Triple gear clearance

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Model T Ford Forum: Forum 2014: Triple gear clearance
Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Owens on Thursday, September 11, 2014 - 07:11 pm:

Hi, So Glen, Herm, Ted Did we finally get to the bottom of the misunderstanding?
What is " Running Fit" , Scott


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Thursday, September 11, 2014 - 07:55 pm:

I did! Glen Did!, and Ted Did!

Just with different answers!

Herm.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Thursday, September 11, 2014 - 08:17 pm:

http://www.mtfca.com/cgi-bin/discus/show.cgi?tpc=411944&post=660057#POST660057


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Thursday, September 11, 2014 - 08:44 pm:

Way to go Herm! I'm actually chuckling because you said what I was about to say!

All are well intended, all 3 are trying for a rationalized answer that all others beyond the 3 who explore triple gear system can understand...all are getting each others way because the official answer is...

1-It is an imponderable as in the time era that phrase showed up in the shop manual there was no real accepted definition for 'running clearance' and while I don't know where Running Clearance came from in Ford shop jargon...by 1934 it meant a completely different thing within Ford which STILL (?) did not comply with the emerging national standards that GM and others were embracing (source...Page 12, Ford drafting room standards, 1934 edition)

2- The answer lies in etymology (the history of words), specifically with etymology as clearance and fit and tolerance relate. Change the syntax of the service manual to 'At assembly a 0.002" running clearance must still exist" (not Glen def. but rather absolute) and compare it to the actual detail drawings for the pin and gear following bush insert and a funny thing does happen...it IS possible to get the 0.002" by NOT using each parts individual 'tolerance' to the fullest that we see today as allowable. We as a society of mechanics do NOT understand that in big shops like Ford, in the era, our fathers and grandfathers as machinist never got to see an actual print. They were given a diameter to drive to and could not go over...impossible for them to go over because the grinders had fixed stops on them set to the 4th decimal place and only a portion of it at that...and reamers first used were cycled in and out for diameter ON PIECE COUNT and size BEFORE the rake edge could even start to dull (by default I think all of might agree that could be 4th decimal place accuracy)! When they reached the volume point where all they were doing was exchanging reamers constantly, Ford did go to ball ream to size. I have seen the white paper on it, was amazed at how they took material spring-back out of the equation permanently. (really d'uh simple at that...but unfortunately I can't recall the source!

3- It is feeble to keep debating the issue of which came first and why, the chicken or the egg as no one today anywhere has claimed to use the same tight tolerance that Ford used with success!

4- I'll say it again, with today material supply, and mixed up ideas as to oil grooving, and no one knowing how to get a proper surface finish...the only thing that works is 0.003" total clearance for those whose attention to detail is stellar still after doing dozens...and for the rest of us minions, better shoot for 0.004" total clearance. Once we get all on THAT same wavelength...then maybe all of this knowledge used in parrying back and forth can go into 'best practices' for the modern era :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dennis Henrichs on Thursday, September 11, 2014 - 09:07 pm:

"Running fit"? That's when one is the age of a lot of us on the forum and can still almost do a 4 minute mile. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Glen Chaffin on Friday, September 12, 2014 - 04:27 pm:

More food for thought. Just received a copy of the original Ford specs for the 3314 triple gear bushing from Snyder's. The spec for the 3315 pin O.D. is 0.6770-0.6775. The spec for the 3314 bushing I.D. is o.6785-0.6790. That a clearance of 0.00125-0.002. We all know that this is too tight. The question is were these just manufacturing tolerances or operating clearances, I believe they were manufacturing tolerances and that the clearace was increased at assembly for the operating clearance. If that is true we still need to know what that clearance was. The chart for running clearance published by Mark from the Machinery's Handbook, 29th edition says 0.001-0.0047 But we still do not have a definitive answer from Ford.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan McEachern on Friday, September 12, 2014 - 05:08 pm:

The numbers mean nothing until you know the max and min press fit created by the bushing OD/triple gear ID size difference. From the interference, you can calculate the reduced bore of the bushing. In my opinion. the un-mounted bushing bore size is not an important consideration.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Sosnoski on Friday, September 12, 2014 - 05:49 pm:

Someone should look at the triple gear/bushing assembly drawing and see if there is a dimension that the ID of the bushing needs to be finished to after it is pressed into the triple gear. I don't think looking at the spec for the bushing is going to give the answer you are looking for.

Dave S.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Friday, September 12, 2014 - 06:35 pm:

Tried to get an assembly drawing from Benson Library, but there is none. I have obtained the drawings and change order sheets for the pin and the bushing and the gear.

My authorization for use of these prints is only for hobby information of certain specs, not for production or commercial use, so I have attached just partial views to discuss the dimensions.

The print for the triple gear bushing does have the call-out for "Ream after pressing the bushing in place" This is the tolerances given by Glen. That is the Ford tolerance.

The pin tolerance is the same as Glen posted.


IMG_7759 (519x560) (519x560) (519x560) (2) (463x500).jpg


Triple Gear, later style not the riveted early to show the bore size made for the bushing to have a press fit.

IMG_7725 (413x550).jpg
Bushing for the triple gear.

IMG_3775.JPG
Detail on the Bushing drawing showing the tolerance for "Reaming" the bushing AFTER it is pressed into the gear. .6785" to .6790"

IMG_7725 (413x550).jpg
Triple Gear Pin drawing of the key elements, note the pencil marks on the original, this is the -AR part, for replacement use, as the end is slightly larger than the factory first-use. The pin must be larger for the replacement to press into the flywheel hole when the original pin is removed.

Notice: All prints are property of the Benson Ford Research Library, used by authorization for non-commercial purpose only.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Friday, September 12, 2014 - 06:43 pm:

For some reason when I open the last post the pictures didn't show.

Will try this again.

Notice: All prints are property of the Benson Ford Research Library, used by authorization for non-commercial purpose only.


Bushing drawing



Ream dimensions after pressing the bushing in the gear.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Friday, September 12, 2014 - 07:46 pm:

Dan
So that is really interesting. If I have read the tolerances right, they are .0015-.003" clearance. Unless they are "select fit" I assume that a pin on the large side of the tolerance could be run in a bushing on the small side of the tolerance.
So we come back to how did Ford get away with this? I wonder if Mark Chaffin's theory might explain this?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Glen Chaffin on Friday, September 12, 2014 - 07:56 pm:

Your right Dan, The dimensions given are for after the bushing is installed. So they are true dimensions but just not enough clearance. I have NOS gears with bushings reamed to these dimensions. I too wish we had the assembly information. I am sure that they reamed a little more before assembly and that these were just manufacturing dimensions. But we now have more than we had before.


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