cam replacement and leak down test

[jbrown]

I have a couple of questions.
I want to do a leak down test just to see the numbers. I have a crank fire ignition system in the car. The book I have tells me how to get the cylinders to top dead center with a distributor ignition set up. How do I know when the piston is at top dead center on a crank fire ignition.
Second I have a minor tap, one of the lobes on my cam is pitted and I want to replace it. I purchased a book on how to rebuilt the 911 motor. It shows me how to take the motor apart. I am looking for a manual or book, internet , something that shows me in some detail how to do a replacement of the cam only. The book is great but I think it has you take alot of the motor apart before moving on to the cam. I dont think I need to do all that the book says just to remove the cam.
Thanks John

[lindy 911]

John,

There are a couple of ways to find TDC. One is to use the Z-1 mark on the crank pulley; this shows TDC for cylinder #1. The second way is to pull a spark plug and use a pencil inserted into the plug hole and feel the piston come up to TDC while turning the crank. The Z-1 mark is more accurate because there is a certain amount of dwell when the piston is at the top of its stroke.

Your second question will require an engine drop. Waynes rebuild book will have the information as to replacing the cam but you'll have to extract the info you need. In simple terms it would be:

1. Drop the motor.
2. Pull the timing chain covers.
3. Pull the tensioner.
4. Pull timing gear.
5. Remove rocker covers.
6. Remove all rockers.
7. Pull three bolts for cam carrier and pull carrier.
8. Pull cam.

Install:

1. Install cam.
2. Install cam carrier with O-ring, gasket and three bolts.
3. Install sprocket flange shims, sprocket flange, tensioner, timing chain and bolts. (Use Waynes book).
4. Time cam after installing intake rocker on #1.
5. Install remaining rockers.
6. Install rocker covers.
7. Install motor.

Lindy

[Flat6pac]

But remember, the cause of the problem is the oiler tube in the cam carrier and the lack of oil. The rocker will be wasted too.
Bruce

[Steve@Rennsport]

Originally Posted by Flat6pac

But remember, the cause of the problem is the oiler tube in the cam carrier and the lack of oil. The rocker will be wasted too.
Bruce

Bruce,

Another major cause is the oil that many people use. We see an increasing number of motors with bad cams where the spray bars are not obstructed, but where insufficient ZDDP in the oil caused the problem.

[jbrown]

thanks guys, I already no why the cam lobe went bad. the squirter had a block. It was cleaned out and works fine. That we did with the motor in now it is time to change the cam and check the rocker also and if need replace.

[gsjohnson]

Originally Posted by Steve@Rennsport

Bruce,

Another major cause is the oil that many people use. We see an increasing number of motors with bad cams where the spray bars are not obstructed, but where insufficient ZDDP in the oil caused the problem.

Oil suggestions?

[Flieger]

Brad Penn 20W50 Racing

Ultimate Motor Oil Thread or Why we hate CJ4/SM oils

[gsjohnson]

Thank you