Quick question about TDC... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

n737nc · 07-26-2004, 01:27 PM

When the #1 cylinder is at TDC, where should the valves for that cylinder be positioned?

Should the intake valve be just closing?

Thanks,
Nick

**COBALT** · 07-26-2004, 02:20 PM

It should be already closed I think, since the upstroke to TDC in the charge part of the cycle is compression of the fuel/air charge. It has to be in there to be compressed, so the fuel and air is homogenious for burning.

n737nc · 07-26-2004, 02:24 PM

So basically, when the intake valve closes on the #1 cylinder the next TDC mark on the balancer will be the TRUE TDC?

shuttermutt · 07-26-2004, 02:32 PM

Quote:

Originally Posted by n737nc

So basically, when the intake valve closes on the #1 cylinder the next TDC mark on the balancer will be the TRUE TDC?

Yep, assuming your marks are correct, it has to be. TDC is during the compression stroke. As such, both valves must be closed. Otherwise, you'll be exactly 180 degrees off (exhaust valve will be open).

n737nc · 07-26-2004, 02:39 PM

Alright, thanks!
I think I stabbed my dist 180 out. I am just looking for a way to check and make sure before I crank it over anymore.

jimfulco · 07-27-2004, 02:56 AM

Might be easier to just switch plug wires at the cap. Swap each one with the one that's 180* across from it. If it starts, it was 180* out.

07-26-2004, 02:20 PM	#2
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	It should be already closed I think, since the upstroke to TDC in the charge part of the cycle is compression of the fuel/air charge. It has to be in there to be compressed, so the fuel and air is homogenious for burning. __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

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07-26-2004, 01:27 PM	#1
n737nc Registered User Join Date: Jun 2004 Location: Dallas, Tx Posts: 207	Quick question about TDC... When the #1 cylinder is at TDC, where should the valves for that cylinder be positioned? Should the intake valve be just closing? Thanks, Nick

07-26-2004, 02:24 PM	#3
n737nc Registered User Join Date: Jun 2004 Location: Dallas, Tx Posts: 207	So basically, when the intake valve closes on the #1 cylinder the next TDC mark on the balancer will be the TRUE TDC?

07-26-2004, 02:39 PM	#5
n737nc Registered User Join Date: Jun 2004 Location: Dallas, Tx Posts: 207	Alright, thanks! I think I stabbed my dist 180 out. I am just looking for a way to check and make sure before I crank it over anymore.

07-27-2004, 02:56 AM	#6
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	Might be easier to just switch plug wires at the cap. Swap each one with the one that's 180* across from it. If it starts, it was 180* out.



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