Checking the default timing and Cams

From pcarworkshop

Thisarticle is about getting into the cams and checking the timing. I wanted to see what the factory timing was set at. Of course, with an engine with 75,000 miles the chains have streatched a bit so the timing will be a bit different.

Lets remove the chain covers..they came off pretty easy but there was a mixture of bolts vs studs...

Here is the right hand cam chain assembly. You can see the tensioner on the lower part pushing the ramp upwards.

On the left hand side the tensioner is actually on the top pushing downwards.

Here is the left hand tensioner being pulled out. They are simplier and robust and mine seem to be in good shape.

Now we have to pull all the rocker arms out. Again on the 993 its much easier than on the older 911's, its just two bolts and out comes the shaft with the rocker. You don't have to worry about the leaks like the older 911's...Yahoo!

I am cheating a bit on the pictures since the cams have already been pulled on this shot but you can see all the rockers have been removed.

I thought it would be a good idea to check the timing as set by the factory on my car. Unfortunately the Z block that holds the dial indicator designed for the older cars do not work on the 993..they changed the stud locations (or at least I could not get it to work).

I built a makeshift stand using my magnetic base and used the cover studs to hold it down. It seems to work fine.....oh did you notice my $5 tool to fake out the tensioner? Its an old brake piston tool that I modified...it puts a much pressure on the ramp to tighten the chains as I want.

I also put in an old mechanical rocker and set the lash to .1mm. You cannot the old method of using the Intake Valve Overlap lift with the hydraulic lifters...so its best to backdate just for the measurements. The old rocker had to be ground a bit to fit since the head design is a bit different.

So what did I find? Well, here are the measurements for the Intake Valve Overlap as set on my car (comfirmed by measuring 4 times):

Piston 1 : 0.65mm

Piston 4 : 0.66mm

When I took Jerry Wood's rebuilding class he indicated that he sets the 993 to a 1.00mm lift when he does the timing (he does not have the factory tools either). I asked the question on the Pelican engine rebuilding forum. John Dougherty of Dougherty Racing Cams was kind enough to post the 993 cam profile (it just follows this text). He recommended that I increase the lift to 1.2mm which essentially advances the cams. Apparently the cams are installed at the factory a bit retarded.. (no jokes intended...LOL ).

Next step, take the cam towers off, heads off and checking out the SAI ports..

Links to Rebuild Tour

1. Getting started, dropping the engine and superficial stripdown
2. Checking the default timing and Cams
3. Looking at the heads and the SAI passages
4. Valve guides, valves and carbon
5. Further Dissassembly
6. Exploring the SAI passages
7. Cleaning and getting ready to put it all together again
8. Rods and last minute checks before putting the case together
9. Sealing the case (or tomb)
10. Putting the pistons/cylinders back
11. Camshaft timing Part I
12. Camshaft timing Part II
13. Messing up a clean looking engine
14. Not quite there
15. Cranking it up