your cars' best base timing won't be in any book
03-17-2005, 07:16 AM
#1
Race Director
Thread Starter
your cars' best base timing won't be in any book
Check out how much slack is in YOUR engine.
Remove the distributor cap.
Crank it so the mark is in the middle of the timing tab.
If the balancer has a center bolt, use a breaker bar to turn the crank slowly back and forth. see how many degrees it takes to get the rotor to move. (Get your wife to watch the rotor. She won't lie to you.)
slop city
report your slop here!
Remove the distributor cap.
Crank it so the mark is in the middle of the timing tab.
If the balancer has a center bolt, use a breaker bar to turn the crank slowly back and forth. see how many degrees it takes to get the rotor to move. (Get your wife to watch the rotor. She won't lie to you.)
slop city report your slop here!
Last edited by Matt Gruber; 03-17-2005 at 07:21 AM.
03-17-2005, 12:16 PM
#2
Team Owner
Member Since: Oct 2000
Location: Washington Michigan
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That will primarily show the amount of slop in the end-play of the distributor drive gear-to-housing, which is usually WAY out of spec; when the engine is running or being manually turned clockwise, the thrust load on the distributor mainshaft is upward, and the shim pack for the gear will be fully compressed. If you turn the crank manually back and forth, the drive gear will pull the mainshaft DOWN when the crank is rotated counter-clockwise, and that's where you'll see the slop.
The drive gear shim pack clearance spec is .002"-.007" to avoid erratic timing; most used ones I see are .060"-.125", which lets the mainshaft move up and down, and the helical gears translate this into timing variation. Most folks pay no attention at all to distributor maintenance, and this excess clearance condition is frequently mis-diagnosed as timing chain slop.
The drive gear shim pack clearance spec is .002"-.007" to avoid erratic timing; most used ones I see are .060"-.125", which lets the mainshaft move up and down, and the helical gears translate this into timing variation. Most folks pay no attention at all to distributor maintenance, and this excess clearance condition is frequently mis-diagnosed as timing chain slop.
03-17-2005, 03:01 PM
#3
Drifting
A Camaro I bought awhile back had about 0.075 slop. Shimmed it up and the car ran a lot better. Unfortunately, the distributor has developed other issues, so I'm replacing it with a Pertronix unit.
03-17-2005, 09:06 PM
#4
Drifting
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As John stated, this has to be a function of incorrect end-play in the distributor shaft. I removed the dist. from my newly acquired 67 L-79 last summer and discovered that the "mechanic" who rebuilt it omitted all the shims and (of course) installed the distributor gear 180 deg out of phase, making it impossible to set the timing properly. The end play was about 0.060" if I remember correctly. LICS sells three thicknesses of shims for this purpose.
If the play isn't in the distributor, then my next guess would be a severely worn cam sprocket. The OEM sprockets are infamous for deteriorating with age (not just mileage).
If the play isn't in the distributor, then my next guess would be a severely worn cam sprocket. The OEM sprockets are infamous for deteriorating with age (not just mileage).