Playing around a little last night with the timing. Decided to check timing specs at front end TDC, absolute TDC, and back end TDC. I found that depending on where you register TDC, timing influences are changed a great deal. For instance, at leading edge of TDC an engine timed at 19* will advance to 23* merely by squeezing TDC to the trailing edge of it. And the pin...don't get me started. I played with pin position to actual piston position, and realized there is a reason I time with a dial indicator!! The pin method offers up as much as 3* of timing flux and is not consistent evry time to be in the same spot. For those of you not using a dial indicator...I recommend it if you do your own timing.

Now out of curiousity, those that DO time with a dial indicator, at what point in revolution do you consider TDC for the purposes of timing your engine?

 

Piers told me several years ago the pin can vary as much as 5°, totally unacceptable.
When I set TDC I remove the #1 injector and use a dial indicator to find the top of the piston stroke. Can't get any closer to TDC than that.
I've never been able to insert the injection pump timing pin when I use this method to find TDC, indicates to me that it's rare for the pin to be right. Close enough for valves, but not for timing.

 

I drop a valve and use a dial indicator on the tip of it ( the valve ) You can get TDC pretty fast that way. Just let the valve drop right on the piston top and it will move up and down with it. Sometimes the valve will stick from the seal resistance. I just give it some help to fall. Make certain the piston is near or at TDC. LOL


I also use the pin after I get a reference point for quick changes in timing when it is not super critical.

Don~

 

We all agree that dial indicator timing is the most accurate, especially when small adjustments are crucial, or we are at a supposed ragged edge. So my real curiousity is again this....

once the piston rises to tdc, it's the cam over area that I'm curious about. From the TDC position there are a certain number of degrees of crankshaft travel before the piston will fall off TDC. After playing with the numbers I found timing can be influenced as much as 3* depending on where you stop the crank. At what point do you consider TDC to be TDC? I've talked to shops that call it on the front end "just at" TDC, I've also heard other mechanics call it "just as" it's falling off. Or is splitting it for absolute the way of the gods...much like finding it using a drop valve method without a dial indicator.

It really doesn't make either way right or wrong, consistency is the name of the game, just curious the most popular way.

 

I split it! This is mostly because when I measure camshafts in the dummy block I have I use a degree wheel and split the piston stop marks in half.

It just comes naturally so I keep in consistant.

Don~

 

sorry i dont exactly get this. im about to buy a timing kit,

as got...diesel said, you recommend a dial indicator to find the TDC? (when the piston is on the very top?)

and do you use the same dial indicator to find out the plunger lift on the injection pump?

wher can i buy the timing kit the cheapest?