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Old 07-10-2007, 06:25 PM
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Posted by decathlete:
"Until then, if you have any ideas as to measuring the lift/duration of the cam ( yeah, i know, good luck) let me know."

It's not really that difficult to measure with the motor assembled, assuming there is enough flat shoulder on the spring retainer to accomodate the plunger of a dial indicator. It is a labor intensive project though.

If you don't have a dial indicator with magnetic base, step up and buy one. It's an inexpensive addition to your tool collection and everyone should own one. Here's an adequate example with 0-1.000" travel. Don't buy one with less than 1" of travel, it will limit you on your projects.....

The other things you will need are a good degree wheel and a piston stop. I've used a Moroso 11" wheel for years and have found it adequate.....
Here's an inexpensive stop that will work......

Also, measure the outside diameter of the harmonic damper ring and buy the appropriate degree tape....

A pointer for the wheel can be made from a piece of clothes hanger wire with a pigtail formed in one end using a needlenose plier in order to mount it on a water pump bolt and the other end sharpened to a point with a file or grinder.

If the motor is in the car, remove the fan, shroud, lower crank pulley and all belts. I also drain the radiator and block of coolant and remove the water pump to make things easier to get to. Use solvent and hot soapy water to clean the harmonic damper so the timing tape will stick well to it. Dry thoroughly. Mount the degree wheel to the crank and the pointer to any close bolt and bend the wire so the end of it is pointing at the edge of the wheel, close to the numbers on the wheel. Remove all spark plugs to make the motor easier to turn over by hand. Remove the inner threaded rod from the piston stop and screw the outer housing only into the #1 spark plug hole (driver's side, closest to radiator) and snug it up. Remove driver's side valve cover.

With a socket and long cheater bar on the damper retaining bolt, rotate the crank clockwise while your buddy holds his thumb over the hole in the piston stop housing. As you rotate the crank, he'll begin feeling air pressure coming out the hole. This tells you that the piston is coming up on the compresssion stroke. Normally, you can watch the TDC notch indicator on the damper ring as it comes closer to the timing tab on the timing cover to see when the piston is at top dead center, but if the ring has slipped very much on the elastomeric material, the mark could be way off. Rotate the crank so that the notch on the damper ring is about 1 1/2 to 1 3/4 inches to the right of the timing tab on the front cover. Loosen the damper retaining bolt and position the degree wheel at 20 degrees ATDC (wire pointer to the left of TDC on the degree wheel). The motor will try to rotate backward as you loosen the damper retaining bolt, so I usually have my buddy crawl under the car, remove the inspection cover and hold a long flat-blade screwdriver into the ring gear teeth and wedge it against the bellhousing while I loosen and tighten the bolt.

Insert the threaded probe into the piston stop housing until the probe meets resistance against the piston crown. Go easy here, just screwing it in by hand until it meets the piston. Rotate the crank nearly one full turn clockwise until the piston comes up against the piston stop again. I'll say this again, GO EASY. If the wire pointer stops at 20 degrees before top dead center on the degree wheel, then the TDC mark on the degree wheel indicates true top dead center when aligned with the wire pointer. If not (yeah, right, what are the chances you nailed it the first time), move the degree wheel radially half the distance of the error. For instance, if the wire lines up at the 30 degree mark BTDC, then you want to rotate the degree wheel COUNTERCLOCKWISE 5 degrees and try it again. If the wire pointer shows, for instance, 10 degrees BTDC, then rotate the degree wheel CLOCKWISE 5 degrees. It's less work at this point if you simply rotate the crank counterclockwise and come up against the piston stop. You can do it if the bolt remains tight in the crank. Bring the piston up against the stop again and note the number of degrees ATDC where the wire pointer is on the degree wheel. Rotate the crank clockwise up against the stop again BTDC and note where the pointer is on the degree wheel. If your patience holds up, you'll eventually get to the point where you have the same number of degrees BTDC and ATDC. When you've done that, remove the piston stop and rotate the crank so that the wire pointer lines up on TDC on the degree wheel and you're at absolute TDC.

Affix the timing tape to the harmonic damper ring with TDC on the tape aligning with the tip of the timing pointer on the timing cover. Now, you'll be able to time the motor later with a timing light and know you are correct.

Mount the dial indicator magnetic base onto the head. Rotate the crank until the exhaust valve is visually fully open (spring compressed). Mount the dial indicator stem on the spring retainer next to the rocker arm tip. Compress the stem into the indicator tool by about 0.100" to pre-load it. Sight with your eye from the side and front of the motor to assure that you have the indicator stem parallel with the exhaust valve.

Remove the piston stop inner plunger from the housing, leaving the housing in place in the spark plug hole. Rotate the crank clockwise with your buddy again holding his thumb over the piston stop housing hole to determine that you are coming up on TDC compression stroke. Zero the dial on your indicator. Rotate past TDC until the exhaust valve just begins to open by watching the dial indicator. This should be somewhere between 50 and 90 degrees BBDC on the power stroke. From the exact point of the valve beginning to move, rotate the crank until the dial indicator shows the valve open 0.075". With a 1.5 rocker, this will be 0.050" tappet lift. Note the reading of the wire pointer on the degree wheel and write it down as "exhaust opens ____ degrees BBDC @ 0.050" tappet lift". Continue rotating the crank until the dial indicator shows max lift. Count the number of degrees from this point to TDC on the degree wheel. Write this down as "exhaust max lift ____ degrees before TDC". Continue rotating the crank clockwise until the dial indicator shows the exhaust valve full closed (spring relaxed). Rotate the crank COUNTERCLOCKWISE until you have opened the valve 0.075". Write this down as "exhaust closes _____ degrees ATDC @ 0.050" tappet lift".

If the cam is a mild grind, the valve may close (measured at 0.050" tappet lift) BEFORE TDC. If so, write it that way. "exhaust closes _____ BTDC @ 0.050" tappet lift"

Now, you have all the information for the cam timing for the exhaust lobe. If the valve closed ATDC @ 0.050", add together the number of degrees from opening to BDC, then add the 180 degrees it was open from BDC to TDC, then add the number of degrees from TDC to close. This will give you the exhaust duration @ 0.050" tappet lift. If it closed BTDC, add the number of degrees from open to BDC to the number of degrees from BDC to close.

Now, move the magnetic base and indicator to the #1 intake valve right next door and do it again to find the intake valve timing.

Having the exhaust max lift point BTDC and the intake max lift
point ATDC will allow you to find the lobe separation angle of the cam. Simply add the two figures together and divide by two.

To determine the 0.050" tappet lift point with 1.6 rockers, open the valve 0.080" from where it just cracks open. To determine it with 1.7 rockers, open the valve 0.085". For 1.72 rockers, 0.086". For 1.75 rockers, .0875".

It has easily been 10 years since I did this, so if I messed anything up, please respond before I post this to Crankshaft Coalition. Thanks for your patience in reading this.

Last edited by techinspector1; 07-10-2007 at 06:31 PM.
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