Tdc, Where Is It! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

69GMC910 · 07-06-2002, 04:11 PM

I seem to be having trouble following the directions given to me by bigvinnie. In the notes he hyperlinked me it says that TDC should occur right after the intake valve closes. This occurs nowhere near the timing mark on the balancer. Just as I am coming up to TDC my exhaust valve has just closed. What is going on here, I think it's something simple but the heat is getting to me.

Help please!!!

Mitzki5 · 07-06-2002, 04:16 PM

I believe that when you are at TDC, both valves should be closed. Take #1 spark plug out, hold finger over hole and have someone bump the ignition turning over motor until it blows your finger out. You're mark on balancer should then line up. Hope this helps.

69GMC910 · 07-06-2002, 04:19 PM

Both valves are closed at the moment, I haven't got the Intake on so it is really easy to see what is happening. Just to clarify, the intake valve is the second from the front on the drivers side right?

Mitzki5 · 07-06-2002, 04:22 PM

Yes, To be sure, just look and see where your exhaust comes out.

69GMC910 · 07-06-2002, 04:28 PM

What I don't get is how can the ignition fire at TDC on the exhaust stroke, it's not possible. Is my timing mark 180 degrees off or something?????

Mitzki5 · 07-06-2002, 04:30 PM

You probably have dist in 180 deg off. Did you just put in the dist.

69GMC910 · 07-06-2002, 04:35 PM

Intake is not on, distributor is not in, trying to time the valves without all that stuff in the way.

Mitzki5 · 07-06-2002, 04:41 PM

Ok, do this at your own risk. You could possibly strip bolt on crank and that wouldn't be good. Take out #1 spark plug. Place finger over #1 plug hole. Put ratchet on bolt that holds balancer on. Turn clock wise until you get compression. As soon as mark on balancer lines up with compression in cylinder, you should be at TDC. I hope I explained this right. This is how I got mine at TDC. Don't force the balancer bolt. I don't want you to strip those threads.

Mitzki5 · 07-06-2002, 04:43 PM

If you have someone to help they could turn the motor over by the fly wheel. Need to be fairly strong and wear gloves. Make sure you turn it the correct direction.

69GMC910 · 07-06-2002, 04:43 PM

Okay, I'll try that then, thanks mitzki5!

Mitzki5 · 07-06-2002, 04:44 PM

Good luck and post what you come up with. Later

tom hand · 07-06-2002, 04:53 PM

OK I got ya, intake not on, distributor not in. I always adjust the valves at this point. Use a wrench and turn the motor over. When the intake valve opens, that is the intake stroke. When both valves close, that is the compression stroke, use a pencil in the sparkplug hole to see when it is at the top of the stroke,and that is TDC. If your balancer is in time you can use it to get to zero. Confused yet? Hope this helps.

greasemonkey · 07-06-2002, 06:05 PM

Eastwood has a whistle you screw into the spark plug hole, you turn the engine and the compression whistles through it. When you reach TDC it stops. Kinda corny but I don't see why it wouldn't work. Good luck.

69GMC910 · 07-06-2002, 06:15 PM

Okay, It must be the 32 degree weather messing with my head! that's about 90F for the imperial guy's. TDC was right where it should be on the flywheel with both I and E valves closed. So I was adjusting the rockers and everything was going swell until I got finished and checked them all again by hand. Some of them were loose again, is this because I drained the oil pressure out of the hydraulic lifters?????

Thanks for all your help guy's

Mitzki5 · 07-06-2002, 06:43 PM

I believe they will loosen some due to bleeding the lifters.

jlmtrout · 07-07-2002, 08:40 PM

Just a thought, could you have jumped a tooth in your timing gear? Good luck and keep on truckin'!-----------Jerry

P.S. When you ask people for help,
don't get pissed when they ask
questions you may find insulting
to your ability. We weren't there
when it broke and don't know
any more than what you tell us

Blue68 · 07-08-2002, 01:05 AM

Yes the lifters will bleed down when you go back again.

It is a bear to find TDC with the dist out. You'll need to watch your valves closely and turn the crank the correct direction.

You will find it CONSIDERABLY easier to turn the engine with all the plugs out. As in by hand with no problems. If you have the timing cover off it is easy as well.

