Phelps.

 

[nkt267]

Basically you slacken the 3 nuts holding the large idler boss and push the large idler into mesh with the cam,breather and dynamo pinions. Then as Phelps says find the best fit half time pinion so that there is near enough '0' backlash.
One point to be sure of though is to rotate the idler, after making some location marks on the pinions, so that the cam rotates at least 1 turn. The reason is that if there is '0' backlash and the cam bush is not completely centered then you will get tight spots in the timing gear causing other damage. I had to return my cam because of this as it was 3 thou off center..John

 

[ray vinmad]

Basically you slacken the 3 nuts holding the large idler boss and push the large idler into mesh with the cam,breather and dynamo pinions. Then as Phelps says find the best fit half time pinion so that there is near enough '0' backlash.
One point to be sure of though is to rotate the idler, after making some location marks on the pinions, so that the cam rotates at least 1 turn. The reason is that if there is '0' backlash and the cam bush is not completely centered then you will get tight spots in the timing gear causing other damage. I had to return my cam because of this as it was 3 thou off center..John

2 points-
I would suggest at least one revolution of the large idler to check clearance
and
Take the pushrods out first.

Too much clearance is better than too little.

Ray

 

[davidd]

The problem that I encountered was that the small idler gear was not small enough and would produce tight spots when turning just the cam and the small idler. I have a selection of small idlers and I had to use a used one. When holding both gears and wiggling (one of the gears, not me), it produced very little back lash. After that, it is just a matter of adjusting the large idler to engage both the cam and the half time pinion in the same way, with little play when holding each and wiggling. I found I could use any size half time pinion because the large idler would move in the direction necessary to adjust to it. This cannot be done with the twin because the idler has to be pushed into the two cam wheels, so the half time pinion needs to be selected to fill in the correct distance to the large idler.

David

 

[clevtrev]

The problem that I encountered was that the small idler gear was not small enough and would produce tight spots when turning just the cam and the small idler. I have a selection of small idlers and I had to use a used one. When holding both gears and wiggling (one of the gears, not me), it produced very little back lash. After that, it is just a matter of adjusting the large idler to engage both the cam and the half time pinion in the same way, with little play when holding each and wiggling. I found I could use any size half time pinion because the large idler would move in the direction necessary to adjust to it. This cannot be done with the twin because the idler has to be pushed into the two cam wheels, so the half time pinion needs to be selected to fill in the correct distance to the large idler.

David

And it cannot be done with a Comet with a dynamo in place.

 

[chankly bore]

Better in my experience to get everything else to about zero and then to centre the generator in its seals (you can use two).This component is usually LESS noisy with a little backlash.