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ayglass 10-30-2006 07:03 PM

Average valve adjustment interval?
I am looking for some input from the group on valve adjustment interval. My '86 turbo apparently wants it's valves adjusted again after only 4500 miles. Today I noticed a single ticking valve on the driver's side, probably exhaust.

When I purchased the car I drive it from Arizona to Georgia and noticed it ticking when I arrived home. I carefully adjusted the valves at that time. (about 4500 mi ago) and noted that the intake side of the driver's side was the source of the noise. Following the valve adjustment it was quiet until today.

I dare not ignore it because as sure as I do, a non-ticking valve will be tight and I will burn it. I don't take the car out on less than 30 minute trips and most are longer. I am careful with the temperature cycles as it's still running Dilivar studs and I don't want to rush their demise. The total mileage is 108,500 and the top end was rebuilt around 98k. Why they didn't replace the studs at that time I can't tell you.

I expected somewhere between 8k and 10k miles between adjustments, so I'm wondering if my expectations are wrong. I'll certainly adjust them before driving it again, but as I don't remember my '77 S wanting it's valves adjusted quite this often I thought I would ask. Are Turbos harder on valve adjustments?

Ideas gentlemen?

AFJuvat 10-31-2006 04:02 AM

"By the book" a 930 or 911 should not require valve adjustment more frequently than every 15K miles. Track cars get adjusted a bit more often - normally every 5 - 10K miles.

If you have valves loosening up significantly before that, I would suggest the following:

1. Redo the valve adjustment, making sure that the feeler gauge is well oiled before adjusting each valve. Make sure that the jam nuts are not and have not previously been overtightened. If they have, you should replace the jam nuts (they are about $1.00 each).

2. Make sure that your rocker shafts are not "walking" in their bores. A walking rocker can seriously throw off a valve adjustment. If they are, put them back in their correct position and tighten them down, then readjust the valves.


Porschephd 10-31-2006 04:53 AM

Typically the issue is the feet on the adjusters of the rockers. Cars that have been driven hard or not seen regular adjustments will beat down the center of the adjuster. When you go to make your adjustment you feel the outer edge of the foot rather than the meat of the adjust hence giving a looser adjustment. Also wearing guides, beat valve stems all will cause premature wearing.

sand_man 10-31-2006 04:54 AM

And you are checking and adjusting these valves cold, right? As for the frequency, it should be 15,000 miles...unless you have just undergone a rebuild, in which case you should check the valves (adjusting as needed) maybe a couple times within a 5,000 mile period before settling in for the 15,000 mile duration.

sand_man 10-31-2006 04:55 AM

give the "backside" method a shot for your next valve adjustment...I plan to:

ayglass 10-31-2006 03:25 PM

I am going to go with the assumption that since I'm less than 15k miles into the top end rebuild that I'm just readjusting because things are breaking in. I will look over the rocker shafts and adjustment parts. I have ordered a few extra parts in case the same valve is loose as was loose last time. Thanks for all the information. I will let you know what I find after I crack it open this week.

Porschephd 10-31-2006 04:50 PM

Please keep us posted.

ayglass 11-04-2006 11:24 PM

Here's the summary so far:

Number 2 exhaust was the loud one. I needed over 1/4 turn to get it back into spec. If I remember correctly it was number 2 intake that was loose the first time I adjusted the valves. (loose enough to hear anyway)

Number 6 intake and exhaust were both a little tight (maybe 1 thousandth)

Number 3 intake was a little loose.

From what I can determine from the records on this car this is the second valve adjustment since the top end rebuild. Though I am slightly paranoid about toasted valves, I am going to chalk this one up to break-in. I awarded #2 exhaust and a couple of the other adjusters new lock nuts as they were very tight or a little beat-up from previous adjustments.

I did adjust cold, check the rocker pivot shafts (this time anyway), and I was careful about not overtightening the lock nuts. I'm going to keep my fingers crossed that everything holds together and that I can get a few more miles on this adjustment.

Your suggestions are very much appreciated. Thanks!

ayglass 11-05-2006 02:38 PM

Like all good first run movies, there's a sequel. I drove the car 50-100 miles last night and today. The ticking is gradually getting worse again. I got out the automotive stethoscope and isolated it to exhaust side near number 2. This means that number 2 changed after I adjusted it and re-checked it. Is this the point where I start replacing the foot and/or the pivot shaft? I'll have to take it apart again to recheck the adjustment, but the odds of a mistake in adjustment hitting 1 out of 12 twice in a row are pretty long odds.

