Camshaft Timing and degreeing the cam?
Administrator
Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
If the cam timing is off, wouldn't you want to offset the cam sprocket relative to the crank sprocket to correct for that? Now if you adjust the cam timing by using an adjustable cam sprocket, I agree that you will throw off the low res pulse signals, but if you use an offset key in the crank sprocket, if seems to me that the ignition timing relationship to the cam position will not be affected and you will bring the cam to its correct relative position with the crankshaft.
When I degreed my cam, I found it to be 2* retarded so I installed a 2* offset crankshaft sprocket key which brought the cam timing spot on. And, just as Javier said, PCMforless agreed that this was the proper method to correct the cam timing.
When I degreed my cam, I found it to be 2* retarded so I installed a 2* offset crankshaft sprocket key which brought the cam timing spot on. And, just as Javier said, PCMforless agreed that this was the proper method to correct the cam timing.
Using a key is the correct way to index the cam to the crank. Then you have to address the issue of the cam dowel pin, and whether it is located correctly, relative to the crank.
Registered User
Joined: Jun 2005
Posts: 387
From: Brandon, Fla.
But moving the cam sprocket relative to the crank sprocket means the Opti is no longer correctly indexed to the CRANK. Spark timing has to be correct relative to the position of the piston, not to the position of the cam. Since both valves are closed on the compression stroke, spark timing has nothing to do with cam timing. Injector timing is another story. You have to consider the movement of the start and end of the pulse width, relative to the opening and closing of the valve, and what happens to the part of the pulse width that exceeds the duration on the intake valve.
Using a key is the correct way to index the cam to the crank. Then you have to address the issue of the cam dowel pin, and whether it is located correctly, relative to the crank.
Using a key is the correct way to index the cam to the crank. Then you have to address the issue of the cam dowel pin, and whether it is located correctly, relative to the crank.
Moderator
Joined: Dec 1999
Posts: 3,853
From: Jupiter (NPB), Fl
But moving the cam sprocket relative to the crank sprocket means the Opti is no longer correctly indexed to the CRANK. Spark timing has to be correct relative to the position of the piston, not to the position of the cam. Since both valves are closed on the compression stroke, spark timing has nothing to do with cam timing. Injector timing is another story. You have to consider the movement of the start and end of the pulse width, relative to the opening and closing of the valve, and what happens to the part of the pulse width that exceeds the duration on the intake valve.
Using a key is the correct way to index the cam to the crank. Then you have to address the issue of the cam dowel pin, and whether it is located correctly, relative to the crank.
Using a key is the correct way to index the cam to the crank. Then you have to address the issue of the cam dowel pin, and whether it is located correctly, relative to the crank.
So I guess it just works!
Registered User
Joined: Dec 1969
Posts: 27,725
From: Little Rock, AR
Moderator
Joined: Dec 1969
Posts: 10,745
From: Buffalo, New York
The injector timing is trivial. A couple of degrees off will make no difference there. However, if you are installing the cam anything other than straight up you absolutely should adjust the spark timing. For every degree you advance the cam, retard the timing one degree, and vice versa. Of course, most often a tune is done after a cam swap and you will be setting the timing to optimum anyway. But even in that case, keep in mind that what the PCM commands is going to be offset by the same amount the as the cam timing in the opposite direction. If you are not doing a tune, you may want to adjust your timing to avoid damage or poor performance due to excessive advance.
Rich
Rich
Thread Starter
Registered User
Joined: Sep 2007
Posts: 53
From: Severn, MD
I have read through everyone's responses and I'm still digesting what has been discussed. I'm just hoping that when I degree the cam, it comes in where it should and I won't have to fiddle with it.
I will be installing an MSD Opti which has an adjustment for timing, I don't know if that will help or hinder.
Thanks for all the responses so far, I'm still all ears on this one.
I will be installing an MSD Opti which has an adjustment for timing, I don't know if that will help or hinder.
Thanks for all the responses so far, I'm still all ears on this one.
Registered User
Joined: Jun 2005
Posts: 387
From: Brandon, Fla.
OK, I thought about it. When the cam is degreed straight up and you find it to be 2* retarded, for example, doesn't that mean that the cam timing (and the ignition timing in the LT1 because the distributer is driven directly off the cam) is 2* behind where it should be relative to the position of the crankshaft?
So to compensate for this, the 2* offset crank key is used to advance the cam to the straight up position (or another way of looking at it is that you are retarding the crankshaft position relative to the cam). Thus, the ignition timing in this case is not affected.
So to compensate for this, the 2* offset crank key is used to advance the cam to the straight up position (or another way of looking at it is that you are retarding the crankshaft position relative to the cam). Thus, the ignition timing in this case is not affected.
Banned
Joined: May 2003
Posts: 6,661
From: LA (lower Alabama)
OK, I thought about it. When the cam is degreed straight up and you find it to be 2* retarded, for example, doesn't that mean that the cam timing (and the ignition timing in the LT1 because the distributer is driven directly off the cam) is 2* behind where it should be relative to the position of the crankshaft?
So to compensate for this, the 2* offset crank key is used to advance the cam to the straight up position (or another way of looking at it is that you are retarding the crankshaft position relative to the cam). Thus, the ignition timing in this case is not affected.
So to compensate for this, the 2* offset crank key is used to advance the cam to the straight up position (or another way of looking at it is that you are retarding the crankshaft position relative to the cam). Thus, the ignition timing in this case is not affected.
This will depend on where they put the opti pin in relation to ICL.
Administrator
Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
There are two very different scenarios being mixed together here.... one is moving the cam to correct for an incorrect grind, the other is advancing or retarding a correctly ground cam.
Moderator
Joined: Dec 1999
Posts: 3,853
From: Jupiter (NPB), Fl
The purpose of the discussion I believe is installing "dot to dot" or "straight up" while correcting a production error, whether it be due to the timing set, or the cam itself.
My purpose on installation with the offset key was to correct for a two degree error I found when installing. I corrected, and installed "straight up" using the offset key.
I don't see the discussion going in the direction of advancing or retarding the cam from the ICL.
Thread Starter
Registered User
Joined: Sep 2007
Posts: 53
From: Severn, MD
My original question was indeed to figure out how to ensure that my cam is installed correctly as indicated on the Cam Card. It indicates that the cam needs to be installed @ 105.0 intake center line. So what I understand is that I need to install my gears straight up, dot to dot and then degree the cam. It should measure 105.0* at #1TDC on both the piston and cam lobe. Am I correct so far?
If this measurement is off, then I need to advance or retard the cam timing by shifting the crank gear to either the advance key or retard key. Am I still on here?
The only problem is that the cheap chainset I bought to replace my stocker has only one keyway in it. I'm going to return it and get the Cloyes CLO-C-3039. I think that will do it.
If this measurement is off, then I need to advance or retard the cam timing by shifting the crank gear to either the advance key or retard key. Am I still on here?
The only problem is that the cheap chainset I bought to replace my stocker has only one keyway in it. I'm going to return it and get the Cloyes CLO-C-3039. I think that will do it.
