Lee,

I don't think you should do that. Why would you install a specialty high performance cam like the Webcam 20/21 so far out of spec? 1.65 is way off of 1.80 mm, or 1.95 which is actually the goal time. Sure, if you retard the cam far enough, sure you will find a point where your intake clearance is >1.5 mm. But you will lose performance. Not to mention it sounds like there is something wrong with your engine as it is. I would think that if you are trying to avoid an expensive rebuild, at least put in a milder cam that you can install properly. Like a stock SC cam. You can sell your 20/21's off to recover some of the cost. Just my 2 cents.

If at first...
 

lee,

Sorry to see you are still at this, I was hoping you nailed it with the last round.

Just to throw a few more wrinkles in to continue your living hell of a cam timing project.

You bent the valves, so you got new ones, it could be that when the new valves were cut they were not set deep enough in the valve seat, and with a higher deck height you have one, or more that are starting with reduced clearances right from the get go.

When the new valves were set in did the shop check the thickness of the valve relief? You can be a bit sloppy with a factory grind on a CIS motor but with an aftermarket cam all bets are off. I don't know who you used but they may not have checked.

It's hard to say if there is any consistency to the stem length but you might measure the installed height of the spring retainer to the head and compare it for any wild variance. If the valve seat height of the #6 exhaust is considerably shorter that the rest, then I think you have your culprit.

Anyway let me know how it shakes out, I'll be stripping out the rest of the goo in the racecar, I can run out and give you a second set of eyes if you like, drop me a pm. Keep up the good fight!

Later

jim

Thanks Jim... DJ from Don Jackson gave me the name of the machine shop he uses. I'm sure they've done their share of Porsche heads over the years. As the owner of the machine shop put it, "We did work for Don, and that meant we'd better get them right the first time."

I think any prior incosistencies were with my valve adjustments.

Hmmm... Then NOT so simple. Sorry for the glib response. :(

With many cams advancing it gives more torque, retarding it gives more HP (gross simplification). The standard SC spec is around 1mm lift. at 2.1 you've got 1.1mm more lift at TDC. That doesn't sound like much clearance over the stock cam actually... I wonder if there is something else going on. I'll noodle on this.

I think folks here are ont he right track... The webcam 20/21 grind is widely used in the SC engine without trouble or interference, so this means that something in your engine ain't quite right. Some thoughts..

1. Your valve timing method is flawed? (Sounds like you have it though)
2. Your dial-indicator isn't set right or is placed in the wrong position (you're on the valve spring keeper right?)
3. TDC mark is off?
4. Heads have been shaved a lot... Or deck height is too low?
5. New valves out of spec or not seated properly...
6. Faulty cam?

Basically what's happening is that your valve is opening too much, or your piston is higher than normal in relation to the head. Something caused this and we need to find out why.

You said you overrevved... How bad? Did you replace the rod bolts as a result? Was there any machine work on the heads or cylinders?

(subscribed)

Chris,

Valves were just barely bent. I don't know the exact rpm that was reached. It was just a split second visit to 2nd at 80 mph. P&Cs stayed in place during the rebuild and nothing was machined from the heads. Heads were reassembled using the same intake valves. In theory, the engine has the same dimensions that it did when I was out running even with Boxster Ss, and stripped 3.2 Carreras at the track.

Low deck height is my guess...

What would happen if these were actually stock cams instead of 20/21s? Would setting the stock SC cams to 2.1mm result in any clearence issues?

Original Question
 

Lee,

Let me know how it works out, hopefully it's just your valve lash technique being off a bit.

To answer your original question about the timing card, it is for a more detailed and precise way of timing the cams. I've done this on a lot of ford motors but not on a 911 because the factory's process is a simplified version of it, but the technique is the same:

Go down to the race shop, Lopers etc.. and get a timing dial, basically an aluminum disk with the full 360deg timing marks all the way around it. it comes with a little alumn pointer that you bolt to the case to mark tdc (z1).

Preliminarliy adjust the cams straight up per factory tech.

put the dial guage on and adjust your lash to zero on number one.

Turn the motor until you reach the specified lift of .050 on the dial guage, the timing disk should read the specified lift on the timing card, if not adjust the cam sprocket until you have the proper timing.

Continue to turn the motor and check the full duration of the valve opening, it will be "closed" when the dial reads .050 on the back side of the lobe.

For serious race motors this is the way you check each valve (including exhaust), on each cylinder, and you can average the timing between each cylinder by advancing or retarding the cams.

