Question for Six Engine People, TDC and Z1 mark Options

[Robarabian]

I have a 911 engine I am working on. I am practicing setting cam timing so I can feel comfortable with it prior to the tear down. My Crankshaft pulley has a Z1 mark that has 2 lines. So I have seen 911 pulleys with Z1 and 1 line.

The question de jour is which of the 2 lines at Z1 is TDC? Or are the 2 lines giving me the dwell of where TDC is and if so, where should I put them in relation to the case to set cam timing and do valve adjustments.


it looks like " Z | | 1"

It is a 2.4


Somebody knows this answer.

[Robarabian]

I may have found the answer looking at 50 different pulleys on Ebay... maybe someone can verify.


The line closest to the "Z" is TDC. The line closest to the "1" is 5 degrees before TDC.

Can someone verify this?

[targa72e]

That is correct . 911 of that vintage had vacuum retard (not advance). The is the purpose for the 5 deg before TDS mark. That said the factory setting of that era are all about meeting emissions, not making the car run good. Many people when switching to carbs for example disconnect the vacuum retard system all together for better day to day driving performance.

john

[Krieger]

I think the 5° BTDC is the timing mark at idle. It should be to the left of Z1. Put up a picture. Good for you practicing cam timing. It's a good check of your tools and what you may need.

[ClayPerrine]

A suggestion for setting the cam timing.

Only put on the intake rocker for #1. Leave the rest off. Set the cam timing per the book. Then put the #4 intake rocker on and set the cam timing on it.

Check it about 20 times before putting the rest of the rockers on. I like to have a dial indicator on each side and repeatedly recheck to make sure the numbers match side to side.

All 911 motors are interference motors. If you don't put the rockers on, then you can't accidentally bend the valves.

I had to replace a chain box on the 4.0L engine recently. I pulled all the rockers on that side before I started just to be sure. It's cheap insurance.

[gereed75]

I would emphasize one of Clays comments -put a dial indicator on both 1 and 4. You can then repeatedly spin the crank and double/triple/quadruple check the timing on both cams quickly and repeatedly. This will catch any error but also give you complete confidence in your work. No guessing or questioning

For the relatively cheap price of a second indicator setup, it is well worth it.

[930cabman]

I would double check with a dial indicator

[IronHillRestorations]

To add confusion the 2.4 and 2.7’s crank is indexed differently than the 2.0 and 2.2’s.

You can use a 2.0 (same as 914-6) flywheel on 2.0-2.7 and it will bolt up, but with 2.4 and 2.7 the timing marks on the flywheel will be off.

I always re-mark Z1, 35*, 120*, and 240*. With a 6 it’s much easier to set the timing and adjust the valves using the marks on the flywheel.

[Robarabian]

So my pulley actually has the Z1 mark and the second line is after it. So I assume the mark after the Z1 is 5 degrees ATDC versus some of the other pulleys Ive seen with the mark before Z1 5 degrees BTDC.

You will see the sharpie thick line (that ends at a mark in the pulley) and the black from the sharpie in the Z1 line.


BUT... is the TDC mark the actual Z1 mark here?

Thank you to who chimed in, this is an assembled motor so I am not monkeying too much with things until I understand it all better. I am just trying to determine the current travel of the valve at overlap, which depending on the mark of this pulley, is 2.5 mm or 3.5 mm.

If Z1 is TDC, then the valve overlap appears to be 2.5 mm. Anyone have a chart with all the cam specs? I have Wayne's book and will dig through there to see if there is a chart.

[Robarabian]

I was wondering about that. I installed a new flywheel on the 2.7 motor when I was working on it and was confused about why the Z1 mark on the pulley didn't line up with the Z1 on the flywheel. I ended up marking it as you said.

To add confusion the 2.4 and 2.7’s crank is indexed differently than the 2.0 and 2.2’s.

You can use a 2.0 (same as 914-6) flywheel on 2.0-2.7 and it will bolt up, but with 2.4 and 2.7 the timing marks on the flywheel will be off.

I always re-mark Z1, 35*, 120*, and 240*. With a 6 it’s much easier to set the timing and adjust the valves using the marks on the flywheel.