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MG MGA - Pre-ignition

I have chronic pre ignition in my 1622 motor. After turning off the ignition it will run on for up to 30 sec. We have set up the carbies correctly and balanced them, tried altering the timing by up to 10 degrees dynamically it is now 15 BTDC and vacuum is in the mid range.

The car pulls and runs well. I am going to try a petrol additive to bring the octane from 95 to about 98 and will try slightly cooler plugs ( I am running with NSK equivalant to Champion N8Y). Is there any other remedies that I can try.
Graham Hamilton

Now 15 degrees BTDC
Jesus wept!!!

You have done the opposite to what is required. You need to retard the timing NOT ADVANCE it!!

Try setting the timing up to 32 degrees at 4500RPM and vac disconnected to be right or to stop pre ignition for now try 3/4 degrees BTDC static
Bob England

There was always a tendency for A and B series engines to run-on and pink a bit when fitted with the extended nose plugs like Champion N9Y. You would hear it all the time when you walked down the street in the 60s and 70s and a BMC product drove past. I always reckoned it was due to the plug side wire getting hot enough to ignite the mixture before the spark, so I stuck with the Champion N5 non extended nose and had no problems at all. Today I use NGK B6ES plugs and have no running on or pinking. This is a non-extended nose plug and if you go to the official NGK web site http://www.ngkpartfinder.co.uk/car_commercial_search.php?type=SPARK%2520PLUGS&manufact=MG&model=MGA&engine=1.6 you will find it is the recommended plug for your engine. Try it and see if it helps.
Lindsay.
Lindsay Sampford

Together with the fuel, Robert and Lindsay have it covered. How about the temperature of the engine? When it gets very hot this contributes too.

Let us know how you get on.

Neil
Neil McGurk

When you turn off the ignition, put the car in gear and release the clutch with your foot on the brake - that will stop the running on. Higher octanes, weaker mixtures, hot engine, and advanced timing all contribute to pre-ignition. MGA engines were designed to run on low octane fuels, unless the head has been skimmed and the compression is higher.
Peter.
P. Tilbury

Surely, once the ignition is turned off, the timing of such is irrelevant?
Lindsay Sampford

Thanks everyone for your comments. I have had the engine retarded down to 5d BTDC and get pinging so now suspect a higher octane will help down at 5 degrees. The engine runs at normal temperature at all times. Will let you know how I go.
Graham Hamilton

Thats good Graham but the engine should NOT pink at all IMO.
So before doing anything else can you confirm which NGK plugs you are using?
You ought to be using BP6ES or maybe if they pink you could try BP7ES.
Robert (Bob) Midget Turbo

Bob I am using the NSK BP6ES would I be right in saying the BP7ES is a hotter plub.
Graham Hamilton

It's why you've got pre-ignition. Try B6ES http://www.ngkpartfinder.co.uk/car_commercial_search.php?type=SPARK%20PLUGS&manufact=MG&model=MGA&engine=1.6
Lindsay Sampford

Graham,

Why are you using 95 octane and then an additive to bring it to 98 octane? The 98 octane is available at most pumps in New South Wales.
I have used 98 octane in a 1622 MK11 Deluxe without any running on.

Peter,

Remember that the 1622 has a higher compression of 8.9 compared with the 8.3 of the 1500/1600.


Mick
M F Anderson

Lindsay

Useful web link. Good to see I have the correct plugs in my 1800.

Thanks.

Steve
Steve Gyles

We still have the question of not pinging while running but running on after the ignition is turned off. Running on presents different but related conditions to the ignition on or normal running of the engine. Symptons presented in running on can have an impact to the performance (by preiginiton) of the running engine. I have owned and driven my 1500 since 1965, the car has been in the family since new. After raising the compression ratio of my 1500 (skimed the head) I have had to "clutch it dead" or put it in 2nd gear and carefully release the clutch with the foot brake on as I turn the ignition off. It would occasionally run on even before the engine was modified, cured by a good long blast down the road. (we could do that long ago...) The usual suspects for running on were: carbon build up: mitigated as above, lean idle mixture: seems to have been addressed, the "hot spot" in the combustion chambers between the siameesed exhaust port side of the combustion chambers where the head is subject to cracking: good cooling passages and resist skimming the head plus lots more that I can't remember or haven't a clue about, the point in the combustion chamber where the top of the heart shape around the valves and around the spark plug join: remove all sharp edges in the combustion chamber, and around the cylinder bore. All the above require careful attention to the quality of the head gasket, flat metal surfaces, and careful releaving of the area around the stud areas.
Russ
Russ Carnes

