$10 tool, 10 minutes work and you never have to guess if TDC is TDC.
Finding Top Dead Center
Thread Starter
Burning Brakes
Joined: Oct 2003
Posts: 1,090
Likes: 74
From: New Carlisle IN
Finding Top Dead Center
I was wondering how to find TDC if you arn't sure the distributer is in correctly or that the balancer and timing mark havent' slipped. I think I am having problems with my new HEI dist. and want to make sure the rotor is pointing at #1 at TDC, but I don't think my timing mark is correct. My dad owned the car before I did and says he could never go by the marks when timing the car. How do I go about finding TDC with out taking off a head to watch the piston?
The car runs good at idle and will come off the line well. It will rev fine when standing still. When I shift into 2nd gear and start to climb in RPM the car will fall flat on it's face and won't recover. I have changed the ignition moduel, cap, rotor, coil, tried rebuilding my carb and then replaced the entire carb. My only other thing to try to replace is the fuel pump, but I want to make sure the dist is correct before I spend anymore money. Any help will be appreciated.
The car runs good at idle and will come off the line well. It will rev fine when standing still. When I shift into 2nd gear and start to climb in RPM the car will fall flat on it's face and won't recover. I have changed the ignition moduel, cap, rotor, coil, tried rebuilding my carb and then replaced the entire carb. My only other thing to try to replace is the fuel pump, but I want to make sure the dist is correct before I spend anymore money. Any help will be appreciated.
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
Use a piston stop. Screw it in the spark plug #1 hole :
http://www.summitracing.com/parts/SU...9/?image=large
I've done it recently, works great, very accurate and you don't need to remove the heads. It's a 10 minutes work
http://www.summitracing.com/parts/SU...9/?image=large
I've done it recently, works great, very accurate and you don't need to remove the heads. It's a 10 minutes work
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
there are a lot of tutorials on youtube about how to do this,
good info there.
short version
get a degree wheel,
make a pointer
piston stop into #1 hole.
put balancer so that its 0 mark and the timing mark are aligned to get close.
back off a few degrees
screw in piston stop.
rotate crank until piston touches stop
record where pointer is
go the opposite direction on crank until stops
record pointer
true TDC is half way between those two numbers.
remove stop
move crank so that pointer is now pointing at the true TDC # on wheel
remark crank.
thats the basics anyway.
good info there.
short version
get a degree wheel,
make a pointer
piston stop into #1 hole.
put balancer so that its 0 mark and the timing mark are aligned to get close.
back off a few degrees
screw in piston stop.
rotate crank until piston touches stop
record where pointer is
go the opposite direction on crank until stops
record pointer
true TDC is half way between those two numbers.
remove stop
move crank so that pointer is now pointing at the true TDC # on wheel
remark crank.
thats the basics anyway.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
If you suspect that the harmonic damper (balancer) has slipped, and can remove the crank pulley and balancer, the TDC line should be 10 degrees counter clockwise from the center of the keyway. If the balancer is an early one (pre-'69), the index line will be 2 degrees CCW from the keyway.
As an alternate, on both BBC and SBC, the keyway aligns with the number one crankshaft journal, so that when #1 is at TDC, the keyway will be aligned with the cylinder centerline of the left bank of the engine (45 degrees towards the driver's side).
As an alternate, on both BBC and SBC, the keyway aligns with the number one crankshaft journal, so that when #1 is at TDC, the keyway will be aligned with the cylinder centerline of the left bank of the engine (45 degrees towards the driver's side).
Burning Brakes
Joined: Jan 2007
Posts: 1,057
Likes: 4
From: Concord Calif
there are a lot of tutorials on youtube about how to do this,
good info there.
short version
get a degree wheel,
make a pointer
piston stop into #1 hole.
put balancer so that its 0 mark and the timing mark are aligned to get close.
back off a few degrees
screw in piston stop.
rotate crank until piston touches stop
record where pointer is
go the opposite direction on crank until stops
record pointer
true TDC is half way between those two numbers.
remove stop
move crank so that pointer is now pointing at the true TDC # on wheel
remark crank.
thats the basics anyway.
good info there.
short version
get a degree wheel,
make a pointer
piston stop into #1 hole.
put balancer so that its 0 mark and the timing mark are aligned to get close.
back off a few degrees
screw in piston stop.
rotate crank until piston touches stop
record where pointer is
go the opposite direction on crank until stops
record pointer
true TDC is half way between those two numbers.
remove stop
move crank so that pointer is now pointing at the true TDC # on wheel
remark crank.
thats the basics anyway.
