Eagledriver

What I tried to do was re-phrase Webcam's instructions to help LeeH with his understanding. Obviously, assuming that the piston combination an deck heights are correct, he is having some problems degreeing the cams.

Certainly there are many ways to do this and the best, in this case is with a degree wheel. Cams can be run "straight up", advanced or retarded with each combination affecting the torque or the HP depending on the specific need. Every cam should be indexed since that allows you to check how accurately the cam profile has been ground and hence how the engine will perform.

You are correct, the measured duration at .050" lift is a "standard" not followed by all manufacturers because it is very difficult to find the precise base of the cam lobe since it is so broad.

My best guess is that Leeh has the cams 180 deg out of time as mentioned before or the timing chain is not tensioned sufficiently. So he must start afresh again.......

A couple of things to remember are:

1) Always rotate the engine in the normal direction of rotation
2) On the valve to piston clearance look for a minimum of .060" on the intake and .100" on the exhaust
3) The easiest way to measure the valve/piston clearance is to set the engine at TDC for the cylinder in question, place a dial indicator straight down on the spring retainer and set it at zero. Loosen the lock nut on the rocker arm adjustment screw and screw the adjustment down slowly forcing the valve open until it stops after it contacts the top of the piston, note the reading on the dial indicator and write it down. Do the same for the other valve and the rest of the cylinders. If everything checks out you are ready to go, otherwise correct the problem.

BTW, the 20/21 cam is a relatively mild grind, quite similar to the "964" cam, so if there is valve to piston interference there is something very wrong......stop, do not pass Go and do not collect $200.

After this engine Leeh will definitely know how to index Porsche flat six cams.....good luck to you Leeh. Practice makes perfect.

Lee,
You should never set the valve timing with all the valve actuators(rocker arms) installed. It may work one time, but the next, you may bend some valves when you're rotating the crank.
Set your valve timing with cylinders #1 and #4 only. Check and double check, then install the rockers for the remaining cylinders. I think the previous post is right.....you have the right side cam out of phase.

Several people have suggested that the right cam is 180 degrees out of phase. I wish it were that simple. My reason for thinking it's not (and please correct me if I'm wrong)... #1 and #4 intake valves alternate being depressed for every 360 of crank rotation.

So... I mount the gauge to #1. Gauge starts to move before Z1. At Z1 the gauge reads 2.1mm (climbing the lobe - not decending). Without touching anything I move the gauge to #4 and set it to zero. I rotate the crank 360 degrees and read 2.1 mm on the gauge at Z1- again the 2.1 mm is climbing the lobe - not decending.

I changed the setting yesterday to around 1.8 mm (spec is 1.9 - 2.2mm) of lift at Z1 with .10mm of lash. At 1.8 everything clears, but measuring the clearance using the adjuster screw I only have 1mm of clearance on the #6 intake valve. The exhaust was >2mm.

I know the intake clearance is closer than desired, which is what has kept me from putting it all back together... especially since so many people have told me that there should not be any clearance issue with the 20/21 cams.

Lee,

It seemed you have timed your #1 and #4 correctly with #4 being 360 crank degrees out of phase with #1.

Looking at other things, you think the valve stem in your #6 could be too long?

Leeh

What you mentioned on your last pot is proceduraly correct. If the cam's are timed correctly as well as the valve lash there should be no piston/valve interference accross the diferent cylinders as the crank is turned. It is always advisable to check the valve/piston clearance at TDC as I aluded on an earlier post......peace of mind is priceless.

Apparently you are still having problems Webcam's cam timing instructions......that leads me in other direction. I assume by your post that you are working on a 3.0 engine.

Have you changed out the pistons? or P/C set?
Have you milled the heads?

The above will potentially lead to where you are today.

I checked the specs of your cam against the specs of the Porsche factory cams, as found on page 207, Appendix A of Waynes book and your cam is within a few degrees from the second choice shown for the 78-83 911 SC....the one with the....... Intake Opens at 7 deg BTDC.

Your cam and the one on the book display simlar valve events albeit significantly different cam timing instructions, the Porsche cam range is 1.4 mm to 1.7 mm with a 1.55mm midrange, that makes me wonder if the cam timing instruction is the correct one for your cam. The same goes for the fact that you had to set the timing at 1.8 mm to ge away from the valve/piston interference. Moving in the direction of the Porsche cam set-up!!!!!

