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Registered User
Join Date: Feb 2003
Location: Georgia
Posts: 36
Exclamation Valve Issues = low compression when warm?

I'm new and my 914 is older than I am. I've posted recently about having a little (500rpms - 100rpms) idle when warm. The car starts fine cold. Had valve adjustment done by a professional. The car ran perfect before they touched it but now has problems. I've looked at my "new" and "$$$" fuel injection system (Tank to injectors) and have come to a conclusion it has to be a valve problem. The mechanic said, after the recent adjustment, cylinder 3 & 4 had its valves "3-4 treads" tighter than cyliners 1 & 2. Now, the timing was also adjust along with the dwell. By having a problem with vavle 3 & 4, would this cause a problem with idle compression when warm? Would this also clarify the loud tapping I hear on cylinder 4?

With this said, what is the best way of going about fixing this problem of vavles having a chronic tightness? Should I have a complete engine rebuild (I still read of vavle problems 100 miles after) or isolate the problems to just the intake and exhaust vavles? Can this be done with the engine in the car? In doing so, would it be a good idea to go ahead and replace all the rocker springs, push rods and tubes, etc, etc? What else would I have to replace? I'm clueless since I'm use to successfully tracking down air leaks and common fuel injection issues.

All of this is in theory w/out a compression test but I think there will be a "rebuild" of some kind when the compression test is done. Sorry for the long and saturated topic but I've spent hours trying to fine some insite, and have, but still have questions.

I've put a messured 3,500 miles on the car since January of this year with no problems. Fill the tank up and drive. Did it for 3.5 months and the stress went away about the car. Now its back. It just doesn't make any since but what on this car does? Still love it but the wife hates it. Sounds familiar?
73- 914 1.7
01 New Beetle 1.8t w/an attitude
Old 04-20-2003, 10:30 PM
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Jim Smolka's Avatar
Join Date: Aug 1999
Location: Hickory NC USA
Posts: 2,491
Since you are in GA, how close are you to another wrench?
I would find antoher wrench to adj the valves, unless it is someone like Jake.

Another approach is to learn to do your own valve adj.

Simple things first
'75 914-6 3.2 (Track Car)
'81 SC 3.6 (Beast)
'993 Cab (Almost Done Restoring)
Old 04-21-2003, 03:06 AM
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norustscott's Avatar
Join Date: Jun 2000
Location: sykesville, MD
Posts: 912
I would be highly suspect of anyone who describes a valve adjustment as " 3-4 threads tight". On a stock adjuster that would equal something like .100". Way too tight, as in valve is propped open and never shuts. I would run from a mechanic that describes the adjustment as such. He/she should be speaking in thousands of an inch as in .006".

Lets assume he meant .003-.004" tight. With a valve adjusted cold to .003" you could get a tight valve when hot. Tight to the point of poor compression, yes. At idle the engine will run rough. almost like a miss. Rev it up and it might smooth out, but not much. Easy to check. run a compression test. A cylinder with a tight valve will have less than the others.
An engine in good condition, you would expect to see 135 or better psi. On a cylinder with a tight valve, I would expect to see 90 psi or worse even 35 psi or zero depending on the open clearence.

Now, If you don't have a compression tester, let the engine idle, if it is running rough, start pulling plug wires one at a time. you should hear a change when the plug wire is removed, a drop in rpm and an even rougher idle. If not that cylinder is probably the tight one. If it is a tight intake valve, then you will find a black soot coated plug, while the others will be clean.

If you have hydrualic vavles...this is a diferent story. The "Thread" description holds a little more water, Hydro are adjusted hot...1.5 to 2 turns past contact with the valve stem....the noise could be a bad hydro lifter not pumping up. Once the correct hydro adjustment is made, the lifter may have too much clearence...We can go further into hydro details if this is the case.

Better yet, print out the pelican parts how to adjust your valves article and tackle the job yourself...nothing bonds you to an aircooled engine like adjusting valves...An gives you total peace of mind...

Vavle noise is typically form a Loose senario. .008" and up will have a diffinitive clicking rather than the plesant "sewing machine" sound. A tight valve is really quiet...

1982 911 SC
1962 sunroof bug
1991 WE Vanagon CARAT WRX conversion
Old 04-21-2003, 06:30 AM
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Registered User
Join Date: Feb 2003
Location: Georgia
Posts: 36
Thanks for the information. I have found a local wrench after years of trial and error. This wrench DIDN'T set me up for all the non important "tests" and a $800 bill just to adjust the valves like the previous famous ATL wrench. The previous adjuster even said those 2 valves were tight when they made adjustments. It also had problems when the car warmed up by having no idle. At the time, they retimed it to make it run. Today I dropped the car off to my newly found wrench in ATL. They are part of the Porsche club of N.Georgia. Ive heard nothing but good things so far.

I've made my mind made up to have the engine rebuilt. That little voice in the back of my mind keeps telling me to rebuild. The car has unknown mileage. Its best to replace all worn parts, grin and bear the bill and ride on with the top off.

Before I made my mind to rebuild, I pulled the plugs on all cylinders and all were caked in carbon. I didnt have a compression guage but the car's idle wasn't there when warm. The starter is pretty tired by now!

I hope this rebuild will take care of this problem. If it does, I'm going to attempt to adjust the valves. I've gotten to know everything about the car except for the engine. Thanks again for all the information. I seems that idle problems aren't always related to sensors, hoses and such going out. Thanks again.
73- 914 1.7
01 New Beetle 1.8t w/an attitude
Old 04-21-2003, 08:32 PM
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