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I'm putting the front end of my 350 back together and noticed something with the timing chain alighment. When the dot over dot position is set up, is this tdc of the exhaust stroke? I looked at it for a few minutes and it didn t seem logical. And, how much play should there be in the chain? The timing chain might have 2000 miles at the most, but I want to make sure.
 

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The timing gear marks are TDC compression #6. You need to rotate the crank 360 and back 10 (350 degrees from the timing gear marks) to install the distributor at TDC compression #1, (10 degrees initial timing).
 

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Paul Wright said:
The timing gear marks are TDC compression #6. You need to rotate the crank 360 and back 10 (350 degrees from the timing gear marks) to install the distributor at TDC compression #1, (10 degrees initial timing).
So if you do that, that means that when the mark on the balancer is at 0, you already have 10*?

Matt
 

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No, that means you are at 10 degrees before TDC.

When the timing chain marks are aligned and you put the timing cover, balancer and pointer on the line on, the balancer should be at zero.
HOWEVER.... it's not TDC Compression. This position is TDC exhaust overlap. You don't want to fire your plug when both the valves are open.

Rotate the crank 360 degrees, or one full revolution and the mark comes around to the same spot but the cam is now at TDC compression.
Back it up 10 degrees and the mark is at 10 degrees BEFORE TDC compression. This will be your base timing when you drop your distributor in. You can use 12 or 14 or whatever but 10 is a good start if you don't know.

If you plop the distributor in at zero you are not where the engine want's to be. Then you are stuck twisting the distributor while looking at a timing light. If you installed a new cam you are wasting precious seconds trying to get the engine to fire. The cam lube won't stay on forever and you run the risk of flattening a lobe the longer it takes to fire up and run at fast idle. I'm willing to bet that more cams are ruined by this mistake than any other.

People make this very common mistake because they assume that the timing gear marks are TDC (which they are) but they forget or don't know that there are two Tdc's for every full revolution of the cam sprocket. It's bigger than the crank sprocket because a four stroke engine makes two full revolutions of the crank for every revolution of the cam.
 

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Ah, so you get the mark to zero and then move it 10* and put the distributor in, and the mark ISN'T at 0. The last post sounded (to me) like there was 10* of timing but the mark was at 0. :confused:

Makes more sense now. :)

Matt
 
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