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MG MGB Technical - Help me stop the pinging

Unless I set up my 68 B for less than about 5 to 7 degrees total advance it pings whenever accelerating. Pinging occurs whether acceleration is heavy or light. If I use heavier advance springs, remove the vacuum advance and set the static timing to no more than about 7 degrees there's no knock at any RPM or load, but the performance stinks. As soon as I introduce any more advance I get the "can full of marbles" sound. The pinging is not any more noticable under heavy load and I don't get any run-on or dieseling. I have what I think is a stock 68 high compression engine, according to the numbers, but I don't know for sure if it has ever been modified. I'm currently using 94 octane unleaded gas with about 4 cans of octane booster with no improvement. A local supplier has 110 octane race fuel (at $8 per gallon) and I'm thinking of trying that as a test to see if the pinging is strcitly compression related. The engine runs well otherwise and with the timing set to factory specs it's pretty peppy. But I'm afraid I'll be draining out pieces of piston with the oil if I let the pinging continue. ...Help!

Bill
Bill Boorse

Octane booster for me has proven to be a waste of my precious beer and bait fund. Doesn't seem to do much for my car, either. My first B, a '64, with high compression engine, would even occasionally ping running the old leaded high tests like Super Shell and Sunoco, especially if I pushed it hard or let the rpm's drop much below 2000. You're caught in the same predicament as muscle car owners....spend a fortune for high octane fuel, or, retard the timing a bit.
R. L Carleen

Hi Bill.

I have been wrestling with this one for a long time.

My own observations are :

1) make sure there is no 'coke' in the cylinders.
The B engine with it's relatively loose tolerances does burn a little oil, and modern high-detergent oils do produce coke when burned.
I had an 'A' series engine that was prone to pinking, and a simple decoke cured it, but not for long.

2) make sure that the cooling system is in A1 condition.

3) one step colder plugs don't make a noticeable difference, but do cause rough running when cold.

4) there is usually a fairly sharp edge on where the conbustion chamber meets the cylinder head face, I intend to try smoothing this to prevent hot spots.

HTH.. Don
Don

Just to clarify, when you "use heavier advance springs, remove the vacuum advance and set the static timing to no more than about 7 degrees" are you talking doing all of those together or any one change on its own clearing the pinking? If the vacuum removal cures things, then that could be your problem as it should be giving no advance as you accelerate and so may be sticking "on".

Have you got another dizzy you can beg/buy/borrow to substitute and rule out the mechanical and vacuum in one go?
Steve Postins

"Decoke" first. The hydro-frac method is easiest but I am a little sketchy on details (as I've never had to do this).

THen check dizzy for proper operation.

Mike!
mike!

Thanks for all he replies.
RL,
Most of the opinions on octane booster are the same as yours. But I thought I would give it a try as Sunoco 94 was not working.

Don,
I don't know if the cylinders are coked, but that's a good possibility. I tried colder plugs; no change. Cooling system seems good, gauge runs at less than mid range with a 180 t-stat.

Steve,
It only clears up with all those changes (no advance at all). Vacuum advance responds as it should: with heavy springs installed and vacuum connected to the manifold the timing light shows advance at idle that drops off when revved and I get a brief knock when the throttle is first opened; when connected to the carb throat I get no advance at idle but increasing advance when revved and increasing knock when accelerating. When tested with a vacuum pump advance increases up to about 10 deg at 13" vacuum then goes back when released. With normal springs installed and vacuum advance disconnected I get incresing advance on the timing light as revs go up and increasing knocks when accelerating at higher RPMs. I have replaced the dizzy with similar results before and after.

Mike,
Tell me more about hydro-frac.