Any suggestions on what I should take apart to insure I find the problem here? It still runs fine, and I have played in the boost, so I hesitate to call it "carbon on the valve seat".


ayglass 11-05-2006 02:42 PM

Oh yes... and this might be a clue. It's not consistently loud. I get louder and softer from time to time regardless of RPM. Temp is an unknown factor at this point because I haven't been through that many cycles. I was struck by the fact that it wasn't noticable at one stop light, then became noticable at another one. If this was a Chevy I would be tempted to feed it some water/carb cleaner in a effort to "decarbon" the heads. I'm going to go off and think about this for a while....

ayglass 11-06-2006 09:49 PM

Ok, this is beginning to look like a diary. Any input is greatly appreciated.

I popped her open again tonight and sure enough #2 Exhaust is loose. It was very loose and the lock nut was still tight. I backed out the adjuster and felt the elephant foot and the top of the valve - both smooth. Put a finger on the cam lobe (some texture, but not enough groove to feel with a fingernail). The rocker moves back and forth a little on the shaft, but it will not deflect up/down like a worn out shaft or rocker. No cracks visible.

I didn't dare take the pivot out, but I adjusted the valve again about 4 times checking, rechecking, etc. Buttoned her up, started the car and it sounded perfect. I guess I'll have to blast through the national forest for a while and see if I can troubleshoot with the lead foot.

NOTASIX 11-07-2006 04:39 AM

Wow, Cleveland is growing...

You are probably within 10 miles of Aircooled Heaven and didn't even know it.

I'd be willing to looak at it for you, I work primarily with Vintage engines, but I can still diagnose the issues for you....

ayglass 11-07-2006 05:47 AM

Hey Jake,

Mark Keck and his son Pete have both mentioned your work. They both suggested that I drop by and take a look at the engines you build. I've met some of the most interesting people here in Cleveland. Thanks for the offer. I'll come by and visit.

911rudy 11-10-2006 03:19 PM

You probably already know this but you are also just a few miles from GAD, (German Auto Dismantlers). They just moved up the road near you. They are great people to work with. I just take my tools and go remove what ever I need and then pay for it.

ayglass 11-10-2006 03:46 PM

Hey Rudy,

I have met Joe already. He's been great. He saved me quite a bit when I replaced the oil lines. (one of the P.O.'s apparently owned a floor jack). I haven't tried bringing my tools, but he did let me wander around in the warehouse a bit. It's good to know that I can scavenge small parts myself and give him cash when I find them. I feel a little guilty pulling him away from an engine sale for a trim ring. Nice to meet you!

The update so far is that there is some "valve-like" noise at some RPMs (around 1500 to 2300) but at idle I just hear a little piston slap or maybe chain noise) I don't want to take it open again for nothing so I am driving it a little and listening. I guess I will eventually stop suspecting sounds I hear, but it's hard not to worry. It's been a long time since my last 911 and I don't have a good ear for normal any more.

ayglass 11-13-2006 09:50 PM

The problem is now supersized...
Well, after about 100 more miles it didn't sound right. Idle was better, but 2500-3500 rpm sounded like it had a loose valve. After reading some posts about valve springs I opened her back up to check. The valve spring strength on #2 compares favorably with #3 so no problem there.

Then I began to suspect something with the rocker, shaft, or foot. I took them out and bingo! The cam lobe is worn and the rocker has an "interesting" profile. New guides and a valve grind was done about 2 years ago. There is a charge for "make piece for back of cam" which I believe was when he installed the 911SC cams.

I don't think there have been a lot of miles since that time as a month previous there were 90k miles on a reciept. There are currently 108k miles on the car.

So here's the big $$$ question. Where do I go from here? If the cam is lubricated by a faulty sprayer then I need to check/fix it. I don't know what the chances are of a single bad lobe on these cams, but not knowing the origin of the cams I am concerned.

Given that the rocker has a double cup profile now I suspect that one cup is the original cam's life and the second one was the SC cam wearing down. What else should I think about replacing when I go in to take care of this? The can of worms is now open...

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