One last compression stroke question.

[brokemerc]

I thought I had this whole TDC thing figured out until just talking to my son who is an ASE master tech and ford master tech,,, maybe he's just messing with me on this.. when i was finding TDC I would hold my finger over the #1 plug hole, every 360 degree rotation of the rotor I would get a burst of air out the cylinder, he says one of these bursts of air is the compression and one is the exhaust,,if so how do you know which is which.. He tells me for every 360 degree rotation of the crank shaft I get 180 degree out of the cam shaft.. True/False.. Was each burst of air indicating TDC??

 

[JustJason]

Re: One last compression stroke question.

you may feel pressure on the exhaust stroke... but on the compression stroke it should be enough to blow your finger off the hole.

 

[searay3]

Re: One last compression stroke question.

You will feel a push of air on every stroke. Look with a light, fell the air with your finger, either way when the piston is at the top of it's stroke, the harmonic balancer will show either close to the tdc timing mark, or it will be 180 out. If it's 180 out, you are not on the compression stroke. This is assuming the harmonic balancer isn't spun. The only other way is to pull a valve cover and look at the valves. Both closed, piston up, compression stroke.

 

[brokemerc]

Re: One last compression stroke question.

Yea I probably jammed my finger over that hole for about 20 rotations and can't remember any difference between any of them, but I wasn't really comparing them and thought each 360 degrees was the compression stroke. I was watching the rotor and it blew my finger off at the same spot each time. I really don't want to pull the valve cover to watch these valves..

 

[Coors]

Re: One last compression stroke question.

with the exhaust valve open, it won't blow your finger off.

 

[Fishermark]

Re: One last compression stroke question.

You will not get a compression "blast" every 360 degrees. It is a four stroke engine - piston goes down (180 degrees), pulls air fuel in - goes up and compresses it (another 180) - goes back down in a power stroke (180 degress) - goes up in an exhaust stroke (180 degrees). Your timing mark will line up on the balancer every revolution, but it will be on the compression stroke only every other revolution.

Here's a neat video to illustrate:
http://video.google.com/videoplay?docid=-5815350492893860613&pr=goog-sl

 

[a70eliminator]

Re: One last compression stroke question.

Your son is correct, the cam will make 1 revolution for every two of the crankshaft.

 

[Don S]

Re: One last compression stroke question.

when i was finding TDC I would hold my finger over the #1 plug hole, every 360 degree rotation of the rotor I would get a burst of air out the cylinder,

Every 360? of rotation of the rotor. That is 2 complete revolution of the crankshaft.
When you feel the cylinder start making compression, that is when it's on the compression stroke, the exhaust stroke is pushing, but you won't feel it because the exhaust valve is open.
So, when you start feeling compression building, watch the vibration dampner and when you get it turned to where the line on the pulley lines up with the 0 mark on the indicater tab, you are at 0? TDC on the compression stroke.

UNLESS: You have a bad vibration dampner.

 

[MikDee]

Re: One last compression stroke question.

Your son is correct, the cam will make 1 revolution for every two of the crankshaft.

That's the bottom line, just think of it this way, a bare 4-Cycle chevy block, a 4cyl (1,& 3, will be at TDC at the same time), a V6 (1,& 4, will be at TDC at the same time), and a V8 (1, & 6, will be at TDC at the same time),,, the cam shaft, (which makes 1/2 a turn with each 1 turn of the crank, will determine which cylinder is ready to fire), it takes 2 turns of the crank to make one complete cycle.

 

[starsnstripers]

Re: One last compression stroke question.

Do yourself a favor and take the valve cover off. (2min job) Locate the #1 cyl. rockers. Turn your eng. until you see the intake valve closing. Now as you continue to rotate engine when the TDC. mark lines up to the pointer it should be TDC. Stick a clean screw driver in the cyl. and the piston should be at the top. Look where rotor is pointing and thats #1 on the cap. Thats how i had to figure mine out. Worked like a charm. good luck

 

[starsnstripers]

Re: One last compression stroke question.

Everyone here is right but if you don't do it alot it can be confusing. Thats as simple as I can type it.

 

[MikDee]

Re: One last compression stroke question.

.
UNLESS: You have a bad vibration dampner.

This doesn't really even matter if you feel compression, put a tool of some type in the Cylinder, then finish by carefully turning the engine over by hand in the proper direction to reach TDC physically. The TDC mark should be close, that will tell you if your balancer is off, or not. If it's off, make your own TDC mark on the balancer, this will remain the same for both cylinders at TDC, unless the balancer moves again.

 

[brokemerc]

Re: One last compression stroke question.

Every 360? of rotation of the rotor. That is 2 complete revolution of the crankshaft.
When you feel the cylinder start making compression, that is when it's on the compression stroke, the exhaust stroke is pushing, but you won't feel it because the exhaust valve is open.
So, when you start feeling compression building, watch the vibration dampner and when you get it turned to where the line on the pulley lines up with the 0 mark on the indicater tab, you are at 0? TDC on the compression stroke.