On the other hand, it would be really cool if changing the plug type would help, I'll have to try it!
Russ
Russ Carnes

Running on after being turned off is a typical sign of wrong plugs, timing too advanced and coke build-up in the head. Check the B Technical archive for all the solutions - it's very common with early B engines
dominic clancy

Graham the BP7ES is a COOLER plug that we use if we suffer detonation (pinking) or running on. The otherside of using a cooler plug is that it may "foul" up under certain conditions especially if the engine is a bit of an oil burner. I would certainly try a cooler plug and also I would want to check the timing at 4500 RPM and vac disconnected to ensure the dissy was function reasonably well.

Lindsay I have always used NGK "extended nose" plugs without problem but I have never heard of them causing pinking over and above the basic NGK plugs. I thought the reason why such websites as the one you directed to chose the basic plug was that an extended nose was perhaps not available in 1960?

However there is certainly logic in the arguement and I would be interested in knowing if reverting to basic B6ES plugs would cure this particular problem. Unfortunately I at least am asking Graham to buy a good number of plugs.. :-)
Robert (Bob) Midget Turbo

A high idle can also contribute to running on after being turned off.

Ken
k v morton

I can remember the extended nose plugs (Champ. N9Y) appearing on the scene in the late 60s. They were supposed to give a cleaner pick-up in stop-start traffic due to the tip being "immersed" deeper into the mixture, they were less prone to fouling than the likes of N3, N4 and N5. I think it is probably true that an engine performs better with this type of plug, most if not all modern car engines run with extended nose plugs. The downside with our old cast iron, hot-running lumps is the tendency to carry on running after being told to stop. I was told years ago by someone who knew their stuff that the problem was with the long side wire getting too hot and acting like a glow plug. From my experience with A and B series engined cars there was always a tendency to pinking at low revs and heavy load, and running-on when these plugs were fitted and the engines were "hot and bothered". Out of the traffic and on the open road there were no prolems at all. I stuck to N5s or their equivilents in my 1100 midget and my ZA Magnette and never ever had trouble with running-on or pinking and the same applies to my 1500 MGA. I can't really speak for the 1588, 1622 or 1800 but if running-on is a real problem, it's got to be worth trying a non-extended nose plug to see if it's the answer isn't it? Wasn't there a special valve device you could fit to MGBs to stop them running-on?
Lindsay Sampford

An anti run on system was fitted to later Triumphs and MGB's. On turning off the ignition an electrical solenoid valve was operated which applied engine vacuum to the overflow fitting on the SU fuel bowls. This lowering of pressure in the bowl pulled fuel back into the bowl and therefore away from the SU main jet. An extra terminal on the oil pressure sensor switch then broke the electrical circuit of the solenoid when the pressure went to zero.
Sounds complicated but it is really simple.
It could be fitted to a MGA but you would have to fit a pressure sensor somewhere in the oil pressure system (e.g. a "T" fitting at the current oil pressure fitting).

Mick
M F Anderson

My experience backs up Bob. I have always used BP6ES plugs without problem in my MGAs.
My first experience substituting the "P" protruding tip plugs was while working at a Datsun dealership in the 70s. The early Datsun J series engines were copies of BMC B block engines and their A series engine were a direct descendant. They used the B plugs in most of these until the BP plugs came out. We then retroactively applied the P plugs to all the cars. We found they ran better and fouled less.
Graham in NGKs nomenclature the number refers to how well the plug dissipates heat hence the bigger the number the cooler the plug. So yes to Bob, a 7 is cooler than a 6.
R J Brown

