Question regarding TDC and cam timing...

Jim_0068 · 09:10 AM

Well i bought Wayne's book "How to Rebuild and Modify..." and it has been a great tool. It has made setting the cam timing really easy as before i was thoroughly confused as to the setting of the valves before the timing.

But there is a problem. I am having issues finding TDC on the motor. I am looking at page 178 in Wayne's book and it says that the tip of the rotor should be facing the notch in the distributor. When the distributor rotor is lined up there, the motor should be at TDC and from my understanding it should also be @ Z1 on the crank pulley right?

Well that isn't the case for me. If i get the rotor to face the notch i am not on the Z1 mark, i am on another notch on the pulley.

Now someone has been in this motor before, could they have put the pulley on the wrong way? Where the notch that is lining up currently is the "new Z1" mark for me?

thanks for all your help

Edit:

One last question: I need to have tension on both idler arms to set the cam timing right? Is there another way i can get enough tension on the 4,5.6 cylinders without the mechanical chain tensioner tool? Anyone use something else that is easy and handy? I don't think i can get one to use in time

WERK I · WERK I's Garage

Jim,
Try it this way. The distributor runs at half the crankshaft speed. Therefore, there are two possible scenarios in which the rotor will line up. One with the crankshaft at Z1 and the rotor pointing to the notch or the crankshaft at Z1 and the rotor 180 degrees out. I generally use the Z1 mark and check the lobes of the camshaft for cylinder #1 at their lowest state. That is, both intake and exhaust valves are closed and the rockers are are at maximum lash(.004" when adjusted).

Jim_0068 · 07-19-2004, 09:01 AM

Ugh...i can't believe my post didn't get up there.

The one thing that transfer over from my domestic motor experience (this is my first foreign motor) is that distributors and cams rotate half as much as the crank. The only problem is that on either stroke that the rotor is lining up on the notch the Z1 mark doesn't

Now i could take off the cylinder head and get TDC but that is a much more than i want to go through since i am doing my best to get this motor running by the weekend. Now if i have to, will i be able to re-use the o-ring cylinder head gaskets? Sorry if this is a stupid quesiton i just don't know.

Thanks

Jim_0068 · 07-19-2004, 09:07 AM

I also wanted to mention that i am at the point where i only have the #1 intake/exhaust rockers on and need to get TDC at #1 so i can set the timing and then proceed with Wayne's instructions in the book.

Thanks

WERK I · WERK I's Garage

Jim,
I would back from what you're doing and start back at the reference point which is Z1. Pull the distributor out since this is one of the last things you do when buttoning up the engine. Time the cams first when the crank is at Z1. Just remember, as the book points out, that the crank is rotated 360 again at Z1 for the right bank. You do not have to pull the heads to find Z1. Z1 is TDC for #1, period. People have stated on this forum that they have found Z1 to be off by a couple of crankshaft degrees. In my case, an 85 930, the mark was spot on. The crankshaft pulley is keyed, so it is impossible to put on any other way.
Yes, after setting the cam timing for cylinder #1, the chain for the right bank(cylinder #4) has to be pre-tensioned as well. It makes a HUGE differance in the timing if the chains have any slack in them.
I did my first 911 engine last year so I can appreciate your concern on the cam timing. Sorry for my basic approach on this matter, but I did not know your background.

Jim_0068 · 07-19-2004, 12:00 PM

Werk...thanks for your response. I have yet found out something very odd.

I am going to post it here for you but make a new thread on it.

My first question is i believe the distributor was installed incorrectly. Reason for this is because at the Z1 mark on the crank, my rotor in my distributor is pointing at the #2 plug (according to Wayne's book page 190).

I proceeded to install the distributor cap back onto the distributor (as i never took the distributor out just the cap off since this is a top end rebuild) and every one of my plugs is off by 2 from what the book says. And i'm 99.9% sure it is not the angle that i am looking at.

So now i know someone was in this motor before i got to it and the question becomes could someone have installed the distributor that many teeth off and compensated for it by a timing adjustment?

I mean i know on domestic motors if you install the distributor off a couple teeth it just won't run right and you'll have to compensate for it HUGE with timing but the car ran basically fine when we got it. It was just blowing smoke on the de-cel hence the top end rebuild.

You know of any good sponsors or shops i can call and talk to on this matter?

Jim_0068 · 07-19-2004, 12:16 PM

Can someone install a distributor wrong and compensate for the motor to run?

link to new thread on the subject

WERK I · WERK I's Garage

What year and displacement is the engine?
Where are you located?
All my reference manuals are packed up for my big move back to Wisconsin, so I'm kinda working in the blind.
As far as tech help or shops go, if we find out where you are located, I'm sure others will chime in with recommendations.

Jim_0068 · 07-19-2004, 12:20 PM

1973 911T

I am located in Chicago, IL

I think you'll find my other thread quite interesting

mtelliott · 07-19-2004, 12:43 PM

This is my thought. They put the distributor in wrong (sounds like a position off). They then just rotated the wires around so that it fired properly. They took the #1 and placed it where the #6 goes. They then took the #6 and placed it where the #2 goes, and so on (or whatever the firing order might be on your car).

Therefore, when the engine is at TDC, the rotor is pointing to where normally the #6 goes, which they placed the #1 on. I don't think this would really matter to how the engine ran, would just throw you off if you didn't know it.

I like to have things like they are suppose to so I would pull the distributor, put a new seal on it, set the engine at TDC verified by cam timing on #1 and the Z1 mark, then reinsert the distributor so that it is aligned properly.

Michael

Jim_0068 · 07-19-2004, 12:45 PM

Quote:

Originally posted by mtelliott
This is my thought. They put the distributor in wrong (sounds like a position off). They then just rotated the wires around so that it fired properly. They took the #1 and placed it where the #6 goes. They then took the #6 and placed it where the #2 goes, and so on (or whatever the firing order might be on your car).

Therefore, when the engine is at TDC, the rotor is pointing to where normally the #6 goes, which they placed the #1 on. I don't think this would really matter to how the engine ran, would just through you off if you didn't know it.

I like to have things like they are suppose to so I would pull the distributor, put a new seal on it, set the engine at TDC verified by cam timing on #1 and the Z1 mark, then reinsert the distributor so that it is aligned properly.

Michael

This is exactly what they did, i called around to a few peole got the number to a good porsche shop locally and that is what they told me.