cam timing for 911sc

[jerkan]

I am troubleshooting a 79 911sc and suspect the cam timing is out. The cams for this car were sent to Web Cam who reground them to the Carerra C2/C4 3.6L (964) specification. I do not have the specs to check the valve timing. can anyone help? also, is the timing to be set at the normal valve lash of .004"? can the valve timing be checked without dropping the engine?

[lucittm]

What makes you suspect the cam timing? Were the cams that were sent to Web Cam, original to the car? Was the car running with those cams installed? Do you want the factory specs?

I believe the factory spec for your car is .050" +/- .004" of intake lift at TDC (firing) on both #1 and #4.

Yes, you must set the rocker arm clearance to .004" on at least #1 and #4 in order to set the cam timing.

Can you do this with the engine installed...
1. You need to verify if you are on the firing stroke by checking the distributor rotor position - check.
2. You will need to mount the dial indicator on #1 and #4 intake valves - check.
3. You will need to turn over the engine several times by hand after you pull the plugs, you can do this via the alternator - check.
4. You will need to be able to see the TDC mark exactly line up on the crankshaft pulley or use another dial indicator in a spark plug hole - check.

Yes, you can check the valve timing with the engine in the car. Can you adjust it? That may not be possible. You would have to remove the cam chain covers and use the P-tools to loosen the cam sprocket retaining nut while holding the cam. I would need to see your car to determine if this was possible. Things like exhaust pipes, muffler, engine tin, A/C, and rear engine mount; all these and more would be in the way.
I would not attempt it on my car. Perhaps someone with more experience in the '79 SC could chime in.

Good Luck,
Mark

[jerkan]

when the cams came back from web-cam they told me to set them at 1.7-1.9mm at .004" valve lash. I rebuilt my engine and put them in to this spec and the car worked fine. I later blew a piston requiring another rebuild and I contacted webcam to confirm the cam specs again. they told me the spec for the 964 cams is 1.25mm at .1mm valve lash. this is where i set them and now the car will not start. so I am not sure what spec is correct.

[WERK I]

Setting your cams at that spec (1.25mm) won't affect your starting. I don't know what the correct cam timing spec for your cams is, but the vendor who manufactured those cams should.
I suspect the problem with your starting, is either your cams were timed improperly or the fault lies in the ignition/fuel systems.

[lucittm]

I composed a long detail reply but the server at PP lost it.

Suffice it to say you may have your cams swapped.

Thanks,
Mark

[jerkan]

I was very dilligent when I installed the cams and I am absolutely sure I did not swap the L and R. I did a compression check and all cylinders are sat. I swapped out the gas and flushed the system out and ran new fuel thru the system and injectors via separate containers. I wanted to check the cam timing to make sure it is ok first and than do the logical fuel system checks with gauges.

[mca]

Originally Posted by jerkan

when the cams came back from web-cam they told me to set them at 1.7-1.9mm at .004" valve lash. I rebuilt my engine and put them in to this spec and the car worked fine. I later blew a piston requiring another rebuild and I contacted webcam to confirm the cam specs again. they told me the spec for the 964 cams is 1.25mm at .1mm valve lash. this is where i set them and now the car will not start. so I am not sure what spec is correct.

.004" = .1mm

I was told that 964 cams in the SC should be set to 1.26mm. If you want to advance them they can be set between 1.4mm and 1.5mm.

At 1.25mm you should be fine as far as the cams are concerned.

[jerkan]

I will try to get ahold of webcam first thing monday morning. It sounds like if I set the timing for 1.25mm at 1mm valve lash, I can't go wrong. I believe that if the cam timing is retarded, than the top end performance is improved and I know porsche has changed the timing specs from year to year trying to get the optimum performance.

[mca]

So what exactly are you troubleshooting?

[WERK I]

Originally Posted by mca

So what exactly are you troubleshooting?

Engine won't start.

[JohnJL]

You describe your fuel, compression and cam timing troubleshooting, how about Ignition? Have you confirmed spark, gap and timing also?

Just working Occam's razor here...