GRAHAM WHAT DO YOU MEAN "THAT THE VACUMN IS IN MID RANGE " AS A GOOD ENGINE WILL PULL 18 INCHES OF MERCURY MID RANGE IS 9 . TELL ME THAT THIS IS NOT SO ! A VACUMN GAUGE WILL READ ENGINE CONDITION LIKE A BOOK A RULE OF THUMB IS , AT A CLEAN IDLE, MAX THE VAC READING VIA IGNITION TIMING AND THEN RETARD ONE INCH OF VAC. IF THE MAX. MECHANICAL ADVANCE AT AROUND 3500 RPM IS 32DEG. THE TIMING IS PRETTY CLOSE.USE 98 OCTANE PETROL ( NOT SHELL ! ) AND SET IDLE TO AROUND 700 RPM. IN THE FIFTIES WE WERE FOR EVER PULLING HEADS FROM A AND B SERIES ENGINES TO GRIND AWAY THE SHARP POINT BETWEEN THE VALVES FOR THIS SAME PROBLEM. APPARENTLY UNLEADED PETROL EQUALS HOTTER ENGINES. I RUN RICH NEEDLES AND HAVE DONE EVERYTHING I CAN TO EVACUATE THE HEAT FROM THE ENGINE COMPARTMENT. I HAVEN'T SEEN MY PLUGS FOR A LONG TIME , I CAN'T REMEMBER WHAT THEY ARE SEAN
S Sherry

Sorry I should have said the engine was in normal range on the vacuum gauge it is pulling 18 inches of mecury.

Mick , I have been using 95 octane and because the car is stuck on the hoist at my neighbors place I bought the additive just to try the engine out at a higher octane. I will go anyway to the 98 octane, I usually use Shell but will try another brand. I will also try the cooler plug.

Sorry just have done nothing very much on the car as it has been 38 degrees yesterday and 41 today.

Everybody have a very good and prosperous New Year and thanks again.
Graham Hamilton

Graham
A couple of questions
How long is it since it has had a decoke
Is it a standard engine or a hotty
What is your idle speed
How are them valve clearances

On another note---The term preignition --I know a lot of people use this term to describe running on after the ignition has been turned off but----- You have run on problems.
To me preignition is just that--Something before ignition. i.e. pinging or detonation caused by too early ignition-- but that's only my opinion I guess


Willy
WilliamRevit

William the motor was a Wolseley 1620 and was rebuilt some two years ago to MGA MK2 specs and other than a slightly higher compression ratio (it measures 180psi on each cyl on the compression gauge) it is bored one size over.
Since the rebuild it has only done 2800 miles.

Went up to buy spark plugs and was told that the B6ES is no longer made so have bought BP7ES to try. I looked up the NGK website and B6ES is no longer listed but BP6ES is?
Graham Hamilton

Sorry forgot to answer your other questions ; my idle speed is 900rpm and valve clearances are as per specs.

When I had the motor done I also had it fully balanced and the only differance was the original distributor was knackered so a friend who was the mini king in the area put in a Mini Cooper S 1250 dissy which is weights and not vacuum operated. He has moved from the area so I have lost contact.
Graham Hamilton

The compression ratio appears to be very high with 180psi. I think that 130-140 is more ususal.
dominic clancy

Graham , I think you may have some self inflicted wounds ! Wrong distributer and 180 compression ? ?
No wonder the engine is unhappy Sean
S Sherry

Not sure if I am reading the Lucas database correctly, but it seems you are using a 23D4. It gives 30 degrees of mechanical advance at 3800, but no vacuum advance to add to that. As Sean mentioned, your advance curve is likely to be incorrect for the MGA.

