Cam Timing...... Again

[cole930]

Cam Timing:


Crankshaft to Camshaft Relationship:

Always rotate the crank in a clockwise direction. All ignition and cam timing operations will reference Z1. Z1 is the designation used for the position of the number one piston in relation to the rotation of the crankshaft. Z1 is stamped and marked on the face of the crankshaft pulley. There is also a corresponding marking (just above the crankshaft pulley) located on the bottom edge of the fan housing and directly in line with the case split where the right and left engine case halves come together. If the Z1 mark on the crank pulley is directly aligned with the case split or fan housing marking it indicates that the No.1 piston is at the very top of its stroke (TDC or Top Dead Center). This gives us an accurate and consistent reference point for timing and assembly of any engine components referenced off crankshaft rotation.

The Z1 mark alignment with the case split indicates piston No.1 is at Top Dead Center. To complete one full 4 stroke combustion cycle the crankshaft must be rotated clockwise 2 complete revolutions or a total of 720*. If you start at Z1 (Top Dead Center) and rotate the crankshaft clockwise 360* back to Z1 you have completed the first 360* of the 720* combustion cycle. Then, again, rotating clockwise from Z1 (Top Dead Center) another 360* back to Z1 (Top Dead Center) we have completed the 720* combustion cycle and the Z1 mark is aligned with the case split, for the second time, indicating piston No.1 is at Top Dead Center again. As demonstrated there are two distinctly different positions in that 720* combustion cycle where the Z1 marking on the crank pulley will be directly aligned with the split in the engine case. One Z1 (TDC) position is at the end of the compression stroke or (TDC compression point) this is also the point where the ignition is timed and the distributor is installed. The second Z1 (TDC) position is 360* later at the end of the exhaust stroke/start of the intake stroke or (TDC the crossover point) this is the point where cam timing is set.


Setting Up for Cam Timing:

To understand the set up sequence and timing cams you must first understand that this entire process is nothing other than connecting the crankshaft to the camshafts. The crankshaft will turn as much as you want and it does not care where it’s at and the cam shafts will do the same because they are not connected to the crankshaft in any way until you insert two little retaining pins through the chain sprockets and into the cam sprockets. Once those two retaining pins are in, the crankshaft drives the camshafts through the intermediate shaft, chains, and sprockets. Your task is to connect the crankshaft to the camshafts by inserting the retaining pins in the correct orientation so the valves open and close in correct unison with the rotation of the crankshaft, that’s cam timing.
In order to connect the crankshaft to the camshafts in the correct orientation there has to be some reference to use as a starting point to position the crankshaft and camshafts correctly before inserting the retaining pins. For the crankshaft we have a known reference it is Z1 TDC. For the camshafts we use the cam markings on the snout of the camshafts. For most Porsche cams you will see a punch point or dot and a SC or a 930 stamping.
Starting at No.1 cylinder (left bank first cylinder on the crank pulley end of the engine) Turn the crankshaft clockwise to the Z1 TDC (crankshaft reference point) and turn both camshafts, using a 17mm open end wrench on the flats of the cam snout, so the dot/stamping/930 marks are straight up (camshafts reference point). Insert retaining pins into each camshaft sprocket in whichever hole will allow insertion. On No. 1 install the large cam washer and nut and snug the nut. Using vice grips or hand clamp, securely clamp idler arm to the case to apply firm tension on the chain. Now adjust No.1 intake valve to .1mm /.0039 in. spec. After the valve lash is set install your Z block on the valve cover stud just above the No.1 intake valve. Insert the dial gage into the Z block and pre load the dial gage about 1 inch. And then secure it with the stem resting on the outer edge of the intake valve retainer. Rotate the outer rim of the dial indicator face to zero, your good to go.


Recheck everything:

Crankshaft is set at Z1TDC, make sure sprockets, chains, chain ramps, and idlers are installed correctly. Chain tensioners removed, cam dot/930 stamp pointing up, sprocket retaining pins inserted, cam washer, bolts and/or nuts installed and snugged, and idlers clamped. No.1 valve lash adjusted to .1mm /.0039 in. Z block and dial indicator positioned, secured, preloaded, and dial set to zero. Write down your particular cam spec range, do it in both millimeters and inches and keep it in your work area for quick reference.


