Thread: I am stumped??

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if you know where TDC is it dont make no dif where you put it on the HB as long as the 0 on the tab and the mark on the HB line up.

Ok, that makes sense. Boy, the more ya learn, the harder it gets. Wait..... is that supposed to be the other way around?

LT1, do you agree with my plan to find TDC?

you need a tool to screw into the #1 spark plug hole to find out what the true TDC is. screw the tool in the plug hole turn the motor over untill the piston hits the stop on the tool, mark the HB at the 0 on the tab, then turn the motor back the other way untill it hits the stop on the tool again, then mark the HB at the 0 on the tab. you have 2 marks on the HB now and the true TDC is in between the 2 marks. if the original mark is there then there is nothing wrong with you HB , but you will know for sure.

hey s10streeter, dont use the starter to turn the motor.

Does that tool go in the HB? whats the tool Mike is refering to?

Man, that looked alot bigger on screen. Never thought it went into the spark plug hole? What is the tool called? Is it mandatory to do this or try and sight it using intake rocker and compression?

It's called a piston stop and it's the only dead-nuts way to find top dead center with the motor together.

Let's review to make sure you understand.
Remove the #1 spark plug. Turn the motor over with a breaker bar and socket on the harmonic balancer retaining bolt head clockwise in the direction of rotation until a friend feels air being pushed out the spark plug hole with his finger or thumb. When you are about an inch from the timing mark on the damper, stop and insert the piston stop, turning the inner threaded rod down against the top of the piston. Don't try to torque it, just contact the piston. Make a mark on the damper ring at the timing pointer. Now turn the crank back the other way (counterclockwise) all the way around until the piston is again coming to the top of its travel and stops against the piston stop (which you haven't moved). Make another mark on the damper ring at the timing pointer. Halfway between these 2 marks is absolute TDC. Measure carefully. It works best if you use a 6 inch caliper.

Thanks Tech, what a mess I've gotten into. Have you read all of this thread? Is there any other thing I can do? What about repositioning the dist.? This is turning out to be quite a project for me. Removing rad, fans, to get to the HB to turn the crank, man that doesnt sound like fun.

"what a mess I've gotten into."

Not really. You're learning to do it the right way and this procedure will stay with you the rest of your life. You'll be able to amaze others with your knowledge down the road.

You should be able to do this procedure without removing the fan or belts. Just use an extension of the proper length with your socket and breaker bar.

One additional thought, this whole thing will go much easier with all the spark plugs removed. You needed to change them anyway, huh???

Oh well, your right. Physics and numbers dont lie.

Caught your edit late. Yeah, and with headers to boot! Another learning experience!

You don't absolutely have to remove them all, it just makes the motor easier to turn and prevents it from "rocking back" against the compression of a cylinder.

To find TDC, take off the tappet cover and turn the engine til the exhaust is closing and the intake is opening. When they're equal, that's split overlap. With the great majority of cams, that's TDC (but half a turn out on the distributor). Then check your HB timing marks, they should read zero. If you have your cam specs, that'll tell you how much it will be off zero.

Originally posted by R Pope
To find TDC, take off the tappet cover and turn the engine til the exhaust is closing and the intake is opening. When they're equal, that's split overlap. With the great majority of cams, that's TDC (but half a turn out on the distributor). Then check your HB timing marks, they should read zero. If you have your cam specs, that'll tell you how much it will be off zero.

While I agree with this method for getting close to TDC, there are factors which might keep you from getting exact TDC.

1. The ability of the operator to determine exact split overlap by the naked eye without the use of a dial indicator. (not likely)

2. The assumption that both rocker arms are the exact same ratio (not likely)

3. The assumption that there is zero slop in the timing chain/gears (not likely)

4. The assumption that the builder installed the cam straight up, neither advanced nor retarded. (not likely)

5. The assumption that the cam specs are available (not likely)

6. The assumption that the hot rodder doing this possesses a level of expertise in math (not likely)

On a 6" diameter damper ring, a movement of only 0.052" equals 1 degree, so it doesn't take much to be off by several degrees.

I still contend that the best way to find exact TDC on an assembled motor is the piston stop method.

No one seems to stock piston stops around here so I have to wait for UPS to bring me one. Thanks for all the recommendations. I think I can get as close as anyone else using the piston stop and measuring the distance between the two marks and finding TTDC.

You can make a piston stop out of an old spark plug.
Getting the porcelain out without damaging the steel shell can be tough, but it can be done.
A little welding and you're done.

You can also make them from a spark plug extender - available on the KD tool rack - that is used as an anti-plug fouling device in a cylinder that's pumping oil.

The one in the pic was drilled to tap size and a - fairly sure - 3/8-NF tap spun in for the adjuster bolt.

Round off the bolt end and observe the cautions put forth by the other guys when you use this device.