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PV, 120 (Amazon), 1800 General Forum for the Volvo PV, 120 and 1800 cars |
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Spark plug queryViews : 872 Replies : 13Users Viewing This Thread : |
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Apr 2nd, 2020, 13:25 | #1 |
arcturus
Last Online: Today 08:17
Join Date: Mar 2006
Location: Sagres Portugal
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Spark plug query
Hi, two plugs fed from same carb' what could cause this. Champion JC6
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life's too short to drink bad wine Last edited by arcturus; Apr 2nd, 2020 at 13:34. |
Apr 2nd, 2020, 13:55 | #2 |
Master Member
Last Online: Today 13:36
Join Date: May 2017
Location: New Milford, Connecticut
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My first guess would be oil in the combustion chamber. Perhaps worn/defective valve guide or defective valve oil seal (assuming our valves have these). Check on the intake side on the theory that oil is being sucked into the chamber.
My second guess would be rings. My third guess is to question whether the plug is firing. Maybe you are running on 3 cylinders or two plug wires are reversed. If the car is running and you pull the plug wire off the plug, do you notice any difference in how the car runs? In addition to pulling the plug and connecting it to the plug wire and laying it on the engine block to see if it is firing, you can also put a timing light on the wire and look at the light to see if there is induction. |
Apr 2nd, 2020, 16:20 | #3 |
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Last Online: Today 11:51
Join Date: Jul 2007
Location: Connecticut, USA
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Arcturus;
They certainly look very different...I'd do a compression check first...! Good Hunting! |
Apr 4th, 2020, 12:05 | #4 |
arcturus
Last Online: Today 08:17
Join Date: Mar 2006
Location: Sagres Portugal
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Compression fine,equal on all cylinders,10bar hot cold. As I can't see any possibility of using PV for foreseeable future due to cov19 decided to pull engine and examine in detail. Head off and ready for examination. At first inspection bores seem OK but will strip down and check every thing.
The unusual thing was the car ran well on the road ,better than previously But needed about 1000 rpm for tick over and rough. I pulled each plug lead in turn with engine running1-2-4 were fine,engine started to splutter but when I pulled number three there was no change,ran the same with or without lead connected! Changed in turn plug, lead and dizy cap. made no difference at low speed. Checked plug for firing in the usual way and there was a spark, So it seems number three was not working at low rev's but from on the road driving fine.
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Apr 4th, 2020, 14:11 | #5 |
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Last Online: Today 13:36
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Location: New Milford, Connecticut
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Perhaps too hasty on pulling the engine.
I had my MG on track but had no power above say 3,000 rpm. New engine so I thought cam timing was off. I came into the paddock to investigate and the guys in the next spot say: "you have a misfire". I deny the claim, accusing them of trying to mislead me from my cam timing analysis. It was an outrage! Then a mere passerby - I mean, I guy who has nothing but an ear - says "no, you have a misfire". I again deny the claim but I can't really feel any difference when I pull plug wires, but eventually, by default in other causes, I sadly agree. I cleaned the cap to wire contacts and the wire to plug contacts and solved my problem. Probably just a bit of corrosion on the contacts. Maybe also check/examine where the tip of the rotor makes contact under the cap. Due to "slop" in the distributor drive, the rotor may run in a very slightly different plane at low and high speeds. But if you are running fine at top speed, with plug firing, I think it would burn your plug clean. My guess is that you are still misfiring at higher speeds. So when you reinstall the engine, with the set screw, get the engine running fast, then try pulling the plug wire again. The mass of the engine rotating may be giving you a false sense of running smoothly. Just my 2 cents. Good luck hunting. |
Apr 4th, 2020, 15:08 | #6 |
arcturus
Last Online: Today 08:17
Join Date: Mar 2006
Location: Sagres Portugal
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Any way,a good chance to inspect the engine. Number two and three cylinders which looked suspect,I thought perhaps a broken ring, but all OK Whilst I am at it I will check 1 and 4. I am beginning to think that the problem lies in the cylinder head looking at the valves. Will take out valves and check. Got time on my hands with the cov19 lock down. Dizy and rotor are fairly new.Wondering if a problem with valves was spilling pressure into block causing the excess oil drip from breather.
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life's too short to drink bad wine Last edited by arcturus; Apr 4th, 2020 at 15:54. |
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