Ok Time to Get Er Done !!!!

With your recheck done your starting point is Left side No. 1 camshaft ( you’ve just finished setting the No.1 cylinder valve lash, the markings/ dots on the camshafts are pointing up, your dial indicator is loaded on No.1 intake valve spring retainer and the indicator dial is set at zero, and the crankshaft is sitting at Z1 TDC; this is the compression point for No.1, you should be able to reach up and very slightly move the intake rocker arm on No.1 up and down this is telling you are at the compression point and both No.1 intake and exhaust valves are closed so you are feeling the valve lash you adjusted between the rocker arm and the end of the intake valve and there is no load on the valve stem. ) Now slowly start rotating the crankshaft 360* clockwise around to Z1 TDC again. Just as you start coming up on Z1 TDC again the intake valve will be starting to open at about 30 or 40 degrees before you reach Z1 TDC and you will see the dial on the indicator moving. Watch the dial indicator and the upcoming Z1, when you about to reach Z1 stop just short of Z1. Now bump the wrench with the heel of your hand to ease it into exactly Z1 lining up with the case split. ( you are now at the No.1 overlap point, notice the camshaft markings/dots are pointing down, if you reach up and try to move the No.1 rocker arm up and down it will not move because it is in the process of opening the No.1 intake valve so the valve spring pressure has taken up all the valve lash slack that was previously there) this is the point where we measure the valve opening and set the valve timing. If you look at the reading on your dial indicator it is telling you how far the No.1 intake valve has opened. It will be on or near the setting your spec. calls for.
If the reading is not at your spec. you need to remove the snugged cam nut/ bolt and washer and pull the sprocket retaining pin. Then using a 17mm open end wrench, adjust the camshaft to set the correct setting on your dial indicator, reinstall the sprocket retaining pin, reassemble the washer and snug the cam nut/bolt. Now rotate the crankshaft 2 complete revolutions, 720*,( this 720* takes you one complete cycle and back to your overlap point) and recheck your setting. Your setting should repeat as long as you had the cam nut/ bolt snugged enough to eliminate any creep. If you setting is not repeating, using the 17mm open end wrench, adjust the camshaft to set the correct setting on your dial indicator, reinstall the sprocket retaining pin, reassemble the washer and snug the cam nut/bolt, rotate another 2 complete revolutions, 720*, and recheck your setting again. Once you have repeatability, hold the cam snout and tighten the cam nut/bolt tightly but do not torque yet, after you tighten the nut rotate 720* to make sure you didn’t lose your setting. Unfortunately it may take several attempts before you get the cam to fall into spec correctly but don’t give up. As you repeat the procedure you can make adjustments when readjusting the camshaft that will offset the creep when torqueing the Cam nut/bolt.
Once you have completed the left bank cam setting set #1 to Z1 TDC on the compression point (your dial indicator will be back at 0 at this point and you should be able to, slightly, move the No.1 intake rocker arm up and down. Now rotate the crankshaft 360* to Z1 (this is Z1 TDC for #4) because #1 and # 4 fire 360 degrees apart. Set the valve lash for #4 and remove the Z block and dial indicator from the left bank and install it on #4 of the right bank and follow the same procedure you did on #1.





Cole

[Jesse16]

I have a simple question you might be able to answer. I had a friend loan me a very nice Starrett digital indicator. Problem is I think that it only has about .270" or 6.8mm of travel. Will this be enough to do the job? Per the appendix Wayne's book, I'm only looking for a measurement of 1.25 mm on my stock 87 carrera.
I also plan to use his mag base vs the P___ special tool via a little block of steel bolted on to mag to. Hoping to rig this up and get good readings. Since I'm not trying to read the valve at full extension but rather at TDC in two places, wouldn't this work ? I'm pretty good at aligning things so I'm not concerned about not being in line with the valve travel. Also, at only 1mm, the difference would be unmeasureable.