Bill
Bill Boorse

Bill,
"Seafoam" is a good product for de-cokeing (sp?)
http://www.seafoamsales.com/
I set my advance @ 7 degrees as a starting point, then ran the car up a local hill. I then adjusted the vernier adjustment by 1 degree each time I ran up the hill until the pinging stopped...I believe it's 11 clicks to the degree.
Robert Dougherty

Bill,
You can make a do-it-yourself carbon cleaner with just a glass of water. Get the engine hot, put it in park and rev to about 2000 rpm. pour a glass of water down one of the carbs SLOWLY, more like a trickle. As the engine tries to slow down, slow down the pour/ increase your throttle. It does work, but the concept bothers a lot of people.
mike parker

Bill I hope I/m wrong but it dose'nt sound like ping to me if you have to retard the timing that much. It sounds like the noise stops when you remove all the engines power. Have you checked to see if the timing marks have moved on the harmonic ballance (rubber shot). Heat range of spark plugs. Tight tappets causing valves to over heat. The one that worries me engine bearings. You may have eliminated all these but if you have not: Denis
DENIS

We used to blow out the carbon using a bottle of water. We'd put a hose to the vacuum inlet on the manifold and let the engine suck the water in. Easier than trying to pour water into a sidedraft carb. This from the days when a few cars still had updraft carbs.
R. L Carleen

Bill,

If you have not already tried this, get yourself an adjustable timing light and check your dynamic timing over the entire rev range from idle till full advance. I had a similiar problem several years ago, and tried this approach based on good input from this forum and quickly located my problem. Static timing alone is meaningless unless you already know that the distributor is in perfect workingg order. Plenty of data in the web and archives about complete advance curves for all years.

Good luck,

Cliff
Cliff Maddox

Bill, first things first. Recheck the clearances oon your rockers. Make certain the lifers are properly adjusted. Once they're set, check the TDC timing mark. It sounds like you may be worrying about nothing - the timing marks could be way off, as happens frequently from a shifted outer ring on the harmonic balancer. Replace it if it is off more than a couple degrees.

Have the carbs ever been rebuilt? Are they in good condition? If they are tuned for a good idle while they have worn throttle shafts, the mixture will be all wrong for W.O.T.
Jeff Schlemmer

Could be running too lean which causes high combustion temps and increased tendency to ping. My 78 has a low compression engine....I cannot get it to ping even if I wanted to...:(
P J KELLY

Denis,
While I can't completely rule out bearings I don't think thats the problem. The car will pull under load with moderate power and no noise as long as it has no more than a few degrees of timing advance set. Also the noise is definitely the higher pitched "rattling" caused by pre-ignition as opposed to the "knock" of faulty bearings. I did check the timing marks and they are OK. I used a colder sparkplug, no improvement. Valves are set at .013" hot and have been reset recently with no change.
Cliff,
I use an adjustable timing light to set and check timing and all timing measurements have been dynamic.
Jeff,
As mentioned above, rocker clearances are good and timing marks are verified. Carbs were originally setup using the lifting pins, then reset using a Colortune, which showed the proper enrichment at revs increase.
Mike and RL,
I'm a little wary of using the water method but I'll probably give it a try this weekend to rule a coke problem.

Bill
Bill Boorse

So now I'm thinking plugs/plug leads/points/condenser...plug leads breaking down can give a weak spark, poor combustion, coke, unburnt fuel....ping!
P J KELLY

PJ,
plugs- new
wires- new
points- new
condensor- new
cap- new
rotor- new
coil- new
filters- new
result- starts right up, runs like a top, but still pings
Bill Boorse

Pinging on a tuned B series is par for the course , I would like to get capsule that only gives the max advance at very high vacuums, so you get good economy at cruise depresions , but no pinking when you ask the engine to do some work. Pre-ignition and pinking are different effects , in the first the mixture is ignited early by coke or hot rough edges, in the latter the flame front travels too fast and peak pressure arrives when the piston is still on it's way up i.e. the mapping is wrong .
S Best

Is there a possibility that the timing chain is off by one tooth? That could cause this. Also remove your distributor cap and see how many degrees of slop there are between turning your engine forward and backward - this will tell you if your chain tensioner is functioning.

