Cam Timing

GotaT · 10-03-2007, 10:31 AM

After reading and prepairing to assemble my engine I am a bit confused on how to Correctly set the Cam Timing.

In Waynes book on pg 167-168 he says to Securely hold the Cam from turning while backing off the 46mm Nut. Once accomplished, "rotate the camshaft until the dial indicator shows that the valve has moved the amount indicated for the intake vave stroke in overlapping TDC with .1mm valve clearance."

This makes perfect sense.. but then he examplifies it w/ 2 different ways. ONE way he says to turn the CAMSHAFT and the other on a 70 911S he says to turn the CRANKSHAFT

So on my 72 2.4 T cams.. what will I need to Turn the CAM or the CRANK to adjust to my 2.4-2.8 mm

and Which way will I need to Turn it , Clockwise or Counterclockwise?

Any "simpler" explanation is Greatly Accepted

dtw · 10-03-2007, 10:52 AM

Whether doing high-lift or lazy cams, I prefer setting the crank to dead-nuts TDC and then rotating the cam to the specified lift. The key is to adopt a method you are comfortable with and to produce repeatable measurements.

AngM018 · 10-03-2007, 12:30 PM

Quote:

Originally Posted by dtw

Whether doing high-lift or lazy cams, I prefer setting the crank to dead-nuts TDC and then rotating the cam to the specified lift. The key is to adopt a method you are comfortable with and to produce repeatable measurements.

+1 on the high-lift method. Just did my cams, and it was a whole lot easier to leave crank at TDC and rotate the cams.

Eagledriver · 10-03-2007, 04:48 PM

You have to get an understanding of how the camshafts move in relationship to the crankshaft and rocker arm. If you just try to memorize a direction like "turn counterclockwise" you'll be unlikely to be successful. Hook everything up except the rocker arm and rotate things until you get an understanding of how it works. Look at how the cam lobe would push on the rocker arm to open the valve. Notice that the cams turn backward compared to the cranckshaft. Think about which way the cam will have to turn to open the valve sooner or open it later (this is the essence of what you are doing).

-Andy

cstreit · cstreit's Garage

On the early models with the 46mm nut it's easier to turn the cam while the crank is at tdc because the cam-end protrudes past the nut. On the later cam style with the large bolt, there's nothing to hold on to, so I rotate the crank.

GotaT · 10-03-2007, 05:56 PM

Thanks for all the input.. Eagle, your explanation will definitely help me understand the measuring more.

Help me and let me know what I am missing

TDC the Crank,
"Eyeball the Cams when putting them in at TDC Dot pointing UP"
Install the Dial Guage securely on #1 Valve spring w/ the Rocker Arm secured and accurately SET w/ the Feeler guage

Turn the Crank 360 degrees and COUNT / Measure the Dial Guage once one revolution has been turned on the Crank.

The cam should be set on my T to be 2.4-2.8 (2.6)

If it comes in Below the 2.4 or Above the 2.8......
Loosen the Cam nut while SECURING the Cam from turning
And turn the Cam either Counter or Clockwise until the Dial Guage goes to the 2.6 Mark...

Insert the Dowel Pin in the Appropriate Hole

Tourque everything Down , but not to disturb this setting on the cam

... What have i missed/ skipped or explained incorreclty- thanks

sand_man · 10-04-2007, 06:35 AM

Quote:

Originally Posted by AngM018

+1 on the high-lift method. Just did my cams, and it was a whole lot easier to leave crank at TDC and rotate the cams.

I agree. I did mine by rotating the crank until my dial gauge had the proper reading, pulling the pin, rotating the crank around, pin back in, etc. After working with John on timing his cams, it was easier to just leave the crank at Z1 and put the cam where it needed to be.

Now that my engine is pretty well broken in, I'll probably be checking my cam timing at my next valve adjustment. Even though the engine runs smooth as a top, I'm curious to see where the cam timing is.

GotaT · 10-04-2007, 07:43 AM

What ? ?

START at TDC on the CRANK and Eyeball the CAM to TDC

Turn the CRANK until the Dial guage reads the Correct mm

Take out the CAM pin , holding the CAM in place

Turn the CRANK back to TDC

Insert CAM pin

DONE ? ? ?

that easy ???

dtw · 10-04-2007, 08:25 AM

You're getting hung up on 'procedure' - just stop sweating it until the cam timing step arrives. Then follow Eagle's advice and move the parts around until you really 'get' what it is you're trying to accomplish, and how the cams/crank interact. Also, you'll find on your engine that leaving the crank alone (@ TDC) and turning the cam is probably easier than the method you mention above.

Cam timing is the most over-hyped task on a 911. If you've never done it and you read an article or book on how to do it, yes, it blows your mind. When you're actually standing front of the engine with wrench in hand, it is just not that hard. The most critical part, in my opinion, is being able to produce repeatable measurements so you can have confidence in your work.

You can do it, and you've got us all behind you. Go for it!

911quest · 10-04-2007, 09:33 AM

Yeah reading the book makes it alot more complicated then it really is I think the manual's lose a little in the translation from German to English. I have to agree with the rotate it arounf till you get your over lap then pull the pin then move the crank to Z1 and reinstall the pin and tighten the 46mm nut.

cstreit · cstreit's Garage

Agree,reading the books, it's overwhelming if you've never done it.

46mm method:

1. Rotate the crank to tdc.
2. pull the pin and rotate the cam to the correct lift reading.
3. insert the pin and torque the nut.
4. rotate another 720 to verify it.

