MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Oil on spark plug

Just gave the MG a service / pre-MOT check and found that the spark plug on No.2 cylinder was oily. Looking through the plug hole I can see black oily residue on the top of the piston and confirmed this was oily by scooping a bit up with a cotton bud (the other three plugs and cylinders/pistons look ok).

The car is a 1981 MGB which has done 42,000 miles from new. It’s done a very low mileage recently (a total of 1,000 miles in last four years) with long periods off the road. It runs ok and I’ve never noticed any blue smoke from the exhaust. Not sure about oil consumption - because of the low mileage it gets an oil change about every 250 miles.

I suspect the problem may be a sticking oil control ring, so I intend to pour 25ml of Redex into No.2 cylinder this evening (after a short run to warm the engine up) and let it soak overnight, and then annoy the neighbours with the white smoke tomorrow (I may pour more Redex into the carb air intakes if there are no complaints).

I’ve been looking through my old MOT documents and have found the following information which may be relevant:

Lowest HC reading (since 1992): 826

Last 5 years’ emission readings (CO/HC):

2006 – 2.5 / 826
2007 – 2.4 / 869
2008 – 1.8 / 979
2009 – 1.8 / 869
2010 – 1.7 / 1132

Last year’s HC reading is very close to the 1200ppm ‘fail’ value. I realise that the CO readings are quite low; I have a gunsons Gastester and I use this to set the carbs just before an MOT to make sure it doesn’t fail on emissions.

I’d appreciate any ideas/suggestions as to what may be causing this oily problem.
Brian Shaw

Brian

Oil control rings are a possibility but I'd suspect valve stem oil seals. Not sure what type would be fitted to your engine but both are changeable without removing the head.

Bob
R.A Davis

Valve guide/stem/seals usually results in a burst of blue smoke when revving the engine after leaving it idling for a while.

That last HC could be indicating a cylinder may not be firing properly, but all of them seem high to me, on my V8 HC is typically in the low hundreds. The problem with an oily plug is that you don't know whether oiling is affecting its firing, or weak firing is allowing it to oil up. You should try new plugs and compare them for temperature and oiling after running a while.
PaulH Solihull

Hi,

Maybe a problem with your crankcase ventilation, though there would be some evidence in #1 too.

The vented tappet cover may be all gunked up, allowing oil vapour to pass into the PCV system.

Herb
Herb Adler

Paul

I understand your reasoning but a couple of things don't add up, Brian says he's never noticed any blue smoke, with that much oil in one of the cylinders there must be some smoke. That is unless, as you suggest, it's not firing on that cylinder. I could believe you may be able to lose one cylinder on a V8 and not notice it but I think you'd hard pushed to do that on a 4 cylinder engine. I was working on the premise that as the car is only doing on average 250 miles a year it must spend a lot of time idle, this would give any oil sitting on top of the valve a chance to run down the guide, I understand this would probably also require worn guides. If it were my car the first thing I'd do would be change the plug and take it for a long hard drive then see what the situation is.

Bob
R.A Davis

Bob - you and I may realise one cylinder is not firing, but I have to say I have read here and elsewhere of people having two plug wires reversed, and the owner didn't really realise that was the problem.

A long hard drive, on a regular basis, is what *all* MGs need and were built for.
PaulH Solihull

Check valve clearance, and valve lift (bad cam).
Anything that makes the inlets open late causes high vacuum at the beginning of the intake stroke; That sucks oil up past the rings. Bad timing chain does the same but on all cylinders.
Aggravated by low mileage causing sticky rings as well as increased chance of cam failure from corrosion.

FRM
FR Millmore

Thanks for your replies in response to my problem.

The story so far ….

Yesterday I warmed up the engine and poured 30ml Redex into cylinder 2. This afternoon had a look and there was only a trace of Redex still on top of the piston. Checked the dipstick and the oil on it was slightly pink in colour, so it looks like it all ended up in the sump. Turned the engine over on the starter for a few revs but no Redex splashed out of the cylinder.

Put a clean plug in and started up the engine, expecting clouds of white smoke – nothing. A bit lumpy at first but it soon ran smoothly. Then I removed the air filters and slowly dribbled in 40ml Redex into each carb inlet, whilst maintaining 1500 rpm. No trace of smoke from the exhaust. Revved the engine up a few times. No smoke. Took the spark plugs out and had a close look. No.2 was oily again, the others had a trace of oil.

