Hey All,
Just install a built 351 Windsor in my 69 Bronco. I had to pull the timing tab the builder installed on the front of the motor because it was on the wrong side and wouldn't work behind the water pump. I need to remark my balancer with tdc and put timing tape on it. I have been told to get a piston stop and screw it into the #1 plug and slowly bring the piston up till it stops on the stop, then mark the balancer there with the new tab on the other side, then turn the motor the other way until it comes around again and hits the stop. Mark the dampner there and then TDC will be exactly 1/2 way between these two marks. Can anyone veryify this is the proper method without removing the heads etc. Do you set the piston stop so it stops at exactly the top of the stroke or does it not matter as long as it stops in exactly the same spot each time? I thought TDC was the #1 piston on the very top of the compression stroke? That is why I am somewhat confused about the above mentioned method. Thanks in advance for input.
Dan

 

TDC will be where the piston hits the stop on the compression stroke ( both valves closed) What that guy's telling you is wrong. The piston travels to the top of the cylinder twice for every one rev of the cam and for each engine cycle

 

You have been told correctly. The piston will actaul dwell at the top of the stroke or slight pause. The method described to you is how one would degree a cam in. Perform the method described to you and you will have the absolute TDC.

The method describe is kind of like taking a measurement across a gap and you need to know the center of that gap. The best way to get absolute cnter is by measuring the intire gap and divide it in half to get the absolute center. Now you need what we will call the absolute center (TDC) so by placing the stop in the motor for the piston you are creating one side of the gap. Rotate the motor the other way and you have created the other side of the gap. Half the distance between the to points is absolute TDC.

 

If you're rotating the crank around from one TDC to another, then halfway between would be BDC not TDC

 

If you went between the points one way then yes what you say is true. You just select the other middle if that makes sense or not.

Lets try this. When you perform the above mentioned method you will have a certain amount of degrees between points, correct? remember you only have 360 degrees for a complete circle. Now you have two sides to this. One being that you will read from lets say from 10 degrees to 350 degrees. The 10 and 350 are where the piston is stopped by the stopped you would have installed. Now you can see the two windows. One is a total of 20 degrees which is the reading from 350 to 10 and the other is 340 degrees which is the reading from 10 to 350.

If you pick the middle of the 340 degree window you will have BDC but if you pick the middle of the 20 degree window then you will have TDC.

Thats why you use a stop to stop the piston as near the top of the stroke. I should have explain the midldle of the window better. The window that you pick the middle of is the window in which you can not rotate through because of the stop. This is where a degree wheel comes in handy.

Even if you obtain the BDC you're now exactly 180 from where you should be (TDC) so either way with a little thinking you will get the TDC one way or the other.

I've used this method to install timing gear drives with no markings.

 

I see, said the blind man to the deaf guy!! I understand what you're saying now. That's the method used to degree a cam, and setting up the degree wheel.

 

Ok thanks for the info. I think I can figure this thing out. Even if I do hit 180 out I can measure the total circumfrence of the dampner and move exactly 1/2 way around for TDC.

 

After you get your tdc marked you'll want to crank the engine with your finger stuck in #1 plug hole to find the compression stroke tdc so you dont stab distributor 180 off. Unless dist was never removed.

 

Good point circledirt. I remove the valve cover and watch the rocker arms. When the intake valve closes you are then on the compression stroke.