This is probaly basic engine 101, but how many revolutions of the crank pulley does it take for piston #1 to travel TDC to TDC.

I'm trying to determine TDC; I have a piston stop like this:
http://store.summitracing.com/partde...5&autoview=sku

I've inserted it into sparkplug hole #1 and turned the engine CW till it hits the stop, then backed off the adjustment bolt a little and continued to turn the engine CW till it hits the piston stop again. At one point the piston starts it travel downward; I then turn in the adjustment bolt to the last point where it hit the piston. I continue to turn the engine CW to make sure I've got the highest travel on the piston. I figure it's going to come around again and hit the piston stop. I'll turn that engine twenty revolutions and never hit that piston stop again!

I've read post's on how to determine TDC, but I can't seem to get exactly the highest travel on piston #1 to get that first mark.

 

2, the engine needs one revolution to exhaust the spent gases. Trace the #1 spark plug wire back to the distributer and note the lug it plugs into. Remove the cap and rotate the engine till the rotor points at this lug and you'll be close to TDC.

 

Another method is to spin the engine until the piston touches the stop. Mark the balancer where this occurs. Rotate the engine in the opposite direction until the piston touches the stop again. Mark the balancer again where this occurs. Make a third mark exactly between the first two marks and that is where the piston is at TDC.

 

I remember this from an earlier post...you need to have the valve cover remove to ensure that both the intake and exhaust valves are closed!....then do the Piston Stop just as Marsh Rat is saying

 

The question was "This is probaly basic engine 101, but how many revolutions of the crank pulley does it take for piston #1 to travel TDC to TDC."
The technical answer is actually 1.

 

Also want to add that it has nothing to do with the valves.
As stated eariler; spin one way and mark, spin the other way and mark, then TDC is 1/2 way between those marks.

 

Please explain this? I have read this before too, but it confused me. Wouldn't the piston be at BDC at this point?

 

http://auto.howstuffworks.com/engine.htm

 

You are both right and wrong. For sake of discussion lets say the circumference of the balancer is 20" and is marked every inch. Rotate the crank until it hits the stop. Lets say it stops at the 19" mark. Spin it the othe way and now it stops at the 1" mark. Half way between them would be at the 0" mark. That is TDC. However the 10" mark is also halfway between 1 and 19. That would correspond to BDC and is 180* opposite the 0 mark.

 

Now I'm really confused.

 

Here's what I think I know.
If the cam dots are lined up, the #1 piston is at TDC, but on the exhaust stroke. If the balancer is rotated once around, then #1 will be at TDC compression stroke. The #1 piston reaches the top of the cylinder each time the mark on the balancer lines up. On the compression stroke TDC, the rotor should point to #1, on the exhaust stroke TDC, the rotor should point to #6. This is how a distributor can be 180 degrees out.

Here's where I'm confused...
Is the piston stop set so it contacts the piston at TDC, or just below it?

Maybe I can answer my own confusion?
If the piston stop is set so it contacts the piston at TDC, you would rotate the engine umpteen times and the mark you make on the balancer would line up everytime, so the piston stop has to be set before TDC.

 

Well I'm done with this project. Can only find the first mark with the piston stop. I've bent the adjustment bolt on the piston stop tool, making it hard to move. And believe me I've moved the engine by hand very gently to make sure I don't slam the piston into the tool.

Can I learn anything from just one mark? It is almost exactly 90 degrees from the factory TDC mark.

 

The TDC locator does not give you tdc on contact, what you do is as mandm1200 instructs, you touch the piston, mark the balancer, spin the eng back till it touches again, mark it again then measure the distance between the marks and half way between is tdc.

 

Here's my theory, you get a ttt even if I am wrong.

If you point the mark on the dampner to the timing tab, then set the piston stop to the top of the piston, you should be able to turn the engine CCW (backwards). The piston will travel down the cylinder, past BDC, and back up to the piston stop. The next time it contacts the stop you should be able to make another line. As you have stated the first line is 90 degrees from the dampner line, the next line should be 90 degrees the other way on the dampner. The measured middle of these lines should be the balancer groove. If not, the balancer has slipped and needs replacing.

edit - just like Fevre says, he must type faster than me.