I think there could still be carb problems as well. Is there a local shop you can bring your car to and check your fuel mixture / exhaust gas? I've found that the Colortune only screws up my mixture, although the piston pin method gets it close.
Jeff Schlemmer

Bill-
Jeff's ideas about the camshaft being out of phase and/or the timing marks having shifted on the harmonic balancer pulley are both a possibile cause of your problem (I've seen both happen myself). However, since the problem happens under acceleration I have to wonder if the bushings/throttle shaft are worn, allowing lean running. Test for this by squirting some carburetor cleaner onto the bushings while opening the throttle. While you're at it, do the same with the intake manifold gaskets.
Steve S.

You will get pinking/pinging if either the timing is too advanced per-se, or if the timing is correct at the quoted rpms (usually pretty low) but then becomes too advanced for the engine and fuel characteristics. These engine vary wildly in their characteristics, and hence how much advance they can take. The manufacturers figures were supposed to take account of the worst case, and then add a bit of safety factor. But throw todays fuels and wear on components including slack centrifugal advance springs into the mix, and you can throw the manufacturers figures into the bin. UK 4-star leaded was supposed to be about 98, which is the same as Shell Optimax, but that pinks worse than leaded did on my roadster. You can still get leaded in the UK from specialist outlets and they claim 99 or higher, which could explain why mine pinks worse now. In the 70s I used to set my timing on my then BL car using a vacuum gauge which takes account of many engine and fuel characteristics, and I could set it noticeably higher than the manufacturers figures, and get the benefit of increased performance if I used it or improved economy if I didn't, and was obviously at the better end of the characteristics distribution. Tried the same thing on my roadster and ended up with the manufacturers figures, so obviously this engine is at the worst end of the distribution. I have been experimenting with alternative vacuum capsules as S Best suggests, and whilst I have been able to prevent pinking without as much loss of performance as before, I'm sure the economy is slightly worse. It's difficult to tell with the performance though, just by the Mk1 seat-of-pants, as my other car is a V8 ...

Have you tried plotting the centrifugal and vacuum advance curves against the manufacturers data? An adjustable timing light makes that relatively easy. If your standard springs *are* weak, and you put in replacements that are *stronger* than the originals, then you *will* flip from from a too-aggressive curve causing pinking to a too-modest curve causing poor performance. But if your engine characteristics coupled with the grade of fuel you are using *do* require a modest curve, then you will have to accept the poor performance as the price of no pinking.
Paul Hunt

Bill: I have a 69 with 88,000 miles, not too different than yours. I have been running it without any pinging on 93 Octance, and it performs very well with good power to 5,000 rpms. When I first obtained the car I quickly found that the original dizzy was worn out and I replaced it with a new 45D "euro-spec" from Brit-Tek.It was money well spent. I did a comprehensive tune-up, including setting the valves and checking the timing marks, and set the initial timing by the static method. I did the "final" timing by driving the car as described above, in high gear under moderate load and made fine adjustments until the pinging, which was very slight, disappeared. My carbs are in good shape and I am using NGK BP6ESR plugs. IMHO pinging need not be a fact of MGB life.
Regards, Andy
Andy Blackley

Paul , re your comments above .I would be very interested to know what capsule you are now running . I checked some and found that the one fitted to my HC engine seemed to be the most conservative around.
S Best

S Best (Steve?) - I'll have to get back to you as the roadster is in the other garage and not immediately to hand.

You *can* always get rid of pinking by retardation, but sometimes that makes the reduction in performance and increase in running temps so bad that one just *has* to investigate alternatives. I'm still waiting for knock-sensing retardation on the B-series to be practical ...
Paul Hunt

Thanks Paul , I will not be using the car until the 12th March which is the SE centre awards dinner followed by the Chairmans run on the Sunday. So there is lots of time ! In the meantime I will check the timing mark on the pulley against the piston position in the bore, just in case the car is not really set to 10 BTDC static .
The Christian name is Stan BTW , I just never worked out how to enter it when I signed up .
S Best

Stan, As well as mapping the advance curve, it may be useful to measure the vacuum at different throttle positions before selecting a can. FWIW my (modified) GT uses a 5-8-5 can. It was on the dizzy when I bought the car, but disconnected at the time because of the carb set up. I think it came off a midget and it's a lot milder the B versions. I could probably improve fuel economy with a different can, but I'm sure it would cause pinking at part throttle with the mechanical advance set as it is.