Steve
Steve Gyles

Graham
The Cooper S dizzy should work OK but you MUST set your timing at 10' "STATIC" as the advance of an S dizzy starts at very low engine speed and if trying to set it at idle with a timing light you will notice it wandering a bit as it is already advancing a tiddle at idle speed.
Just check with a timing light to make sure you don't go past 32-34max at full advance though to make sure all is well with your dizzy
If this has been happening ever since this engine has been in, there are probably a few sharp edges around the combustion chamber of the head that need to be ground smooth--head off for that but really that's not a real big job just tape an old headgasket to the face of the head and smooth everything that looks sharp inside the ring of the gasket especially the ends of the threads of the sparkplug holes and really round off the beak sticking out between the valves and tidy up any other sharp edges. One of them sandpaper fan wheels do a great job for this sort of job.
If this running on problem is a recent problem it could be a carbon buildup in the chamber if your fuel is as crappy as the stuff we get here-- A pressure pack of carbon cleaner will get rid of that. The Subaru one works well and Ford have got a similar one now as well. It's just a case of aircleaners off and squirt.
Are you running a standard cam
Do you know what the compression ratio is or how much was taken off the head
Willy
WilliamRevit

Plenty of B6ES on Ausralian eBay, how many do you need! Even listed for MGA.
Lindsay Sampford

Just did an eBay search "B6ES MGA" and got 4 listings and then searched "BP6ES MGA" and got "Your search returned 0 items". Got the same result on UK eBay. This is the last time I am going to suggest this simple cure!
Lindsay Sampford

My Mk 2 has the original 1622 motor but rebuilt some 5 years and 5000 miles ago- with a slightly tuned cam -skimmed head with a C/r of 9.5. My compression on all 4 cylinders is around 160-170.
when I purchased the car two years ago it was fitted with a 25d dizzy which I believe could not be timed exactly due to wear. I have replaced this with the 123 distributor with sports coil; and after playing around with the advance settings have now got it right. I initially also had some preignition and overrun after turning off. But by retarding the ign slightly this has now been cured. Idles well at 750rpm, and I use NGK BP6ES plugs with a 30 gap as I do on my Oselli fast road engine in the MGB- just my thoughts
Paul
P D Camp

My local Worldpac warehouse had 8 B6ES and the next warehouse in line (Ontario Ca) had over 100 in stock.
Does not show discontinued.
PS just had a 71 Datsun 510 brought in for a used car check today. Customer ask us to put in the B6ES plugs he supplied when we do the compression check.
Fun old cars here is a picture in my bay.


R J Brown

This may have been covered but just in case. The most often cause of "running on" is idle speed. It must be below 800rpm and 750 is even better. Another problem that can show up now and then is "local boiling" a small hot spot in the cooling system that does not show on the gauge. Can be caused by crook pressure cap. This is why we run pressure in the radiator. A good set of NGK plugs goes without saying as well.

Denis
Denis4

Denis,

That has been my experience too. I would reduce the idle speed before I mucked with anything else.

Ken
k v morton

From my experience idle speed must be below 800 or they will run on every time.
Barry Bahnisch

Put in the B6ES spark plugs and there was an immediate improvement but not the whole solution. Then got the idle down to 750 rpm and I have almost got there. I find if I wait about 15 seconds after stopping before I turn off the ignition there is no more pre ignition. I will also go with the 98 octane.

I can almost hear Lindsay saying I told you so, but thanks to everyone for their input it has been welcome and a learning curve for me.
Graham Hamilton

That's interesting, would suggest the plug getting too hot was the issue. (often the case I think) so was the answer to hide the plug tip into the top of the combustion chamber? or would using a cooler plug have been a better solution?
Go on Graham, you know you want to, buy a set of BP7ESs and tell us what they achieve, I am sure we would all love to know. (I would anyway)
Robert (Bob) Midget Turbo

Just read this thread with interest. I have a 1622 Mk2 and experience running on and a little pinking. My plugs are NGK BP7ES, so am I right in thinking the answer for me is not a simple as just a change of the plugs?
Graham M V

I assume then Graham that you have tried to sort out the pinking problem by fitting cooler plugs? when by the sound of it something else is causing the problem.
I always start by making sure the timing and dissy advance is correct. If this is not the case then every other thing you do will simply try to mask the problem.
Robert (Bob) Midget Turbo

Bob
No I haven't played around with the plugs at all. I have only had the car since April and these were the plugs fitted. I also haven't checked the timing as I have a problem with missing timing marks, so was planning on investing in a timing light that has "a dial" built in. From what you say I assume your advice is that I look at the timing before playing around with the plugs.
The pinking and running on is not the number one priority for me as I need to rebuild the carbs, but having seen this thread, I was obviously very interested to see if this could be an easy fix for me.
Graham M V

No timing marks? What happened Graham?
I am wondering how the previous owner set the timing up?
Sometimes people fit HGK 7s because the urban myth machine says you need em for a modified engine. LOL. Sounds like you need to get a DTI through the plug hole and find out where TDC is.
Robert (Bob) Midget Turbo

Bob, don't tell him that they are underneath!

