Finding TDC without a Flywheel or Distributor

[krispy]

Hi all. Im putting my motor back together and am at Fig 3-56/57 in the Service manual at the part where it asks you to adjust the valve clearance. It says to set No. 1 cylinder to TDC/Compression. Since I don't have the flywheel on and I haven't installed the distributor yet, I'm unsure about "No. 1 cylinder to TDC/Compression". I know when the marks on the crank and cam gear are lined up im at TDC.

But at this point, is No. in Compression or Exhaust? In this position, the springs under the 7th and 9th rocker are compressed, and the manual says im supposed to adjust those. However, since the springs are compressed, you cant. See the image:

When I spin the nut 360 and the alignment of the crank/cam is like this:

The valves are like this:

So which position is "No. 1 cylinder to TDC/Compression", I think, with the marks not right next to each other? Lastly, when im done with these steps. Which position do I want it in for installing the distributor and eventually starting the motor up?

 

[rkymtnflyfisher]

Do you have a FSM?

I believe all of your questions are answered inside.

Factory service manual.

 

[fjc-man]

This picture should help. Which valves to ajust one crankshaft rotation apart.

 

[pb4ugo]

You can drop a couple of lifters for the #1 cyldr in the lifter bores and rotate the engine and watch them go up and down to ID their respective stroke. I suspect when they dots are together would be on the exhaust stroke, but can't say for sure.

 

[cruisermatt]

You’re lacking some fundamental understanding of how an engine works.

Both valves will be closed at the TDC of the compression stroke.

The exhaust valve will be open at the TDC of the exhaust stroke.

Don’t spend too much time on adjusting the valves on a rebuilt engine. You’ll have to completely redo it once you get it running and get some heat in it.

 

[middlecalf]

And this…

That's worth a lot to me. Thank you sir. The manuals I have don't make reference to engine position when the marks line up but just say "line them up". I never would have guessed it was #6 on TDC compression when the marks are aligned. Saving that pic for sure. I converted it from png to jpeg & enhanced it a little to make it easier to save it if others care to. Thanks again.

View attachment 3346384

 

[krispy]

This picture should help. Which valves to ajust one crankshaft rotation apart.View attachment 3355059

Thanks, I have this manual, and am at this step, Im just having trouble figuring out when #1 cylinder is at TDC compression

 

[krispy]

You can drop a couple of lifters for the #1 cyldr in the lifter bores and rotate the engine and watch them go up and down to ID their respective stroke. I suspect when they dots are together would be on the exhaust stroke, but can't say for sure.

Lifters, pushrods, and valves are all in. Up is open, right and down (or flush) is closed.

 

[krispy]

You’re lacking some fundamental understanding of how an engine works.

Both valves will be closed at the TDC of the compression stroke.

The exhaust valve will be open at the TDC of the exhaust stroke.

Don’t spend too much time on adjusting the valves on a rebuilt engine. You’ll have to completely redo it once you get it running and get some heat in it.

Likely, I understand 4-cycle = suck (intake) squeeze (compression) bang (ignition) blow (exhaust). But am having some hardship understanding what is open/closed at different points in the rotation. My intention is to get them close and then readjust when warm.

 

[cruisermatt]

Likely, I understand 4-cycle = suck (intake) squeeze (compression) bang (ignition) blow (exhaust). But am having some hardship understanding what is open/closed at different points in the rotation. My intention is to get them close and then readjust when warm.

At TDC of the compression stroke both valves will be fully closed on that cylinder, hence, there will be lash on those rocker arms which is what you are adjusting.

Just think about what needs to happen with the intake air and exhaust energy for each of the four cycles and what the valves need to do to be able to accomplish each of those cycles. Intake cycle, intake valve opens to let air in, compression cycle, intake valve closes so the air can be compressed, etc, etc

 

[Steamer]

Going by the manual pic that Middlecalf supplied, and using your pics, you could go by this.

When cylinder # 6 is TDC compression, cylinder # 1 is TDC exhaust. And vice versa.

