TDC on cylinder # 8
Thread Starter
Racer
Joined: Oct 2007
Posts: 270
Likes: 0
From: Chapel Hill NC
TDC on cylinder # 8
I wanted to make sure I am on the right path.
1977 SB. Firing order is #1 then # 8 plug.
Set # 1 to TDC. (Distributor pointing to # 1 plug and balancer set to the ZERO mark.)
If I then rotate the engine (balancer) 90 degrees (1/4 turn)... then # 8 is now at TDC. (and distributor is pointing to the # 8 plug)
Am I understanding this correctly?
1977 SB. Firing order is #1 then # 8 plug.
Set # 1 to TDC. (Distributor pointing to # 1 plug and balancer set to the ZERO mark.)
If I then rotate the engine (balancer) 90 degrees (1/4 turn)... then # 8 is now at TDC. (and distributor is pointing to the # 8 plug)
Am I understanding this correctly?
Burning Brakes
Joined: Aug 2008
Posts: 878
Likes: 55
From: Deep South Denmark
Yes
The distributor shaft rotates at half the speed of the crankshaft, so in order to turn the distributor 1/8 turn you turn the crank 1/4 turn.
The distributor shaft rotates at half the speed of the crankshaft, so in order to turn the distributor 1/8 turn you turn the crank 1/4 turn.
Last edited by Danish Shark; Jun 22, 2011 at 10:13 AM.
Thread Starter
Racer
Joined: Oct 2007
Posts: 270
Likes: 0
From: Chapel Hill NC
OK... so if the distributor is pointed at #8 - how do I know if I am at the compression stroke? ( I will be turning the engine by hand)
**************************************** ********
Note: I will have no assistance or help and want to make absolutely sure I have confidence in this part of the procedure before I change the valve seal. Again - thanks to all of you for passing along your experience to a novice.
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Thread Starter
Racer
Joined: Oct 2007
Posts: 270
Likes: 0
From: Chapel Hill NC
OK... I think we are not all on the same page.
My car is running like a dream - I just need to replace a valve seal.
I am trying to understand how to guarantee my valves are up when I start the repair. I was hoping this would be really easy - apparently not.
So the question now is:
HOW CAN I MAKE ABSOLUTELY SURE #8 IS ON THE COMPRESSION STROKE (BOTH VALVES ARE UP)?
1. #1 is at TDC - balancer is at the 0 mark.
2. I rotate the engine 90 degrees (or 1/4 turn).
3. The distributor is now pointing to #8 plug.
Am I now at the Compression stroke for #8?
My car is running like a dream - I just need to replace a valve seal.
I am trying to understand how to guarantee my valves are up when I start the repair. I was hoping this would be really easy - apparently not.
So the question now is:
HOW CAN I MAKE ABSOLUTELY SURE #8 IS ON THE COMPRESSION STROKE (BOTH VALVES ARE UP)?
1. #1 is at TDC - balancer is at the 0 mark.
2. I rotate the engine 90 degrees (or 1/4 turn).
3. The distributor is now pointing to #8 plug.
Am I now at the Compression stroke for #8?
Melting Slicks
Joined: Feb 2006
Posts: 3,428
Likes: 5
From: Japan
If your engine was running OK previously and you haven't changed anything, then YES. Rotate the crank (balancer) 90 degrees past #1 TDC which will bring the #8 piston to TDC on ITS compression stroke. You can confirm this by the position of the distributor rotor (pointed towards the #8 terminal) and the fact that both valves are in the closed position over the #8 cylinder. Enjoy!
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
OK... I think we are not all on the same page.
My car is running like a dream - I just need to replace a valve seal.
I am trying to understand how to guarantee my valves are up when I start the repair. I was hoping this would be really easy - apparently not.
So the question now is:
HOW CAN I MAKE ABSOLUTELY SURE #8 IS ON THE COMPRESSION STROKE (BOTH VALVES ARE UP)?
1. #1 is at TDC - balancer is at the 0 mark.
2. I rotate the engine 90 degrees (or 1/4 turn).
3. The distributor is now pointing to #8 plug.
Am I now at the Compression stroke for #8?
My car is running like a dream - I just need to replace a valve seal.
I am trying to understand how to guarantee my valves are up when I start the repair. I was hoping this would be really easy - apparently not.
So the question now is:
HOW CAN I MAKE ABSOLUTELY SURE #8 IS ON THE COMPRESSION STROKE (BOTH VALVES ARE UP)?
1. #1 is at TDC - balancer is at the 0 mark.
2. I rotate the engine 90 degrees (or 1/4 turn).
3. The distributor is now pointing to #8 plug.
Am I now at the Compression stroke for #8?
Your on target in what your saying above.
Just make sure the ign rotor is pointed at #1 spark plug wire contact in the dist and the balancer mark is at 0
(If you have any question about #1 TDC let me know and I can post a couple pics of how the valves need to look to insure your at #1 TDC compression stroke.)
#1 TDC is a very important starting point and can be confusing and has been the downfall of many.
Last edited by ...Roger...; Jun 22, 2011 at 12:35 PM.
Thread Starter
Racer
Joined: Oct 2007
Posts: 270
Likes: 0
From: Chapel Hill NC
Yes - I would love to see those pics!!
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
In pic #1 focus on #3 intake valve and #5 exhaust valve,they are both open=this is where you want to be for #1 TDC compression stroke.
Pic #2 is not where you want to be,#1 piston is up ,balancer mark is up but #1 is on its exhaust stroke.
Many thanks to Motorhead for these picture of his very sharp looking motor.
Pic #2 is not where you want to be,#1 piston is up ,balancer mark is up but #1 is on its exhaust stroke.
Many thanks to Motorhead for these picture of his very sharp looking motor.
Safety Car
Joined: Sep 2007
Posts: 4,451
Likes: 326
From: Indy Indiana
doesn't matter anyway, its a moot issue. if you are replacing a valve seal, then loosen your rocker anyway to the point that you can remove it, even if both valves are open, when you loosen the rocker, the valves will close. you will have to re-set your lifter lash anyway when done.. TDC should not matter anyway. the valves will be up when you remove your rocker
what if you were replacing all seals?.. no way could you be at a point when all valves are closed, so crank position does not matter...
crank position does matter when you are resetting your lash, depending on if you are running solids or hydraulics, then do your 90 degree at a time thing thruout the entire firing order.
but to answer your question.. YES
what if you were replacing all seals?.. no way could you be at a point when all valves are closed, so crank position does not matter...
crank position does matter when you are resetting your lash, depending on if you are running solids or hydraulics, then do your 90 degree at a time thing thruout the entire firing order.
but to answer your question.. YES
Racer
Joined: Aug 2000
Posts: 434
Likes: 3
From: Cleveland Ohio
Can also put your finger or thumb in the spark plug hole while turning the crank by hand. You will feel the pressure trying to come out the spark plug hole if you are on the compression stroke. Since you have the valve covers off you can simply watch the rockers. When on the compression stroke both valves will be closed as mentioned above. 
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Once you get the valve covers off, you will look at the rocker arms, and it will be obvious which valves are open and which are closed. Be careful not to lose the valve keepers, they can fly off and disappear!
Scott