So at this juncture I would punt and call Webcam explain your problem and question if the set-up instructions are the right ones for the cam you have. Honest mistakes do happen.

If a mistake has been made, Webcam needs to get their cams back and re-verify if lift and durationt met the specs for the cam you ordered and return the right set with the right set-up instructions to you.

If you want pm me your phone so we can talk. I would be most interested on the outcome.

Lee,

What engine do you have? Is it an SC 3.0? Euro or US? What pistons and cylinders do you have in them?

Just wondering, with respect to your valve clearance problem.

The Valve timing information supplied by Web Cam is correct. every single detail is correct.
The perfect theoretical setting with the dial indicator is 2.049mm.

Let's see why.
First going from the intake opens @ 6 degrees BTDC.
It means @ 6 degrees BTDC with ZERO lash, the cam has opened the valve .050" off the intake seat.

Notice two duration figures are quoted. 258 degrees and 238 degrees @ .050".

This means the cam begins to lift the valve 10 degrees BEFORE it reaches .050" and the valve reseats 10 degrees AFTER the valve is at .050" upon closing.

258-238=20 degrees, 20/2=10 degrees on each side.
So it takes the cam 10 degrees to open the valve .050".
Or stated another way, for every degree of rotation of the cam from 16 degrees before TDC the valve is lifted .005".

Now here comes the kicker.

All the previous numbers were quoted with ZERO valve lash.
But on the line Grind # "Set @ 1.9-2.2mm/ .10mm lash".
We've changed the numbers from ZERO valve lash to .10mm lash.

No wonder it's confusing.

We are mixing mm's with inches then halfway through all this we change from ZERO lash to .10mm.

What is this, some kind of mystery everyone must solve before he can time cams. Yes it is a mystery.

First take the 1.9 -2.2mm spec and convert it to inches.
1.0mm equals .003937" 39.37 thousandths of an inch.
So 1.9x39.37=74.8. and 2.2x39.37=86.6. So the spec is .0748" to .0866

Halfway in between is 80.7. Thats .0807". 80.7 thousandths.
80.7 thousandths is the theoretical perfect timing point at Z1.

Interesting if you have read this far.

Back off 6 degrees @ 5 thou per degree and we get .0507" call it 50 thousandths.

The difference between the Web cam and the stock cam at Z1 is .020", 20 thousandths more lift at Z1.

It's 20 thousandths closer to the pistons than the stock cam.

Since the piston is hitting #6 intake and not the rest, the stack up at #6 is not the same as the others.

The solution: Check all cylinders for the height specification. #6 is shorter or the base gasket is thinner or missing.

All the cylinders should be the same height spec. They are marked on the side.

Check all pistons for valve clearance. The others may be closer than they should be.

The fix: increase the thickness of the cylinder base gaskets at least .025".

This is a lot of math to digest, but it's what you need to know to build these engines.

Good luck,

Thanks so much for all the input. I really appreciate the time required to compose such well thought out responses.

Here's what I know:
The engine is a US 3.0L from 1982. It did have the heads redone and new rings installed (on Alusils) the same time the cams were installed 4 years ago. An experienced mechanic looked at the heads when I got them out of the machine shop and said they'd never been cut. I spoke to the mechanic who built the engine and his opinion was that 2.1mm was too high for an SC, so my guess is that he originally installed the cams retarded from their specs.

I guess my question is what to do next. At 1.8mm everything clears, but my intake valve clearance is right at 1mm (measured by turning the valve adjuster). Exhaust clearance seems to be fine (>2mm). The engine ran so well before this happened. It's just frustrating that I'm having issues since nothing should have changed that would cause a difference in any dimension of the engine. Should I put it together as is? Dial it back to 1.70mm for added clearance then put it together? Would it run well at 1.7mm? Tear it back down and raise the cylinders or cut the pistons? This whole process has been a stress on my time and resources.

I did assemble the engine using sealants as I didn't anticipate dimensional changes with the limited work that was done so going back in would involve a lot of cleanup.

Question: Could the rod bearing have deformed from the over-rev to the point that two of the pistons could be sitting higher? The mechanic who saw my barely bent exhaust valves felt there was no need to be concerned with the bottom end.

