Printable Version of Topic

Click here to view this topic in its original format

914World.com _ 914World Garage _ Gear Ratios

Posted by: yeahmag Apr 15 2016, 03:21 PM

I have Dr. Evils DVD (bought it forever ago and have yet to watch it) and am hoping to have some fun building up a shorter ratio gear box. I have a huge box of 914 gears and was wondering if I can use the "Ratio Calculator" in the 914/901 gear ratio workbook to pair them back up. For example:

KA 22 : 31 1.41

In this case would a KA be a 22 tooth gear and a 31 tooth gear?

I understand that they are typically matched sets and I may get noise or increased wear if they are paired wrong.

Thanks.

-Aaron

Posted by: Mark Henry Apr 15 2016, 03:26 PM

Not sure what you mean... two different gears half sets?
You can't do that because the gears will be tight or loose. The two stacks have a fixed distance between them.

Posted by: yeahmag Apr 15 2016, 03:30 PM

I have a box-o-gears from taking apart 901 transmissions. I wasn't smart enough at the time to keep them paired up. I'm curious if you can tell what they are by counting the teeth.

Posted by: Mark Henry Apr 15 2016, 03:38 PM

Oh OK

IIRC they are marked, the 911 gears are marked better, on the 914 gears the markings are there, but hard to see.
I think counting will work but not positive, put them on the stack they will either spin, be too loose, or tighten right up.
Could be noisy and premature wear.

Posted by: 396 Apr 15 2016, 04:41 PM

If you pair two two different gear set together as mentioned, they will be loose or tight....thus will cause noise and possibly other related issues.

Posted by: toolguy Apr 15 2016, 04:52 PM

OK try to get your head around this example

we'll use a J and K gear set for example
j is 21 :31
K is 21:30

IIRC, the 21 tooth gear from these 2 sets are NOT the same outer diameter even though they have the same number of teeth
It is the distance from the centers that
determine if they match. . and even gears of the correct diameter may not be a 'matched' pair. . meaning while they will fit on the gears shafts, the backlash may be too much or too little. . too much and they will whine and have slop. . to little and they will bind, run hot and probably not even fit. .

Likewise gearsets for N, O, and P all have a 23 tooth gear on one side
but a 23 tooth from O is not the same as a 23 for the P set
N= 23:29
O= 23:28
P= 23:27

what makes a gearset matched has to do with pressure angles and diametrical pitch, not necessarily the number of teeth. .Easiest explanation is it has to do with the location of the contact point of the 2 gears in relationship to the distance from each gear centers.

Posted by: Mark Henry Apr 15 2016, 08:36 PM

What you could do is paint the gears with dykem blue, lightly coat them with fine valve grinding compound and then spin them in a jig, Take them out carefully clean them enough to see the contact patch. You more or less want to see it in the middle, but not to deep on the root of the gear.

Once done you have to be sure to clean up the valve grinding compound 100%,

Posted by: oldie914 Apr 16 2016, 01:21 AM

First you need to sort the gears to see if you can get them back to the original pairs. If they are 901 gears, they will have engraved match numbers. 914 gears don't have match numbers.
All gears should have a Roman Numeral I that shows that it belongs on the mainshaft or a II that shows it belongs on the pinion shaft.
Once you have paired them, you can shift the pairs around on the 3rd, 4th and 5th positions.
I don't think you will have durability problems with mismatched gears but can have some gear noise. Why don't you try it and let us know the results.