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54 Chevy 05-01-2002 06:05 PM

Sure fire way to find TDC ?
What is the best way to find TDC on a small block Chevy? The engine is assembled (not by me) and I think the distributor was installed wrong by a few degrees. I'm using a HEI distributor.

Ive heard something about pulling the rocker covers cranking the engine and watching for some particular valve set to be open or closed or something. How will I know when they are open or closed? Do I have to crank it enough to pump up the lifters?

Once I determine I'm at TDC shouldn't the timing tab line up with the timing mark on the harmonic balance?

Thanks <img src="confused.gif" border="0">

dmorris1200 05-01-2002 06:26 PM

I like the old finger in the hole trick. This assures you are TDC on compression stoke. Take out #1 spark plug, stick your thumb or finger in the hole and turn over engine with socket on crankshaft bolt. When you feel it push your finger out of the hole thats compression stroke on #1. Then just line up 0 degree timing mark and check distributor. Now I've never done this on a brand spankin new engine cause usually I'm installing the distributor myself after assembling engine. I also usually pump up my lifters before putting them in the engine and then I'll spin the oil pump shaft with an air drill before installing distributor.

[ May 01, 2002: Message edited by: dmorris1200 ]</p>

F-1Rodder 05-01-2002 06:32 PM

[ May 01, 2002: Message edited by: F-1Rodder ]</p>

F-1Rodder 05-01-2002 06:38 PM

Generally I agree in principal to Dmorris 1200. However, don't trust your wife with the starter trigger. I suggest the use of a piston stop which screws into the spark plug hole. You screw it in until it contacts the piston just before TDC and note the position on the harmonic balancer. Then reverse the rotation and do it again without adjusting the depth of the piston stop. Again mark the location on the balancer. The exact difference between the two marks is exactly TDC or BDC. Note that this does not take into consideration that the cam runs at half the speed of the crank, so the distributor can still be 180 degress out of phase. To determine which it is you would have to take the valve cover off to see if the intake valve is just closing for TDC.

But I don't go to that trouble. If the engine won't run one way, I pull the distributor and move it 180 degrees or move the wires and it will start.

57Chevyman 05-02-2002 04:51 AM

I always turn the damper so the timing mark is at about 5 degrees BTDC (before top dead center). This gives enough advance for the motor to start easily on the first crank. Then go through procedure and set your timing to factory specs.

Phat 05-02-2002 06:37 AM

Only correct way to do it is as F1 has said ..Make a piston stop out of and old spark plug with a bolt welded in to it.Now turn the engine over by hand till the piston touches the stop ..mark the turn the engine back the other way till it stops ..mark the damper..Exactly in the middle of those 2 marks is TDC(This why you would do good if you could get a degree wheel in place) never do this with the starter motor or you will damage the motor..i also remove all plugs it just makes it easer to turn the motor over. This is one of those things that is wrong on 90% of the engines out there... It should be the first thing you do when building and engine and the heads are off. Bolt on tabs and damper's are allways wrong..i do mean allmost all the time. Plus the OEM ones slip all the time. Timing and engine by ear is just not and option any more 2 degrees is a lot to miss. So its a good rainy day project that costs nothing to do and helps with power..econmy...starting..and overheating problems. Set timing also at total advance(2500 rpms roughly 32-38 degrees total) and work back from there. Not static.(you know 4 degree before or 8 degrees thats just not getting your moneys worth)

dinger 05-02-2002 07:27 AM

you would be surprised at how many people don't realize there are 2 tdc. dang near got into a fistfight trying to help my old roommate, walked off, let him fiddle til the battery was almost dead, he gave up, i spun it 180 and it started immediately i agree with f1, spin it 180 if results are off, hey you have a 50/50 chance, i'll take those odds.

Henry Highrise 05-02-2002 10:13 AM

Go to the RBBO How To section, there are step by step instructions for doing this . We are in the process of getting lots of tips and How Tos to put on this page so earmark it because you will want to come back. :D

54 Chevy 05-02-2002 04:22 PM

Thanks for the great response to a pretty basic question. I'm going to make my own piston stop and go at it that way. Seems more sure fire.

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