A couple cam timing questions:

[bbh03]

Hi, hopefully someone can set me straight on a couple things.

Rocker arm shafts: Wayne's book claims that they should almost be flush with the edge of the shorter-side-rocker-arm-hole in the cam tower, but it doesn't in which way (just inside, or just sticking out). Anyway, I am assuming the shaft needs to be centered on the rocker itself, right? Since the method mentioned is approximate, why not just approximate by lining up another rocker arm shaft and eyeballing the one inside to on center?

Also, he mentions separate timing instruction for high-lift, long-duration cams. I am assuming my 964's in a 3.0 case falls under this category and should NOT be timed according to CIS instructions, correct?

Thanks in advance, all!

Brian

[Jeff Alton]

Time the cams the same way as the CIS cams. The 964 cam would be considered low lift and short duration compared to some of the available cams. They are "mild" in the world of Porsche cams.

As for the shafts. the book also makes note of way to use a feeler gauge to check when the groove in the shaft is just past the arm, then it specifies a distance to further move it. I don't have the book here in front of me, but are there not some pics in it showing the correct poition?

That said, your idea should also work well too.


Cheers

[2.7RACER]

Brian,
Jeff is correct.

The rub is SC's were timed to open at 7 degrees BTDC for model year 78-80.

For 81-83 they were changed to open at 1 degree BTDC.

For Carrera's, 84-89, they split the difference and opened at 4 degrees BTDC.

964's open at 4 degrees BTDC with a bit more duration. 240 deg. vs. 234 deg.

I would time the 964 cams to open at 4 deg. BTDC. 1.5mm.

[bbh03]

Thanks Guys! Wayne's book notes 1.16 - 1.36 mm for 964. So I should time within that range using the short-duration method (like CIS)?

[Jeff Alton]

You bet, get them as near the middle of that range that you can. That is what I do on the 3.0 and 3.2 motors. Do your best to get both sides even. Use the short duration cam method. They are good cams for use in motors with a single throttle like CIS and motronic motors that need to pass smog.

Cheers

[bbh03]

I had the 964 cams made by John and he recommends 1.26 - 1.40 with my 9.5:1 CR motor. Now, when I go to time the left side, Wayne's book says you should reach that number (I'm shooting for 1.33) just before Z1 lines up, however I'm hitting that number just after (just over 360 degrees rotation). How should I proceed? Should I just keep it there, pull the pin and rotate the crack CCW back to Z1 (a degree or so) and replace the pin or am I doing something wrong.

Incidently, I'm using an inch dial gauge, so I conerted 1.33mm to 0.0534 in. I have the gauge reading 0.4 in when I start and as I rotate the crank, it rotates backwards to about 0.348 (0.4 - 0.052 of travel) and stop there. That's the point where the Z1 is just past the case parting line. Is this correct?

Thanks,

Brian

[Mike Juzenas]

I thnk the ZI should be bang on the line.

Does not your dial guage have the ability to rotate the dial to zero it? Preload the dial when there is no pressure from the rocker on the valve at about 1/2 the range of the diak and then zero it. Then rotate untl TDC and see how much the valve was depressed...I found it very easy to read if you zeroed the guage.

I would put the dial gauge at the correct spot, pull the pin and rotate the crank back to TDC, find the pin position, snug up the bolt, rotate 720 degrees and see how you did. I also checked right a left a few times to make sure they were as close as possible. In addition I found enough slack in the pin hole that you can get variations even with a pin setting which is why I snug up the cam each time.

Cheers,

Mike

[bbh03]

I did zero it as you suggest - it happens the counter dial (in 1/10 inch increments) was between 3 and 4 for this hence the .348.

The Z1 definitely wasn't right on, it ended up a few degrees past.

[2.7RACER]

Brian,
When you are past Z1 at .0534", the cam is retarded a degree or two.
You need to rotate the crank clockwise until the rocker is on the back of the cam, pull the pin in the cam sprocket, back up the crank a degree or two, repin the cam sprocket. Then rotate the crank to Z1 (TDC).
Recheck, adjust as necessary.
Check for the correct .0534" at Z1 (TDC) a couple times before you move on to the other side.
Remember the dots or numbers stamped on the end of the cams must both be up when at TDC compression number one. Keyways up as well.
One up and one down won't work.
When you are done leave the motor in TDC compression number one.
Install the distributor with the rotor pointing at number one, about 3 o-clock.

