TR2/3/3A TR3 tining without marks on crank pully

[jfarris]

Greetings,
I just had a 25D distributor rebuilt by Advanced for my early TR3. Jeff recommended leaving the vacuum advance on it. He said to time it at 11-14* BTDC, at idle, with the advance disconnected. My crankshaft pulley has no markings on it. I static timed the current distributor at TDC, then moved it a little before TDC and played with it for a long time to look for a sweet spot.
Any suggestions or is that what I need to do again?
Thanks,

 

[Geo Hahn]

I'd be tempted to make a timing mark and work from there. In addition to being possibly simpler - you will also know where you are when you finally get it right.

A simple piston stop (made from an old spark plug in this case) is one way to find TDC with precision:

But it seems odd to me that you have no TDC on the pulley - you would be looking for a hole in the rear lip.

 

[TR3driver]

I agree with Geo. However, the hole may be nowhere near TDC if the pulley was assembled wrong.

Once you've found TDC, make another mark 1/2" to the (drivers) left of it, measuring around the edge of the pulley half. That should be about 10.5" BTDC if my math is correct.

 

[CJD]

There are timing guns that allow you to dial in the advance. It makes setting odd timing values as simple as dialing what you want and then "0" the marks.

The alternative is to measure the diameter (d) of the pulley and use the formulae:

(22 x d)/2520 = distance along the pulley per degree. So take that number times the number of degrees you want and mark the pulley that distance clockwise when looking from the front of the car.

Personally, I REALLY like my dial advance gun!

 

[jfarris]

Thanks guys, I knew there would be an engineer or mathematician in the group that could solve that, "where is 11-14*' problem.
I'll look specifically at the back side of the pulley for the hole that I may have missed.
Geo - good idea on a more precise TDC stop - my son and I used one similar when building go-kart engines.
Off to the garage, I decided 48* was too cool for cars and coffee this morning.

 

[martx-5]

The alternative is to measure the diameter (d) of the pulley and use the formulae:

(22 x d)/2520 = distance along the pulley per degree. So take that number times the number of degrees you want and mark the pulley that distance clockwise when looking from the front of the car.

I know that formula works because I just tried it, but basic geometry says the formula would be Distance per degree = Circumference/360° or (Pi x Diameter)/360°...multiplying Pi and the degrees by 7 just seems to mystify a very simple formula.

 

[CJD]

It's using the simple approximation for pi, which is 22/7. Using the "real" pi will make it accurate to more decimal places!