TDC Question

[JSDSKI]

Question for engine and machinist guru's - This is from Stomski's website: TDC INDICATOR TOOL - "To ensure the utmost in timing precision, the true TDC of all engines should be checked to confirm the accuracy of the pulley TDC mark in relation to real TDC. This tool screws into the spark plug hole and gives you a mechanical indication where the piston is in relation to the pulley."

Let's say it had a graduated mm (in thousandths) scale on the rod. If you put it in each cylinder, would it be accurate enough to measure a bent or twisted rod by measuring maximum stroke relative from one cylinder to another ?

[HawgRyder]

The method of using this tool....
Tool into spark plug hole (#1)....
With the tool....you can rotate the engine very slowly until the tool reaches it's highest mark....rock it back and forth to get the highest...that should also be at the TDC mark.
I have seen engines as far out as 12 - 15 deg.
If you have a problem....compare your pulley with another one....maybe the keyway is incorrect.
Bob

[JSDSKI]

Thanks, Bob. I was also wondering if it was possible (or made sense) to attach a depth gauge read out to the tool to measure TDC on each piston relative to each other... ?

[BK911]

This tool does bring up an interesting point. Some people are starting to verify cam timing when installing new tensioners. Awesome idea, I don’t know why you wouldn’t. But how many people verify TDC before cam timing? Even if you’re only a degree or two off, the overall cam timing is off. Could be the difference between a good running engine and a great running engine.

[JSDSKI]

Agreed BK, a "benchmark" before you do much with cam timing is probably a good thing! This method also allows for the "slop" in higher mileage engines.

Also might be a good check for valve kiss damage from a missed shift or overrev. A slightly hammered rod might show up and account for uneven running after the usual ignition / fuel checks were made.