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TheLurker · 04-14-2006

I did a thing on cam timing a few years ago. Depending on year, it can move dramatically. Early models (375 hp) with one flat on the venier can swing easily 6 degrees either way. Later models with two flats are tighter but still can move. Doing the timing according to factory procedures does not yield consistant results at all.

To get good timing you will need a piston stop to get TDC accurate. You need to get a standard timing wheel to do this. If you have a good CAD program you can make one out of paper, back it with cardboard, and tape it to the dampener. I have done this several times when timing the cams in the car. You will need a dial indicator to place on the lifter with a fixture you make to go around the cam shaft and sit atop the lifter. You will need a crank locator pin as well as two temporary cam chain tensioners. You will also need temporary cam retainers to secure the cams to the head. You will need a torque angle meter for the cam bolts. Finally you will need four cam locator pins.

As far as parts you will need four new cam bolts. This is at a minimum. You may need new tensioners if you cannot reset the old ones. I did a photo set on the Corvette Forum explaining how to do this. If you don't know how to do it then you will probably screw one up before understanding how it works. Quickly, when resetting the tensioners you are resetting the travel snap rings in order that the tensioners can be installed cocked. Once installed, a quick tap in the tensioners will fire them allowing for full travel.

First, you will need to time the cams according to factory procedures. This is done mainly to assure that there is no interference with the pistons and valves. Next, find TDC on the #1 cylinder. Do this using the piston stop. Now you can set up the dial indicator on the #1 cylinder.

Measure the timing on the cam you are working on. This can vary widely as you will find out. You measure the timing on a cam by turning the crank clockwise. Determine the max lift in the lobe approximately. Turn the dial indicator pointer to that setting. Now, to make an accurate measurement, you turn the crank clockwise until you are about .020 on the dial indicator before your pointer. Say that is 124 degrees on your timing wheel. Next, keep turing the crank past your pointer on the dial indicator until you get back to the .020 you took the first measurement at. Read the timing wheel, say it's at 95 degrees. Now you add 124 and 95 to get 219 and divide that by 2 to get 109.5. That is where the cam is timed at. If you don't understand this procedure then you don't need to be timing cams.

When timing cams you can be close and that is fine. Just make sure they are close to equal for intakes and close to equal for exhaust. On the intakes you can go anywhere from 108 to 114. 110 is ideal, 108 gets more power but less torque. I have gone down as far as 103 before. On the exhaust you can go between 114 and 116.

The hardest part of cam timing is locking down the cam bolt. There can be no movement. I have found that when I have gotten the proper timing I take a small piece of cardboard and place it under each of the temporary retainers and torque them back down. Do this one at a time. Next, get someone to hold the rear of the cam in place with a wrench. Now you can begin the torquing. When you are doing the torque angle you have to keep a close eye on the dial indicator. It has to stay in one place. If you see it move you have just killed your timing and must repeat the procedure over. You will be turing the cam bolt 80-85 degrees all the while keeping a close eye on the dial indicator. Meanwhile, your assistant at the other end of the cam is applying opposite pressure trying to maintain the cam in the proper place. EASY!

Needless to say, if you have never timed a cam you are pretty assured of not getting it right the first time. If you know someone close to you doing a timing then by all means go there and watch and help.

04-14-2006	#3
TheLurker Join Date: Sep 2005 Location: Dallas, Texas Posts: 14	Re: cam timing I did a thing on cam timing a few years ago. Depending on year, it can move dramatically. Early models (375 hp) with one flat on the venier can swing easily 6 degrees either way. Later models with two flats are tighter but still can move. Doing the timing according to factory procedures does not yield consistant results at all. To get good timing you will need a piston stop to get TDC accurate. You need to get a standard timing wheel to do this. If you have a good CAD program you can make one out of paper, back it with cardboard, and tape it to the dampener. I have done this several times when timing the cams in the car. You will need a dial indicator to place on the lifter with a fixture you make to go around the cam shaft and sit atop the lifter. You will need a crank locator pin as well as two temporary cam chain tensioners. You will also need temporary cam retainers to secure the cams to the head. You will need a torque angle meter for the cam bolts. Finally you will need four cam locator pins. As far as parts you will need four new cam bolts. This is at a minimum. You may need new tensioners if you cannot reset the old ones. I did a photo set on the Corvette Forum explaining how to do this. If you don't know how to do it then you will probably screw one up before understanding how it works. Quickly, when resetting the tensioners you are resetting the travel snap rings in order that the tensioners can be installed cocked. Once installed, a quick tap in the tensioners will fire them allowing for full travel. First, you will need to time the cams according to factory procedures. This is done mainly to assure that there is no interference with the pistons and valves. Next, find TDC on the #1 cylinder. Do this using the piston stop. Now you can set up the dial indicator on the #1 cylinder. Measure the timing on the cam you are working on. This can vary widely as you will find out. You measure the timing on a cam by turning the crank clockwise. Determine the max lift in the lobe approximately. Turn the dial indicator pointer to that setting. Now, to make an accurate measurement, you turn the crank clockwise until you are about .020 on the dial indicator before your pointer. Say that is 124 degrees on your timing wheel. Next, keep turing the crank past your pointer on the dial indicator until you get back to the .020 you took the first measurement at. Read the timing wheel, say it's at 95 degrees. Now you add 124 and 95 to get 219 and divide that by 2 to get 109.5. That is where the cam is timed at. If you don't understand this procedure then you don't need to be timing cams. When timing cams you can be close and that is fine. Just make sure they are close to equal for intakes and close to equal for exhaust. On the intakes you can go anywhere from 108 to 114. 110 is ideal, 108 gets more power but less torque. I have gone down as far as 103 before. On the exhaust you can go between 114 and 116. The hardest part of cam timing is locking down the cam bolt. There can be no movement. I have found that when I have gotten the proper timing I take a small piece of cardboard and place it under each of the temporary retainers and torque them back down. Do this one at a time. Next, get someone to hold the rear of the cam in place with a wrench. Now you can begin the torquing. When you are doing the torque angle you have to keep a close eye on the dial indicator. It has to stay in one place. If you see it move you have just killed your timing and must repeat the procedure over. You will be turing the cam bolt 80-85 degrees all the while keeping a close eye on the dial indicator. Meanwhile, your assistant at the other end of the cam is applying opposite pressure trying to maintain the cam in the proper place. EASY! Needless to say, if you have never timed a cam you are pretty assured of not getting it right the first time. If you know someone close to you doing a timing then by all means go there and watch and help.