Cam timing question
 

Once both cams are timed, are they opposite? Meaning if the 930/911 mark on the left is up, should the one on the right be down?

I timed my left side, then moved to the right. However when I turned to get the correct reading on the dial gauge, I was just past TDC. Waynes rebuild book then instructs to turn clockwise until TDC, but for me that would be an entire 360 therefore causing left/right to be 180 off. Is that right or should I back it off and set them both the same?

Pat

The dot corresponds to pointing up when you're at TDC - correct...

-Wayne

Hey,
Pg 175, para 1 of section "Timing chain covers" states "The Z1 mark should be at the case parting line and the dot, 930 mark, or camshaft keyways on both camshafts should be facing up."

That is incorrect then right? Because only on is pointing up?

Pat

Re: Cam timing question
 

No, when you're done timing both cams, the dots should be in the same position - usually around 12 o'clock.

Quote:

I timed my left side, then moved to the right. However when I turned to get the correct reading on the dial gauge, I was just past TDC. Waynes rebuild book then instructs to turn clockwise until TDC, but for me that would be an entire 360 therefore causing left/right to be 180 off. Is that right or should I back it off and set them both the same? Pat

When you start the dot on both cams will be pointing up and:
- You are at TDC for cylinder #1
- The #1 valves are at their overlap position
- You adjust valve #1.
- You set the dial indicator to zero when timing the left cam
- You measure the lift when timing the right cam

After one revolution of the crank, the dot on both cams will be pointing down and:
- You are at TDC for #4
- The #4 valves are at their overlap position
- You adjust valve #4
- You set the dial indicator to zero when timing the right cam
- You measure the lift when timing the left cam

Does that help?

-Chris

I think you are confusing TDC for number one with TDC for number four. I'm not trying to be condescending, but read through the cam timing section a few more times. I think that you forgot to place both pins into the timing sprockets when you aligned everything at TDC...

The cam timing section was the one section that I spent more time on than anything else in the book, so I'm 99.99% sure that everything in that section is correct...

-Wayne

Okay,
My problem was that after going through the instructions
- Set the pins in the sprocket cams both with the 911 (in my case) pointing up and the pulley at Z1 on the case line
- Turned the crank until the valve on cyl 1 was depressed .8mm (stock CIS 74 cams)
- Pulled the sprocket pin on left cam and rotated crank to line up Z1 to case line
- Torqued down left cam, then double checked the reading by rotating the crank 720. (I actually did this whole process for the left side about 8 times before I got a good reading that I was happy with)
- I then moved to the right
- When I rotated the crank to the point where the valve was depressed .8mm I was just a few degrees past the Z1 mark lining up with the case line.
At this point I could either turn the crank just a hair counter-clockwise and be on, or turn the crank 358 degrees clockwise and be on. If I had backed off I would have the 911 marks both facing the same direction. But I went clockwise as directed and it puts them 180 off.

It looks like my right side must not have been perfectly up and down and I should have hit .8 just before the Z1 lined up with the case, there for only requiring a few degrees of turn clockwise instead of nearly a full revolution.

Thanks for correcting me and no condesending implied.

Wayne, way does your book say to add 10mm of preload to the dail indicator before setting up the right cam??

Yes on page 165...

-Wayne

That sould say WHY ?? I have never seen that advice in any other mauual

Correct so far. This means that both cams will turn together as you turn the crankshaft. This is important so that the pistons don't hit the valves.

I'm assuming you turned it clockwise. It should reach this value just before the Z1 mark is reached. You will be very close to TDC for cylinder number four here, not TDC for cylinder number one.

Okay, you pulled the pin and aligned the crankshaft with the camshaft. At this point, the engine is at TDC for cylinder number four, and you have just timed the left side camshaft.


