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- Oct 7, 2007
- Messages
- 720
- Location
- Amherst, NY
- Corvette
- 1996 Torch Red Coupe (Prior 1988 and 1989)
I've always trusted timining marks. Is there any easy way to confirm that top dead center is indeed correct without getting into the engine?
Any easy way to confirm TDC?
- Thread starter TedC
- Start date
T
tonylong
Guest
Good question. I'd like to know too.
JAKE
Well-known member
If you're looking for ABSOLUTE Top Dead Center there's no "easy" way I know of.
Without having to dive into the engine, per se, you can use the positive stop method and a degree wheel/pointer arrangement.
It's not really "difficult" but can be a little time consuming.
You'll need to remove all the spark plugs which will allow you to manually turn the engine more easily.
You'll need to bring the #1 piston up to a spot several degrees (10 or 15 degrees or so) before TDC ON THE COMPRESSION STROKE, Then screw a positive stop into the #1 spark plug hole and install the degree wheel and pointer. The pointer should be pointing close to ZERO on the degree wheel.
Now manually turn the engine in the normal direction until the piston contacts the positive stop. That'll stop the piston's movement. Make note of where the pointer is pointing; that is, at what number on the wheel its pointing to.
Reverse your turn until the piston goes all the way down to BDC then back up to again touch the positive stop. Again, note the number the pointer is pointing at.
ABSOLUTE TDC is halfway between the two readings you noted.
Move the pointer to point exactly at that mid-point then do the manually turn procedure all over again. After doing it a second time, the pointer should be pointing an equal number of degrees either side of ZERO.
If it isn't, move the pointer half the number of degrees to account for the difference. As an example, if one reading is 12 degrees and the other is 8 degrees, move the pointer 2 degrees away from the 12 making it read 10 and which also makes the one which read 8 become 10.
Once you've equalized the readings, remove the positive stop, manually turn the engine until the pointer is pointing at the ZERO mark on the wheel and that'll be ABSOLUTE TDC.
Of course, if your damper has degree marks around its circumference, you can use those instead of a degree wheel. You'll still need a pointer though. I piece of coat hangar will work fine.
Some guys like to use the dial indicator method but that method doesn't account for the dwell time which occurs when the piston reaches the very top of it's movement but BEFORE it begins moving downward. There are a few degrees of dwell as the pistons sits at TDC. What happens is, the crank will turn but the piston won't actually move any.
Only other way I know of is to pull the driver's side head and use a positive stop (metal plate) bolted across the #1 hole and, using a degree wheel, do the same thing.
Jake
Without having to dive into the engine, per se, you can use the positive stop method and a degree wheel/pointer arrangement.
It's not really "difficult" but can be a little time consuming.
You'll need to remove all the spark plugs which will allow you to manually turn the engine more easily.
You'll need to bring the #1 piston up to a spot several degrees (10 or 15 degrees or so) before TDC ON THE COMPRESSION STROKE, Then screw a positive stop into the #1 spark plug hole and install the degree wheel and pointer. The pointer should be pointing close to ZERO on the degree wheel.
Now manually turn the engine in the normal direction until the piston contacts the positive stop. That'll stop the piston's movement. Make note of where the pointer is pointing; that is, at what number on the wheel its pointing to.
Reverse your turn until the piston goes all the way down to BDC then back up to again touch the positive stop. Again, note the number the pointer is pointing at.
ABSOLUTE TDC is halfway between the two readings you noted.
Move the pointer to point exactly at that mid-point then do the manually turn procedure all over again. After doing it a second time, the pointer should be pointing an equal number of degrees either side of ZERO.
If it isn't, move the pointer half the number of degrees to account for the difference. As an example, if one reading is 12 degrees and the other is 8 degrees, move the pointer 2 degrees away from the 12 making it read 10 and which also makes the one which read 8 become 10.
Once you've equalized the readings, remove the positive stop, manually turn the engine until the pointer is pointing at the ZERO mark on the wheel and that'll be ABSOLUTE TDC.
Of course, if your damper has degree marks around its circumference, you can use those instead of a degree wheel. You'll still need a pointer though. I piece of coat hangar will work fine.
Some guys like to use the dial indicator method but that method doesn't account for the dwell time which occurs when the piston reaches the very top of it's movement but BEFORE it begins moving downward. There are a few degrees of dwell as the pistons sits at TDC. What happens is, the crank will turn but the piston won't actually move any.
Only other way I know of is to pull the driver's side head and use a positive stop (metal plate) bolted across the #1 hole and, using a degree wheel, do the same thing.
Jake
- Thread starter
- #4
- Joined
- Oct 7, 2007
- Messages
- 720
- Location
- Amherst, NY
- Corvette
- 1996 Torch Red Coupe (Prior 1988 and 1989)
Jake, Appreciate your detailed answer. Sure dosen't sound like any easy 10 minute task.
JAKE
Well-known member
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