VR92,,
Finding Top Dead Center
Team Owner
Joined: Sep 2003
Posts: 25,295
Likes: 4
From: I'm the walkin dude I can see all of the world...
St. Jude Donor '03
Pull the valve covers.
Watch the valve cycles on the number 1 cylinder while rotating the crank.
Thats how I always did it when the motor was together. Other than that you have to use the timing marks / harmonic balancer marks.
The FSM has a great procedure on this.
Watch the valve cycles on the number 1 cylinder while rotating the crank.
Thats how I always did it when the motor was together. Other than that you have to use the timing marks / harmonic balancer marks.
The FSM has a great procedure on this.
Race Director
Joined: May 2006
Posts: 10,691
Likes: 71
From: Phoenix Arizona
Two ways, a). pull number one spark plug, put screwdriver into hole. Rotate engine BY HAND, you will be able to feel the piston reaching and then falling past TDC. b) pull either valve cover. When the exhaust valve closes and the intake just starts to open (#1 on left/drivers, #6 on other side) you have reached TDC. I use a 5/8 wrench on the front damper bolt . On an LT1 ( I'm assuming your working on the opti) Use the #6 cylinder. The piston reaches TDC twice , once to release exhaust gasses, once in compression, which is when the distributer/opti is on #1
Last edited by zr1fred; Jul 31, 2007 at 12:52 PM.
Race Director
Joined: Jun 2004
Posts: 13,961
Likes: 707
From: WI
I turn the crank pulley bolt. Re finding TDC, you can put your finger over the plug hole and feel for compression, or use a TDC stop tool, or put something in the spark plug hole to watch for TDC. There are many ways to check. Both valves are closed to from what I remember, check by twirling the push rods.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
I am always a bit squeamish about rotating an engine when
non-compressible objects are in a cylinder.
If a compression tester is available, it can be modified into a TDC
finder by removing the gauge from the hose. Thread the plug end
into the hole and listen for air purging out the open hose end as
the harmonic damper is rotated and the timing marks begin to line
up for #1 as suggested by others.
This is a variation on the suggestion to hold a finger over the plug
hole. It is just a little easier to manage if you are by yourself and
happen to have a suitable compression tester to adapt to the task.
.
non-compressible objects are in a cylinder.
If a compression tester is available, it can be modified into a TDC
finder by removing the gauge from the hose. Thread the plug end
into the hole and listen for air purging out the open hose end as
the harmonic damper is rotated and the timing marks begin to line
up for #1 as suggested by others.
This is a variation on the suggestion to hold a finger over the plug
hole. It is just a little easier to manage if you are by yourself and
happen to have a suitable compression tester to adapt to the task.
.
Thread Starter
Le Mans Master
Joined: Nov 2000
Posts: 5,689
Likes: 0
From: Cape Coral, FL 33904
I'm doing this for my leakdown test. I just have the plugs out. Valve covers are still on, along with the timing cover, opti, etc. Just thought there was an easy way to do this.
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Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Your leak-down tester probably has a detachable hose, yes?
.
Intermediate
Joined: Feb 2007
Posts: 49
Likes: 0
From: Near Daytona Florida
I assume you want to find TDC for each cylinder for the leakdown test and you have a true two guage/orifice style leakdown tester. If that is true, connect the leakdown tester to say #1, inject air pressure but with the regulator set to a low value , say 10psi. Rotate the crank, and as the piston comes up on TDC, the cylinder guage psi will rise, then carefully continue to rotate the crank to the where the piston/rod are in the dwell position (no change in psi ==TDC), now be careful and increase the regulator to the value you use for leakdown, typically 80psi and measure the cylinder pressure. Then move to the next cylinder in the firing order and rotate the crank to slightly less than 90 degrees and repeat. I said be careful because if you are not at exactly TDC, when you increase the pressure, the piston may start down the bore and with a nice kick. If you use a breaker bar rather than a ratchet to turn the crank, you can hold the crank in position. If it is an MN6 put it in 1st or reverse before increasing the pressure. The crank may move a few degrees, but that shouldn't matter....Good luck, Mark
Edit: Ok, so I spelled gauge wrong! Oh, if its an MN6, apply the emergency brake!
Edit: Ok, so I spelled gauge wrong! Oh, if its an MN6, apply the emergency brake!
Last edited by Zabman; Jul 31, 2007 at 01:49 PM.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
pulley/harmonic damper?