Porsche has simplified this process, but it assumes everything is per factory specs, so this is just another way to confirm everything is cool.

Most cam manufacturers, I don't know about web, make recommendations for advancing or retarding cams to shift the power range, advanced low end, retard for higher rpm power. You might chat with them. I don't have it handy at the moment, but I think bruce andersons book talks about his attempts at ad/ret cams for adjustment of the rpm ranges, and he didn't get much out of it, but he did give a range, you might check it.

Anyway good luck, everyone's pullin for you...

jim

Lee,
When measuring deck height, measure directly above the wrist pin area on the piston's edge to minimize any error induced by the piston rocking in the bore when it is either in an up stroke or down stroke. If your deck height is 1 mm, I would think you are spot on.
If your deck height is anything less than that, you may have to remove your cylinders to remove the spigot base gaskets and use a greater thickness.
You don't happen to have a picture of the piston crowns that are in the engine that you can share with us? Just to rule out any possibility of another type of piston in there.

Thanks. Those are definitely CIS pistons.
I don't know how you are going to get accurate deck height and/or valve to piston clearances until you de-carbon the pistons. Also, you may want to grind/polish down the valve marks left on the piston tops to prevent any possibility of pre-ignition when the engine is under high loads. Of coarse, all these steps require removing the cylinders, not a popular choice, I know. :(

I cleaned them up a bit in place. One of the many mechanics I've talked to suggested bringing each piston to TDC and using a wire brush -taking care to cover everything and vaccum, wipe etc. afterwards. He described this as something he'd never do to a customer's car, but might do to his own in this situation. Originally I was going to leave the carbon undisturbed, but over time it got looser and flakier being exposed to the air.

Lee,

If you have loose carbon floating around it could cause some trouble. Getting just a little bit between a valve and seat will hold the valve off the seat and have the same effect as the valve problem I outlined before. This is a common source of compression and leakdown test errors on 911 motors. Get out the compressor!

jim

Lee

And the saga continues.....reading the latest posts something came to mind.

Since all the exhaust valves were replaced:

Are they the correct lenght for the application?
Has the spring height been set correctly?

The answer is probably yes, but at this stage everything is questionable. I have a degree wheel that I can loan you if you want to abolutely check the cam specs and validate your set-up.

I wished that I lived closer to you and would come over to help....hey, maybe you should see if there are some helpful Porsche afficionados that might be willing to come over and lend you a hand.

That motor needs to be put back together and please. please let us know what was the problem.

Al... I'm really thinking this is an issue with deck height from the previous rebuild. But, short of tearing the entire motor down and measuring every spec I'm not sure this will be confirmed. My approach right now is that this motor ran great and was super strong before. Nothing I did should have changed any internal dimensions. Chances are the person who built the motor retarded the cam timing or they would have had clearence issues also.

So, in a grand experiment (or roll of the dice - depending on your point of view) I'm going to put it back together and put it in the car. The way it's currently set up there should be no danger of interference. Absolute worst case scenario is that it won't make as much horsepower as it could. In a previous post I mentioned that the current setting is 1.65 mm at Z1 - the high side for stock SC cams, but below 20/21s. At the current setting it's only 2.5 degrees of crankshaft rotation from where it should be. I'll certainly report back when it's in the car.

Best of luck to you....keep us posted.

The engine went in today. There was a few minutes of panic when it didn't start. One of the many Pelican's on hand, DonDavis noticed that one of the spark plug ground straps was touching the coil's power terminal. Once that was corrected it fired right up. It runs great and seems to make excellent power. Thanks for all the guidance and input!
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Wow, that is great! I was holding my breath. I hope I have as much success with my first engine reinstall this spring.

Congratulation! I love it at the end of the video when you say "Oh Yeah."

That's DonDavis who said, "Oh yeah." Don put a 3.2 in his '72 last year and had a fair amount of trouble getting it running. I think he was as relieved as I was that it started.

There's no better feeling... Congratulations!

That wasn't me, it was the Kool-Aid monster,
no wait, it was the guy from the Ferris Bueller song....

ok ok it was me and Chris, you are correct, sir. No better feeling!!

It was a great time yesterday, Lee, and even better when it started.http://www.pelicanparts.com/support/.../pimpflash.gif

For a bunch of yahoos, I think we did pretty good. We actually began work at what, noon? And it was in and running by 4pm. Plus, there was a lot of standing around and yappin' and whatnot.

We need to do a drive to Prescott/Sedona sometime soon!

Lee,

Sweet... I'm glad it worked out, see you at the next Pclub event...

jim