Spark plug query

[arcturus]

Hi, two plugs fed from same carb' what could cause this. Champion JC6

[blueosprey90]

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.

[Ron Kwas]

Arcturus;

They certainly look very different...I'd do a compression check first...!

Good Hunting!

[arcturus]

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.

[blueosprey90]

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.

[arcturus]

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.

[blueosprey90]

Isn't this already a new engine, or am I confusing you with someone else?

[mocambique-amazone]

Who did the job on the head George?

Stop to dismantle the engine please.

First step: are all tips if the valves at the same hight over head?
Please measure the hight over all.
Get out Exhaust valve 3 and 2 please.
Post a pic of the valve seat surface. I believe the contact area is waaaaay to with/big. And the valve seats are cut too deep into the head.

Good luck, stay healthy. Kay

[arcturus]

That is already in progress. For my peace of mind I had the pistons out and did a check on rings and they are OK.so I know what it isn't. At this time I have the head on bench and testing for leaks/cracks by filling combustion chambers with paint thinners to level of plug holes and leaving for some time to see if the levels are still equal. Tomorrow I intend to examine the valves and seats which I now suspect are the cause of my problems.I know that the seats were at the limit of wear and hoped to get away with it.The second pic' shows head after grinding valve seats previously.

[arcturus]

So, the chambers after one hour and allowing for evaporation. Number 1 OK. Number two bone dry. number three almost dry number four better but not as good as number one.Will strip down tomorrow. Who does exchange re con' heads for B16b? Hope it doesn't come to that.