ARRRRGGGHHHH! Need Cam/Valve timing help!

[porsche_virus]

.

[TimT]

Are you saying that Z1 is stamped twice on your pulley? or is there just another mark close to Z1?

If it is just another mark close to the Z1 mark it represents 5 deg. (I believe) to find the real Z! measure from the 120 deg marks and find which Z1 is equidistant from the other marks. You now have assured you have the firing marks 120 deg apart.

[CamB]

Never timed the cams. Have had decent backfiring - two spark plug leads were swapped... Check carefully (hey, its easier than some of the other options).

[stormcrow]

You've got to use a dial indicator to get it right. Guessing will get you in trouble (bent valve, etc). Set your #1 cylinder to TDC (Z1 position) as a starting point. Next, check to see that flat on the end of the cams are straight up. Next, set the dial indicator (preloaded) against the inlet valve spring retaining cap on #1 cylinder.

Next rotate the engine to the overlap position - this requires one complete revolution on the engine. This should return it to the Z1 position again. Read your dial indicator to see what the variance is. If the cam is within specs then you are good to go to the #4 cylinder. If it isn't then you need to rotate the engine back to TDC (Z1) and adjust the cam accordingly.

To adjust the cam, remove the locking nut, remove the pin in the sproket and rotate the cam ever so slightly. Install the pin, tighten the locking nut and start over. If you are out of spec on the negative side, then the cam needs to be rotated counter clockwise. If you are out of spec on the positive side, then you need to rotate the cam clockwise.

Do the same with the other side using #4 cylinder intake valve making sure the piston is at TDC on the compression stroke when you start - not the exhaust stroke. The procedure is the same as #1 cylinder. Good Luck (I think I got it right)

Steve

"A Porsche does more then just go fast in a straight line"

[BK911]

Cam timing is one of the most important tuning aspects of any engine. If your valves aren't opening and closing when they're supposed to bad things will happen, anything from poor performance to destroying the engine. I wouldn't even try to start the engine until I was 100% sure the cams were timed correctly. If you remove the muffler and rear engine tin the cams can be timed with the engine still in the car.

Steve's description is pretty close, but I do it slightly different. When you rotate the crank 360 degrees to get your overlap value, you can loosen the lock nut and rotate the cam slightly to get the proper value. Then tighten the lock nut and rotate the crank 720 degrees to make sure the value maintains. Using this method there is no reason to get close, you can get it exact.

Of course there's a little more to it but this should get you started.

Good luck!
BK

[zuffenhausen]

The mark directly above Z1 is the TDC position you're looking for. The other mark is for ignition timing.

Um, how exactly did you do the cam timing if you didn't do it with a dial indicator?! Not to alarm you, but you may have already done internal damage by trying to crank a mis-timed engine. I hope you're only a little off and the exhaust valve is opening early. That would explain popping through the exhaust.

Good luck!

-zuff

[john walker's workshop]

lift is the valve opening.
set the crank pulley to the Z1 mark lining up with the mark on the fan housing. either #1 or #4 cylinder is now at TDC firing position. to determine which one, see which intake rocker has clearance. (you can also see which plug wire the dist rotor is pointing to, if you think you have the wires on right, or the dist installed correctly). set the clearance to .004. set up the dial gauge with it's pin resting on the edge of the spring retainer. set the gauge to 0. rotate the engine clockwise one full revolution back to Z1 lining up with the fan housing mark. at this point the gauge tells you how far the valve opened with one revolution of the engine. that is what the cam timing spec relates to. the cam is then moved to correct the spec if necessary.

[zuffenhausen]

I just realized the first thing you need to do if you think your engine is mis-timed is to back off all the valve adjusters to minimize the risk of (further) valve damage. To be absolutely sure you actually should remove the rocker arms, but at this point it's probably not worth the trouble as you've cranked the engine and the damage, if any, is done.

After backing off the adjusters, go through the timing procedure methodically. If there are specific steps you don't understand, post them and we'll try to help.

-zuff

[stormcrow]

KC

If you are not sure if you are on the exhaust stroke or compression stroke, check both the intake and exhaust rocker arms on the #1 cylinder. Both should move a little when you lift one end up.

On the compression stroke, both valves will be closing as the piston comes to the top of its stroke and at the top of the piston stroke, both rocker arms have a little movement (.004). If they don't move then you need to back off the adjustment screw and set both to the required specs.