This is the right way to find true TDC. But don't be surprised if the mark is not correct even if there is no problem with the Damper. The mark from the factory is usally not right on, but it should be within 2 or 3 degrees either side of TDC if no problems with the damper useing the factory TDC marks. With that said I would advise to correct the factory TDC if off no more than the 2 or 3 degrees, more than that shows something is probaly wrong with the damper.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
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Thread Starter
Burning Brakes
Joined: Oct 2003
Posts: 1,090
Likes: 74
From: New Carlisle IN
I know the symptoms seem more like a fuel problem, but I never had any problems before changing to he HEI. It ran fine with the points except a little miss at 4-5k rpms. I was hoping the HEI would solve that. My first step is to make sure the dist is in corectly. If not , the I will fix it and see what it does. If the dist is in correctly, I wll try putting the points dist back in and see if it runs. If that still doesnt' fix it, I will change the fuel pump and go from there.
I will try the piston stop and see what I get. Thanks for all the replies.
Last edited by vettehardt; Jul 28, 2009 at 12:27 PM.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
Here is a really easy way with easy parts you may already have, but it assumes you have a good balancer and timing mark too.
Try this way.
Looking at the front of the engine from the front of the car the balancer turns clockwise. The distributer turns clockwise looking down at it.
Almost foolproof method:
Get an old sparkplug that fits the engine.
Knock the guts out of it with a punch and hammer.
Stretch a balloon over the sparkplug leaving the threads exposed. (Balloons from Dollar Store)
Hand tighten the balloon/sparkplug into the #1 hole.
Disconnect power to distributor or make sure ignition is off.
Slowly turn over engine in clockwise direction with a socket and ratchet on the harmonic balancer center bolt.
Balloon will fill with air when approaching #1 firing position. It won't stay full so you have to watch it closely.
The mark on the balancer will be at approx 6 o'clock, so forget about the ballon and continue turning the engine over.
Continue to turn engine until the mark on balancer reaches the 10° BTDC mark.
This is close to the initial timed firing position.
Install dist with the rotor pointing approximatedly at the #2 terminal on the cap. (Just before #1 on cap)
Push down slowly and you will feel the gears mesh and the rotor will move toward the #1 position.
If it is going to go past #1, then slowly pull up on the distributer until you feel the gears "unmesh". then turn the rotor more towards the #2 direction with slight pressure down until you feel you have moved over 1 more tooth.
Then push down as far as it will go again to see if it is close to lining up with #1 terminal.
If the distributer housing base where you clamp it tight has a gap between it and the intake manifold, then the oil shaft has not lined up.
If this is the case, then the rotor should be between the #1 and #2 terminals on the cap.
Then just push down lightly on the distributer housing (watch out for spinning rotor) while someone cranks the starter over, and it will drop in place and the timing will be correct to fire up.
It may sound a little confusing, but try it and it's pretty simple and is is the easiest way I have found.
To check it, do the balloon thing again with the distributor now being fully seated on the intake. Turn the distributer housing until the rotor leading edge meets the #1 cap terminal. If the housing is oriented properly as in the first pic then you will have ample room for the vacumn advance can to turn the distributer for timing. Now clamp the distributor fairly tight and use you timing lite to time engine to your specs.
Use one of the papers in a sticky at top.
Looking at the front of the engine from the front of the car the balancer turns clockwise. The distributer turns clockwise looking down at it.
Almost foolproof method:
Get an old sparkplug that fits the engine.
Knock the guts out of it with a punch and hammer.
Stretch a balloon over the sparkplug leaving the threads exposed. (Balloons from Dollar Store)
Hand tighten the balloon/sparkplug into the #1 hole.
Disconnect power to distributor or make sure ignition is off.
Slowly turn over engine in clockwise direction with a socket and ratchet on the harmonic balancer center bolt.