[bbh03]

So the idea is to have the dial read that number on the back of the cam (as the cam is begining to subside, not the side that first touches the rocker)? I am taking this to mean that 0.0534 occurs twice (once on each side of the lobe) and is not the tippy top of the cam? SO basically I want to do this:

-If it read 0.0534 and Z1 is just to the right (just past) of the case parting line, I am reading the front half of the cam lobe.
-That means I should remove the pin, move the crank back to a few degrees before the parting line (can I move it CCW or must I go all the way around?). Then, re-pin and find the point it reads 0.0534 where z1 ends up just to the left of the parting line (just before it). Then, remove the pin, move Z1 to TDC and pin again. THen tighten w/o moving anything.

Do I have this right now?

Thanks alot for your patients, guys, I want to make sure I understand this correctly!

Brian

[Mike Juzenas]

The basic idea is that the lift (or the depression) of the intake valve should be 0.0534 at TDC on the intake stroke of that piston. You should see, as you turn the engine over and its approaching TDC intake/exhaust for that piston (either #1 or #4 depending on which side you are doing) the intake rocker start to climb on the cam and start to depress the intake valve. When the crank reaches TDC exactly you want to read the amount the intake valve has been depressed.

So the measurement is on the upside or front side of the cam. If you are setting it to the backside of the cam the cam will be significantly off.

If the measurement is too large when you get to TDC this means that you are too far along the camshaft and the camshaft is running ahead or advanced of where it should be. If the measurement is too small than you have not gone up the ramp on the camshaft enough so the cam is behind or retarded from where it should be.

Since the cams are set relative to the crankshaft if the cam is deemed as being retarded (i.e. the valve movement is too small) then you have to advance the camshaft relative to the crankshaft. You can do this two ways ; hold the crank still and move the cam or hold the cam still and move the crank. I like to rotate the engine so I get exactly the lift I want, undo the nut on the camshaft carefully so nothing moves, remove the pin and then rotate the crankshaft until it gets to TDC (backwards or forwards). You should watch to make sure that the camshaft sprocket slips on the camshaft, sometimes it will rotate the camshaft as well if the tension on the chain is quite a bit. If you rotate the crankshaft to TDC and you don't see the reading change, put in the pin to the best position and then tighten it all down, rotate the crank two full turns (for one full turn of the camshaft), align until TDC and read the amount the intake valve has moved. If its off adjust again, if not torque down the cam and go do the other side.

Remember the other side is 180 degrees out. To confirm you have done this correclty when you are timing #4 for example and are at TDC exhaust doing your measurements, #1 should be in compression, both inake and exhaust valves are closed and both the rockers not close to any ramps on their cams. This is a common mistake which I made as well!

I found the whole timing process an iterative one. I went back and forth from the left cam to the right cam to make sure both were the same.

The measurement is taken when the pulley is exactly aligned with the parting line not to the left or right.

Clear as mud? ;-)

Cheers,

Mike

[bbh03]

Thanks Mike, I think so. I'll give it a try tonight and see if all this has sunk in!

One thing: The other thread it was mentioned that even with the pin in, there is significant play that affects timing and that is why you must hold the cam aboslutely still when torquing. I can understand chain preload being a reason, but not the play with the pin in place. It seems to me that under running conditions, the sprocket would eventually move until the pin is pinched under stress anyway and then stay at that timing position. Thoughts?

I am clear on setting the left vs right. I know to check I don't put them 180 degrees out of phase and will pay particular attention to that when I finish!

[bbh03]

Okay, I think I have timed the left side. As I reach TDC, the dial gauge is just beginning to turn (indicating valve depression) and reads 0.0524 Z1 hits the seam. As I continue past, the dial makes several spins (several 1/10th of an inch) as the rest of the cam lobe (rotating CCW) passes the rocker and then subsides back to 0. After the crank rotates a full 720, we are back at 0.0524 as the cam is just beginning to act again on the rocker. All good? I',m going to attempt to get the right side to meet the same spec. Wish me luck!

Brian

[bbh03]

I have the left at about 0.0545 to 0.0550 and the right at 0.0535. That's a difference of about 0.03 mm. Okay, or do they need to be exact? My problem is getting a consistent measurement based on where I think Z1 is hitting the seam. I am trying to be consistent, but there is bound to be some paralax error which I think is accounting for the difference in readings I get. I can't be sure though. Thoughts?