[304065]

[Eagledriver]

Jesse16,

The only problem I see with your plan is finding some steel to mount the magnetic holder to. Maybe you could bolt a plate of steel to one of the rocker cover studs.

-Andy

[Jesse16]

Thats all I planned to do, a piece with a 5/16" hole in it for the magnet to attach to.

[911hutch]

great...sequential and straight forward.....now where is that 914-6 motor with the cam box leak......

[cole930]

Cam Timing Tips:

Notes: Some of the little facts that may help us better understand the process.

1.Never rotate the crankshaft with one or both retaining pins removed once you have started the cam timing process. The only time you should ever remove a retaining pin, during the process, is when you pull a pin to adjust the cam position to get your timing spec set.

2.When starting the process you set the crankshaft at Z1 TDC and turned the markings/ dots on the cams up and install the retaining pins in both cams. You then set the valve lash on No.1; it’s helpful to take the time to set the valve lash for No.4 at the same time. To do this, once you have No.1 valve lash set, simply rotate the crankshaft 360* and set No.4 valve lash then rotate another 360* and your back to No.1 and ready to start timing No.1. Setting the valve lash on both No.1 and No.4 at the beginning will be a big help later in the process. With both set, if you get lost in the process or take a much needed break and forget where you were at, you can always rotate to Z1 TDC and feel the rockers to see which one moves and which one doesn’t. The one that moves is at TDC (Compression Point) the one that doesn’t is at TDC (Overlap Point.

3.Piston No.1 and Piston No.4 are always in the same position in their respective cylinders at the same time when the crankshaft is at Z1. Both are always up or both are always down they are never opposite.

4.You start the process at Z1 TDC and by pinning the sprockets and you always pin them with the markings/ dots up. The camshaft markings/ dots are always either both up or both down, they are never opposite. If you ever see them opposite, one of the cams, is 180* off. This is why we always start At Z1 TDC and both cam markings/ dots up and then set the retaining pins to keep them in sync.
Always remember when the cam the markings/ dots are both up at Z1 TDC that indicates No.1 is at the compression point and No.4 is at the overlap point. When the cam marking/ dots are both down at Z1 TDC that indicates No.4 is at the compression point and No.1 is at the overlap point.

Cole

[RoninLB]

[OldTee]

I use two dial indicators, both digital. They were not expensive and the two engines I used them on are working fine.

[cole930]

Old Tee,

Defiantly a nice way to go, would really make the process easier. Great looking build
also !!!!!!

Thanks for your input !!!!!!

Cole

[Jesse16]

I found that these cheap squeeze clamps worked amazingly well at keeping the chain tight during the timing process. I had two on at the same time and had no variance during many turns of the crankshaft/camshaft. Only non-issue was that this indicator had waayy too many digits and led you to believe your accuracy was off. 5 places shown past the decimal when in inch mode. No instructions and too many buttons to figure how to change to MM.

[cole930]

Ronin,

Thanks for the information. While I was putting this together I searched for that quote, I had remembered seeing it somewhere, but couldn't find it. I couldn't remember how many rotations it was so I didn't mention it. Appreciate your adding it. It is good to know if you continue to get different readings of lift each time your rechecking. This inconsistency is usually caused by wear on the retaining pin, the cam flange slots, or the sprocket holes. By rotating the crank 9 - 10 times you can pick up a different tooth to reference off of and then it falls right in on recheck. Another method is to pull the retaining pin, nut, and washer take the tension off the sprocket, lift the chain, slide the sprocket off the cam and rotate the sprocket a quarter turn. When you button things back up and reset it start you in a different sprocket hole.

Cole

[cole930]

Jesse,

Nice addition !!!! I always use these squeeze clamps also, they allow you to add
good tension without overstraining the chains. I have seen screw type C clamps used and if the motor sits for a prolonged time under that extreme tension the chains stretch.

Cole