You make the comment====
"What I don't get is how can the ignition fire at TDC on the exhaust stroke, it's not possible. Is my timing mark 180 degrees off or something?????"

Yes, you are missing something. Something very important, the crank rotates twice to each rotation of the cam. Thus your piston goes up and down twice to each rotation of the cam. Once is the intake/compression stroke and the other the combustion/exhaust stroke. It is not my intention to talk down to anyone who knows this, but everyone gets confused about something some time in their lives.

Now what were we talking about?

Sinister · 07-08-2002, 01:16 AM

if ya got the front cover off,
you can check the marks
on the cam and crank timing gears...
if there facing each other i believe that's TDC...

johnnyp · 07-08-2002, 12:13 PM

A picture's worth a . . . . well, you get the idea:

http://www.howstuffworks.com/engine2.htm

07-06-2002, 04:16 PM	#2
Mitzki5 "TRUCKLESS" Join Date: Jan 2002 Location: Tuscola IL Posts: 457	I believe that when you are at TDC, both valves should be closed. Take #1 spark plug out, hold finger over hole and have someone bump the ignition turning over motor until it blows your finger out. You're mark on balancer should then line up. Hope this helps. __________________ Mitzki5 No longer have an old truck! But always looking for another one!

07-06-2002, 04:19 PM	#3
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	Both valves are closed at the moment, I haven't got the Intake on so it is really easy to see what is happening. Just to clarify, the intake valve is the second from the front on the drivers side right? __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

07-06-2002, 04:22 PM	#4
Mitzki5 "TRUCKLESS" Join Date: Jan 2002 Location: Tuscola IL Posts: 457	Yes, To be sure, just look and see where your exhaust comes out. __________________ Mitzki5 No longer have an old truck! But always looking for another one!

07-06-2002, 04:28 PM	#5
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	What I don't get is how can the ignition fire at TDC on the exhaust stroke, it's not possible. Is my timing mark 180 degrees off or something????? __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

07-06-2002, 04:30 PM	#6
Mitzki5 "TRUCKLESS" Join Date: Jan 2002 Location: Tuscola IL Posts: 457	You probably have dist in 180 deg off. Did you just put in the dist. __________________ Mitzki5 No longer have an old truck! But always looking for another one!

07-06-2002, 04:11 PM	#1
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	Tdc, Where Is It! I seem to be having trouble following the directions given to me by bigvinnie. In the notes he hyperlinked me it says that TDC should occur right after the intake valve closes. This occurs nowhere near the timing mark on the balancer. Just as I am coming up to TDC my exhaust valve has just closed. What is going on here, I think it's something simple but the heat is getting to me. Help please!!! __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

07-06-2002, 04:35 PM	#7
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	Intake is not on, distributor is not in, trying to time the valves without all that stuff in the way. __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

07-06-2002, 04:41 PM	#8
Mitzki5 "TRUCKLESS" Join Date: Jan 2002 Location: Tuscola IL Posts: 457	Ok, do this at your own risk. You could possibly strip bolt on crank and that wouldn't be good. Take out #1 spark plug. Place finger over #1 plug hole. Put ratchet on bolt that holds balancer on. Turn clock wise until you get compression. As soon as mark on balancer lines up with compression in cylinder, you should be at TDC. I hope I explained this right. This is how I got mine at TDC. Don't force the balancer bolt. I don't want you to strip those threads. __________________ Mitzki5 No longer have an old truck! But always looking for another one!

07-06-2002, 04:43 PM	#9
Mitzki5 "TRUCKLESS" Join Date: Jan 2002 Location: Tuscola IL Posts: 457	If you have someone to help they could turn the motor over by the fly wheel. Need to be fairly strong and wear gloves. Make sure you turn it the correct direction. __________________ Mitzki5 No longer have an old truck! But always looking for another one!

07-06-2002, 04:44 PM	#11
Mitzki5 "TRUCKLESS" Join Date: Jan 2002 Location: Tuscola IL Posts: 457	Good luck and post what you come up with. Later __________________ Mitzki5 No longer have an old truck! But always looking for another one!

