Distributor Gear Change ?
East bound and down...
Joined: Dec 2004
Posts: 987
Likes: 3
From: Jonesboro Arkansas
I'm not sure if you are referring to the orientation of the distributor to the cam as a function of timing, or if you are referring to the orientation of the gear itself. If you are talking about the latter, it is possible to put the distributor gear upside down. At first glance you may not notice it to be incorrect, but when you try to drop it in you will certainly figure it out (ask me how I know.) But, if you referring to the orientation of the distributor itself, it is very easy to get one put in 180 out. The easiest way to fix this is with the ole' finger over the spark plug hole trick. Hope this helps.
Tech Contributor
Joined: Aug 1999
Posts: 14,384
Likes: 6,408
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by Hvymtlc5
I have read that there is an "orientation" on the distributor drive gear. Can someone explain how the gear could be installed 180 out??
Thanks.
Thanks.
There is a dimple on the distributor gear for the clocking. The dimple on the gear needs to point the same way as the firing tab on the rotor. If you flip the gear 180 the other way, the distributor will be 1/2 tooth off its clocking.
Thread Starter
Melting Slicks
Joined: Mar 2004
Posts: 3,472
Likes: 18
From: Lake Ozark, MO
I beginning to think this is like looking for a muffler bearing. I had heard there was a stamp mark on the dist. gear that had to be installed one way or another in relation to the distributor shaft or it would be installed wrong....can't see how it would / could make any difference.
Race Director
Joined: Aug 1999
Posts: 18,126
Likes: 174
From: WI
and if there is no "dimple" look at where the pin goes through (on both sides) in relation to the teeth on the gear, one side lines up with a tooth where the other side splits two teeth. Install the gear so the rotor button is facing the split teeth.
...redvetracr
...redvetracr
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by Hvymtlc5
I beginning to think this is like looking for a muffler bearing. I had heard there was a stamp mark on the dist. gear that had to be installed one way or another in relation to the distributor shaft or it would be installed wrong....can't see how it would / could make any difference.
Thread Starter
Melting Slicks
Joined: Mar 2004
Posts: 3,472
Likes: 18
From: Lake Ozark, MO
Reason that I'm asking (my other post this morning) is that I got the 4545 running good with the Demon and stock HEI. I changed that out with a Mllory HyFire and a Mallory distributor (I put the gear on). Car idles really bad and labors to start at 18 degress initial..the HEI was set the same and it cranked good. I was wondering if the gear could be a factor in the problem.
Can I still set initial timing at 18 degress and really be more advanced than that...due to the gear??
Can I still set initial timing at 18 degress and really be more advanced than that...due to the gear??
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
Tech Contributor
Joined: Aug 1999
Posts: 14,384
Likes: 6,408
From: At my Bar drinking and wrenching in Lafayette Colorado
If the gear is installed 180 off, it does not affect the timing or the operation of the engine - it only affects the clocking of the distributor in the engine once the timing has been set - it's cosmetic as long as the distributor has no interference with other engine components. It would not be the cause of your rough running or a miss.
It makes a difference because the pin hole in the gear is drilled from a "tooth" location on the one side, and exits at a "valley" location on the opposite side. If you rotate the gear 180 degrees on the distributor shaft, you effectively change the relative position of the distributor shaft a full tooth from its normal orientation. This is then made up by twisting the distributor that much farther when you set the timing. Normally, a correctly timed HEI distributor will be visually "square" in the engine compartment (the coil on top appears square in the engine, with the wires attaching directly 90 degrees on the driver's side). If you rotate the gear to the wrong position, the distributor will be at an angle in the engine when properly timed. This has no functional detriment - it looks cosmetically odd.
Originally Posted by Hvymtlc5
I beginning to think this is like looking for a muffler bearing. I had heard there was a stamp mark on the dist. gear that had to be installed one way or another in relation to the distributor shaft or it would be installed wrong....can't see how it would / could make any difference.
Last edited by lars; Jan 17, 2006 at 10:55 AM.
Tech Contributor
Joined: Aug 1999
Posts: 14,384
Likes: 6,408
From: At my Bar drinking and wrenching in Lafayette Colorado
Good pic, Paul.
Hvymtlc5: If you notice in Paul's picture, the roll pin is aligned with a "valley" in the gear. On the opposite side of the gear, the roll pin is aligned with a tooth, making the gear non-symmetrical in its clocking. If you pull the pin out and rotate the gear 180 degrees, the clocking of the shaft relative to the gear (and therefore the camshaft) will change, and this will change the installed orientation of the distributor in the engine once timing has been set.
Hvymtlc5: If you notice in Paul's picture, the roll pin is aligned with a "valley" in the gear. On the opposite side of the gear, the roll pin is aligned with a tooth, making the gear non-symmetrical in its clocking. If you pull the pin out and rotate the gear 180 degrees, the clocking of the shaft relative to the gear (and therefore the camshaft) will change, and this will change the installed orientation of the distributor in the engine once timing has been set.
Thread Starter
Melting Slicks
Joined: Mar 2004
Posts: 3,472
Likes: 18
From: Lake Ozark, MO
Very good picture, and a picture speaks a thousand words......checked it last night and the dimple lines up with the rotor pointer....so I'm good there. Must be the Mallory distributor lack of vacuum advance that causing the rough idle.
