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Valve lash - Questions and cam and rockers

I'm in the middle of adjusting the valve lash on my 911 SC for the first time.

My process has been to rotate the crank to the correct timing mark for a given piston, indicating top dead center, and adjust both the intake and exhaust valves.

I use the Kirk Engine Valve Adjustment Tool to get the adjustment close, and then check the lash with .004 feeler gauge. I also check the clearance between the cam lobe and the rocker using the "backside" method using .0025 and .003 feeler gauges.

I've done this for each cylinder, keeping the process consistent. I'm not rushing. I then re-checked each cylinder using the .004 gauge between the rocker foot and valve stem as well as the "backside" method. More often than not, the .003 "no-go" feeler gauge would slip between the cam and rocker indicating the adjustment was loose. I tightened them again, and repeated the process.

Third pass across all cylinders and I'm still finding some loose valves using the "backside" method. I'm wondering if I am missing something, or if I am making a mistake.

The engine in question is a 3.0 with GE60 camshafts and 930 rocker arms. From reading, 930 rocker arms have the standard 1.4 ratio. Do different camshafts change the valve lash specification?

Any guidance is very appreciated.

Old 09-29-2020, 06:45 AM
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What kind of gauge holder do you have? Leave the gauge in place and tighten until you feel some resistance when you TWIST the holder back and forth. Just tight enough so you can get it out with a couple of twists.
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Old 09-29-2020, 07:25 AM
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Thanks John. The Porsche specific holder was out of stock so I ended up purchasing a Starrett feeler gauge holder and bending .004 gauge stock to form an "L".

What I don't understand yet, is how the .003 gauge will not fit between the rocker and cam, then I will rotate the engine over and re-check, and it will fit.

Last edited by Locker537; 09-29-2020 at 07:45 AM..
Old 09-29-2020, 07:32 AM
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Don't know why you need to check backside when you use the gauge in the normal way. Newbies tend to adjust on the loose side, so when you feel some resistance to twisting the gauge, hold the screw from turning, tighten the nut and see if there's still resistance and you can still twist the gauge out. redo if needed. What's a Starrett holder look like?
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Old 09-29-2020, 08:33 AM
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Quote:
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Don't know why you need to check backside when you use the gauge in the normal way. Newbies tend to adjust on the loose side
I wanted a way to check my work. Admittedly, there's so much discussion on the topic that it is possible I'm trying to be too precise in my adjustment.

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so when you feel some resistance to twisting the gauge, hold the screw from turning, tighten the nut and see if there's still resistance and you can still twist the gauge out. redo if needed. What's a Starrett holder look like?



I could buy the Porsche specific tool, but the replacement blades are still backordered.

When adjusted, how should the rocker movement feel? The slightly little click? I would have assumed I was over tightening the valves as I find it tricky to hold the adjustment screw steady while tightening the lock nut.
Old 09-29-2020, 09:20 AM
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The way your gauge sticks out, it's going to be impossible to get a good feel. The 90 degree end needs to be a lot shorter. Just needs to be about the same width as the rocker foot or it's too flexy, and too hard to get it position. Snip with scissors and file off the burr. Same goes with the bend. it needs to be right up against the holder, or again, too flexy. Hopefully the holder gets a tight grip on the blade.
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Last edited by john walker's workshop; 09-29-2020 at 11:51 AM..
Old 09-29-2020, 11:44 AM
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Old 09-29-2020, 11:48 AM
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Thanks John. I appreciate the knowledge and that picture is a helpful reference.

I'll follow up as I make some progress.
Old 09-29-2020, 12:02 PM
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Quote:
Originally Posted by john walker's workshop View Post
Don't know why you need to check backside when you use the gauge in the normal way. Newbies tend to adjust on the loose side, so when you feel some resistance to twisting the gauge, hold the screw from turning, tighten the nut and see if there's still resistance and you can still twist the gauge out. redo if needed. What's a Starrett holder look like?
Isn't that the truth. Did mine for the first time last year, had to redo them this year because they were noisy. Turns out the tightest valve was at the top end of the spec. Better than being tight, but they were likely all fine before I touched them.
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Old 09-29-2020, 01:10 PM
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John,
Thank you again.

I started fresh, following your advice, and finished my first valve adjustment yesterday. I trimmed the gauge as you stated and focused on the feeler gauge having a good amount of resistance. I would be able to twist it as you noted, and be able to slide it back under the rocker with a little bit of fiddling.

I also changed the spark plugs. A couple of the old ones were darker than the others and had a fuel smell. There was also paper towel in the spark plug areas! If I had to guess, maybe someone forgot a spark plug socket and needed an impromptu way to hold the plugs?

I did have wires 5 and 6 swapped when I first started it, but I figured that out quickly. Surprised me given I double checked them. I'm not sure if it's necessary but I will pull plug 5 and 6 to inspect them.

I adjusted the valves because I was hearing a noise, which I put a video in another thread:

Help diagnosing an engine noise

The noise does seem less now, but I still hear something and it sounds like it is coming from the trans crossmember area. I will post another video.
Old 10-04-2020, 06:08 AM
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Quote:
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John, I prefer Dunlop Primetone plectrums for my valve adjusting

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Old 10-04-2020, 06:41 AM
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