Dial Back Timing Light
Thread Starter
Team Owner
Joined: Aug 2007
Posts: 58,061
Likes: 7,146
Army
Dial Back Timing Light
I have an Actron dial back timing light I've used for the past five years. When I put it on the 283ci '61 Corvette and crank the reading back to align the marks at TDC I get the correct 12* (with vacuum advance plugged).
The same timing light on the 396ci '67 Chevelle (with vacuum advance plugged) and the light dialed back to TDC gives me 38*. Driving me nuts. The '67 has an HEI distributor and is running on ported vacuum with a rock steady vacuum at 750RPM idle of 19". The spec for the motor is 4* initial timing.
The only thing I can figure is that the timing mark on the balancer is way off.
Number 1 cylinder is the frontmost one on the driver's bank on both engines ... right ?
Any insights ??
The same timing light on the 396ci '67 Chevelle (with vacuum advance plugged) and the light dialed back to TDC gives me 38*. Driving me nuts. The '67 has an HEI distributor and is running on ported vacuum with a rock steady vacuum at 750RPM idle of 19". The spec for the motor is 4* initial timing.
The only thing I can figure is that the timing mark on the balancer is way off.
Number 1 cylinder is the frontmost one on the driver's bank on both engines ... right ?
Any insights ??
Race Director
Joined: Jul 2002
Posts: 11,593
Likes: 173
From: Clayton NC
I have an Actron dial back timing light I've used for the past five years. When I put it on the 283ci '61 Corvette and crank the reading back to align the marks at TDC I get the correct 12* (with vacuum advance plugged).
The same timing light on the 396ci '67 Chevelle (with vacuum advance plugged) and the light dialed back to TDC gives me 38*. Driving me nuts. The '67 has an HEI distributor and is running on ported vacuum with a rock steady vacuum at 750RPM idle of 19". The spec for the motor is 4* initial timing.
The only thing I can figure is that the timing mark on the balancer is way off.
Number 1 cylinder is the frontmost one on the driver's bank on both engines ... right ?
Any insights ??
The same timing light on the 396ci '67 Chevelle (with vacuum advance plugged) and the light dialed back to TDC gives me 38*. Driving me nuts. The '67 has an HEI distributor and is running on ported vacuum with a rock steady vacuum at 750RPM idle of 19". The spec for the motor is 4* initial timing.
The only thing I can figure is that the timing mark on the balancer is way off.
Number 1 cylinder is the frontmost one on the driver's bank on both engines ... right ?
Any insights ??
David
Melting Slicks
Joined: Apr 2010
Posts: 2,142
Likes: 282
2018 C2 of Year Finalist
2015 C2 of the Year Finalist
Are you sure your centrifugal advance isn’t kicking in even at idle? Try JohnZ’s trick (from his timing article) of using a rubber band wrapped across the weights to make sure they’re not moving. Otherwise, I don’t know why the light would read differently on that engine. I always have trouble with my dial back timing light turning on me???
Thread Starter
Team Owner
Joined: Aug 2007
Posts: 58,061
Likes: 7,146
Army
I don't see how I could have full advance at 750RPM if the dizzy springs have any tension at all but I'll still check. The car runs out great. I also think I have a regular old 'dumb' timing light buried in a cabinet somewhere I may dig out to verify readings. Now I'm wondering if somebody re-clocked the distributor on me (which I'll also check tomorrow).
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Dennis
Tech Contributor
Joined: May 2005
Posts: 15,576
Likes: 118
From: Conroe Texas
Thread Starter
Team Owner
Joined: Aug 2007
Posts: 58,061
Likes: 7,146
Army
Burning Brakes
Joined: Oct 2004
Posts: 953
Likes: 27
try using a piston stop to determine true TDC.
http://www.jegs.com/i/Comp-Cams/249/4795/10002/-1
http://www.youtube.com/watch?v=PD0ZRc7Dy28&feature=plcp
http://www.jegs.com/i/Comp-Cams/249/4795/10002/-1
http://www.youtube.com/watch?v=PD0ZRc7Dy28&feature=plcp
Thread Starter
Team Owner
Joined: Aug 2007
Posts: 58,061
Likes: 7,146
Army
The distributor housing is rotated about 45* clockwise from the stock location, but more strange, with the timing marks at TDC the rotor is pointing at the #8 spark plug tower and the wire from that tower does indeed go to the #8 spark plug.
Either the #8 piston is also at TDC when the marks align (or the car wouldn't run) or the balancer mark is off.
Either the #8 piston is also at TDC when the marks align (or the car wouldn't run) or the balancer mark is off.
Burning Brakes
Joined: Jul 2003
Posts: 786
Likes: 15
From: Emporia, pay no attention to that man behind the curtain, KS
60