Brian

[Mike Juzenas]

Originally posted by bbh03
Okay, I think I have timed the left side. As I reach TDC, the dial gauge is just beginning to turn (indicating valve depression) and reads 0.0524 Z1 hits the seam. As I continue past, the dial makes several spins (several 1/10th of an inch) as the rest of the cam lobe (rotating CCW) passes the rocker and then subsides back to 0. After the crank rotates a full 720, we are back at 0.0524 as the cam is just beginning to act again on the rocker. All good? I',m going to attempt to get the right side to meet the same spec. Wish me luck!

Brian

Sounds perfect! If you can rotate it around 720 degrees and still get the same reading, move all your gear to the other side, time it and then recheck this side and you still get the same reading you are good to go!

Cheers,

Mike

[Mike Juzenas]

Originally posted by bbh03
I have the left at about 0.0545 to 0.0550 and the right at 0.0535. That's a difference of about 0.03 mm. Okay, or do they need to be exact? My problem is getting a consistent measurement based on where I think Z1 is hitting the seam. I am trying to be consistent, but there is bound to be some paralax error which I think is accounting for the difference in readings I get. I can't be sure though. Thoughts?

Brian

I think I got mine to 0.01mm or less of each other but you often have to fiddle within the pin slop to get that.. We tend to get really anal on this list about this but I think in fact that chains tend to load/unload when the engine is accelerating/deaccelerating so the timing moves around more than the tolerance we seek.

You also might find your timing will change depending on the chain tension..if you really crank on the chain tensioner you can stretch the chain and have the cams advance at bit, at least 0.01mm or more (at least I saw that on my car).

I guess if you use the next hole on the indexed sprocket that gets you too far out? If so then you are talking the slop within the hole which is pretty close. You can definitely work the pin slop though. The sprocket is not supposed to move when its torqued down ; the pin will not have that much pressure on it but the locking is because of the friction and clamping load of the pins. In fact, the later 993's do not have the pin but rely only on the friction. Yes they are known to slip but only on over-revs.

I also used a straight edge clamped to the seam that extended the seam out to the pulley. You can also put the fan housing onto the block and the will give you a marker directly above the pulley.

You are getting there!

Cheers,

Mike

[bbh03]

I seem to be at 1.38mm. John recommended 1.26 - 1.40 for this specific motor (964 cam in 3.0 with 98mm 9.5:1). Wayne just recommends 1.16 - 1.36 for 964 cams (no other things specified). Does 1.38 seem okay? That means the cam is a bit more advanced than the center of the range, right? Wayne mentions somepeople do this (expecting more power) but he doesn't say it is bad for the motor.

Mike, yes I do get consistent results within 0.001 in (about 0.0254mm) but I think the Z1 being exact (by eye) thing is more error than anything else at this point. The way you and 2.7Racer broke it down made alot of sense to me. Thanks!

I think where Wayne's book becomes confusing is where he says at first, you won't quite make a 360 degree rotation before meeting your spec. Mine was after. It seems to depend where you begin with the pin that depends on which way you need to go.

Brian

[bbh03]

I have to say, I still can't imagine the tiny bit of play allowed by the pin can have a big impact on timing. I think the lining up of Z1 is more error, but that is just based upon my experience. The concensus seems to be the slop is important. I did my best to keep the sproket in the right spot during torquing. In fact, I used the cam holding tool to hold the dial (hence the cam) in the right spot as I torqued.

[2.7RACER]

Brian,
Sounds like you've got this thing figured out.
It's one of the proedures that seem complicted when you first study it. Then once you do it a couple times you wonder what seemed so hard.
Yes, we do get anal about accuracy.
It just makes sense if moving the sprocket one pin hole right or left gets the timing closer, it should be done.
Keeping in mind this series of engines SC's through Carrera's were timed from 1 degree BTDC to 7 degrees BTDC.
I doubt if many, if any, could tell without measuring whether a motor was timed at 1 or 7 degrees BTDC.
Of course where ever we end up timing wise, we want right and left banks to be as close as possible.
Ultimately your care and understanding of the entire rebuild process will pay dividends when you fire it up.

[bbh03]

Thanks Doug!

I just installed the tensioners and remeasured. The right stayed put, but now the left is advanced a little out of range (moved about 1.5mm). I will have to retime them tomorrow. It appears the left can be timed with the tensioner in place. Will that provide enough tension for timing or should I put a clamp back in there?

Thanks,