1 out of 4 Spark Plugs Looks Odd. Ideas?

[svenedin]

I was checking the gap on my spark plugs today. 1 plug (cylinder 3) looks different to the others. The plugs have probably only done 1,500 miles and are standard NGK plugs. 3 of the plugs look normal, 1 looks pale as if the mixture is too weak and the plug got too hot. I had noticed this same plug looked like that about 500 miles back when there was a very subtle misfire on that cylinder. At that time, the gap on that plug was mysteriously far too small and I corrected it. The misfire disappeared with the correct gap. Now looking again 500 miles later that plug still looks odd.

The car drives fine, there is no noticeable misfire, subtle or otherwise. I have swapped the odd looking plug round with the plug from cylinder 1 and will check again in a while. Any ideas? Is it worth me checking the valve clearances? They were done only a few months ago but the car did have a sustained run at high speed (65 mph for 2 hours) and does sound a bit "tappety" now.

Stephen

[Bill_qaz]

Try spraying brake cleaner or wd40 around inlet to see if any air leak, with engine at idle. It will speed up if so, a leak possibly making weak mixture.
Checking valve clearances as you said is a good idea, wrong clearance alters valve timing so can be on one cylinder. Is the spark as strong as on other cylinders.
Post a pic of the plug and a good one

[svenedin]

Try spraying brake cleaner or wd40 around inlet to see if any air leak, with engine at idle. It will speed up if so, a leak possibly making weak mixture.
Checking valve clearances as you said is a good idea, wrong clearance alters valve timing so can be on one cylinder. Is the spark as strong as on other cylinders.
Post a pic of the plug and a good one

Thank you Bill. I will look for an inlet manifold leak and test the spark. I'll take some pictures if this problem persists because I've given all the plugs a clean and they all look the same now!

[svenedin]

I have been working on the car this morning bright and early. The manifold brass nuts were loose so I have tightened them as per specs to 15 Lb/ft (cold). I did not test whether it was leaking but I suspect it was. I have adjusted all the valve clearances to 15 thou. I know the manual says 12 thou but I understand 15 thou for exhaust valves keeps the valve cooler with unleaded fuel (this NOT an unleaded head) and that 15 thou for inlet is also acceptable.

The weather is too bad for a test run but I have had the engine up to temperature in the garage. It runs well but the 15 thou valve clearance has made the engine quite noisy at the top. I might put the inlets to 12 thou and see if that makes a difference. When I was a teenager I had a professional mechanic friend who taught me the basics (he had 2x Morris 8 and a Morris Minor 1000). A well adjusted A-series should sound like a Singer sewing machine he used to say and mine would not meet Dave's approval with those valve clearances but we had leaded fuel back then...... The valve adjusting nuts seemed to have been tightened by a gorilla, most of clearances were less than 12 thou (I could not get a 12 thou feeler gauge in).

Running up to temperature in the garage the exhaust (though not sooty at all) does smell more of petrol than usual. I think the explanation for this is that the inlet manifold was indeed leaking and now that it is not drawing in outside air the mixture is a bit rich. I will check later.

One thing I must check is the accelerator cable. The car has a habit when idling of gradually creeping down in revs to the point it runs too slow and sounds sickly. I think what happens is, I set the idle speed screw on the carb and it seems fine but perhaps because the cable or linkage is a bit sticky it gradually ends up idling too slowly. A blip of the throttle brings it to normal and then it creeps down again.

Thanks for the tip Bill!

Stephen

[Grumpy21]

Is there any possibility that coolant could be getting into the combustion chamber? That tends to make plugs look like they are running lean.

[svenedin]

Is there any possibility that coolant could be getting into the combustion chamber? That tends to make plugs look like they are running lean.

That is a very valid point. Yes there is a possibility. I think the head gasket might be on its way out. There is evidence of a slight oil ooze from the junction between head and block and a very small quantity of oil in the coolant.

The test will be whether the spark plug I swapped from cylinder 1 to cylinder 3 develops the same odd appearance in cylinder 3 after a few good runs.

[ManyMinors]

Have you tried a compression test at any point?

[svenedin]

Have you tried a compression test at any point?

I don't have a compression tester but ESM did a compression test back in December 2022 and said it was fine. Whilst setting the valve clearances I didn't take the spark plugs out and it certainly feels like it has normal compression with the starting handle (though I know this is very imprecise). In terms of performance the engine seems to pull up steep hills as well (or badly depending how you look at it) as it ever did.

