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Old 09-16-2002, 05:18 AM
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Post Top Dead Center

Isn't top dead center also zero degree's? When number one piston is at the top if it's stroke the harmonic balancer is at approximately 1:00 position. Is this normal or should I get either a new balancer or use timing tape?

I'm getting closer to finishing my motor.

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Old 09-16-2002, 05:50 AM
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TDC should correspond to "0 degrees" on the timing tab, if this is what you are referring to. It is common however to find some error here, especially with OEM timing tab and balancer. For optimum performance I would recommend that you find actual TDC and verify that your tab is correct. If TDC does not line up with the 0 on the timing tab, adjustable tabs are available from numerous aftermarket sources and will correct the problem without having to purchase a new balancer. Hope this helps.
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Old 09-16-2002, 08:02 AM
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thanks engineguy, I thought your response cleared it up but now I'm confused. I had a guy tell me that actual tdc will not line up at 0 degree. I always thought 0 degrees would be lined up with the balancer.

Is tdc measured as soon as the piston reaches the top or is it when the piston starts down. There's a point in there that the piston doesn't move which will effect the degree's.

The balancer I have was originally on this motor but I don't know if it was ever lined up correctly.
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Old 09-16-2002, 08:16 AM
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In theory, when at TDC, the mark on the harmonic balancer will line up with the "0" on the timing tab. But the best way to verify is to remove the #1 plug and put a screwdriver in the hole to feel where the piston is (height). When the motor is at TDC, the #1 piston will be at its top most position. You can do this by disconnecting the coil (so the motor doesn't fire) and have someone tap the motor, little-by-little using the starter. When you determine where TDC is by the screwdriver, correlate this with the timing mark...it should be very close to zero.

Also, b/c the crank moves 2 turns to every one turn of the cam, TDC is when air will be blown out of the spark plug hole...you will notice that everyother time the screwdriver comes up with the piston, the air will blow out of the hole, b/c TDC is on the compression stroke. I hope this helps you out.
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Old 09-16-2002, 08:21 AM
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I did forget to mention this is a new motor still on the stand (350). What do you mean you guys can't read my mind, LOL.
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Old 09-16-2002, 08:22 AM
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Hey MH, when I built my motor I spent a lot of time finding TDC to make sure it was right. Here is what I did, you may find it help full. First, make a new timing pointer that is sturdy and align it so it is in a straight line between your eyes and the balancer. It doesn't matter if it points to the right place or not. It is safest to assume that your current marks are wrong, and that you will have to remark them all. Next, take an old sparkplug and knock the electrode out of it and weld a 1.5 inch bolt onto the end. Now, rotate your motor BY HAND until you are on the compression stroke, now insert the altered plug in the #1 cynlinder. Rotate the motor BY HAND until you feel the piston touch the bolt on the end of the spark plug. Now, mark on your balancer where your new timing pointer is pointing. After you do that rotate the motor the other way until the piston touches the bolt and mark the damper again. Now, find the midpoint between your two marks and you have top dead center, referenced to your new improved pointer. Now you can put timing tape on the damper making sure to put the 0 on TDC. If you have any more questions you can email me or post again. Good luck
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Old 09-16-2002, 09:19 AM
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Remember that the piston will "dwell" for a few degrees at TDC as the rod swings across and this will be affected by the rod length. Therefore it is real hard to determine exact TDC without a degree wheel. Fashion a piston stop as explained by drgnwgn and turn the engine both directions, recording your reading at each stop. Divide the readings by two and this gives you TDC. Remove the piston stop and rotate the engine to this reading and WALLAH you have TDC. Now you can determine the acuracy of your timing tab. (Good thing the engine is still on the stand, this is a bear to do in the chassis.)
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Old 09-16-2002, 09:36 AM
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Wallah=Voila
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Old 09-16-2002, 11:27 AM
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This is too easy, you send in a problem and someone else solves it for you.

Thanks guys
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Old 09-16-2002, 12:24 PM
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Good Explanation drgnwgn289!

There's a lot of knowledge on this board...

BTW I use a whistle connected to No. 1 with a reinforced hose as in a compression tester (in chassis or on stand with the head installed). The cylinder is at top dead center when she stops whistling. If it is within reason to the mark on the balancer, all is well. If it is not close, it is time to find mechanical TDC as you described.

And of course, all of this is assuming that the chain is not stretched (check for that first).

[ September 16, 2002: Message edited by: KULTULZ ]</p>
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Old 09-16-2002, 01:42 PM
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MH!!! You're From Lubbock?? Do I know you?? This is cool.....if you see the black primered 54 stude wagon drivin around stop me

[ September 16, 2002: Message edited by: drgnwgn289 ]</p>
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Old 09-16-2002, 03:43 PM
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Cool

Never thought about that wistle thing, thanks for the idea, KULTULZ!!!
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