Balloon will fill with air when approaching #1 firing position. It won't stay full so you have to watch it closely.
The mark on the balancer will be at approx 6 o'clock, so forget about the ballon and continue turning the engine over.
Continue to turn engine until the mark on balancer reaches the 10° BTDC mark.
This is close to the initial timed firing position.
Install dist with the rotor pointing approximatedly at the #2 terminal on the cap. (Just before #1 on cap)
Push down slowly and you will feel the gears mesh and the rotor will move toward the #1 position.
If it is going to go past #1, then slowly pull up on the distributer until you feel the gears "unmesh". then turn the rotor more towards the #2 direction with slight pressure down until you feel you have moved over 1 more tooth.
Then push down as far as it will go again to see if it is close to lining up with #1 terminal.
If the distributer housing base where you clamp it tight has a gap between it and the intake manifold, then the oil shaft has not lined up.
If this is the case, then the rotor should be between the #1 and #2 terminals on the cap.
Then just push down lightly on the distributer housing (watch out for spinning rotor) while someone cranks the starter over, and it will drop in place and the timing will be correct to fire up.
It may sound a little confusing, but try it and it's pretty simple and is is the easiest way I have found.
To check it, do the balloon thing again with the distributor now being fully seated on the intake. Turn the distributer housing until the rotor leading edge meets the #1 cap terminal. If the housing is oriented properly as in the first pic then you will have ample room for the vacumn advance can to turn the distributer for timing. Now clamp the distributor fairly tight and use you timing lite to time engine to your specs.
Use one of the papers in a sticky at top.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
An easy check that you can do and I do all the time and will be accurate to a couple of degrees or accurate enough to set my valves. I actually used to set my valves this way until I got a balancer that was marked all the way around.
Take both valve covers off and rotate the motor and look at number 6 rocker arms and watch the exhaust valve come up and as soon as the exhaust stops and the intake begins to move or the rockers are both equal you are in overlap on number 6 meaning you are at TDC on number 1.
Now look at the timing mark if you are near 0 degs. you are OK
Take both valve covers off and rotate the motor and look at number 6 rocker arms and watch the exhaust valve come up and as soon as the exhaust stops and the intake begins to move or the rockers are both equal you are in overlap on number 6 meaning you are at TDC on number 1.
Now look at the timing mark if you are near 0 degs. you are OK
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
Take both valve covers off and rotate the motor and look at number 6 rocker arms and watch the exhaust valve come up and as soon as the exhaust stops and the intake begins to move or the rockers are both equal you are in overlap on number 6 meaning you are at TDC on number 1.
Now look at the timing mark if you are near 0 degs. you are OK
Thread Starter
Burning Brakes
Joined: Oct 2003
Posts: 1,090
Likes: 74
From: New Carlisle IN
The coil is a brand new Accel super coil.
The miss before HEI was just a slight little hesitation between 4-5k at the top end of 2nd and 3rd gears. What is happening now is the car falls flat on it's face and almost dies when it gets to around 3k after shifting into 2nd. It's like it completly cuts off the fuel and the engine just turns over slowly. I have to come to a stop and pump the gas before it starts idling corectly. It is a completly different problem.
I was out working on it today and think I found TDC. My timing mark on the balancer seems to be pretty good. I took the cap off the rotor and the rotor was past the #1 so I turned it back 1 tooth. I didn't have a chance to start it up today, but I will set timing and take it out for a drive tomorrow. We'll see what happens. If this doesn't fix it, I will try the old dist and then a new fuel pump.
The miss before HEI was just a slight little hesitation between 4-5k at the top end of 2nd and 3rd gears. What is happening now is the car falls flat on it's face and almost dies when it gets to around 3k after shifting into 2nd. It's like it completly cuts off the fuel and the engine just turns over slowly. I have to come to a stop and pump the gas before it starts idling corectly. It is a completly different problem.
I was out working on it today and think I found TDC. My timing mark on the balancer seems to be pretty good. I took the cap off the rotor and the rotor was past the #1 so I turned it back 1 tooth. I didn't have a chance to start it up today, but I will set timing and take it out for a drive tomorrow. We'll see what happens. If this doesn't fix it, I will try the old dist and then a new fuel pump.