As long as this is turned in the clock-wise direction, the crank will turn
and the bolt will not loosen.
Given the luxury of a hoist, there is a flywheel turning tool that engages
the teeth on the flexplate ring gear. This offers more leverage and
easy access from the bottom side, but many people do without.
.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
You cannot accurately locate TDC by watching the valve action with the valve covers off. You can use the valve action to identify the proper stroke, but there are much easier ways of doing that. Pulling the valve covers to do a leak down test is a wasted effort.
I have found that an easy way to rotate the engine, if you don't have accessories removed, is to put a socket on the alternator pulley nut. Not only is it much easier to get to, but due to the gear ratio created by the pulley sizes, it makes for reduced effort in the turning.
RACE ON!!!
I have found that an easy way to rotate the engine, if you don't have accessories removed, is to put a socket on the alternator pulley nut. Not only is it much easier to get to, but due to the gear ratio created by the pulley sizes, it makes for reduced effort in the turning.
RACE ON!!!
Le Mans Master
Joined: May 2005
Posts: 7,355
Likes: 2,280
From: Central Maryland
To find true TDC, you need to use a piston stop. Proceed as follows:
Install the piston stop into the #1 spark plug hole.
Remove the other spark plugs.
Rotate the crankshaft, gently, by hand until the #1 piston contacts the stop. Mark the damper at this point relative to the timing mark (or create a corresponding mark on an engine that has no timing tab).
Rotate the crankshaft, gently, by hand, in the reverse direction until the stop is once again contacted. Mark this point on the damper.
Place a third mark exactly equidistant between the first and second mark.
Presuming you measured correctly between the first two marks, this third mark will be exact TDC for #1.
CFI has given you good advice about using the alternator shaft nut to rotate the crankshaft. It works well.
Be well,
SJW
Install the piston stop into the #1 spark plug hole.
Remove the other spark plugs.
Rotate the crankshaft, gently, by hand until the #1 piston contacts the stop. Mark the damper at this point relative to the timing mark (or create a corresponding mark on an engine that has no timing tab).
Rotate the crankshaft, gently, by hand, in the reverse direction until the stop is once again contacted. Mark this point on the damper.
Place a third mark exactly equidistant between the first and second mark.
Presuming you measured correctly between the first two marks, this third mark will be exact TDC for #1.
CFI has given you good advice about using the alternator shaft nut to rotate the crankshaft. It works well.
Be well,
SJW
Thread Starter
Le Mans Master
Joined: Nov 2000
Posts: 5,689
Likes: 0
From: Cape Coral, FL 33904
what are the much easier ways?
You cannot accurately locate TDC by watching the valve action with the valve covers off. You can use the valve action to identify the proper stroke, but there are much easier ways of doing that. Pulling the valve covers to do a leak down test is a wasted effort.
I have found that an easy way to rotate the engine, if you don't have accessories removed, is to put a socket on the alternator pulley nut. Not only is it much easier to get to, but due to the gear ratio created by the pulley sizes, it makes for reduced effort in the turning.
RACE ON!!!
I have found that an easy way to rotate the engine, if you don't have accessories removed, is to put a socket on the alternator pulley nut. Not only is it much easier to get to, but due to the gear ratio created by the pulley sizes, it makes for reduced effort in the turning.
RACE ON!!!
Safety Car
Joined: May 2006
Posts: 4,290
Likes: 140
From: Salem NH
I guess theres a few different ways it can be done.
-- Joe
Thread Starter
Le Mans Master
Joined: Nov 2000
Posts: 5,689
Likes: 0
From: Cape Coral, FL 33904
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by CFI-EFI
You cannot accurately locate TDC by watching the valve action with the valve covers off. You can use the valve action to identify the proper stroke, but there are much easier ways of doing that. Pulling the valve covers to do a leak down test is a wasted effort.
Originally Posted by KDuniverse
what are the much easier ways?
RACE ON!!!
Thread Starter
Le Mans Master
Joined: Nov 2000
Posts: 5,689
Likes: 0
From: Cape Coral, FL 33904
Ok, today I was going to do the leakdown test because the weather was nice, and I had some spare time. Being my first time with such a task, I had only what was said in this thread. Needless to say, I got frustrated, and decided to pull the valve covers. I was going to change the gaskets around the bolts on the cover anyway due to some misc minor leaks. Anyway, here's what I found. It looks to be only on the underside of the covers.
