C2 tach -- Mechanical Engineer's perspective?
Thread Starter
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
C2 tach -- Mechanical Engineer's perspective?
For years I have wondered about the design of the distributor tach drive on my C2.
It would be nice to hear a Mechanical Engineer's view of this.
From what I see, the tach driven gear has a thrust washer on the side that mates to the brass bushing screwed into the distributor housing -- but, that is not the side of the gear that takes the thrust. The nose of the driven gear is pushed into the housing of the distributor by the rotation of the distributor. On my car, this eventually caused the driven gear to "lock up" and destroy both the driven gear and the distributor shaft/gear. I'm told this is a common occurrance.
It seems to me the thrust should be applied to the side with the thrust washer. Was this just a mistake by the people that designed it, or is there a logical reason (that I am missing) for this design?
Tom Piper
It would be nice to hear a Mechanical Engineer's view of this.
From what I see, the tach driven gear has a thrust washer on the side that mates to the brass bushing screwed into the distributor housing -- but, that is not the side of the gear that takes the thrust. The nose of the driven gear is pushed into the housing of the distributor by the rotation of the distributor. On my car, this eventually caused the driven gear to "lock up" and destroy both the driven gear and the distributor shaft/gear. I'm told this is a common occurrance.
It seems to me the thrust should be applied to the side with the thrust washer. Was this just a mistake by the people that designed it, or is there a logical reason (that I am missing) for this design?
Tom Piper
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
Later distributors had a "button" installed in a recess machined in the end of the housing to cure that issue, and many later cross-gears have a thrust button as part of the gear; I'm sure the guys at Delco never envisioned that system having to live for 40 years. 
Safety Car
Joined: Feb 2003
Posts: 4,068
Likes: 27
From: St. Joseph Mo
My original dist with well over 200,000 was still in fine condition when I finally "overhauled" it. Actually just cleaned throughly and regreased/reassembled it with the small parts kit.
Another I got at a swap meet had a stripped cross gear and a deep pit eaten into the housing. No telling how many miles it had on it but it was short on lubricant for sure. I rescued the housing with a 5/16-24 set screw and jam nut and using it untill I get my Trans Ignition sorted out.
Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,271
Steel (or bronze) against cast iron is okay in a lightly loaded situation as long as there is some lubrication, which is the key. Different operating conditions yield different rates of lubricant dryout/loss.
The distributor should be disassembled, cleaned, and relubricated at least every ten years, regardless of mileage, but my bet is that many have NEVER had this simple service.
Duke
The distributor should be disassembled, cleaned, and relubricated at least every ten years, regardless of mileage, but my bet is that many have NEVER had this simple service.
Duke
Last edited by SWCDuke; Sep 14, 2005 at 08:47 PM.
