help finding TDC

[Jack O.]

Hi,
I'm using a TDC Locator tool to find TDC on a completely assembled engine but have a question on the procedure. The tool is the simple device that screws in cylinder one and acts as a piston stop. The procedure I followed is:

- Insert tool
- Rotated engine clockwise to stop
- Mark location on balancer
- Rotate engine counterclockwise to stop
- Mark location on balancer

What's next? Should TDC be half way between the two marks in a clockwise or counterclockwise direction?

Thanks.

[Clem Z.]

Re: help finding TDC

TDC is half way between the 2 marks if you marked the damper at the 2 stop points using the "0" mark on the timing tab.

[Jack O.]

Re: help finding TDC

I did use the "0" mark on the timing tab but is it between the 2 stop points in a clockwise or counter-clockwise direction. It wouldn't matter if the 2 stop points on the balancer were exactly 180 degrees apart but they're not.

[Clem Z.]

Re: help finding TDC

you should adjust the piston stop so the engine stops the damper a inch or so from TDC mark on the damper. when the engine stops in the CW direction mark the damper in line with the "0" on the timing tab. do the same in the CCW direction and half way between the two marks is the engines TDC. if this is not where the damper factory TDC mark is just make a new mark.

[Jack O.]

Re: help finding TDC

I did use the "0" mark on the timing tab but is it between the 2 stop points in a clockwise or counter-clockwise direction. It wouldn't matter if the 2 stop points on the balancer were exactly 180 degrees apart but they're not.

[Clem Z.]

Re: help finding TDC

i have no idea what you are trying to say.

[Michael W.]

Re: help finding TDC

Turn the crank in the direction that gives you less than 180 degrees between the stops. TDC is halfway.

[Clem Z.]

i thought this was simple but for some reason

you now have me confused what the hell you are talking about this 180 degrees.

[Michael W.]

Re: i thought this was simple but for some reason

Clem,

Just show up at Jerry's during HBB3 (never mind this silly Daytona thing) and I'll show you. It helps if you're left handed and don't drink Badweiser.

[Clem Z.]

i have checked for the correct TDC on dozens and

dozens of engines in my time and it sure seemed a lot simpler that you guys are trying to make it.

[Chuck S.]

Re: i thought this was simple but for some reason

Clem, I think your first response was the correct one...things have gotten obfuscated.

If the piston stop is adjusted where it is too far down into the cylinder, then the angle on the damper between the stopping points is LARGE. If the stop is adjusted to where it is JUST BELOW TDC, then the angle between stops is smaller. Ideally, if you could set the stop AT TDC, the two marks would be on top of each other...NO ANGULAR DIFFERENCE.

A smaller angle between stops would eliminate questions like "Do I go CW or CCW to get there?"...It don't matter which direction you go...TDC is the angular position mid-way between the marks. If the angle between the marks is enough to raise this question, then you have your piston stop too far down.

Where the 0 deg indicator falls on your damper at TDC is another problem.

[Michael W.]

Chuck of course is right, but his eloquently

worded explanation sort of spoils my plans to get Clem to show up at HBB3.

[Chuck S.]

P.S. i thought this was simple

Actually, if you are meaning how do you rotate the crank to TDC while the piston stop is in place, it can't be done.

The piston stop is preventing you from going "over center". When you are "marking" the stops, you are determining the range of piston travel that the stop is PREVENTING...mid-way in that prevented travel is TDC. You have to compute, record and/or mark the TDC angular postition, remove the stop, then you will be able to set the number 1 at TDC.

I am no expert, but I believe the closer you can set the stop to TDC, the less error you are likely to have in the determination. A degreeing wheel is the most accurate way to find TDC. If the angle between the marks is more than 20-40 degrees, you probably should readjust your stop.

The reason for determining TDC this way is that it is much easier to measure the angular position than the linear travel of the piston...a lot of rotation is occurring with only few thousandths of an inch piston travel near TDC.

[Chuck S.]

Oops, Sorry Mikey...

But, I suspect Clem was never confused about finding TDC...he was only confused about how something so simple for him could so confusing for others. The only way I understand it is that I sat down with some cam degreeing instuctions once, and slowly reasoned through what was happening when you make the marks...sort of like the first time in freshman statics.

[Clem Z.]

this has been fun but

what i do is mark the damper with center punch at both the CC and CCW roation stop,then i use toolmakers dividers in those centerpunched marks to find the exact center between the marks and that will be TDC on the damper. happy motoring!!!