Initial 993 timing specs...is this what to expect?

Mike Juzenas · 01-03-2006, 12:29 PM

Hello All!

Well, I have started on my journey to rebuild my 993 engine. It definitely needs guides so that is the first goal but I am also thinking of tearing the engine down to the crank since its not that much more work. THe engine has 77,000 miles on it with 60,000 being the previous owners....where I have partial maintenance records but really don't know how well the car was treated. I am sure while on this journey I will be posting lots and asking questions...especially since the 993 is a bit different and not totally covered by the typical sources (such as Wayne's book).

Anyways I have the engine out and stripped down to a long block. Since its a 96 it does not have the nice indexed sprockets for the cam timing but the "friction fit" system. My spec book does not specific the Intake Valve Overlap so I thought I would measure it out.

I got the following readings (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).

Has anyone else measured this and have a value? I am going to backdate the sprockets (after machining a keyway) so I need to know the value of what to use anyways.

Here are some picts so far. I was having trouble with restricted size uploads (even if the web site says large images are no problem) so I will post more later. :

At the start...it still runs!! ;-)

Why use one jack when three will do?

Lifting up the rear over the engine saves taking any trim or bumpers off...its handy having a 16" I beam across your shop! ;-)

2.7RACER · 01-03-2006, 07:35 PM

Mike,
It looks like your cams are running about 3 degrees retarded from the Porsche spec. Jerry Woods spec of 1.0mm is spot on to open the intake valve at 0 degrees TDC, crossover. This would be with zero valve lash, not the 0.10mm you set the valve lash once the motor is all together.
Timing chain stretch plus normal tolerances account for the 0.65mm you are reading.
Good catch and question,

Mike Juzenas · 01-03-2006, 09:23 PM

Thanks for the help!

I noticed that my cams have a 964 part number (I am not in the shop at the moment). In my spec book the specs for the 964 cams are at 1mm valve stroke and zero play.

So when I put this all back together do I set the timing with zero lash to 1.0mm? BTW I am using mechanical lifters for the measurements of course.

Cheers,

Mike

2.7RACER · 01-04-2006, 10:37 AM

Mike,
It's your call on setting the cam timing. 1.0mm with zero lash or 0.9mm with 0.10mm lash.
Have fun with your rebuild.

Tyson Schmidt · 01-04-2006, 07:21 PM

Do you have an adjustable rocker arm to substitute in for the cam timing adjustment? You know you can't rely on the hydraulic lifter.

Mike Juzenas · 01-04-2006, 08:54 PM

Quote:

Originally posted by Tyson Schmidt
Do you have an adjustable rocker arm to substitute in for the cam timing adjustment? You know you can't rely on the hydraulic lifter.

Hi Tyson,

I used an old-fashioned adjustable rocker arm during the measurement. I have two "spares" that I got from a junker that I will use for both the timing and checking the piston/valve/head clearances.

Cheers,

Mike

camgrinder · 01-04-2006, 09:50 PM

I have measured the 993 cams at the valve with my Cam Doctor. The measured lobe seperation is 114.8 degrees. With the cams set at straight up with .004" lash I get .048" lift at TDC on overlap.
I would set the cams to 1.2mm using the mechanical rocker arms and .004" lash.

Mike Juzenas · 01-04-2006, 11:37 PM

Thanks John!

I am not sure how you arrived at your figure (likely because its what you do for a living and I am just an amateur)...can you fill me in a bit? Did those cams have a 964 part number?...I will post my part numbers tomorrow.

Lets see if I get it...I understand you have measured the 993 cam will lift the rocker end riding on the cam .048" at TDC on overlap with the cam set perfectly upright. In order to get a 1.2mm lift I will need to advance the cam so it starts the rocker earlier to obtain the 1.2mm lift at the valve at TDC.

If that is correct how did you calculate the 1.2mm number? I guess the cam will not be in the "stock" position as set by the 993 tools...what is the risk of the valves hitting the pistons?

Thanks for any help or corrections!

Cheers,

Mike

camgrinder · 01-05-2006, 07:41 AM

Hi Mike,
Here is a screen shot section of the valve lift curve graph. The blue line is the intake valve lift curve. The 360 degree position is TDC at overlap. If I set the cam to straight up in the program it shows .048" valve lift at TDC (360 degrees)
It was a 993 camshaft from an N/A car, not a turbo cam.
I have a cylinder head set up with the cam carrier which I use with linear and rotory encoders hooked to the "Cam Doctor" computer.
Your measured .65mm would set the cam slightly retarded in the engine. Going to 1.2 mm is advancing the camshaft. As with any engine build, you should check valve to piston clearance unless it is 100% original. And even then it doesnt hurt to check.

