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Confiming Crank TDC


tibZ

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I have the head off my engine along with everything but the crank and pistons. Everything was set at TDC before removal. What I am wondering is as I was cleaning up everything I was assuming ( I know) that if I went 1 revolution the 1st piston was now on the exhaust stroke so I went another turn to be back on the firing stroke. Is this correct or does it not matter without the timing chain in place? It will be awhile before I start re-assembly but I was just wondering if this will be an issue. In other words, is there a difference when my #1 piston is at TDC on what stroke it is? I haven't removed the timing gear or oil pump gear from the crank. Thanks for any help.

Mike

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Yes it matters. Your distributor timing will be off. The rotor in the distributor turns once for every two turns of the crank.

Put the distributor back in - and look at the position the rotor is pointing to. If it's pointing to around 3:30 - you are one revolution off. If it's pointing to around 10:30 your at/near BTDC.

FWIW,

Carl B.

Edited by Carl Beck
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Hi Bill:

He said he still has the oil pump installed - the "0" notch on the crank pully will pass the pointer once, then return to "0" again - before the rotor returns to fire the #1 cylinder.

Just putting the "0" mark on the pointer is not enough to be certain that eveything is back where he started.. Turning the crank over once as he said he did, then again - SHOULD put him back were he was....but far better to be certain by verifying it with the rotor position.

Also -while he'd doing that - it is always good to assure that the pointer is correctly positioned. Put the piston in the #1 cylinder at its top dead center (just before it starts to go down again)... then check the pointer position in relation to the "0" mark on the crank - looking from were you would see it while using a timing light.

FWIW,

Carl B.

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Thanks for the replies.

I have the timing cover off so I can't put the distributor on. The crank pulley is 1 to 1 so the timing mark is always in the same position when the #1 cylinder is at the top. I guess I'll have to confirm my TDC when I start assembling, I was just wondering if there was another way to confirm it with everything off. Thanks again, Mike

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The reason I asked why you used BTDC is because TibZ wants to locate TDC for #1 on his engine. If you refer to TDC, then you need to say that or its equivalent, 0 degrees BTDC. Of course, the spark happens just before TDC, as in 5deg. BTDC, but it's a different thing then the actual TDC.

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I believe he said he had the oil pump gear installed (not the oil pump) and I assume when he said everything was off except the crank and pistons, that he means the front cover as well. The #1 piston should be at the top of it's stroke (crank key at 12:00) ,with crank sprocket timing mark at approximately 4:00.

Edited by Diseazd
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You are correct Diseazd, only the "worm" gear is on the crank in front of the smaller timing gear. If I slip the pulley on, the timing notch comes back to the same place each revolution when the #1 piston reaches TDC. I get the feeling there is no way to determine Firing/exhaust position until I start assembly. Thanks to all for the input.

Mike

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Carl and all,

After reading this I'm confused again. Here's my current situation:

Oil pump and distributor still in car. The head is off.

If I move cylinders 1 and 6 to their highest point. The rotor points to around 7 o'clock, which lines up with the number one spark plug wire. Also, the timing pointer is a 0 degrees. Is this where I want to set up for TDC?

Bob

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Bob....With the head off you can't rotate the crank because your timing chain is jammed with the special tool that keeps it from falling into the oil pan......but...if you remove the head with the #1 piston TDC compression stroke, the pointer will be at "0" and your rotor will be at 9:00 or thereabouts pointing in the vicinty of the #1 distributor wire. Yes you are right! Then you have to set timing at about 10 degrees BTDC on the distributor using a timing light after everything (head etc.) is reassembled.

Edited by Diseazd
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The rotor points to around 7 o'clock, which lines up with the number one spark plug wire. Also, the timing pointer is a 0 degrees. Is this where I want to set up for TDC?

Bob

Hi Bob:

The short answer to your qestion is - Yes. If that was where your #1 spark plug wire was to begin with - and if that allowed enough movement of the distributor housing to fine tune the ignition advance/retard... Yes that will do.

I used 10:30 - and 3:30/4:00 off the top my head at the time -Sorry if that confused you - the factory position is closer to the 9:00 o'clock that Guy used.

However, if someone sat the driven gear/distributor drive shaft position up to use 7:00 as the #1 spark plug wire the last time it was done - then that's fine too.

FWIW,

Carl B.

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