Once you have determined the cylinder is at Z1 on the compression stroke, and your rocker arms are properly set to spec, you can then start working on your cam timing.

Steve

"A Porsche does more then just go fast in a straight line"

[ChrisBennet]

Here are some tips.
The essence of measuring something accurately is being able to do it consistently. Lack of proper tension on the chain, too much cam lube on the cam, etc can lead to bad readings. Repeat the measurements a few times and make sure they are consistent. If they aren't consistent you aren't measuring, you're guessing.
Using a crayon, mark the hole that you first put the sprocket holding pin into. Move the pin a single hole at a time. Otherwise, it is easy to keep going back and forth reusing the same hole.
-Chris

[Wayne 962]

Wow. I'm certainly not thinking: "jeez, what an idiot", but I am thinking that you have a very high probability of mis-timing the cams, and seriously damaging your engine. Expert home mechanics who 'know' what they are doing have been known to mis-time the cams and send the valves crashing into their pistons.

Firstly, don't test the engine by starting it - if you have something off, then you may bend your valves, and it will be top-end rebuild time.

Secondly, re-read the Cam Timing section in 101 Projects - it's a very good overview.

Thirdly, I have a *whole* sub-chapter dedicated to timing the cams in the new engine rebuild book, along with lengthy explanations of why you need to do it, and the general operation of the camshafts with respect to the engine. Get the preview edition of the book:

http://www.101projects.com/rebuild.htm

and get yourself some cheap insurance against doing thousands of dollars of damage to your engine.

The folks here can probably walk you through the entire process, but it's very tricky, and if there is one thing out of whack, you *will* detroy your engine. My editor and I reviewed and revised the section on cam timing ELEVEN times to make sure that it was 100% correct, and easy to follow, because it is just about the most important step.

-Wayne

[82SC]

well I am doing my cam timing now too

I am a dummie

I read waynes engine book and BA's valve chart

I figured it out

I am going to write up something entitled

"Cam Timing (964 swtich) for Dummies and Those Who Want To Spend the Least Amount of Money"

but I won't write it till the engine is running and I don't have holes in my pistons

keep your fingers crossed

MJ

[Doug Zielke]

KC,
Did you *remove* the cams from the cam towers, before you tried to time them???
In other words.....have the cams ever been out of the motor and then replaced?

[john walker's workshop]

like i posted previously, on Z1, the engine is on either #1 or #4 firing position. the intake valve (1 or 4) that is all the way closed and has clearance at this time is the one to put the dial gauge on. the other side of the engine with the valve partially open is on overlap, and you do that side next.

[zuffenhausen]

Originally posted by porsche_virus
Now I have the dial indicator figured out, but my MAIN QUESTION now is, what does it matter how much the valve travels up and down, if its not open or closed at the right point? Does that make sense?

You are close. When you started at Z1, you were at what's called TDC Overlap on cylinder 1 and the intake valve was open just a little. That's how it's supposed to work. When you turned it over to Z1 again, cylinder 1 is at TDC Ignition and both valves on that cylinder should be closed. Meanwhile, cylinder 4 is now at TDC Overlap. All you need to do now is measure the valve lift with the dial gauge at those two points and correct it if it's wrong. What does your dial gauge read now on the intake valve of cylinder 1 when you are at TDC Overlap?

Now, to answer your question: You *are* making sure the valve is open and closed at the right point by measuring the lift at a known point, TDC Overlap. The cam designers take care of the rest. All you need to worry about is the lift at the TDC Overlap measuring point.

If anyone is within a reasonable distance from here and can come by and help this week, I can pay.

If I were anywhere close I'd be glad to help you for nothing more than a cold beer! Unfortunately, Kansas is a little beyond my range. Surely there's a Pelicaner who's timed cams somewhere in your area.

-zuff

P.S. The cam timing of some engines (like some 'merican V8s) is set at full lift (completely open), but they can do that by using a degree wheel on the crank pulley that shows *every* degree of rotation. On the 911 engine, we don't have that, we only have three reference points per revolution, so the cam designers tell us how far the valve should be open at the TDC Overlap (Z1). If you set it to that spec, the valves will be fully open and fully closed at the right time.

[jim72911t]

Oh boy....................


