911 Camshaft Timing Help Needed Options

[Cfletch]

Hey there everyone, Newbie to Cam timing in general and working on putting the engine back together after repairing an oil leak from the Cam Thrust Plate o rings.

I am having what I hope is just a simple issue of misunderstanding on the timing of the cams and can use some help.

Engine is a 1974 2.7 CIS that retains the stock camshafts:
L:911.105.141.00 R:911.105.142.00

I currently am running into an issue where I am unable to get more adjustment out of my cam because I am hitting the piston with the valves when trying to rotate it in either direction.

Current process has been having the engine at Z1, having my distributor facing #1 cyl and having my piston at the top of the stroke confirmed by a whistle adaptor in the cylinder. Camshaft have the "911" at 12 o clock and the part number listed at 6 o clock. I have my #1 Intake Valve installed and set to correct valve clearance and have the timing chains tensioned by the stromksi tensioners. Pin is installed and nut is snugged up to the cam to get a reading for when rotating the engine. I have a drop gauge and z bar set up on the #1 intake valve and when rotating the engine over, the valve does not seem to lift at the correct position on the crank, and I am also not able to get the same lift I once had of 3745 Thousandths. I would like to rotate the cam at this point to get it adjusted slightly to get it to start raising at a better time relative to the crank, but when attempting to rotate it, I can feel interference with the valve and piston. I feel this going either clockwise or counterclockwise. I am stuck at this point and called it for the day and am looking for some help here.

Based on various videos and my 911 rebuild book from Wayne Dempsey. I seem to be doing everything correct, but just am not getting it to raise the correct amount and when trying to adjust the cam I run into clearance problems with the valve so I am clearly not in the right spot there. I am looking for any guidance here either in text format or possible a phone call tomorrow to walk through stuff. I have everything more or less set up ready to go and this is my last step before I am able to get it buttoned back up and reinstalled into the car.

One thing I had noticed is that we were getting relatively close to the expected measurement, but it was very far away from, Z1, probably about ~100 off from where it would be expected.

Today I had the help of Robert A, he drove up and we worked on repairing the leaky seals but had ran out of sunlight and time today. He left me his tools to hopefully wrap this job up and we were both stumped on this after a long day of work. Any help is most appreciated!

[rudedude]

I don’t know your cam stamping but the key slot should be facing up at z1

[Cfletch]

I don’t know your cam stamping but the key slot should be facing up at z1

Confirming the cam key slot is at 12 o clock

[rudedude]

Could you have switched sides? Left 1-3, has the further lobe separation

[rudedude]

Are you using z1 on the pulley or flywheel? The z1 mark on my 2.0 flywheel is some 40 degrees off z1 on the pulley

[Robarabian]

Not possible.

We only removed one cam at a time. We removed the 1,2,3 side first, removed the cam chain housings, changed the gaskets / seals, and re-installed that cam. Then we did the 4,5,6 side.

We thought we were being smart and measured the overlap prior to tearing into it, so we could replicate it. Now we cant for some reason. The overlap it had was slightly off from the book (Colin, you can speak to this) so we will approach it from the "book spec" versus what we measured with the stomski setup prior to removing it all.

Z1 on power stroke. Turn the crank and the overlap is not coming on til we are just about at TDC and the numbers rise After TDC. My experience has always been that the overlap happens prior to TDC.. hence the "overlap."


The keyways were facing up both sides when we index the cams. On his cams, the part number is on the bottom, "911" is on top and I think there is a small dot as well.

Could you have switched sides? Left 1-3, has the further lobe separation

[sixnotfour]

If #1 is at TDC and rotor pointing at firing #1..It should be on compression stroke intake valve closed ..
and # 4 will be at overlap..

[sixnotfour]

0.03745 ??? #1 at overlap Rotor pointing to #4 at z1

[sixnotfour]

Is .3745 total lift ? (IMG:style_emoticons/default/idea.gif) (IMG:style_emoticons/default/popcorn[1].gif)

[rudedude]

My spec book is in the shop but I suspect a cis cam would have about 1mm overlap when timed at z1 for #4 for #1. It will have more lift but not at z1

[DennisV]

Hey there everyone, Newbie to Cam timing in general and working on putting the engine back together after repairing an oil leak from the Cam Thrust Plate o rings.

I am having what I hope is just a simple issue of misunderstanding on the timing of the cams and can use some help.

I am looking for any guidance here either in text format or possible a phone call tomorrow to walk through stuff.

I ran into issues with my first cam timing as well. These few videos helped me. There is more than one way to approach it, and I found one more intuitive than the other.

Mastering Valve Train & The Art Of Porsche 911 Cam Timing

Timing Camshafts on a Porsche 911 Engine

How To Set Porsche Cam Timing

Cam timing & valve overlap basics tutorial

Also make sure you're setting the timing that corresponds to the grind on your cam shafts.