Poured another 20ml Redex into No.2 cylinder and fitted clean plugs. Started up again, still no exhaust smoke visible. Went for a drive down the main road, most of the time at about 3,000 rpm, for 13 miles. Engine ran smoothly, as always. I’d unzipped the rear window and watched out for any smoke when accelerating and on overrun. No smoke. When I returned I remover the plugs for a close look (see attached photo).

Not sure what to do next. Is there any easy way to check if the inlet valve stem seal is doing its job? I though maybe to turn the engine by hand until the valve was open, stuff some clean white rag through the plug hole, and then pour or force some oil (Redex, or some coloured oil) down the valve stem and see if it gets onto the rag.



Brian Shaw

It doesn't really surprise me that the Redex ran through after 24 hours, although I've never had occasion to do it. Pouring oil in a cylinder before laying it up is more to spread oil over the bore above the rings than to keep a pool lying on the piston.

I *am* surprised that pouring Redex in to the carbs while running the engine produced no smoke, again while I have never done that myself I have heard many times that it usually produces so much you want to park outside someone else's house when you do it.

The plug is obviously oiling up very rapidly, but how did the temperature of that one compare to the others after fitting a clean plug and running the engine?

Surely a wet and dry compression test should have been done by now.
PaulH Solihull

Pouring Redex into the carbs usually makes you very unpopular indeed. The plug in question, just looks to me like it's not been firing at all. Have you checked for a spark by just putting a plug on No2 lead, earthing it and cranking?
The engine is not that old, even without decent valve stem oil seals, the guides shouldn't be worn enough to lead to heavy oil by-pass.
Allan Reeling

I did once put some Redex in the cylinders as part of the spring wake up. I left it 24 hours and when I started the car there were big clouds of white smoke for a long time.
It seemed to have no effect on the engine however, never bothered again.
The fact that the Redex went straight in the sump hardly touching the sides does point to ring problems
Stan Best

have you checked the compression pressure on all the cylinders with Gunson hi gauge.
p wilkins

Further to the 'is it firing or not?' issue. With new plugs (or at least one in the problem cylinder) ease back the boots on the plug leads on the distributor cap, push an earth wire down each cap socket in turn to kill the spark on that plug. Do the revs drop equally on all four cylinders? Or barely or not at all on the suspect cylinder. This is the only (and safest) way to determine whether there is a satisfactory spark actually *inside the cylinder* (which is the important thing) or not.
PaulH Solihull

Some interesting suggestions there. This is what I did today:

1. Gunson Hi Gauge compression test (cylinder/dry/wet):
1: 190 / 217
2: 189 / 211
3: 185 / 208
4: 185 / 212

2. Temperature of plugs after a hard drive:
all 72 - 77 degC (thermocouple pushed inside recess at plug tip)

3. Crankcase ventilation:
Hose from crankcase pulled off the Y-connector. Blew down it - appeared to be clear flow down into engine until pressure built up.

4. Valve clearance and valve lift:
I serviced the car last week, but I re-checked the valve clearance = 0.35mm. Not sure aboout the valve lift, but I turned the engine by hand whilst watching all the rockers and valve stems operate.

5. Removed each plug lead in turn and checked with Gunson Flashtest. All showed strong spark up to 15kV, and maintained spark to 20kV+, spark started to break down somewhere above 20kV (off the top of the scale).

6. Pulled off the lead to No.2 plug and connected it to a new plug - earthed this and ran the engine - good spark.

7. With the engine idling I pulled off each plug lead in turn (rubber gloves!) and noticed something odd:
Plugs 1 and 4: a noticeable drop in engine revs (audible) confirmed by a drop on the rev counter (the idling speed of 1,000 rpm dropped to about 900).
Plug 3: a slight (just about audible) drop in revs, hardly registered on the rev counter.
Plug 2: very slight, if any, drop in revs.

I repeated this with 4 new plugs and got the same results.

8. Smoking.
The only blue smoke I noticed was just after the compression wet test, the residue of the oil in all 4 cylinders causing the exhaust to smooke for a few minutes.
I also gave No.2 cylinder another 25ml Redex and did a 20 mile run. Still no smoke from the Redex (I wonder if it's a new environmentally friendly formulation - I used Redex years ago and it produced an enormous amount of white smoke).

I've got an MOT test booked for tomorrow morning. Bearing in mind it only just scraped through last year (HC was 1132) I can't decide whether to go through with it (and put new plugs in when I get to the MOT station), or cancel/postpone.