Later method.
1. Rotate the crank untill lift reading on dial is correct.
2. pull the pin and hold the cam.
3. move the crank back to tdc.
4. Insert the pin and tighten the bolt.
5. rotate 720 to verify.

efhughes3 · efhughes3's Garage

I'll be at this point in a couple of weeks. I've been semi-stressing over it, as I did with the case sealing. I'm glad that more than a few of you have pointed out that it will be rather straight forward when it's in front of you, and you can visualize the setup.

Having said that, I did order some mechanical tensioners and a TDC indicator. My thought here is getting a little closer to perfection and accuracy, and then I can opt to sell the tools slightly to recoup some of the cost, which wasn't so much when compared to the rest of the build costs.

Eagledriver · 10-04-2007, 05:05 PM

The moving of the crank method sounds like it would be easier (I haven't done it that way). The problem with any of these methods is the execution. Keeping things from slipping and moving while looking at readings of thousanths of an inch are the hard part.

Take care to turn the crank slowly when you approach TDC so that if your timing is off far enough to hit the valve you won't do any damage.

I'm beginning to think it would be a good idea for people to check the timing on the engine before they disassemble it so they see how it works.

-Andy

AngM018 · 10-04-2007, 10:45 PM

Quote:

Originally Posted by sand_man

I agree. I did mine by rotating the crank until my dial gauge had the proper reading, pulling the pin, rotating the crank around, pin back in, etc. After working with John on timing his cams, it was easier to just leave the crank at Z1 and put the cam where it needed to be.

Now that my engine is pretty well broken in, I'll probably be checking my cam timing at my next valve adjustment. Even though the engine runs smooth as a top, I'm curious to see where the cam timing is.

Mr. Sand_man brought up a great point in a PM the other night. After timing your cams, dont trust just one rotation of the engine to verify your cam timing. It will take 9 or so Z1 (TDC) rotations to get to the same position on the chain that you were when you pulled the actual timing.

Thus, be sure to rotate the engine about 9 times so you can get an average of where you are at. I did this last night, and I pulled numbers anywhere from 1.70mm to 1.73mm. I really just made sure both sides were within .01mm on each rotation, and left it at that.

Dont be too concerned if you pull random numbers after tightening the nut/bolt. just be sure to keep both sides within .01 of each other, and make sure your not way off of your target number, when you do all the rotations (may want to use chalk to mark the chain).

ChrisBennet · ChrisBennet's Garage

The key to accurate measurements is repeatability. Repeat whatever measurement you are doing several times.

As you increase the tension with your tensioning tool the readings won't bounce around as much (less error) - to a point.

I always mark the first hole I put the pin in keep track of how many holes I am from the start. I don't try to move the cam or the crank to the get the "right" reading directly - it changes a lot when you tighten the nut or bolt.

Instead, I back the the crank off a little to relieve the tension on the pin and then move the crank a little until the next hole becomes visible through the sprocket, then I put the pin in and tighten the nut (a little burp with the impact gun) and repeat the measurement process a few times.

Rinse and repeat, then torque the cam bolt/nut and repeat measurements again.

-Chris

GotaT · 10-26-2007, 01:56 PM

Stepping up to Play this role this weekend! Ive got the E cams and will be checking for clearance and setting the valve overlap .. and hopefully Reinstalling the Engine!

munsonbw · 11-10-2007, 01:42 PM

OK, call me slow...

I really do understand what is going on here, with the exception of one little detail. Wayne says to set the dial gauge to 10mm of preload then proceed to rotate the crank and reproduce the valve lift number from the left side over on the right. This seems simple enough, except I am using a digital indicator and I am afraid that I may have my orientations bass ackwards and instead of 1mm of lift I'll get two, or even have less than the needed lift.

Now, after studying this over and over again, it appears that cyl 1 and 4 are 180 apart? Meaning in terms of the cam setting, TDC for cyl 1 is 360 degrees of crank rotation from #4. So as mentioned above just set to TDC for the cyl you are working on and get the lift reading that way. If this is true, it is a whole lot more intuitive than what is in the book, at least for me.

Please help. Oh, I have the 46mm nuts, so I have been setting the crank to TDC and moving the cams.

Eagledriver · 11-10-2007, 08:35 PM

You are correct #1 and # 4 fire 360 degrees apart. If they didn't they would be trying to fire at the same time. (you'd need a funny distributor to make that work). As far as preloads and readings go you have to figure out what you are doing so you measure how much the valve depresses when you turn the crank to TDC on the compression stroke. How you get there is not important.

-Andy

hcoles · 11-11-2007, 07:54 AM

after all is done and before you button things up.... check that each cam matches the firing order by looking at the distributor and noting e.g. #1 is ready to fire because the intake has been closed for a long time and not near to opening the exhaust... and the rotor is pointing to #1 wire... check other cam as well... it has happened that one cam got 180 out... but "perfectly" timed - I know

munsonbw · 11-11-2007, 09:15 AM

Thanks for the help. A talked with GotaT last night and he confirmed that I was making more out of the instructions than was really needed. I hate to be critical of other's work, since I certainly don't have the talent to do it, but I think that section really could use a re-write. As many have said here, if you understand what is going on it is a very simple task. I got caught up trying to melt the instructions and my understanding of the process and somehow ended up with confusion.

I'll double check with the distributor on, good advice hcoles.