Difficult to change spark plugs in C4??

Brian:

A compression test is one way to measure the general health of your engine, by deterimining how much compression it actually produces in each clyinder. Good cylinder compression generally indicates healthy rings, valves, and valve guides.

It's any easy procedure. Remember that I do not yet have the manuals, but this is how I did it:

1. While the upper spark plugs are installed, remove all of the lower plugs.
2. SAFETY NOTE: Remove the fuel pump relay so you don't spray atomized fuel everywhere during the procedure.
3. Install a compression gauge into one cylinder at a time, by threading it into the lower spark plug hole. (Because of the location of things, spend a little extra for a quality gauge (like, $40) that has a quick connect fitting where the gauge meets the hose.
4. After it is snuggly installed, rotate the engine using the starter motor, making sure the engine rotates at least 2-3 times.
5. Read the gauge, then move on to the next cylinders.

This will seem obvious but Don't forget to disable the ignition system or disconnect the ignition leads from the upper plugs prior to cranking.

Don't ask how I learned to double check this!

Bob
90 C4

Oops.

Add Step 2.b. SAFETY NOTE: Disconnect both leads from the coils to the distributer caps.

Thanks!

Gentlemen,

You don't have to use a metric dial indicator ... as long as you DOUBLE-CHECK ALL OF THE mm-to-INCH CONVERSIONS TWICE! It wouldn't hurt to do your conversions in a spreadsheet and print the results for quick reference, or for entry into your spec book, in the margins!

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Warren Hall
1973 911S Targa

Good point Warren. Double, triple, quadruple check things if you have to. In knowing my limitations, I understand that haste and over-confidence are the things that will eventually make me do something stupid.

On the dial indicator - my problem is the few tough to reach valves, especially the number 6 intake valve hiding under the power steering pump and the number 3 intake valve just because of how long you're bent over at a bad angle. I invariably spend 5 minutes just trying to get that feeler gauge in there, and another couple getting comfortable with the fit and measurement reading. Would the dial indicator make this process easier - of course, understanding that it would only be a "luxury" item for valve adjustments? Also, would it be more precise than the human determination between "slight drag on the blade" and "moderate friction"? Thanks.

Steve:

Out of curiousity, what did you get for your compression readings? Also, why use the upper rather than lower plugs .....easier access?

TIA,

Bill Wagner

Compression:

Front of car
3. 170 6. 185
2. 170 5. 175
1. 170 4. 170

I felt the bottom plugs were simply easier to access while the vehicle was on the jacks for the valve adjust anyway.

I don't have a spec book, so I don't know what the actual compression should be. Assuming they are within range, the only concern I have relates to No. 5 (broken stud is top, forward (front of car)) and No. 6 compression. Since my understanding is that the heads are independent, perhaps there is some leak by through the valve guides??

[This message has been edited by sms1305 (edited 03-04-2001).]