I did look carefully inside the rocker cover when it was off to do the valve clearances. There is no cottage cheese whatsoever and there are also no bubbles apparent in the coolant when the engine is running. This would seem to suggest against a failing head gasket but I will see what the compression test shows.

Edit: I have a Draper compression tester winging its way to me. I think it is worth the investment. It is not as expensive a tool as I thought it was.

[svenedin]

I had a good look around the engine. I am not convinced there are any leaks from the head. The car had a major oil incontinence some time back when the breather system completely blocked (oil was spraying out of the dipstick etc). I think it is just oil from that. I have cleaned off the block and will keep an eye on it.

I decided I could not live with rocker clearances of 15 thou. The car sounded like a tractor so I put the clearances back to 12 thou and I am much happier with that. The difference in rocker noise is very significant. I appreciate the reasoning behind a bigger gap but noise is wasted energy and wear to my mind as well as sounding awful. I found a very loose valve cotter spring that was not holding on at all. I fished it out and bent it more closed and refitted it. Fits well now.

Stephen

[JOWETTJAVELIN]

Don't discount wear on the rocker shaft and arms. A little noise from the valvegear is usual but should be imperceptible when driving the car.

[philthehill]

Cotter spring clips are not required and were discarded by BMC on later engines as was the oil shroud fitted under the valve spring cap.
The 'A' Series will live happily without either the cotter or oil shroud.

[svenedin]

Cotter spring clips are not required and were discarded by BMC on later engines as was the oil shroud fitted under the valve spring cap.
The 'A' Series will live happily without either the cotter or oil shroud.

Fair enough but I didn’t want the spring clip to fall off and go wandering in the engine. It would also really bother me to know that 7 valves had a spring clip and 1 did not!

[philthehill]

Then remove all eight.

[svenedin]

Then remove all eight.

Not likely!

[Bill_qaz]

Are your rocker arms worn where they contact the valves? If pocketed your feeler blade will bridge the high spots, so the actual clearance is bigger than you set, so possibly why noisy.
Just a thought. There used to be a tool I remember made by SPQR, it screwed down until clearance was zero then backed of so many clicks to set actual clearance.

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[svenedin]

Are your rocker arms worn where they contact the valves? If pocketed your feeler blade will bridge the high spots, so the actual clearance is bigger than you set, so possibly why noisy.
Just a thought. There used to be a tool I remember made by SPQR, it screwed down until clearance was zero then backed of so many clicks to set actual clearance.

It’s quite possible and indeed likely. This is the original engine and is way past 100,000 miles having never had any major work. I can’t really see the wear. Yes that tool is now made by Gunson and called the “Clickadjust”. I actually had the tool delivered today but haven’t had a chance to play with it. It will be interesting to compare the adjustment made using the Clickadjust as compared to a feeler gauge

[philthehill]

Did the SPQR rocker adjustment tool come with the correct special socket?
Most of the SPQR tappet adjusting tools are supplied with a 1/2" A/F socket.
I did managed to adapt a Gedore D19 1/2" drive 7/16" A/F ordinary socket to fit.

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A standard socket tends to fall off the end of the tool. The SPQR socket has a retaining hole aligned with the retaining spring backed plunger of the tool.
Bill your photo of the rocker adjustment tool shows a female slot!! The 'A' Series rocker requires a male blade.
As regards wear to the rocker shaft - you will not see any wear as the wear takes place mainly on the underside of the shaft.
It is rare for the bush in the rocker arm to wear.
The hammer end of the rocker is case hardened and over time the wear breaks through the hardening. You can stone the hammer pad but it must be done to the same arc as original. If the wear to the hammer pad is more than a finger nail deep the rocker arm should be replaced.

[svenedin]

I haven’t had a chance to investigate. The Gunson tool is supplied without any socket

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[Bill_qaz]

Phil my picture was just generic from Internet to show what I was referring to.
Most quality sockets have the internal groove to click onto the spring loaded ball. Some a hole on one side only so have to be aligned.single hole is common on impacts for air tools.
A used 11mm will usually fit 7/16"

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[philthehill]

Bill
Many thanks for the reply.
The SPQR/Draper rocker adjuster seems to have socket peculiar to the tool so to get a 7/16" A/F socket to stay on the socket boss I had to drill a hole in the side of the socket as per the SPQR/Draper 1/2" socket.
This rocker clearance tool appear to have been made by several different companies over the years so not unexpected to find variances.
Phil