UNLESS: You have a bad vibration dampner.

My reason behind doing this check was to make sure my plug wires were on right,, just so happens that it appears that my distributor is rotated 90 degrees clockwise from standard, or at least that's where the rotor is pointing each time I get a blast from cylinder 1. I also placed a plastic rod down the plug hole and rotated the motor by hand to bring the piston full up (neglected to check the timing mark though). I'm just gonna see if it runs,, pretty sure it will,, heck it did when i had every wire on the wrong plug.. If not I'll pull the valve cover and the distributor and set it the way it should be... Thanks for the great input...

 

[Don S]

Re: One last compression stroke question.

The engine doesn't care where #1 is on the distributor cap, as long as that is where the rotor is pointing. Timing will be the same and all. You may not like it like that, but the engine doesn't care one bit.

 

[brokemerc]

Re: One last compression stroke question.

Exactly what I was thinking,,, thank you.... Didn't think a 3.0 could be that smart,,, obviously occasionally smarter than I am,, but not THAT smart..

 

[Don S]

Re: One last compression stroke question.

The 3.0L or any other engine for that matter, isn't smart as far as where #1 is located on the distributor. The rotor goes around in a circle and does the same exact thing every time. As long has you have the #1 piston at TDC on the compression stroke, you can put the distributor in any ole place. Then just put the cap on and see where the rotor is pointing at the time. That IS #1 for how the distributor was installed. Not just put the wires on in the proper order and you are ready for the timing light.
You may have to turn the distributor a little one way or the other to get it going, but it will work.

 

[MikDee]

Re: One last compression stroke question.

The 3.0L or any other engine for that matter, isn't smart as far as where #1 is located on the distributor. The rotor goes around in a circle and does the same exact thing every time. As long has you have the #1 piston at TDC on the compression stroke, you can put the distributor in any ole place. Then just put the cap on and see where the rotor is pointing at the time. That IS #1 for how the distributor was installed. Not just put the wires on in the proper order and you are ready for the timing light.
You may have to turn the distributor a little one way or the other to get it going, but it will work.

I respectfully disagree, on a breaker point distributor, you have to have the points on the high lobe of the cam for it to fire, as your rotor is directly under your Dist cap on #1 and the plug wire has to be on Cyl #1. The base of the Distributor has to be in synch with the cap. If it is off a little bit, one way, or the other, the spark will be advanced, or retarded, and no moving of the distributor will correct this fact. You can put #1 anywhere on the distributor, as long as you follow these same rules. It is no different with an electronic distributor, that uses any type of trigger system, the trigger, and it's target has to be lined up when the rotor is on #1. I'm using #1 as an example, but it could be any cylinder, it all has to be in synch. It used to be you had a diagram showing the hold down screws of the Dist. cap, and the correct spot to put #1 to start with, followed by the firing order, & rotation, so it would automatically come up in synch,,, Not any more, they take too much liberty's with vague sketches on this now, so people have no concept as to how this all works.

 

[Don S]

Re: One last compression stroke question.

To prevent going into TOO MUCH detail, I did say.

You may have to turn the distributor a little one way or the other to get it going, but it will work.

 

[achris]

Re: One last compression stroke question.

I respectfully disagree, on a breaker point distributor, you have to have the points on the high lobe of the cam for it to fire, as your rotor is directly under your Dist cap on #1 and the plug wire has to be on Cyl #1. The base of the Distributor has to be in synch with the cap. If it is off a little bit, one way, or the other, the spark will be advanced, or retarded, and no moving of the distributor will correct this fact. You can put #1 anywhere on the distributor, as long as you follow these same rules. It is no different with an electronic distributor, that uses any type of trigger system, the trigger, and it's target has to be lined up when the rotor is on #1. I'm using #1 as an example, but it could be any cylinder, it all has to be in synch. It used to be you had a diagram showing the hold down screws of the Dist. cap, and the correct spot to put #1 to start with, followed by the firing order, & rotation, so it would automatically come up in synch,,, Not any more, they take too much liberty's with vague sketches on this now, so people have no concept as to how this all works.

I respectfully disagree with you respectfully disagreeing... Don's right.. Engine don't give a rat's where the distributor is, as long as the cylinder gets a spark around the TDC of it's compression stroke. A really good example of this is Bond-o's avatar.

An easy test to prove this.... pull the distributor out of the engine.... more the shaft 90 degrees (4 or 8 cylinder engine assumed here) and put the dissy back in. Now more all the plug leads around in the same direction as you turned the shaft.. Fire up the engine and it will run like nothing happened.

Chris........

 

[Bondo]

Re: One last compression stroke question.

I respectfully disagree with you respectfully disagreeing... Don's right.. Engine don't give a rat's where the distributor is, as long as the cylinder gets a spark around the TDC of it's compression stroke. A really good example of this is Bond-o's avatar.

Ayuh,........ I Agree with your respectfully disagreeing with his respectfully disagreeing............

And,...... I'm only posting here to insert My Avatar,....
As this Same topic by the same poster is covered in Another thread,.......Again......