Finding TDC

[82 GT]

I have my bottom end completed on my 351w I'm building. I bought timing tape from summit so it will be easier to adjust the timing after the engine is running.
I already have the timing cover and water pump installed.
How do I know when I have TDC and not the exhaust stroke when #1 is at the top? My heads aren't installed yet either.
Is there a way to tell TDC judging from another piston(s) at their TDC?
I know I should have installed the tape before the timing cover but I forgot and I don't want to rip everything off again.

[richd]

If you think about it in terms of the firing order, 8 fires right before 1. So if you have cyl 1 at TDC and you look down the lifter bore of the exhaust side of cyl 8 you should see the lobe basically pointing straight at you, give or take a few degrees.

Basically when cyl 1 is at TDC, cyl 8 is halfway through it's exhaust stroke.

Sound right? I'm assuming your firing order is still 1-3-7-2-6-5-4-8. I think some aftermarket cams change it. At any rate, if your firing order is different, use the last cylinder in the order in place of cyl 8.

Good luck,

Rich D.

[PKRWUD]

Your pistons will always be in the same relationship to each other. It doesn't make any difference as far as the tape is concerned, because the crank spins twice for every one rotation of the cam. In other words, the balancer will be in the exact same place at TDC for the #1 piston regardless of the cam.

Take care,
~Chris

[richd]

Whoa! Guess I over thought that one...not to mention I was wrong anyway. If cyl 1 is at top of compression, then cyl 8 will be halfway through power and cyl 4 would be at bottom of power, transitioning to exhaust.

So you would see the cam lobe just starting to push the lifter in cyl 4 exhaust to know you are at cyl 1's power TDC.

Thanks for simplifying it, PKRWUD.

Later,

Rich D.

[mpj76]

The first time I put my engine back together with #1 piston TDC, it was on exhaust stroke. When I tried starting it wouldn't try to catch at all. It just cranked. I spun the distributor crank around about 180 degrees and tried again. It would catch but die without the throttle down half way. I had a friend keep it running at rough timing while I quickly used the light to fine tune it.

[82 GT]

so will Rich's method work for me?

[mpj76]

It seems to be O.K. I've only done it once, and messed up. I was trying to share my experience in case you run across the same symptoms if you also get it backwards by accident. Sorry if I added confusion.

[Jacsracing]

What are you trying to accomplish?

If you want to install the timing tape correctly, then as pointed out, it makes no difference whether you on the the #1's intake or exhaust cycle. Just find TDC of the #1 piston then install your tape. What you have to be careful of is insuring you have the true TDC. A dial indicator is a good way to determine this. Another method that works is using a stop on the #1 piston. Have the stop installed to stop the piston near the top. Take a reading on the balancer. Rotate the crank in the opposite direction until it stops again. Take another reading. Look at the two readings then find the middle spot between the two. That will be the true TDC.

If your trying to determine something else related to valve timing (e.g. installing a distributor), then while watching your balancer watch the #1 intake valve or lifter. When the intake opens, then closes up, then when TDC is reached on the balancer you have the "correct" TDC for timing.

John

[PKRWUD]

Originally posted by richd
Thanks for simplifying it, PKRWUD.

LOL, I've been told I'm rather simple...

[82 GT]

Originally posted by PKRWUD
Your pistons will always be in the same relationship to each other. It doesn't make any difference as far as the tape is concerned, because the crank spins twice for every one rotation of the cam. In other words, the balancer will be in the exact same place at TDC for the #1 piston regardless of the cam.

Take care,
~Chris

That's right. I uderstand now but actually, in a way, it does matter where you start putting the timing tape on the balancer because TDC could be facing towards the ground when you go to use your timing light. Unless you want to crawl under the car with the timing light while your buddy adjusts the timing.
So what I did was found TDC and then put TDC of the tape in a position where I knew I could find it with a timing light later on.
That's why I was asking how I knew I had TDC and not the exhaust stroke for installing timing tape.......

[PKRWUD]

Originally posted by 82 GT
That's right. I uderstand now but actually, in a way, it does matter where you start putting the timing tape on the balancer because TDC could be facing towards the ground when you go to use your timing light. Unless you want to crawl under the car with the timing light while your buddy adjusts the timing.
So what I did was found TDC and then put TDC of the tape in a position where I knew I could find it with a timing light later on.
That's why I was asking how I knew I had TDC and not the exhaust stroke for installing timing tape.......

Where you place the TDC tape mark is of your own choosing, but it will be exactly the same whether it's the beginning of the compression stroke or the beginning of the exhaust stroke. In other words, all you need to find is TDC for the #1 cylinder. It doesn't make any difference what stroke the piston is on.



Take care,
~Chris