If you rotated the crankshaft 720 degrees, then you should be at the same spot where you left off (which is TDC for cylinder number four). If you rotated and checked it a total of eight times (8*720 degrees) then you should still be at TDC for cylinder number four (Z1 mark lined up with the case parting line, and at this point, the 911 or dot on the camshafts should be pointing downwards.)

At this point, the engine should be at TDC for cylinder number four, the dial gauge should be installed on cylinder number four. Since the gauge is set on number four, and the engine is at TDC for number four, then none of the valves should be open and you should be able to wiggle both rockers for cylinder number four.

When you rotated the crankshaft to where the valve was depressed, you were then at TDC for cylinder number one. The proper thing to do here was to back the crankshaft off and align it with Z1.

Why? Because the timing point for this particular camshaft (actually all of them, I believe) begins before TDC. Unfortunately, you made a bad guess when initially aligning your sprockets together in the first step (this is just a guess step, used to keep the valves from hitting the pistons). If you're off in the wrong direction with a camshaft that is timed close to TDC (like yours), it's possible to be a hair on the clockwise side when you get to the proper valve overlap. In theory, you should be before top dead center, but if the pin was off a bit on the first step, then I can see how it would be confusing.

Whoops, I could have just saved myself 20 minutes by re-reading your last sentence. Yes, this last sentence is 100% correct.

Also, if you check and double-check your camshaft timing (recommended), you would have found this error easily. I think you may have also had piston to valve interference, if you started the engine, or were running a hotter camshaft.

I hope this helps both you, and the next person...

-Wayne

Thanks for correcting me and no condesending implied.

I'm pretty sure it's in the factory manual and the Bentley manual.

The bottomline is that it's good machine shop practice. You don't want your gauges bottoming out and leaving their range of travel. By preloading the gauge when it's at its bottom, you know that you have 10mm of margin so that it won't bottom out when you are turning your engine over.

Make sense?

-Wayne

I'am useing a digtal guage and I'ts pretty cool and very easy to read. I just finished setting the left side and after setting up the right side and rotating the the crank when I got the same reading as the left I was exactly lined up with Z1 thus no adjustment, is this possible!!

Sure. I'm not a huge fan of digital gauges though - as they tend to not be as accurate as analog ones, in general...

-Wayne

Wayne,
Thanks again for the detailed and outstanding support!

Pat

Cosmo,

Yes it is possible. The last time I timed cams, I was within 0.05mm on both cams on the first blind attempt. Hardly worth adjusting when the spec is +/-0.20mm for S-cams.

Just point the dots north and tighten the nuts. Saves a bunch of time. (just kidding)

Well, one of my goals is to make this forum the number one resource for rebuilding 911 engines. I was looking through all of the older threads, examining them for comments about the book (correction list was due), and it dawned on me that this forum has really begun to take off, and that there currently is *a lot* of info here. I'm talking specifically about this Engine Rebuilding Forum now...

-Wayne

For what it's worth,

I had a 3.0L rebuilt and shipped to me. Once I installed the engine and started it, I noticed that the right side of the motor was not running correctly. I sent the car to a local shop and they pulled it down reset the timing on the cams twice. Afterwards they discussed the issue with the wrench that built the motor as well as Brumos Porsche in Jacksonville and another shop in Atlanta GA. After weeks of troubleshooting the problem , The owner of the local shop (Willy Harold) said that since it seams that the right cam is running at 180 degrees out, he pulled it out and replaced it into the motor with the timing mark at the bottom. It ran great afterwards. He claims that the manufacture of the cam marked the cam in the wrong spot. I don't know if this was a problem with a batch of cams or just my bad luck.

I Don't know
Rick

Pat

To answer you question you should have backed the motor counter clockwise to top dead center. Since you didn't and went a full 360 deg. clockwise your right cam is now 180 deg. out. You need to start over with the right cam.

Tim

Also

When timing the right cam the timing mark is on the bottom for both cams.

Tim

Right. I did go back and did it correctly. Engine went in this weekend and runs very well. Thanks.