Cylinder 1 and 2 running hotter than 3 and 4 (1098cc Engine)

[Donald Ross]

Hi

I generally change/ clean my spark plugs in my morris minor about every year or so. Usually when i remove them i notice there is slight variation between cylinders but in general what i would expect. Usually a good colour on cylinders 1 and 2 and a little dirty on 3 and 4 but still reasonable.

Well last week i decided it was time to replace the spark plugs after 2 years. I had champion plugs in the car and with previous experience i decided i would like to change them for NGKs as for some reason my engine seems to run better with them.

When i removed the Champions ( N9yc) i noticed that cylinder one and 2 both appeared very clean, almost too clean like it was running a bit hot. Cylinder 3 and 4 appeared as normal, a little brown but healthy in my opinion. So i replaced the spark plugs and over the last week gave the car a good couple of runs. I have now removed the new plugs to check and they appear to be going exactly the same way as before. 3 and 4 appear a little dirty but healthy and 1 and 2 appear like new with hardly any dirt on them at all. Just a little light coloured residue on the electrode. So it appears cylinders 1 and 2 have decided to run a little hot i think.

I have no other symptoms what so ever, engine was rebuilt around 10 years ago and i use bp premium 97 octane fuel with Duckhams lead additive.

The engine uses no oil what so ever, (i can go a year and the level almost does not move at all), the coolant is about a year old and looks clean in the radiator (never uses any coolant), i have cleaned the dizzy rotor and fitted a new dizzy cap about 3 months ago. I checked the compression a year or so ago and all cylinders were around the 155 psi mark. The engine runs very smoothly and everything appears normal so i am a bit confused it why these 2 plugs seem to be running a bit hot.

The only other event that has happened is about 4 weeks ago i took the car on about a 15 mile drive and the engine cut out. It turned out that the ht lead going into the coil had worked its way loose and had fallen off, so i simply re attached it making sure it was a good fit and has been fine ever since. ( I use high performance ht leads which have been working great for the last 4 years.) The coil is a Bosch oil filled and is about 8 years old. Its a bit of a long shot but i dont suppose with the ht lead working loose it could have damaged the coil. I would think if it had i would notice a change in how it runs but it runs perfectly, pulls like a train up hills.

I have not had to adjust the points for some time but also does not seem like a likely cause to me as the problem only affects 2 cylinders.

Any advice welcome.
Thanks
Donald

[philthehill]

It could well be that you need to run hotter plugs in cylinder 2 & 3.
Not all cylinders burn the same even with one carb and the engine running well.
The plugs should be a nice biscuit brown.

[Donald Ross]

Thanks for the advice.

I would say cylinder 1 and 2 plugs are very clean, almost white on the insulator and 3 starts to get a little brown and 4 is dark brown.

Could adjusting the sparkplug gap affect the burning temperatures?

Thanks
Donald

[philthehill]

Generally I would say no.
With a hotter plug the nose of the plug extends further into the combustion chamber/is less shrouded so the nose runs hotter resulting in any muck on the nose getting burnt off resulting in the biscuit brown colour.
If you aim for a biscuit brown colour for all four spark plug noses you will have a fuel/air mixture that is about right.

[Donald Ross]

Well lets add a bit more to the mystery.

I decided to take a closer look at the champion plugs which were in the car for 2 years to fully examine there condition. What i found i was certainly not expecting.

I noticed that on cylinder 2's plug a tiny bit of the insulator was missing! I have never seen this before and cant figure out just why aa small chip is missing. Could it be a faulty plug? Please see photo.

Also attached is a photo of all 4 plugs cylinder 1 - 4 left to right in the photo.

Followed by a close up of 1 and 2 and a close up of 3 and 4.

Thanks again for your views on this
Regards
Donald

[philthehill]

One and two appear to be running weak and three and four and not too bad.
The gaps look to be very wide. They should be set to 0.025".
I would change all four plugs, set the gaps to 0.025" and see how you go from there.

[kevin s]

Perhaps worth checking there are no air leaks between the head and manifold at the shared 1/2 port?

[oliver90owner]

Perhaps worth checking there are no air leaks between the head and manifold at the shared 1/2 port?

Definitely agree with Kevin on this one. Chip is likely due to serious overheating. It needs sorting before other damage can occur.

[Donald Ross]

Hi

Thanks for all your replies on this all info much appreciated.

Philthehill, thanks for your suggestion and i have checked the spark plug gaps again and can confirm that the gaps are all set at 0.025", think its just the angle i took the photo that makes the gaps look larger than they are. ( I used a macro camera lens to take the photos and i think it makes them look a bit out of proportion.)

I will indeed check if there are any air leaks between the intake manifold and the head, this is a good possibility and in my mind about the only thing that could be causing this problem as it is defiantly a shared issue between 1 and 2 cylinders. Unfortunately i wont get the chance to check this until the weekend due to work but i will update you on my findings.

I have got 1 other bit of information. I notice that on the intake manifold on the cylinders 1 and 2 intake there has been a adapter fitted long before i owned the car for the vacuum to the brake servo. Is it possible a faulty brake servo could be causing air to be drawn in through the vacuum hose, or a split hose and if so could this be the cause?

A bit of investigation is needed i think.

I will have a look as soon as i can and update you all on the findings.

