Oversized distributor gear question...

[stealth]

Oversized distributor gear question:

Just curious, I've heard it said that most distributor gears don't mesh properly on the cam and that a .005 oversize gear is common to correct for this. Does this sound right. How do you check for "proper mesh" of the gear.

thanks

[SchmidtMotorWorks]

I'm not sure what block you are reffering to but I did model a BBC block and distributor to dimensions in the Chevy Power book and some priints from Chevrolet and found that the gear circles didn't intersect exactly as I expected. If I remember correctly they were about 0.010 loose.

[bill jones]

-Regarding Chev V-8 distributors I ended up measuring at the rotor tip for rotational slop.

-Quite commonly I find about .055" of uncontrolled rotor tip rotational movement.

-This really should be checked on a hot engine versus a cold engine to get a relationship of what happens from room temperature to race temperature.

-On a large diameter cap the rotor path diameter is 4.060" which is 12-3/4" of travel the rotor tip rotates---so divide this by 360 degree sand you get right close to .035" per degree.
---------------------------------------------
-You can buy gears with .006" oversize tooth pitch diameter but that only reduces the slop about .018".

-PPPC (Precision Performance Products Co.) used to sell both .006" and .012" oversize tooth pitch diameter gears but only for .500" shafts.
-Their phone used to be 1-800-448-1223.

-Reed Cams used to have the .006" gears for .491" shafts and their phone used to be 1-800-548-2267.

-I can't say that I ever found a source for .012" oversize gears for .491" shafts
-----------------------------------------------------
-Another way to fix the problem is by building an offset bottom bushing for the distributor---where the bushing hole is offset something like .015" max which is about all the offset you can get down thru the distributor hole.
-----------------------------------------------------------
-The bottom of the distributor can also be loose by say .004" in relation to the distributor hole in the block-----and the one side of the distributor can be "knurled" in some manner to move the distributor closer to the camshaft---and tighten it up inside the hole.
-------------------------------------------------
-Two other things that affect this rotational slop is the depth of the distributor gear as it sets into the hole of the block---and the position of the cam teeth forward and aft looking down thru the distributor hole.

-The cam gear needs to be centered front to rear--as least looked at real close----with the distributor removed.

-Then the heads and manifold should be installed on an empty block---to where you can drop the distributor down into place---and look thru the rear cam bearing hole to see if the height of the distributor gear is centered vertically.

[Rusty105]

Maybe I am missing something, but what is the down side to the slight mismatch, other then a wear problem?

[dave brode]

edited due to mis-information on summit's site.

[stealth]

Maybe I am missing something, but what is the down side to the slight mismatch, other then a wear problem?

Timing variations with the slop in gear...unless using crank trigger then its no issue.

[In-Tech]

Due to a certain ignition company now using gears made in China, distributor gear sale are up 240% over the last 2 years.

Hi Chris,
If you don't want to say who it is on the forum, please pm me so I can avoid issues. Something about My Spark Dropped comes to mind.