So that is a stock SC 930/16 engine. That thread I linked you to earlier shows that a 20/21 will definitely fit that engine. It looks like someone did something wrong with the valve installation on #6? That engine has 9.3:1 compression. It looks like it boils down to top end rebuild or try a different cam. I would at least try a stock SC cam for diagnostic purposes.

If you do a rebuild yourself it will essentially be free, won't it? (With the exception of your time.) But if a mechanic does it, it will cost a lot of money. But if the original mechanic did install #6 incorrectly, he should pay for it I would think. Good luck Lee. :)

Lee,

What happens if you set your timing to 2.1 and just back the #6 rockers all the way out so you can continue to adjust the rest of the valves? Do the rest of the valve adjust fine with no hangups and clearance issue?

If so, then the problem is in cylinder/head of #6. If not then you may be able to narrow it down to a certain bank.

#5 and #6 hit, but not #4. I need to put it all together and take some measurements. I'd think #4 should hit, too. I'm going to put it back together and see how much I have to back off of the adjuster to get 5 & 6 to clear... and see how much I have to run #4 in to make it hit. I'm guessing the difference may just be in the carbon build up on top of the piston.

LeeH

Ahhh....bent valves......are the piston/valve clearance issues on the cylinders that the valves were bent? This is really becoming a puzzle.

The only thing to do is go back to square one and measure, measure and measure.......keep us informed.

BTW 2.7 RACER had a textbook explanation of the timing process.....kudos

All six exhaust valves were bent... but not by very much. I finished the session on the track and thought I'd dodged a bullet. The car still ran and even made good power, but didn't want to idle.

LeeH,
I was going thru the posts, looking for information. Do you happen to know what your deck height is?

+1 on 2.7Racer's writeup.

Can't be sure about the deck height. Since no dimensions shoud have changed on an engine that ran like a top, I didn't go out of my way to get an accurate measurement. I did use my vernier caliper to measure from the top of the cylinder down to the edge of the CIS piston and got 1mm, but didn't think this was a valid way to measure.

EDIT: Didn't read the whole post...

Chris - you might not have read the entire thread, but I've got piston to valve interference when set at 2.1mm.

Lee,

Beware of the clearance measurement with the rocker screw method. The minimum clearance is NOT at TDC. You can use this method but you should check the clearance at a couple of places before and after TDC. The minimum clearance seems to be around 5 to 10 degrees before TDC for the exhaust valve and 5 to 10 degrees after TDC for the intake valve.

The reason for this is that when near TDC the piston hardly moves at all and the valves move alot. As you approach TDC the piston is almost stopped but the exhaust valve is closing rapidly. It's easy to see that in the last degree the piston is virtually still and the valve is moving about .005 inches per degree (as calculated above). So at 10 degrees before TDC the exhaust valve is .050 inches further down than at TDC and the piston is not .050 further down (the distance can be calculated but I don't want to try the math).

Same argument after TDC for the intake valve. If you use big clearances at TDC then this doesn't matter. The numbers specified here and in Waynes book are big enough that it shouldn't matter. The factory manual for the 2.0 engine specifies .8mm (about .034 inches) as the minimum clearance on the intake valve of the 911S. There is no mention of a minimum exhaust valve spec.

-Andy

Andy,

From what I understand, it doesn't matter in Lee's case. If it the valve is touching at TDC, then it is touching. I agree with what you say above, but this is important to rule out a false negative result. Do you agree? Also, Lee has a 3.0 liter SC engine. Thanks! Please correct if wrong.:):)

Thanks Andy... yes, I was aware of this and have been checking the clearance in 3-5 degree intervals. Focusing on exhaust BTDC and intake ATDC.

I spent the afternoon retarding the cam timing. One thing I found was that my valve adjustment technique needed work. I had them set way too loose. I read about the method of measuring the valve lash between the cam and follower and found this was much more precise. After adjusting the #1 and #4 valve correctly I found that what had been a cam timing setting of 1.8mm at Z1 suddenly bacame 2.1mm.

I took a sampling at this setting and found my minimum intake clearance was around .25mm. I dialed it back to around 1.8mm again and still only had intake clearance of around .75mm. My next adjustment brought me to 1.65mm at Z1 and a minimum intake clearance of right at 1.5mm and exhaust clearance of >2mm. I think that's where it's going to stay.

So, at the current setting, the intake valve is open 1.65mm at Z1. My original target of 2.05mm comes up 4 crankshaft degrees after Z1. Are there any compelling arguments against putting it together like this?