 Relation between bad spark connection and lower compression? |
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| john_g |
 Apr 6 2013, 07:02 PM
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Member  Group: Members Posts: 110 Joined: 1-November 12 From: british columbia Member No.: 15,100 Region Association: Canada  |
Hey, guys, I'm curious about an interesting coincidence. My latest 914 is relatively new to me. When I purchased it, I noticed that it missed significantly at higher revs, especially in the lower gears. The owner said that it there was a rev limiter in the electronic ignition, but I knew that was BS because I removed the dizzie cap and saw that it had the normal rotor w/o the rev limiter, and also because I never ran it even close to the red line. The other issue I noted was that the #3 cylinder's compression was significantly lower than the other cylinders, but of course I assumed these two issues were unrelated.
When I got it home I found that the spark wire connection at the distributor cap for the #3 cylinder was very poor. As soon as I replaced the spark wires the problem of the engine missing stopped. This has got me thinking. Obviously, from what the PO said, the missing (and the bad spark connection at #3) had been going on for a while. Is it possible that running the car for a long time w/ poor spark at one cylinder could lower compression, through incomplete combustion, unburned gas, etc? And ... if the cylinder and valves are gummed up from this, could I expect that the compression could increase after some lengthy drives and cleaner combustion? |
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| flash914 |
Apr 6 2013, 11:18 PM
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Member Group: Members Posts: 124 Joined: 1-January 11 From: littlerock CA Member No.: 12,554 Region Association: Southern California |
Yes and No. The term is ring wash. If the unburnt gas end up diluting the oil on the cylinders it becomes metal to metal and the rings/ cylinders go away. A miss like this or a over rich carb can also cause this. Give it some time and it may come back around or? Gordon
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| john_g |
Apr 7 2013, 12:18 PM
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#3
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Member Group: Members Posts: 110 Joined: 1-November 12 From: british columbia Member No.: 15,100 Region Association: Canada |
QUOTE(flash914 @ Apr 6 2013, 10:18 PM)  Yes and No. The term is ring wash. If the unburnt gas end up diluting the oil on the cylinders it becomes metal to metal and the rings/ cylinders go away. A miss like this or a over rich carb can also cause this. Give it some time and it may come back around or? Gordon Thanks. Actually, that's what my first thought was - that the rich mixture would dilute the oil and cause wear - which isn't good and isn't reversible w/o a rebuild. Nevertheless, I'm going to monitor it, run it, change oil and adjust the valves more frequently in the hopes that I might clean things out and have some improvement. The compression in #3 is currently 115. |
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Posts in this topic
john_g Relation between bad spark connection and lower compression? Apr 6 2013, 07:02 PM
jcd914
Yes and No. The term is ring wash. If the unburn... Apr 7 2013, 12:53 PM john_g
[quote name='john_g' post='1846574' date='Apr 7 2... Apr 7 2013, 01:38 PM jcd914
[quote name='john_g' post='1846574' date='Apr 7 ... Apr 7 2013, 02:51 PM john_g
[quote name='john_g' post='1846598' date='Apr 7 2... Apr 7 2013, 09:27 PM r_towle It's not terribly hard to re-ring these motors... Apr 7 2013, 05:12 PM |
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