Identical low compression on 1 & 3 only - coincidence?, Peeling back the 914 revival onion Options

[jrmdir]

Hi everyone:

Well, trying to save this 1.7 is just as much of an adventure as I thought (feared?) Last weekend I was stoked that I finally got it started after 3 years of PO neglect and was able to actually drive it. Now of course I'm learning all about the many things that keep it from running well. Seems as if I have a common set of FI revival issues including high idle, very rich mixture and stumbling.

So after a crash course on the many informative threads on this forum, it seems I need to rebuild the MPS - and no-doubt the TPS is also messed up. Not to mention a lot of sketchy looking vacuum hoses.

But while getting deeper into diagnostic mode I decided to check the compression. Since it runs and idles smoothly (except for the stumbles), pulls pretty strongly and isn't blowing smoke I expected no big surprises, but was wrong! I'm getting a reasonable 124 on both 2 and 4, but only 80 on 1 and 3. I know I need to adjust the valves and recheck when warm, but these readings seem so symmetrical and so far apart I don't think those things will make a big difference.

Again, I've read a number of threads here on compression but I'm still hoping I'm missing something about the 1-3 and 2-4 situation. Any thoughts on why the rear two cylinders might not be sealing after sitting for so long? I've only driven it for about a half mile so perhaps it will get better after re-breaking in?

Thanks in advance for any ideas.

Ron

[bzettner]

Adjust your valves, cold, (1.7 = 0.006" tappet clearance on both exhaust and intake valves) then recheck compression once the engine is warmed up. I'll bet you'll see an improvement. (IMG:style_emoticons/default/beerchug.gif)

[sixnotfour]

Doesnt 1 and 3 use the same lobes on the cam ?? maybe worn ? low lift ?

[flyer86d]

Doesnt 1 and 3 use the same lobes on the cam ?? maybe worn ? low lift ?

I have seen that more than once. Big clearance on opposite valves.

Charlie

[jrmdir]

Thanks everyone. I'll recheck and report back. Fingers crossed.

Ron

[mlindner]

I bought a 911 long block years ago, it had sat for a long time. Did leak down on it and 30 to 40 percent leakage was on all cylinders. Could hear air both past valves and rings into the case. After rest of engine assembly and run in the cams, leak down was now down to 4%. All good, just some rust on valve seats and rings not set. Best, Mark

[jrmdir]

Whew!

Thanks again for the great advice. Adjusted valves and rechecked after warming up and all is well. Not over the top perfect but all 4 are at or over 130 and reasonably close.

Now, on to the next revival challenge! (IMG:style_emoticons/default/beerchug.gif)

Ron