Brian Shaw

compression results are really good,as all cylinders are near enough the same - which is what you wan't.
i think that with putting in new plugs,you may be trying to bypass the real problem.what about the distributer cap and rotor arm / points / ht leads,when did you last renew these.they can make a big difference to spark efficiency.
no.2 ht lead could have broken down.
if you have a gunson colour tune,screw this into no.2 plug socket and check the combustion flame colour.
on a long term basis,redex at the specified amount,is ok.just to add to the fuel tank,only squirt into carbs if car has been sitting without use for a long time and maybe become a bit gummy/varnishy inside the carbs.
always use high octane petrol-shell v-power with castrol valvemaster octane booster.
good luck with mot.
p wilkins

With reference to my previous comment:

"7. With the engine idling I pulled off each plug lead in turn (rubber gloves!) and noticed something odd:
Plugs 1 and 4: a noticeable drop in engine revs (audible) confirmed by a drop on the rev counter (the idling speed of 1,000 rpm dropped to about 900).
Plug 3: a slight (just about audible) drop in revs, hardly registered on the rev counter.
Plug 2: very slight, if any, drop in revs."

I just tried the same thing with my other MGB (same engine 18V) and got the same result - so, presumably nothing unusual.
Brian Shaw

I may be3 time to take the head off. A common problem is blowing between 2and3 either because of gasket failure or warped head. My current 1800 ran, "just about" ok, but no real go. When i took the head off it was bowed 4 thou!! Compression test looked even!! It could also be cracked! Faults like this show up better with a "bleed down" test. i.e., cylinder on TDC compression stroke and pressurise the cylinders with an air line through the plug hole. With a gauge in the line you can see how long the cylinder takes to depressurise. Ordinary compression testers hold the max pressure, you don't get to see whether the pressure is leaking away to another cylinder, a waterway or through a hairline crack.
Allan Reeling

Those compression figures are well within the 10% min to max difference usually given as the rule of thumb. If there were a leak between 2 and 3 big enough to cause one of them to oil up (why only one?) I'd expect to see that as very low compression on both of them (notwithstanding Allan's experience).

If the Flashtest got up to 20kV or higher then the prior HT components can't be breaking down unless the plug gaps are huge, the normal HT voltage should be in the range 8 to 10kV with a 25 thou gap (bit higher with 32). If something was breaking down at normal voltages you wouldn't be able to increase the total gap at all and still get a spark.

Little or no drop in revs when a plug lead is pulled off (incidentally pulling a lead off causes the HT to go way up which can cause things to break down, which is why I recommended earthing) definitely sounds wrong to me, ideally each plug lead should cause the same drop, resulting in a definite regular beat in the exhaust. Why two different engines are apparently doing the same thing is even odder. Sure you don't have 2 and 3 reversed?

Was the crankcase breather wet with oil when you removed it?

PaulH Solihull

This afternoon I checked the following:

1. Gunson colour tune: all cylinders produced the same result, on idle and when revved (quick burst up to 2500). Colour tune gave similar results on 2nd MGB. So there seems to be combustion in cylinder 2.

2. Earthed the plug leads as you suggest Paul (had to connect earth to the connection at each plug - my car has angled boots at the dist. end, they won't budge). Similar result to removing leads -
Plugs 1 and 4 - idle speed dropped from 1,000 to 800 to 850
Plug 3 - about 900
Plug 2 - about 950, although this time the fall in revs was definitely audible.

3. The plugs are definitely correctly connected, 1-3-4-2. I got 2 and 3 mixed up a couple of times in the past but only drove a few yards before looking under the bonnet and sorting it. Anyway, just to make sure I've just swapped 2 and 3 to see how it ran and can confirm I've got them right.

4. The crankcase breather hose which I disconnected at the Y-piece wasn't visibly wet. I poked my little finger into it and found there was a slight trace of oil on the inside wall of the hose - I would think this is normal.

I cancelled the MOT test for now.
Brian Shaw

A good idea to do a leakdown test. I have found engines where the compression was good as this one, but air was leaking across the HG between two cylinders. The difference in idle drop leads to that idea.

Past that, if you can get the MOT - I assume you cannot drive without? - put it on the road and drive vigorously.

I once bought a Rover 2000TC with similar miles and signs of recent idleness, and a broken gearbox. 6 months later, gearbox fixed and everything serviced, I did a 300 mile hard test drive across Pennsylvania, and used 3 qts oil, pretty frightening since we were going on a transcontinental vacation. On the 300 back to Pittsburgh, it used 1 qt. Another O&F change and we set out for the Pacific - it used zero oil in 6000 miles before I changed it again, zero in the next 6000, at speeds in the 75-100mph range with lots of hard mountain driving, and zero for several years and more than an additional 100,000 miles after, in daily use.