 

I'll try this again.

1) Remove the drivers side valve cover.
2) Rotate the engine clockwise until the #1 cylinder intake valve closes.
3) Install the piston stop in #1 spark plug hole.
4) Continue to rotate the engine clockwise until the piston makes contact with the stop.
5) Mark the balancer ring.

AT THIS POINT DO NOT ADJUST THE DEPTH OF THE PISTON STOP!

6) Rotate the engine COUNTERCLOCKWISE until the piston makes contact with the piston stop.
7) Mark the balancer ring.

NOTE! IF AT ANY TIME AFTER YOU INSTALL THE PISTON STOP, YOU ROTATE THE ENGINE MORE THAN ONE (1) REVOLUTION, IN EITHER DIRECTION, YOU HAVE MADE A MISTAKE! START OVER! AFTER YOU INSTALL THE PISTON STOP YOU SHOULD NOT BE ABLE TO ROTATE THE ENGINE MORE THAN ONE REVOLUTION IN EITHER DIRECTION! IF YOU CAN, THE STOP IS NOT INSTALLED CORRECTLY!

You should now have two (2) marks on the balancer ring. If you envision the balancer to be a clock, we'll say that the marks are at 12:00 and 3:00. The true TDC of your engine is going to be half way between these two marks. We'll say that the marks are 3 1/4" apart. True TDC is exactly half way between them, 1 5/8".

NOTE! YOU MUST ROTATE THE ENGINE IN TWO (2) DIFFERENT DIRECTIONS TO PREFORM THIS MEASUREMENT CORRECTLY. FIRST CLOCKWISE THEN COUNTERCLOCKWISE!

I really don't know how I can explain it any simpler.

BigBlockk

Later.....

 

Thanks BigBlockk,

I do have your previous post printed and are using it.

My problem is finding the highest point where the piston comes up. How far do you adjust the piston stop bolt? I have it screwed as deep as it will go and it contacts the piston. I then back off the bolt and continue to turn the engine a little more where it contacts the bolt, till I've found just where the piston is heading back down. I am doing this myself and turning that engine from the top is a bitch. Valve cover is off, but those valves don't move much; I can't seem to catch when the intake closes.

I have the concept, it's just my techique sucks. I'll take another try at it today; my friend is back from vacation, so maybe I can use another pair of hands.

Thanks again for all the suggestions.....

 

The Piston Stop Tool is a piston stop tool, not a top deadcenter tool. It stops the piston. It is the prefered tool to use when calculating TDC. You don't find TDC, it is calculated. You screw it in and then leave it alone as the engine is rotated in both directions. If you follow the instructions that are given, you'll get two marks on the damper (one from each direction of rotation). TDC is neither of those marks, it half way between them. This is a one person job. Stand where you want to.
It doesn't matter if the the piston stops 1/4" from the top, a 1/2" from the top, or an 1" from the top.

 

Ahhh...OK, that would simplify things a great deal. I should have TDC figured out shortly after I get home!

Thanks for all your patience...I'm sure you guys/gals are tearing all your hair by now. I'm a little slow.....

 

Understand, It's VERY difficult to tell when the piston is at TDC by measuring it's movement. Near the top, relatively large degrees of turning the crank will have minimal effect on the distance the piston travels. So instead of trying to determine if the piston is actually at TDC, the stop is used to measure 1/4" down from TDC in each direction. These are moe accurate marks in reference to the degree rotation of the crank. Once you know your marks 1/4" before TDC and 1/4" after TDC, then mark halfway in between the 2 marks. That's TDC.
BTW, the 1/4" doesn't have to be 1/4" it can be .100" of 1", as long as it's the same distance befor and after TDC.

 

Big Blockk nailed it, that's the correct way to find it. You should even do it this way when using a bridge and dial indicator since the piston doesn't really move enough to measure, plus it rocks, at TDC. Measuring from both directions and splitting them is the only correct way to be sure you're finding true TDC. Great explanation, by the way.