Thanks again for all your advice its much appreciated.

Regards
Donald

[Guildbass]

While a Moggie novice, I've been playing with carb engines since the early '70's. Your suggestion that the brake servo vacuum take off, positioned as it is on the side of the inlet manifold that feeds cylinders one and two has merit. If there is air being drawn in via that servo pipe it is quite possible for the pots on that side to get a bit more air, especially at lower engine speeds and loads when the ratio of 'air leak to carb feed' is higher.
I think it would be worth experimenting with blocking the tube briefly and doing some plug chops.
Just my tuppence worth!

[Donald Ross]

Hi Guildbass

Well im certainly hoping this could be the issue. Im thinking its this or the intake manifold gasket. I have been able to go out to the car just 15 minutes ago to have a quick look and i have checked the hose vac hose for leaks and it appears to be crack free, except where the jubilee clip was at the manifold end there is a slight split but does not appear to be all the way through, although i cant be certain, i have cut out the affected area and shortened the hose. The vac hose also appears to have a "1 way" valve inline but it appears fine too. So only other suspect is the servo its self which i suppose is a possibility. Strangely i have noticed recently my brakes have been sticking very slight amount when i start driving and it just does not feel 100 percent which is either because i dont use the car often or could be a sign of a faulty servo.

Does anyone know if a faulty servo could cause the brakes to stick on ever so slightly?

At this stage all i can do is wait until weather/time permit me to start the engine ( hopefully in the next couple of days) and i will test for any leaks at the intake to rule that in or out and failing that i think i will block the servo hose as per your suggestion and see if that makes any difference. The servo is about 13 years old so it is possible it has reached the end of its life.

See photo of hose, split is hard to see and dont think it went all the way through but its 1 less possibility now.

Regards
Donald

[Sleeper]

Donald

" Does anyone know if a faulty servo could cause the brakes to stick on ever so slightly? "

Yes, especially the way it's mounted , air can be trapped in the air control valve ,

3000118_995.jpg (40.86 KiB) Viewed 62236 times

John ;-)

[Donald Ross]

Hi all

Thanks again for all your views on this its much appriceated.

So tonight i got a bit of time to go out to the garage and have a look at the car.

So i have done the following
1. Run the engine and sprayed carb cleaner all around the intake manifold and union which the servo hose attached and i can confirm there are no leaks.
2. Held my foot firmly on the brakes and started the engine and there is no movement in the pedal pointing to there being nothing wrong with the servo according to the Lockheed manual.
3. To confirm this i used a vacuum pump tool with gauge to put a slight vacuum pressure on the servo hose and the negative pressure did not drop what so ever so there are defiantly no leaks at the servo.
4. At this point i was very surprised i had not found anything wrong so for no other reason than to rule out another possible cause i did a compression test and it was around 155 psi (and it holds that pressure) (i waited 1 minute and the gauge didn't move) which i am very happy with so thats ruled out too (see photo)

So now i am back to square one again. Im pleased that it appears it is not a serious problem like compression or head gasket but it is annoying i cant get to the bottom of it yet.

So i only have a few ideas left, im not sure if these could cause this problem but please advise!:

1. Try adjusting the fuel mixture (i would think slightly more rich) to try to balance the 4 cylinders a bit better (there is always going to be a variation (wish i knew why) i think) but could this possibly even it out a bit?

2. Check and adjust the valve clearances ( not sure if this would have any effect on this, please advise)

3. Possibly adjust the advance/ retarding on the dizzy ( again not sure if this would help).

Which solution do you think i should try first, im leaning towards trying the fuel mixture and go from there but if anyone has any suggestions please let me know.

Thank again, all your knowledge and help is much appreciated

Regards
Donald

[SEROWMANMICHAEL]

If the servo is working when you started engine with foot on brakes it should have gone down a fraction.

[Donald Ross]

Hi Serowmanmichael thanks for your advice,

I will need to double check this just incase I have the wrong information, but even if the servo was faulty it definitely does not have a air leak as per the vacuum test I did on it so it is not the cause of the engine problem.

Thanks

[Myrtles Man]

Why not follow philthehill's earlier advice and try differently heat-rated plugs in the appropriate cylinders?

[Donald Ross]

Hi all

To answer your question Myrtles Man i agree that using differently heat-rated plugs is very good advice. The reason i have been hesitant to do this is because previously my engine ran no problem with standard plugs so in my mind something must have changed for it to start having this issue.

Anyway problem solved now, i believe the problem to have possibly been that i discovered the vacuum advance/retard on the distributor was sticky, and the valves needed slight adjustment, but i will list all the adjustments i have made and now the issue seems to be resolved, much better colour on all 4 plugs now.

1. Fully Cleaned and re adjusted points
2. Fully lubricated vacuum advance mechanism in distributor.
3. Lubricated distributor shaft and cam
4. Replaced rotor arm
5. Fully checked and adjusted valves where required (note, mainly only need adjusting on the problem cylinders)
6. Checked tightness of all head and manifold bolts to recommended specs.
7. Adjusted carb idle and lubricated all moving parts.

Please follow this link to a Youtube video i have just made of before and after, the difference can be clearly heard :

https://youtu.be/3fMm1ML3w2g

Again, all your advice has been very helpful and all very much appreciated

Thanks again
Donald