 

[pb4ugo]

TDC dots line up with the cam and crank gears or the cam is 180 degrees out from there & inline with the center of the cam and crank and the dot on the cranks timing gear. If the lifter/pushrod is going up or up it is opening the valve. Intake stroke the intake valve opens and the piston is going down sucking air/fuel mix. Compression stroke both valves are closed and the piston is going up to TDC on compression. Power stroke, piston is at the top of the cyldr(TDC) and the plug fires and the piston is forced down. Exhaust stroke, exhaust valve is open and piston is goes up and forces the exhaust out of the cyldr. The crank spins twice as fast as the cam(crank spins 360x2=720degrees). You can adjust the valves according to @fjc-man post in Post #3. You can ID which valve is which by looking at the ports in the head in relation the the intake and exhaust manifold.

 

[Steamer]

Likely, I understand 4-cycle = suck (intake) squeeze (compression) bang (ignition) blow (exhaust)

 

[fjwagon]

Best way I found is know that that flywheel has to rotate twice to open and close all the valves (exhaust and intake) You can see an illustration on the oem where you can adjust one section after you set the flywheel at it's proper position. And then Rotate the flywheel 360 and do the other half. Something else that is helpful to know is when they say set the piston to TDC. This means the piston is at the top and both exhaust and intake valves are closed and compression is at its max. And in real-time this is when a spark is sent to the sparkplug create the explosion.

It's not easy to explain but easier to do. Since the flywheel is not installed use the open/close valve sequence, TDC, and the timing gears. If you rotate it enough you will notice that there is a closing/opening pattern on the valves. Pay attention to where the no. 1 piston (TDC) and timing gear is when complete the cycle complete.

That's why people say you are 180* off when the distributor is installed and wont start. They picked the wrong cycle(and you can by looking at the valve sequence) If that happens repeat the cycle set the the piston to TDC and look at vavles and timing gears. I hope this helps.

 

[peesalot]

4 stroke = first down stroke is intake, up is compression, down on power stroke, and back up for exhaust.
Cruisermatt is correct, watch the valves on the #1 cyl while rotating engine, take spark plug out and stick a long kabob skewer in so you can see piston heigth, watch as you rotate, skewer will be going down and intake valve is open, as skewer comes back up both valves closed, watch skewer, when it reaches the highest point of upward travel thats TDC #1, as you continue to rotate skewer will go down, both valves closed, thats the power stroke, as skewer comes back up you should notice exhaust valve opening actually just before the skewer reaches lowest point and comes back up on exhaust stroke. Hopefully your timing marks correspond to what you find as actual TDC.

 

[cruisermatt]

Like I said there really is not reason to spend much time on this task, just get them close, you are going to have to completely re-do it once you get it actually running in the truck. That's just reality

 

[67azcruizr]

pistons will travel up and down twice per complete engine cycle, compression and exhaust

intake/exhaust valves open once (ea) per complete engine cycle, hence larger gear.

 

[krispy]

Thanks all for the advice! Which position do I want it in for installing the distributor and eventually starting the motor up?

 

[67azcruizr]

Thanks all for the advice! Which position do I want it in for installing the distributor and eventually starting the motor up?

compression stroke

in most engines, your distributor rotates clockwise through the firing order. with that said, as you install the distributor, it will naturally clock clockwise as it seats itself in with the cam drive gear. to counter this, clock the rotor counterclockwise about 20* (I don't know the exact degree as I usually eyeball it) so that the rotor will end up resting, pointing at the #1 spark plug wire location on the cap (some distributor housing aren't indexed).

lastly but EXTREMELY important, make sure the distributor housing is seating 100% onto the oil pump drive gear (the oil drive gear can be rotated with a straight, long screwdriver). if you don't seat it properly, NO OIL delivery will take place.

 

[cruisermatt]

Thanks all for the advice! Which position do I want it in for installing the distributor and eventually starting the motor up?

All of your questions are answered in the FSM.