FRM
FR Millmore

Is there any time left on the MOT (a new one can be obtained up to four weeks before expiry of the old)? If so then drive it hard as suggested. If not then stick new plugs in it at the garage and hope for the best, it will give you plenty of time to resolve it, and it's not that expensive if it doesn't pass.
PaulH Solihull

Brian,

You said:
3. Crankcase ventilation:
Hose from crankcase pulled off the Y-connector. Blew down it - appeared to be clear flow down into engine until pressure built up.

Is there a check valve in the crankcase air intake that would allow you to build up pressure in the crankcase? I would have thought that as you blew the air in, it would just blow out the intake.

If you don't have the cylinder leak down test gauges, you can still get some sense of what is going on just by making an adapter from an old spark plug and pressurizing the cylinders.

Charley
C R Huff

Paul commented: "Is there any time left on the MOT (a new one can be obtained up to four weeks before expiry of the old)?"

Yes, I always MOT early in case of a problem. It expires 19 Sep.

On Sunday (21 Aug) I fitted clean plugs and put another 25ml Redex into cylinder 2 (third time lucky) and drove it hard for half an hour. Had to limp home for the last two miles as the brakes faded badly - I smelled something burning and as I slowed down for traffic lights the car pulled to the right. Smoke was coming out of the LH front wheel arch; wasn't sure if it was from the brakes or from some other fault. After driving a mile or so at 30mph the smoke subsided, and when I got home noticed that both front wheels were very hot. Anyway, checked the No.2 plug which was oil-free. Tomorrow I'll do a few miles in it and check for signs of oiling.
Brian Shaw

That is progress!
Now fix the brakes; Hanging caliper pistons, bad front hoses, or MC fault (possibly sticking on the pedal pivot shaft). All the result of enforced idleness - drive more!
If the hoses have not been changed in the last ten years do that (two front, one rear) first as a matter of course, they die with age, often internally.

FRM
FR Millmore

If you blow in the hose coming off the front cover (which is what I assumed Brian meant when he said he had pulled "the hose off the Y-connector") you are blowing into the crankcase which has a restriction in the only other port that air can get in or out of the crankcase. That will give back pressure when blowing in said hose.

As far as the callipers go you may get away with removing the pads, carefully pushing the pistons out with the brake pedal, and polishing them with a length of cord wrapped one turn around them, then working them in and out. However pulling to the right would normally mean either the right calliper was sticking on if happened without braking, or the left calliper was sticking off if it was under braking. BTW when I at least mentioned driving hard I meant the engine, not the brakes and tyres :o)
PaulH Solihull

This:
"the car pulled to the right. Smoke was coming out of the LH front wheel arch"
is a description of what happens when the LH brake has been dragging and is severely faded by way of being well over the operating temperature of the linings. If both fronts are dragging but the LH is worse, then the pull to the RH would happen both on and off braking. (until the RH lining is equally cooked!)

FRM
FR Millmore

Didn't have time to get out in the B today, but checked the brakes on my drive - they seemed quite effective and pulled the car up in a straight line. I removed the brake pads. The LH ones had that burnt smell which came with the smoking on Sunday. The RH ones appeared to be normal.
I'll be taking the B for a run tomorrow or Friday to check the brakes properly, and to see how much (if any) oil is deposited on No.2 plug.
Brian Shaw

The faults "bad front hoses, or MC fault (possibly sticking on the pedal pivot shaft)." will go away when the car is cold, but return after the brakes have been warmed up. So, check that it is not dragging after use. I do it by releasing the brakes just before coming to a stop on level or slightly slanting ground. If you are on a very slight upgrade, let the car coast to a stop and see if it then rolls backwards. Part of my regular driving routine, and makes sitting in traffic educational and fun. Also, feel the brake temps after a very gentle drive with minimal brake use - if hot they are dragging.

FRM
FR Millmore

FRM - re pulling right with a stuck left - now you say it I can imagine it, although it didn't happen when my left calliper stuck on.
PaulH Solihull

Paul-
All depends on the (transient) balance of drag vs brake efficiency under various conditions: it can easily change as temps and wear change.

