Can a diffrent cyl be used as Z1 TDC ?????

flmont · 10-10-2004, 01:26 PM

I swear I dont understand this,..When I first got my car on the road (77' with a 81' 3.0 with 964 cams) I took it back to the same shop that set my cam timing to get it to run correctly,..I could never get the Z1 TDC to match my Dist notch for the correct setting for Ign timing,( the car would not run at the text book settings).Then they found the Dist. to be bad..Shop said,They got the car set-up correctly now..Dist to go in at TDC on Z1... and I have been driving it like this for 600 miles,untill friday,So today I get ready to do a valve adj...and I find that the TDC is 120 Deg's before the Z1 mark.(as I go C.W.)...I use a long ty wrap to make sure Iam TDC...I thread it in the plug hole,and crank the fan pulley C.W. I can feel the piston move up and down...and I have done this about 6 times(complete rotations) and every time the piston goes TDC its on the first hotch to the right of my Z1 mark.(with #1 rocker arm a bit loose)as I continue to go C.W. the piston now retracts and when I do get to the Z1 mark the piston is on the down stroke..(by at least 3/4 to 1") I feel he set my cam timing but the crank was not at Z1...IS THIS EVEN POSSIBLE.???( the cam notches were at 12 o'clock when they torqued them ) I DO have alot of Valve to piston Clearance and have never heard any engine issue's,The car ran pretty good to me...Iam not sure which Cyl it fire's on but I don't think its #1 Thanks Frank

911mot · 911mot's Garage

The cut-out on the plastic ring your arm is pointing to is not the timing mark on the dizzy.
Pull off the rotor arm, remove plastic ring and you will see a slot cut into the metal of the distributor itself. Line up with this instead...

flmont · 10-10-2004, 02:47 PM

Yes I know...the #1 cyl is TDC set the way it is...I have always had to place the rotor almost that far in front of the notch to get the car to start..Isnt that nuts..But Thanks...FM

911mot · 911mot's Garage

It could be that the HT leads are fitted in the right order but in the wrong place on the cap.

Line up rotor arm to notch on dizzy base. The rotor arm should be pointing to the Ignition wire for cyl#1 in the cap. It sound like yours could have the wires in wrong and you need to swing it to line it up. Try moving the wires round one post on the cap.

Bill Verburg · Bill Verburg's Garage

there are also 2 TDCs for #1,

compression and exhaust, spec is for TDC on compression

flmont · 10-10-2004, 07:17 PM

True...But this car been running just fine...and I needed to do the 500 mile valve adjustment...The only way that it's not TDC on #1 must be due to the timing ..Right FM

911pcars · 10-10-2004, 07:24 PM

I concur with 911Mot. If the car runs as is, the plug wires are "clocked" one hole clockwise further than spec. Apparently the distributor was installed one tooth off and the #1 wire (and all others) were moved over to compensate for the new rotor position.

The distributor gear is a helical shape (slanted rather than straight cut). When the distributor is inserted, the rotor rotates slightly. If the rotor starts off pointing at the notch on the dist. housing, the rotor will end up further clockwise once the dist. is seated.

Sherwood.

flmont · 10-10-2004, 07:37 PM

This is also true,..My Issue is that when the piston is TDC it is not lined up on Z1 mark...it lines up to the first notch on the crank to the right of the Z1 mark which is 120 Deg's off I cant Adjust valves correctly due to I dont know the rotation unless it starts out correctly...FM

911pcars · 10-10-2004, 09:44 PM

How are you determining #1 piston is at TDC? The normal method is by aligning the timing marks on crank pulley and case. However, that's faith-based because you can't see the piston.

If you want to find absolute TDC for #1, do a search on the archives. If you can't find it, come back here for the long answer.

Sherwood

john70t · 10-11-2004, 03:40 AM

A small tangent while on the subject.
On worn engines with metal timing chains, it's also possible for the chains to stretch- which retatds the valve train timing in relation to the crank, and the ignition timing if it's run off the cam.
It happens slowly by a few degrees and engine still will run. The check is with a crankpulley degree wheel and a dial indicator on the cams.

flmont · 10-11-2004, 06:43 AM

911P...I use a ty wrap feed down the spark plug hole,..I can feel the piston moving up and down....FM

Glenn from Denv · 10-11-2004, 10:46 AM

I don't think that the Z1 mark can be made to line up with the case split line on any other cylinder but 1 or 4. It has a hole for a dowel pin that forces the correct alignment on the crankshaft.

911pcars · 10-11-2004, 07:41 PM

"I use a ty wrap feed down the spark plug hole,..I can feel the piston moving up and down"

I've never tried the ty wrap trick. Near TDC, the piston moves more slowly than the crankshaft rotates. The crank pulley uses a woodruff key that lines up with the crank. Maybe the key is sheared off or gone.

Sherwood