07-06-2002, 04:53 PM	#12
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	OK I got ya, intake not on, distributor not in. I always adjust the valves at this point. Use a wrench and turn the motor over. When the intake valve opens, that is the intake stroke. When both valves close, that is the compression stroke, use a pencil in the sparkplug hole to see when it is at the top of the stroke,and that is TDC. If your balancer is in time you can use it to get to zero. Confused yet? Hope this helps. __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

07-06-2002, 06:05 PM	#13
greasemonkey Registered User Join Date: Dec 2001 Location: Pace, FL Posts: 2,155	Eastwood has a whistle you screw into the spark plug hole, you turn the engine and the compression whistles through it. When you reach TDC it stops. Kinda corny but I don't see why it wouldn't work. Good luck. __________________ 1942 Master Deluxe 1969 C/10 1985 Blazer CUCV 1987 Jimmy 2004 Tahoe 2005 Silverado 1500 2005 Silverado 3500

07-06-2002, 06:15 PM	#14
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	Okay, It must be the 32 degree weather messing with my head! that's about 90F for the imperial guy's. TDC was right where it should be on the flywheel with both I and E valves closed. So I was adjusting the rockers and everything was going swell until I got finished and checked them all again by hand. Some of them were loose again, is this because I drained the oil pressure out of the hydraulic lifters????? Thanks for all your help guy's __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

07-06-2002, 06:43 PM	#15
Mitzki5 "TRUCKLESS" Join Date: Jan 2002 Location: Tuscola IL Posts: 457	I believe they will loosen some due to bleeding the lifters. __________________ Mitzki5 No longer have an old truck! But always looking for another one!

07-07-2002, 08:40 PM	#16
jlmtrout Registered User Join Date: Jul 2002 Location: Memphis, Tn Posts: 194	Just a thought, could you have jumped a tooth in your timing gear? Good luck and keep on truckin'!-----------Jerry P.S. When you ask people for help, don't get pissed when they ask questions you may find insulting to your ability. We weren't there when it broke and don't know any more than what you tell us __________________ '68 c-10 long wheelbase fleetside, been in family since new, originally 250 3 speed Now (389) 350 .060 over 3.75 stroke,Edelbrock Performer RPM 70cc heads and Intake 600 cfm Edelbrock,Small Comp Cams retro-roller cam and roller rockers,9:1 cr, headers, HEI,Old Air a/c, 72 power disc brakes w/stainless lines, 3.42 gear,T-56 6-speed, original paint(what's left of it). Dakota Digital Dash



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07-08-2002, 01:05 AM	#17
Blue68 Registered User Join Date: Apr 2000 Location: Frisco, Tx, USA Posts: 606	Yes the lifters will bleed down when you go back again. It is a bear to find TDC with the dist out. You'll need to watch your valves closely and turn the crank the correct direction. You will find it CONSIDERABLY easier to turn the engine with all the plugs out. As in by hand with no problems. If you have the timing cover off it is easy as well. You make the comment==== "What I don't get is how can the ignition fire at TDC on the exhaust stroke, it's not possible. Is my timing mark 180 degrees off or something?????" Yes, you are missing something. Something very important, the crank rotates twice to each rotation of the cam. Thus your piston goes up and down twice to each rotation of the cam. Once is the intake/compression stroke and the other the combustion/exhaust stroke. It is not my intention to talk down to anyone who knows this, but everyone gets confused about something some time in their lives. Now what were we talking about? __________________ http://home.comcast.net/~r.landrum/w...tos.html-.html '68 C-10 LWB, '98 Z-71 350 w/accessories (Serpentine), Edelbrock Performer, Edelbrock 1405 (600cfm) carb, GM HEI, CompCam Extreme 4x4 roller cam, Thorley Headers, Carter Electric Fuel Pump, Vintage Air, 700r4, 3.73, disc brakes and power steering upgrades.

07-08-2002, 01:16 AM	#18
Sinister Between Trucks... Join Date: Mar 2002 Location: Los Angeles, CA. Posts: 3,830	if ya got the front cover off, you can check the marks on the cam and crank timing gears... if there facing each other i believe that's TDC... __________________ Beat it to fit, Paint it to match...

07-08-2002, 12:13 PM	#19
johnnyp Keepin' It Stock Join Date: Aug 2001 Location: Grand Island, Nebraska, USA Posts: 554	A picture's worth a . . . . well, you get the idea: http://www.howstuffworks.com/engine2.htm __________________ 72 Sierra Grande - Maych Forget about "do it right the first time". Do it wrong the first time to learn how, then do it right the second time.

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