OT but of interest: Modern cars with negative scrub radius suspension geometry can pull the opposite way to what you expect. I bought my daughter another Mazda 323 to replace her rusted one, came with new front pads installed. She reported a slight but constant pull right in highway driving. After about 1500 miles, she called with a horrid noise in the LHF, it had a stuck caliper piston that made it eat a pad and disc. It was a 500 mile each way road call for me, so I didn't mess around, but the only real fault was the bad LH caliper piston. New pads, calipers, hoses, and discs later, no more pull right - and the fuel mileage went up about 5-7 mpg. And I taught her the above road tests and to feel the wheels periodically to see if the brakes are dragging!

FRM
FR Millmore

Had a loook at the caliper pistons and cleaned them up with cord as suggested by PaulH. Went for a drive this morning to check the brakes: did a straight five-mile run mostly at 40-50 mph, braking very lightly (and braking with handbrake when safe to do so). Surface temp of both the discs were 17 degC. Drove five miles back, braking normally - disc temp 52 to 55 degC on both wheels.

The oily plug problem has not gone away, however. After just ten miles the No.2 plug looks just as bad as in the photo I posted earlier. So I've given up on the Redex, and I think my next job will be to remove the valve stem seal.

Paul: you seem sure that there should be signs of blue smoke when revving after idling for a while, so I'll try looking for this again before I start dismantling anything.
Brian Shaw

Brian

Having read everything you've tried I now have my doubts about this amount oil finding its way down the valve guides. I believe Paul is on the right track in that it's not firing on this cylinder. The question is why, you've checked you're getting a spark, you've checked the compression, it shares the carb with No1 cylinder so fuel should be ok. As FRM said I'd check the valve lift on this cylinder, a badly worn cam would still give good compression figures but wouldn't open the valve sufficiently.

Bob
R.A Davis

Update:

I obtained a dial indicator this week and checked the valve lift. All 8 valves are approx. the same. I measured them a few times to reduce the possibility of any rogue readings, positioning the tip of the indicator on the flat part of the valve cap near the top of the cotter. Average reading is 0.335". This seems low compared to the spec for my engine (18V-847H) which is 0.3645". I did a similar check on my other MGB (same engine) and the average for that is 0.340".

Valve clearances (cold engine) are all 0.35mm (0.014").

I can't understand why my valve lifts appear to be 30 thou less than spec (I've checked the accuracy of the dial indicator on the bench with a bar of 0.25" thick tool steel). However, as all 8 valve lifts measure about the same I would guess that this is not the reason for just No.2 plug to keep oiling up.

I guess the easiest thing to do next will be to replace the valve stem seal on No.2 intake. I read somewhere that this can be done without removing the cyl head, by pushing some rope through the plug hole and manually turning the engine until it compresses against the valve, then slide the rocker arm to one side and use a screwdriver to lever the spring down and remove the cotter. Is it that simple? Will any rope do? - I've got some 7mm dia polypropelene rope.
Brian Shaw

Brian,

Use a soft flexible rope of somewhere around 1/4 inch diameter, and don't drop the keepers. You might want to plug the holes that the keepers can fall into with a rag. Leave plenty rope hanging out of the spark plug hole so that you are sure of being able to retrieve the rope. Make sure the cylinder you are doing the rope trick to is on the firing stroke so that both valves are closed.

As to the valve lift, is it possible that the spec is published with zero valve lash? In other words, that the spec is full rocker travel at the valve tip end of the rocker.

Charley
C R Huff

Thanks Charley, I'll probably try the rope trick tomorrow.

I think the valve lift stated in the spec probably doesn't include valve clearance so that would account for 14 thou in my case (the spec states 'Maximum valve lift').
Brian Shaw

Update:

Rope trick done on No.2 cyl inlet valve. Attached photo shows the stem seal from this valve (left) which looks a lot different to the new ones recently purchased from Moss (centre). When I disassembled the parts from the valve, the seal was firmly stuck inside the top cap, its bottom edge level with the bottom edge of the cap (is this it's correct location?)

I presume the seal started life as an o-ring, and after 30 years has ended up this shape.

I'll replace all 4 inlet valve seals, and leave the exhausts as they are.


Brian Shaw

After only 30 years as well ...
PaulH Solihull

Update:

I had great difficulty in fitting a new seal to No.2 inlet valve stem - I couldn't keep the valve cap centred whilst compressing the spring, resulting in two seals being damaged before I got them into their correct position on the stem. I spent so much time fiddling about with this I decided to remove the cylinder head and use a proper valve spring compressor.

Whilst removing the head I had a good look at the inlet manifold, and there was no sign of any oil getting in from the crankcase breather hose.

The head gasket looks intact and has not blown/leaked.

So I'm still thinking it's the valve stem oil seal, or a stuck (or failed) oil control ring.

