The Stovebolt Site Forums The Shop Area Engine Shop Bogus timing light.

In the past on my trucks when they had points, I always static timed the engine at full advance, just like I do on my vintage cycles.No problem,I degreed the damper pulleys on all 3 of the engines when I rebuilt them.34 degrees total advance, never cared what the advance was at idle speeds.
So now two of the trucks have Pertronix conversions making static timing not possible.So I get out my fancy light with the set back advance feature,set the total at 34 degrees with the light on zero advance, then cross check it on the TDC mark with the light dialed to 34,right on.
So my wife says her 261 powered 51 pu sounds like it's pinging all the time, I figure it's bad gas or whatever.
Well, not only does it ping, but holding the engine at 2000 rpm in nuetral, the exhaust sounds like it's misfiring, hmmm.
So out comes the old standard timing light,holy crap, the timing is overadvanced by 15 degrees!! I set the distributer back to the correct timing,no pinging,much better.
Flip the fancy light in the trash I guess or who wants it here?I'll give it to ya free!!

I've heard similar probs with Pertronix and, for example, electronic tachometers. Sometimes the old tools work the best!

-Boyo

What brand of delay-flash light are you using? I use Snap-on lights, and they're very accurate. Of course, I also mark the damper about 30 degrees both ways while I'm degreeing the cam, so I've got a reference independent of the timing light, too. If you're really planning to trash the light, I'll take it!
Jerry

Jerry, it's an imported SunPro, heavy chrome case, inductive, has the dial for retard, bright flash about 6 years old, little used actually. I had a Mac tools light, loaned it out,never came back,needed a light right then,bought the Sunpro.Give it to one of your students,send me your mailing addres in an email.I'll mail it to ya.

I am really curious as to how you actually do your static timing at full advance. I'm not offering an opinion or comment. Just asking how you do it. It works for you, so that's good enough.
You said you "static time at full advance" and with "34 degrees total advance". Total advance is; initial advance "plus" mechanical advance "plus" vacuum advance? I'm trying to visualize how you actually do this. For the vacuum advance, do you use a vacuum pump or hold it by hand? For the mechanical advance, do you hold the weights out and turn the advance mechanism? Then, I assume, you turn the distributor to the position that the timing light flashes?
I don't understand why the one timing light would not flash, or that is flash but not at the right point.
I have always static timed a new engine or when the distributor has been out, but only for initial advance. I have used several different timing lights or a spare spark plug on the plug wire and never been more than a couple degrees off when I fired it up. That is with points and HEI, but never tried a Pertronix.
If you want to set the timing at full advance, wouldn't it be easier and more accurate to do it dynamically? I'm not real fond of revving an engine up like that, but I have done it just to see at what rpm max advance is. Good thing I don't own a Porsche 911. I wouldn't have the stomach to set the timing. I understand that they are dynamically timed for total advance at 6000RPM.

Richard,the dampers on my truck are all marked for degrees,I set my made timing pointer on 34 degrees with the engine on compression, ya know both valves closed,turn rotor to fully advanced by hand and check to see if the points are just opening, like a few thousands.You can check with a home made buzzer or light, a piece of cellephane between the point contacts that just gets loose or whatever.But it's been my experience by checking with a timing light afterwards,I'm always with a degree by using the eyeball.The 32- 34 total degrees figure on 235-261 engine comes from personal experience and the advice of others. The vacuum advance is not an issue when doing static timing with the engine stationary, the normal no vaccum position is correct. On the 261 in my 37,the initial adavce is around 14 degrees with the modified distributer so the mechanical advance adds about 20 degrees to that at 2800 rpm.My Brit bikes have no timing marks at all,I use a timing stick to locate the piston distance below TDC that corresponds with the correct total degrees of advance, as in before TDC.In fact the magnetos have no advance system at all,you retard or advance the timing with a handlebar control.Retart it to start and push it to full advance for running,no problem.
On a stock engine, initial advance setting is adequate, but on any performance or modified engine, total mechanical advance is what you should be looking at.

I do something similar, but I use a Sun distributor tester and check the advance curve evdry 500 engine RPM. (250 at the distributor). On the smallblock V-8's, the best centrifugal/initial advance combination is 36 or 37 degrees. Vacuum, if it's used, adds another 10 degrees or so for light-throttle cruise fuel economy. It goes away as soon as a little load is applied. I've found that reducing the centrifugal advance 8 to 10 degrees, and adding the same amount of initial timing helps acceleration with some cam/compression combinations. It takes a lot of road test and dyno work to develop a modified advance curve, however.
Jerry