[jerkan]

during the rebuild, I changed quite a few components, one being the cd box. I replaced it with the msd 6a. It is possible, this could also be the problem, but as in any other problem, i logical means of troubleshooting is necessary in order to rule out "what it is not"

[jerkan]

In checking the cam timing while the engine is in the car,does anyone know if it is necessary to undo the timing chain covers to tighten up the chain while checking valve overlap, or can i rely on the readings that i get without the chain tightened up?

[mca]

The chain should be tight already if you have your tensioners installed. No need to pull chain covers.

Just pull the intake valve covers, make sure that the intake valves on #1 and #4 are adjusted properly, and start testing.

Get to TDC, place dial gage on #1, and rotate engine 360 degrees. That should give you cam timing for the left side.

Now move the dial gage to #4 and rotate another 360 degrees. That should give you cam timing for right side.


PS. Someone correct me if I am wrong. But this is how I checked mine a couple of weeks ago. I also have 964 cams.

[JFairman]

I've got the Webcam welded and reground grind #40 cams (964/Carrera/) in my car too.
You can install and set the cam timing in the car just fine. I did it that way in my 930 with the back of the engine lowered about 6" onto a jackstand.

I did it in my driveway last summer and had no where to put the motor if i took it out. That would have been a heck of alot more work too.
It doesn't bother me to sit on the ground behind the car and work on it.

Obviously you have to remove some things including the rear engine tin and chain case covers to do it.
To just check the cam timing you only need to remove the top valve covers. Don't even need to drain the oil.
When doing the left side cam, the cam holder tools long handle will be straight up so the cut out section clears the chain tensioner, and at about 8 o-clock on the right side cam.
As long as your back can handle the variety of positions your body will be in, it's not difficult at all.

The timing spec for those cams from Webcam is 1.25mm as has been said. If you set it to 1.26mm that is such a small difference you wouldn't even notice a difference and after around 500 miles, depending on how you drive the wear in the timing chains will retard the timing down to 1.25mm anyway.

I set mine to 1.29mm because I wanted more low and midrange power for street driving and I have a K27HFS turbo with B&B headers running at 1 bar to keep it pulling strong up top.
The important thing is to time both cams the same and make sure your cam oil spray bars are clean.

Here's to changing cams, rockers, chains and sprockets with the engine in the car...

I also would have needed a 4x8 sheet of plywood under the car to roll a floor jack or ATV jack around under the car with the weight of an engine and transaxle on it because of the lumpy driveway tiles.

I put a thin smear of hylomar on the chain case gaskets and 0-rings.
Also put the wrightwood racing RSR rocker shaft seals on the new rocker shafts.

I have no oil leaking or sweating anywhere now... nice!

[jerkan]

ok, I will check it this afternoon. I contacted webcam and they told me my valve overlap should be 1.25mm at .1mm valve lash. to get to #1 TDC, i assume I turn engine until rotor is at #1 and timing mark on pulley is at timing mark and there should be play in the rocker arms for #1 intake, is that correct?

[mca]

Originally Posted by jerkan

ok, I will check it this afternoon. I contacted webcam and they told me my valve overlap should be 1.25mm at .1mm valve lash. to get to #1 TDC, i assume I turn engine until rotor is at #1 and timing mark on pulley is at timing mark and there should be play in the rocker arms for #1 intake, is that correct?

Yep. Again, no need to drop (or partially drop) the engine in order to check the cam timing.

Take several measurements just to make sure that you are getting accurate readings. And don't forget to put the car in neutral - not that you would forget, but sometimes when I have a lot on my mind I forget the little stuff.

[JFairman]

If your valve clearence is set right, thats correct

I used a long pencil in the spark plug hole to touch the top of the piston while turning the crankshaft slowly by the timing mark on the pulley to make sure I was at TDC on the #1 and #4 cylinders too.

Just don't let it drop in there... a paper drinking straw is safer in that regard, just didn't have one around.

[jerkan]

greeeaat.....the plot thickens. Let a buddy borrow my dial indicator and he broke it. got me a replacement but the stem is too long and can not use it with engine in car. Guess I will troubleshoot other stuff untill new dial indicator from out host comes in.
more to follow....I will start looking at the fuel system in the interim.

[lucittm]

You did well on a dial indicator with a longer stem. I made one for my Starrett 0-1". This comes in handy for checking TDC through a spark plug hole.

Thanks,
Mark