View Full Version : TR4/4A TR 4 Timing mark

11-22-2014, 09:35 PM

Does anyone know the distance from top dead center around the circumfrence of the crankshaft pully for 4 degrees?
If not, does anyone know the diameter of the pully?


11-22-2014, 09:58 PM
Pulley is 5.5 inches. You might want to search this forum for static timing info. There are several earlier threads on the topic.Tom

11-23-2014, 01:41 AM
Yikes, been so many years, geometry, pulley is 5.5" I assume this is diameter, circumference is Pi x diameter, so 3.14 x 5.5" = 17.27" (circumference) / 360 (degrees) = .048" per degree (rounded). Times 4 (degrees) = .192" inches, a hair over 3/16" of an inch. Correct?

11-23-2014, 08:54 AM
Sounds right but I'd just make a wedge of 4 degrees with a protractor on a piece of paper or cardboard and measure the width at half the diameter of the pulley.
Check Also:

Geo Hahn
11-23-2014, 11:13 AM
The math looks sound, Euclid pretty much got it right.

The thing is, any static timing setting is really just a starting point in my opinion and the final timing is dialed in along the roadside based on running performance that is affected by the state of the engine, altitude, gas being used, how deaf the driver is and other factors.

Where precision does help is in making the process repeatable and measurable. I set the static timing 'by the book' with the distributor vernier at the big mark and then adjust on the road with the dial. That way I know where I have ended up when all is done.

11-26-2014, 07:51 PM
The number that sticks in my head is that 3/8" equals 8 degrees; so that matches glemon's math.

11-26-2014, 08:50 PM
Hey hey, credit where credit is due please, can't believe I remember some of that stuff, although it is pretty basic geometry, a smart math teacher could have used an example like this to get the gearheads attention in math class back in the day!

Geo Hahn
11-26-2014, 09:39 PM
Yeah, I copied your homework.

I'm still waiting for the quadratic equation to be useful around the shop.

11-27-2014, 01:30 PM
I really only static time, then check with the light to see if anything looks wild. That dial on the distributor works well enough and I figure I'm near 4 degrees. 3/16 sounds tight to me based on my blinking white mark, but I'm not touching a thing because after many years of playing with TR engines, my TR4A is going on one full year of great running plus an incredible anomaly. When I shut off the engine, the engine actually shuts off, completely and quietly, like an old Buick. No need to clutch it down, just fizzles right out. Peace for the Holidays.

11-27-2014, 01:38 PM
Took me 4 years to pass 2 years of algebra. God Knows if I took Calculus or Trigonometry I'd still be there 65 years later. IMO, math should be taught by people who don't understand it and have trouble with it - but using examples from real life. When I took my written test for my pilot's license, I scored in the 90s including navigation, weight and balance and time and distance problems. Why? I was interested and it was relevant so it made sense to me. My high school algebra teachers were terrible and had no patience for people like me who didn't have the math gene. I was a journalism major in college but became a lawyer 52 years ago and still at it.Quadratic equations? We don't need no stinkin' quadratic equations.

Geo Hahn
11-27-2014, 01:58 PM
... I'm not touching a thing because after many years of playing with TR engines, my TR4A is going on one full year of great running plus an incredible anomaly...

My favorite quote (of many) from Jules Renard: “There are moments when everything goes well; don't be frightened, it won't last.” .