My suggestion is to get somebody over there who KNOWS 911s before you do anything else. I was just looking at your website, and the first question I have is how were you able to get the cam chains off the sprockets without removing the sprockets? This leads me to believe that the cam timing might be the least of your worries.

Nobody is accusing you of being a technical idiot, (your collection of beautiful R/C airplanes proves you're not) but you might have wanted to do a bit more research before tearing into your Porsche motor. Warren's new book, the Haynes manual, the small "Spec Book," and BA's book should be considered the absolute minimum, and reading each book completely before you turn a wrench should be mandatory.

If you sit down, face to face, with someone who has built a few motors (beer and pizza could be helpful here) and explain step by step the procedures you took during the rebuild , you might be able to put everything back to right with a reasonable amount of effort.

Best of luck
Jim
1972 911T

[stormcrow]

Well, it sounds like you are making progress. Zuff is right on track, when you said the valve was not closed all the way, you were at the overlap position where both valves were partially opened. The next 360 revolution would have put you back to the compression stroke with both valves being closed at the Z1 mark.

This would be your starting point. Now you can set up your dial indicator up for your readings. Also, check your distributor timing to make sure its close to firing with the #1 piston when it is at TDC on its compression stroke. Once you set your cam timing, you can then set your distributor timing.

Once you feel comfortable that your cam timing is right, take a compression test which would further verify that you are doing it right.

Steve

"A Porsche does more then just go fast in a straight line"

[dtw]

In your web page you note "There is still some popping when the engine is cold, so this Winter I plan on pulling
the motor and doing a full rebuild, which will also hopefully stop the oil leaks."

This isn't the "full rebuild" is it?

Did you:
-Check valve guide tolerances? At least wiggle them to see if they feel at all loose?
-Check rod bearing condition at least by wiggling the rods side to side, and standing them up to see how quickly they "fall"? (good seat'o'the pants rod bearing indicators)
-Check tolerances of wrist pins?
-Evaluate cylinder condition, including hone and ID and round?
-Measure piston ring lands to see they're still in spec? Skirt condition?
-Check cylinder head mating surface condition?
-Examine cam sprockets, rocker shafts, rocker/cam mating surfaces and other valvetrain components for wear?
-Reseal cam tower to head, which has surely been disrupted by this disassembly?

HOW did you:
-Take the timing chain off without removing the sprockets?
-How did you put them back on???

[82SC]

I am sorry to hear that you are discouraged...

but on the other hand it is good you realize your situation and know where you and your engine stand at this point...not being stuborn is key...alot of people have been down this road before and you have to learn from THEIR mistakes so you don't trash an engine

but lastly...it can be done

As long as you are interested in fixing the car up and have time and garage space you can definately do it

Its been a year since I bought the car

the most I had done on a car before that was top off oil and coolant

now the engine is getting seals, 964 cams etc...I've a brand new clutch etc...

I'd really review what you've done to the engine and read on this board...buy wayne's book, Bruce Anderson, and Bentley...

and tackle the engine...you've come this far and from your pics I think you've enjoyed the joys of p-car ownership

I think this board is more then willing to help you out in your situation and now that you've made yourself famous with this thread, I am sure you will get alot of replies when you post ques about your rebuild...

Wayne's book says you can get away with a decent rebuild (if your engine does not need much machining) for about 2K...

but regardless good luck and hope things work out ok...

(if not I am sure there are some....hint hint...on this board who are looking for a 3.0L SC engine to buy...hahah...just kidding...but good luck)

MJ

[RSW]

I've recently changed the timing chains on my engine and obviously set the timing. I used the 101 book and the Bentley manual. I haven't started the motor yet as i'm only just about to put it back into the car. But I'm now nevrous about turning the key.

You did say you'd turned the engine by hand - as I have done. If it turned OK by hand then I have to doubt that you have caused the valves and pistons to come into contact.

Wouldn't you hear the valves and pistons hit each other?

When I did mine I removed the tensioners, sprocket bolt and turned the cams out of the way slightly (as described in 101) so I could turn the crank by hand/spanner when I'd done I turned it back again, connected the chain up and set the valve drop to 1.25mm. Mine turned OK by hand - but now I think about it what is to stop someone butting the sprocket on 180 degrees out?
Sure the 930 marks will be at the bottom but it could still be timed up ok couldn't it?
How do you know the cam is in the correct position in relation to the crank? Is it purley down to that dial gauge reading?

Any thoughts?

Richard