My first picture shows pistons at No.3 and No.2 cylinders. No.2 is cleaner, due to the three dousings with Redex. When I first looked into the cylinder (through the plug hole, before I put the Redex in), there was a noticeable 'clean' area on the piston - a band about 8mm wide around the edge, outside the dished part (which was covered in black oily stuff). This seems a bit odd - the other pistons are black all over. The marks on the piston top where I scooped up some of the oily residue with a cotton bud via the spark plug hole.

The second picture show the head at No.2 and No.1. Some of the oily appearance of No.2 may be due to the Redex, which may also have caused some of the deposits to detach from the inlet valve. No.1 is oily around the inlet - I expected it to look like this, as the engine was sitting for a couple of days with No.1 inlet valve open (while I was fiddling around with No.2 valve seal).

The balance (or imbalance) of this engine may be such that when it stops rotating it usually (or always) stops with the No.2 inlet valve open. This would result in oil seeping into No.2 cylinder when parked for several weeks at a time (often the case with this occasionally-used car).





Brian Shaw

Cylinder head




Brian Shaw

Certainly some big differences in valves and pistons there. I've not seen it but I've read that a 'clean' piston can be caused by a coolant leak into the cylinder. With the valve guides sticking up into the rocker area as they do I would have though the amount of oil that could drain down through it would be pretty minimal, and also rapid, meaning the length of time it is left would be immaterial. Removing a plug after switch-off, turning the piston to the top, and feeding cord through the plug hole would show oil if it *was* the guides/valves/seals, and not if it were the rings I would have thought - more at any rate.
PaulH Solihull

Update:

When I removed the valves I found an accumulation (about 2mm thick) of oily gunge on the back side (ie., just below the bottom of the guide) of No.2 intake valve, also some on No.1 valve. On No.3 and 4 the deposits were hard and dry, with no sign of oil. There is no sign of any oil coming down the intake ports from the manifold.

I cleaned up the cylinder head and took it to my local engine shop and had it checked. The casting has no cracks or distortion. The valve guide/stem clearances are good (about 0.0015”). There was slight pitting at the valve/seat interface so they cut/ground and lapped the seats and valves, and also reground the top of the valve stems to eliminate the small amount of wear caused by the rockers.

Then I removed No.2 piston to check the condition of its oil ring. The 3-part oil ring (upper ring + spacer + lower ring) could expand and contract freely and would therefore have done its job wiping the cylinder. There was some sticky oil residue (gumming) in its groove, and although the ring assembly could be rotated, the three separate components would not rotate independently of each other (without applying some finger pressure) due to the sticky stuff. I noticed that the gaps in the two oil rings were in line. I understand that when fitting a piston, best practice is to offset the upper and lower parts of the oil rings by 180 deg (although when the engine is running, the rings are free to rotate randomly, but even so the gaps will not be in line for most of the time).

I removed the compression and oil rings and gave them (and the pistons) a thorough clean, to remove all residue. The rings appeared to be in good condition and undamaged. I also took No.3 cylinder out to compare with No.2. The only difference was that the upper and lower oil ring gaps were not in line (about 90 deg apart).

While I’ve got the sump off, I checked the engine breather was clear by blowing down the hose which is connected to the tappet chest cover.

I can’t think of anything else to check which may be causing No.2 plug to become oily, but any further advice/suggestions/comments would be welcome at this stage before I start putting everything back together.
Brian Shaw

"I also took No.3 cylinder out ..."
Whoops! I meant piston of course.
Brian Shaw

Could be a bad No.2 bore :o(
PaulH Solihull

Bad bore? Now you've got me worried!
I've checked the bore condition and it appears to be ok - no visible damage or excessive wear, and the honing is clearly visible all over.

My new sump (oil pan) gasket supplied by Moss is quite a bit thinner than the original (30 thou vs. 50 thou) and the last thing I need now is a new oil leak. I know Fel-Pro do good ones but I can't find a UK source for these (I've been quoted £30+ including shipping from Rockauto in USA), so it looks like my best option will be the 30 thou paper Moss gasket + Hylomar.
Brian Shaw

Brian, try the valve stem seals that fit on the valve guide.
Art Pearse

Art - I bought some of those seals from Moss (they call them 'improved type'). I also bought some of the original type ('O' ring). Couldn't decide which to fit so I trawled the archive and saw that opinion seemed to be divided so I've fitted the original type.
Brian Shaw

This thread was discussed between 18/08/2011 and 29/09/2011

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.