 Identical low compression on 1 & 3 only - coincidence?, Peeling back the 914 revival onion |
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| jrmdir |
 Jul 4 2021, 01:31 PM
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#1
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Member  Group: Members Posts: 224 Joined: 13-May 21 From: Central Ohio Member No.: 25,544 Region Association: Upper MidWest 
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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 |
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Replies(1 - 6)
| bzettner |
Jul 4 2021, 02:46 PM
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#2
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Member Group: Members Posts: 211 Joined: 2-June 13 From: San Antonio, TX Member No.: 15,951 Region Association: Southwest Region |
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)
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| sixnotfour |
Jul 4 2021, 03:08 PM
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#3
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914 Wizard Group: Members Posts: 10,436 Joined: 12-September 04 From: Life Elevated..planet UT. Member No.: 2,744 Region Association: Rocky Mountains 
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Doesnt 1 and 3 use the same lobes on the cam ?? maybe worn ? low lift ?
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| flyer86d |
Jul 4 2021, 03:15 PM
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#4
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Member Group: Members Posts: 429 Joined: 12-January 11 From: Corea, Maine Member No.: 12,585 Region Association: North East States |
QUOTE(sixnotfour @ Jul 4 2021, 05:08 PM)  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 |
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| jrmdir |
Jul 5 2021, 07:09 AM
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#5
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Member Group: Members Posts: 224 Joined: 13-May 21 From: Central Ohio Member No.: 25,544 Region Association: Upper MidWest
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Thanks everyone. I'll recheck and report back. Fingers crossed.
Ron |
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| mlindner |
Jul 5 2021, 07:51 AM
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#6
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Senior Member Group: Members Posts: 1,529 Joined: 11-November 11 From: Merrimac, WI Member No.: 13,770 Region Association: Upper MidWest
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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
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| jrmdir |
Jul 12 2021, 08:38 AM
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#7
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Member Group: Members Posts: 224 Joined: 13-May 21 From: Central Ohio Member No.: 25,544 Region Association: Upper MidWest
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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 |
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