Steve
Steve Gyles

Hmmm maybe so Steve but I think our mate Graham also owns a frogeye, in which case he will be already very frustrated with timing marks being in a very inaccessable area. is that the case Graham?
Robert (Bob) Midget Turbo

Ha ha. Yes Bob you are 100% correct on both counts.
There really wouldn't be a problem accessing the timing marks if I could see round corners and my arms were about 10 foot longer!
My MGA has just one timing mark which I think is TDC, the others are broken off.
And as I have electronics and not points, I believe I can't do a static test with a test lamp? My timing light is only a cheapish one but am I right in thinking that if I get a better one (with dial, etc) it will make life a lot easier for me?
Graham M V

Graham

It certainly would. Provided you can get the engine to fire up you only need the TDC mark with an adjustable advance timing light. You simply dial in the desired advance you require for a specific RPM, then point the light at the pulley/timing mark, then rotate the distributor until the pulley mark appears stationary against your one and only TDC pointer.

Steve

PS. I was able to get the static set up ok with my electronic ignition using conventional methods.
Steve Gyles

Thanks. Sounds like it is worth investing in one. I will look out on ebay.
Do you know if there is a published list of timing settings v rpm?
Graham M V

Graham

Bob is good on this one. I have usually gone for 32 degrees at about 3500 RPM, with the vacuum disconnected. This ensures you set it up against mechanical advance only. I have seen forum members quote different RPMs. Perhaps Bob will clarify.

Steve
Steve Gyles

Graham,Snap On MT 2261 is a good one. I picked up a second hand one on eBay a couple of years ago.
Lindsay Sampford

Graham

I was referring to Bob the Midget Man above, not Bob West, although I am sure he also has some good data.

My timing light is gunson's Heavy Duty Workshop Timing Light with Dial Advance similar to this, although I only paid about £55 in Halfords : http://www.gunson.co.uk/item.aspx?cat=662&item=3442

One word of warning, some of these lights do not like copper plug leads. They only work well with modern suppressed leads.

Steve
Steve Gyles

Thanks. Appreciate your help
Graham M V

Yes 32 degrees maximum ie above 4000RPM is good, no matter what the dissy is this is about the figure you are trying to get to irrespective of anything in between. If the engine pinks at mid range under heavy load then this overall setting can be reduced to 30 without any problems although MPG will suffer slightly. Naturally under these extreme cercumstances the dissy curve is obviously wrong and too much advance is being applied at mid range but the mechanicals of such a device can only do so much :-)

Back to you Graham you can use a portractor (remember those when we were at school?) to mark a point on the front pulley 32 degrees before the TDC notch. This is how we did it before programable timing lamps were avilable. Once this mark is put onto the front pulley (Snowpake does a good job) use your normal lamp and when the new mark lines up with the static point then you are at 32 degrees BTDC. :-). This is a must to be done first before any other thing is changed as the timing is critical to correct running and detonation supression. It is simply not good enough to do it statically, you can never be sure of the operation of the advance mechanism in the dissy so the only way to be sure is to do it as above.
Robert (Bob) Midget Turbo

Thanks - yes I remember protractors though not seen one for ages and probably easier all ways round to get my hands on a better timing light. I think it will be a good investment.
Can I show up my ignorance by asking a few really simple questions.
1. Maybe it's me but the mark I assumed to be TDC does not seem to be at exactly 6 o'clock. Is that right? Should I just take all plugs out and see when 1st piston reaches top?
2. When setting non static timin, I read that I need to disconnect the advance mechanism. Is that just a case of "breaking" the connecting tube (I have a few breaks connected by rubber hose) and sticking some insulation tape over the end?
3. The clamp bolt on the distributor seems to be located in the most inaccesable position possible! Can't seem to get a spanner or socket on it as access is blocked by the engine drain tap. Any tips, or do I need to find a spanner with just the right angle on it?
Really appreciate your help.
Graham M V