Steve Postins

I've watched this thread with interest and agree that it really is an exasperating problem with the B series engine. It never really was 30 years ago when fuels contained lead and other anti knock additives but the virtual removal of these together with other factors such as distributor wear does nothing to alleviate the problem. Firstly I assume that on this 68 car the vacuum take off is on the rear carb and not the manifold. This will immediately mean that on wide throttle there is no vacuum advance and that at least should be out of the equation. Now setting the valve clearances to .013" is not correct, they should be .015" and I would correct this right away as this will affect the valve timing by several degrees. I do not believe that the valve timing is otherwise out such as a tooth on the sprockets as the performance would be so drastically affected that you would sort that out pretty quickly.

Remove the top part of the distributor shaft clean the whole assembly,lubricate and refit the springs. Now the springs should JUST and no more pull the assembly back against the stop pin, if it doesn't and there is free play then the springs are weak. Someone already mentioned that static timing is pretty useless and if the springs are weak it is doubly so.

Set the engine to 600 rpm and with strobe adjust timing to 10 degrees. I would agree that full throttle pinking from say 1500rpm in 4th gear is a given in your case and that with 94 octane fuel you will have to come back about a couple of degrees from that point but bear in mind that the timing is correct when the pinking is just audible and no more.

All of the above assumes that the engine is in reasonable condition, is not full of coke which I doubt with today's fuels and that it is not overheating which is a very important factor.

If however your advance springs are weak then having set the timing at idle to compensate you will lose out on advance further up the range and replacement of the springs is a whole new issue.
Iain MacKintosh

Thanks to everyone for your responses. I really feel that decoking is probably the next thing I should try. I’ve been through just about every possible variation of timing setting and distributor setup; I’ve verified the timing marks are accurate with #1 piston TDC; I’ve done timing checks at various engine speeds from idle (600 RPM) to 4000 RPM using the stock dizzy, the dizzy from my A, and a newly purchased rebuilt unit from NAPA; I’ve moved the vacuum pickup from the rear carb to the manifold to no vacuum advance at all; I’ve changed advance springs from stock to so stiff they gave no advance at all and back to stock. In every case the result has been predictable and the car appears to be a textbook example. But the one factor that remains is that anything more than about 10 degrees of advance (whether static, vacuum or centrifugal) causes pinging.
I’m not 100% sure that the mixture is not leaning out at some point, but I have tried spraying carb cleaner on the shafts and other potential leakage areas and have gotten no indication of air leaks. Also I’ve used a Colortune to set the mixture and it shows good enrichment when the throttle is opened.
I’m curious how incorrect cam timing would cause pinging. I’m sure that anything that upsets the balance of correct tuning will show some symptoms but I thought cam timing would show up as a performance issue first.
Unfortunately I didn’t get a chance to do anything to the car this weekend, but I’ll keep trying until I find the answer and you guys will be the first to know when I do. Meanwhile, thanks again for everyone’s input.

Bill
Bill Boorse

Whether 13 or 15 is the perennial topic of whether the valves should be adjusted hot or cold. The Workshop Manual specifically quotes 15 cold or 13 hot for the 18V, for example. And since it is easier to maintain a constant temperature when adjusting cold that is when I do them. Although the temptation at this time of year must be to do them hot :o) Then there are those that adjust them running ..., with a ClikAdjust ..., etc. etc.

A lean mixture at some point in the throttle/load range will often show itself as a flat spot.

Stan - you can amend your details by clicking on 'Customise' at the top of pretty-well every screen on the BBS.
Paul Hunt

This thread was discussed between 06/01/2005 and 11/01/2005

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