Kurt at Klassik ATS offers hourly consultations. I've been impressed with his videos and posts.

[sixnotfour]

My spec book is in the shop but I suspect a cis cam would have about 1mm overlap when timed at z1 for #4 for #1. It will have more lift but not at z1

@dennisv

yes he needs to watch some more ...examples of how to..

[Robarabian]

I think he meant .374. the dial gauge is digital and indicated a fraction, meaning almost .375....

And if I remember, the 4,5,6 bank was timed at the higher end of the spec before we disassembled it, around .390.

0.03745 ??? #1 at overlap Rotor pointing to #4 at z1

[sixnotfour]

I think he meant .374. the dial gauge is digital and indicated a fraction, meaning almost .375....

And if I remember, the 4,5,6 bank was timed at the higher end of the spec before we disassembled it, around .390.

0.03745 ??? #1 at overlap Rotor pointing to #4 at z1

that's not overlap....

[Cfletch]

Ok I think I ended up where I need to be here is my process


Wayne D's Book says for my engine, overlap spec is between .7mm-.9mm and to shoot for .8mm.

I started with #1 intake valve adjusted and the dial gauge installed there, engine at Z1 with distributor pointing at #1. Dial gauge read 0.0. I rotated the engine clockwise 360 and saw my gauge start to give reading as I got closer back to Z1. At Z1 I was off a decent ways, but dont recall the number, from my .8mm goal. I then loosened the big nut holding the cam and then slightly adjusted the cam with my 17mm wrench to get to .8mm. I installed the pin to the available slot, and then attached the big nut once again. Torqued nut to spec. Rotated engine 720 degree to verify my measurement. Seemed good there. I removed my mechanical tensioner and reinstalled the factory one on that side then moved to the right side cam. Set up my dial gauge, verified it was Zeroed, and then rotated the engine 360 so that I saw a value in the gauge. Once again, the value was off from my .8mm goal and so I removed the nut and pulled pin, adjusted cam so my gauge read .8mm and then reinstalled the pin and then the washer/nut combo. From there I torqued nut down and then again rotated the engine over another 720 to be sure my number was in spec.

That was the general process I did today. I ended up taking off and on the nut a few different times due to issues with my chain tension not being adequate on one bank and causing issues with my numbers after rotating engine a few times. After all was said and done following the above process I ended up at .87mm on left and .86mm on right bank. I assume that .01mm variance between banks is more than fine and while I was not directly at .8mm I am still within the written spec of .7mm-.9mm and I called it good.

After that I rotated the engine with the correct tensioners installed multiple times and verified that my specs did not shift due to any funny business with the chain tension or anything like that and assume I am good to go with cam timing.

If there is anything I might have missed from the above please comment. I think I am good and watched over videos and videos from last night to mid day today and do not think I am missing anything. Would hate to reinstall this only to find I blew up my motor somehow (IMG:style_emoticons/default/smile.gif)

[rudedude]

It sounds like you figured it out. it always seems to take a couple attempts to get them where you want them.

[gereed75]

Sounds right and if you can rotate the crank through multiple rotations without valve to piston interference it is right

It is very helpful to set indicators on both sides. You can continuously rotate the engine through multiple revolutions and verify the settings time and time again. Not necessary but very reassuring

It’s not really “overlap”, just a measure of valve lift at a degree of crank rotation.

Congrats on getting it right!!

[Cfletch]

Sounds right and if you can rotate the crank through multiple rotations without valve to piston interference it is right

It is very helpful to set indicators on both sides. You can continuously rotate the engine through multiple revolutions and verify the settings time and time again. Not necessary but very reassuring

It’s not really “overlap”, just a measure of valve lift at a degree of crank rotation.

Congrats on getting it right!!

Yeah I rotated it over plenty of times after and 0 contact with valves which is great of course. I was just glad to know I was able to do it correctly. Sadly I only had one dial gauge set up thanks to Robert, but of course was able to just swap it over which was no big deal.

Glad it seems like all is good back in there

[sixnotfour]

Great News,,, a last simple check is #1 intake port look with flash light to make it is closed tight,,..then look down #4 should see valve open..very little..but open... great for guys with one indicator.. and confirms your not 180 out on the right side {456}....

(IMG:style_emoticons/default/beerchug.gif)

[Cfletch]

Great News,,, a last simple check is #1 intake port look with flash light to make it is closed tight,,..then look down #4 should see valve open..very little..but open... great for guys with one indicator.. and confirms your not 180 out on the right side {456}....

(IMG:style_emoticons/default/beerchug.gif)

Would this be at Z1 with distributor at #1 or at #4?

I'll do this today for some extra piece of mind, thanks for the suggestion!