Bob-Graham
Hi guys--- Something else to look at-
As wellas setting your base timing up static and then checking that it doesn't go over 32 max advance, it is important to check the rate of advance against engine revs- I've struck a lot of these older cars and I guess Bob and others have as well with the advance springs in the dizzy rusted or broken making the dist. over advance in the low-mid range causing pinging and poor performance
Hope this helps-somewhere- Willy
WilliamRevit

Also--forgot to mention----
If you measure around the outside of you front pulley with a measuring tape and then devide by 11.25 you get 32 deg---- Measure this distance out clockwise from the tdc mark on the pulley and make your 32deg. mark Willy

I really worry about them adjustable timing lights- I tried three of them on an engine the other day and they all read different-- the worst one was 8deg. out at 36deg giving 44deg-----nasty---I just don't trust 'em anymore
The theory is good BUT Willy
WilliamRevit

Graham

1. As you have observed, the mark is not at the 6 o-clock. Don't worry. This is correct. It is probably set up this way for ease of observation. When your existing pulley timing mark lines up with the TDC mark on the front cover you are at TDC.

2. Yes. I have much the same. I just pull the line out of the rubber tube. I must admit that I normally do not then block the end. I just leave it open to the ambient static pressure.

3. Sounds like you have the base plate fitted incorrectly, or may be you somehow have the clamp bolt in the wrong way round, although this should not be possible. The nut should be to the front as shown in the photo (note that I have electronic ignition, hence the 2 wires coming out of the distributor).

Steve


Steve Gyles

Steve just wants to show us his nice shiny engine again!
Lindsay Sampford

Willy. Thanks, using the tape is a great idea - and like all the best ideas, so obvious now you mention it!

Steve, Thanks. Re (3) You are absolutely right as my bolt is to the rear, underneath. I have attached a photo, and whilst in photo, it doesn't look like access is too bad, believe me it is!
I assume it is just a case of undoing the two bolts to the engine block, removing distributor, and spinning it round. But being a bit of a novice, I would be nervous about doing this, for fear of not getting it started afterwards, especially as I have electronic ignition.


Graham M V

And just for interest, here is a picture from same angle as Steve's pic, - No bolt!!


Graham M V

Graham

You should be okay I think just to take the 2 mounting plate bolts out and rotate the plate around the distributor if you can. However you may find access to the plate rear bolt difficult with the distributor in place. Also, the plate may not rotate easily around the distributor - it may catch in the odd place. You may find it easier to remove the distributor to do the job.

If you do remove it, it can be a bit fiddly getting it back in as the mounting plate central hole has to be concentric with the distributor drive shaft hole for the distributor to push fully home - the plate is adjustable, having elongated bolt holes. The locating pin at the bottom of the distributor is off centre so it will only fit one way into the camshaft off-take drive; it is best to check to see where the distributor rotor is pointing before you take the distributor out and ensure it goes back in the same way (assuming you do not turn the engine over while the distributor is out!

Hope this helps a bit

Steve
Steve Gyles

Steve is right, its much easier to work on the dizzy with it taken out, I used to fit and adjust the points with the dizzy on the bench for example.
If you mark the position of the rotor arm on the outer casing with chinagraph pencil before you take the dizzy out.
Then when you come to refit it, line up the rotor arm with the mark and the distributor will locate in the correct timing position so long as you have NOT rotated the engine.

Just thought Steve, if you had only added some suitably engine coloured RED die to the oil you could have avoided your recent expensive engine rebuild and repaint.
I suppose the downside would be a driveway covered in what would look like bloodstains!
I would have thought that a small sign next to the "bloodstains" that read " Beware of the Dog!!" would be quite an effective anti-theft device though!
Colyn
Colyn Firth

Thanks very much everyone for your help. I am not planning to play around with it until early spring and if I have a problem, I hope you wont mind me posting for some help! Thx
Graham M V

This thread was discussed between 29/12/2009 and 06/01/2010

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