Mike Juzenas · 01-05-2006, 07:58 AM

Wow, thanks Jim! That is quite interesting...I wonder if my cams were slightly retarted because the factory tools are setup that way ?

I will take your suggestion and definitely check the valve/piston clearances as part of the assembly process. Of course i am not near that part yet.... ;-(

Oh If you remember we had a conversation about backdating the old sprockets onto my 993 camshafts and the keyway was the issue...and I was likely to need a keyway cut in order to use the "old" system. It turns out that my cams do have the keyways! The car was built in Jan/96 so they must of still been using the older cams...but it did have the newer style sprockets..

Thanks again!

Cheers,

Mike

camgrinder · 01-05-2006, 08:28 AM

Whos Jim?

Yeah the factory cams are sometimes retarded in the engine. The 964 cams are as well.

Mike Juzenas · 01-05-2006, 08:47 AM

Quote:

Originally posted by camgrinder
Whos Jim?

Woops, my typo! Sorry! ;-)

Mike

911TE · 02-28-2006, 03:36 AM

Picking up this old thread, because I`m not able to find the correct setting data for my 993, where I want to use factory 993 RS cams (still with hydraulic lifters)

Is it right to assume it is the same 1mm lift at tdc like the standard 993 cams?

No word about the timming of these cams in the repair manual, unfortunately!

One question especially for camgrinder: Do you have experiences with the factory 993 RS cam? It seems pretty mild to me, but I´m not sure if I run into piston/valve clearance problems with it.
As the RS always came with 3.8 pistons and my engine still has 3.6 it does not help to compare the partslist.

Sebastian

Mike Juzenas · 02-28-2006, 06:38 AM

Hi Sebastian,

Is there anything else that you are changing (i.e. RS valves, etc?). I thought that without chaning the P/C's and using RS valves plus a software upgrade there was little point to go to the RS cams....it will be interesting to see what you find out.

As far as the lift goes Porsche stopped giving out numbers on the 964. You can check those specs for the 964, that might give you a guideline.

Cheers,

Mike

camgrinder · 02-28-2006, 08:23 AM

I doubt you will have a problem with valve to piston clearance. The important thing to remember is at full valve lift the piston is 114 degrees away from top dead center.
I have had wilder cams (DC22) clear the factory pistons. But I would always check the clearance to be sure.

911TE · 03-01-2006, 12:48 AM

Mike and John,

Thank you for the info!
I`m planning to get a software update, the lighter RS flywheel instead of the DMF and a slightly bigger throttle valve housing.
No bigger inlet valves as it is connected with new valve seats which is to much effort for me in the moment.

John, you would suggest to set the cams so, that the highest lift on cyl. 1 occurs at 114 degrees (crank degrees) after tdc?
Then turning the motor back to tdc and measuring the valve lift at tdc and we have the setting value at tdc for the future?

A little bit off topic here but connected:

All six heads have one very small hair crack between one plug hole and the exhaust valve seat. Anybody seen this before? Is this dangerous or can I ignore the cracks?
If not a single problem of my engine, did ever seat-rings fall out of the heads because of this at the 993s or 964s?

If I need new heads, I would look out for used 285hp heads which have bigger inlet valves.

Sebastian

911TE · 05-02-2006, 03:10 AM

To add some more information and questions to this thread:
I did the cam timing on the weekend by setting the RS-cams to the 993 RS factory manual value of inlet opening at 5 degrees BTDC at 1mm play.
(993 standard is 1 degree BTDC)

The inlet valve is then aproximately 1,8mm open in Overlap TDC.
As John suggested, around 114 degrees after TDC it has the max. valve lift, but this is nearly impossible exactly to measure, because you can turn the engine around 4 degrees at max. lift without reading different values.

The only strange thing is that I´m not able to set both sides at exactly the same lift and the same begin of opening.

On the left side setting the cam exactly on 5 degrees BTDC begin of opening (1mm lift) gives 1,8 mm lift in TDC, on the right side 5 degrees gives only 1,7 mm lift in TDC.

If I set both cams to 1,8mm in TDC, the right side opens 4 degrees BTDC. (left 5 degrees) Which value is more important in real engine life?

Is this a machining tolerance or do I have a mistake in my measurements?

Sebastian

camgrinder · 05-02-2006, 08:09 AM

I would set them using the opening point in degrees.

Trying to measure the intake valve lift centerline can be done by,
taking a measurement 1mm before full lift and 1mm after full lift, adding both of these numbers together and divding by 2.

911TE · 05-03-2006, 09:37 AM

John,

Thank you, I will try it this way.

Sebastian