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MG MGA - Fixed the pinking

The last couple seasons I was encountering preignition that I couldn't resolve. This season I had the distributor rebuilt hoping for an improvement, but still couldn't resolve the pinking. Then I realized that I had put 20k miles on the engine without a proper draft tube, so I figured my combustion chambers might have built up carbon deposits causing hot spots. I scoured the combustion chambers by pouring water down the carb throats at 3000 rpm and blew out quite a bit of black stuff. Took it immediately on an 80 mile trip and it wasn't pinking at all.
Mark J Michalak

I haven't heard of anyone doing that for many years. We were taught that it was a good way to decarbon an engine while attending an automotive techinical school in the early 1960s. I don't think I would do it to a modern car without removing the catalic converter first. It might plug it up!
Ed Bell

What is the procedure for "pouring water". Is there some special way of doing this? Gordon
Gordon Harrison

On modern cars I have used a suitable vacuum port and ran a line to a gallon of water and let it suck it in at a high idle. Too much water at a time can damage an engine. I have seen cars that someone tried to force through a big rain puddle suck in so much water that blown head gaskets and bent rods were the result. On our dual carb cars I would probably run the idle screw in to 2500 rpm and the run water into each carb separately. Remember that too slow just means spending more time doing it while water poured too fast can break things.
R J Brown

This is interesting because the MGA manual does mention that de-carboning now and then is necessary (but I had not found where it said how to do that) - I always thought that you did this by driving on the highway as fast as you can. ;)

R Harvey

The Weslake heart shaped chamber is prone to ping if there are any hot spots (carbon does this) or in any case if the tip of the heart shape is too sharp.

It was always a matter of course to round off the tip whenever an MGA head was removed.

Nice that your water treatment did the trick! The other approach is the Italian tune-up - go and run it at higher RPM for awhile. This often works on cars that have been puttering around town at low RPM all the time.
Bill Spohn

Chaps, We used to do a RedEx decoke in the '60s. You turned the engine by hand until the pistons were half way up the bores with the plugs out, and then filled the bores with RedEx and left over night. In the morning we siphoned out the RedEx and then turned the engine over (still with the plugs out and with rags held against the plug holes to catch the oil). Then we replaced the plugs, started the engine and dripped RedEx into the carb throats while at a fast idle. Very non-pc as you can imagine, since clouds of smoke poured out of the exhaust, but it certainly did the trick (although the exhaust smelt a bit for a while afterwards!!!!). Wouldn't do it today, would get lynched by the neighbours ........ AB
A Bennett

I'm glad everyone didn't think I was nuts. Next time I have the head off I'll do some work and remove the sharp edges. It's a 9.5:1 motor so pinking is almost inevitable unless timing & mixture are tip-top and 93 octane's in the tank.

I had tried Bill's "Italian tune-up" before. It works after you're all choked up from running in the city, but I ran that sucker up past 100mph and it still didn't completely decoke it, so I figured water was worth a shot. I was going to do it by hand until my dad told me he once blew a head gasket and by the time he got it home, the steam had scoured the combustion chambers into looking like new.
Mark J Michalak

Water into the carbs to steam clean the head - Now that's new one on me - how much water and how fast is too fast - and what do you use to "run the water in" ? cheers Cam
Cam Cunningham

In 1976 I had a 1974 Ford T-Bird. It was just off warranty. 9 pm on friday night my wife called and said that engine had blown up in mall parking lot. I* arrived to find at least 50 people standing around and commenting on the flames that had come from my car.All I could see was $$$$$$$ flying up in the air as warranty was over. I could see nothing wrong externally. No coolant or oil stains on ground so I started the engine and the people all moved way back. It ran but sounded like two beer bottles clanging together.Then I sent wife and daughter home with our other car. I decided since that it was running an all 8 that I would try and get it home. 2 miles later I was home in driveway still clattering but running on all 8. Using a teakettle of hot water I poured it down the carb as fast as the engine would take it and remain running. Clinking was diminishing greatly. Topped it off with a quart of trans fluid and stalling the engine. Next morning I made a great goof-up. I started the engine without covering both exhausts with something to control the mess. It started and with great gobs of smoke and gunk which left two trails of black soot out our drive way and onto the street I found that all traces of clinking and rattling were gone.Apparently what happened was a chunk of carbon build-up had loosened and the piston was hitting it against the head.One piece had temporarily held a valve open and thats what created smoke and flames earlier.
The net result was that we drove the car until it reached 198000 miles and the heads were never off.
I have used this system prior to rebuilding MG engines an most of the carbon was gone or was completely soft.
Sandy Sanders
Sandy Sanders

Can you offer a more detailed explanation on how you proceeded with this "water cleaning"? What equipment is needed, what rate of flow, how long do you do it, what RPM's is best...etc. Gordon
Gordon Harrison

Gordon and Cam, I'm not sure that there's an exact science to it. I had my dad hold the throttle while I did the pouring. I'm guessing that about 3000 rpm is good for this. You could also just run up the idle screws. I removed the air filters and ran a flexible funnel down the the carb throats. I filled up the Tudor bottle with water, and slowly poured half the bottle into the front carb with the engine revving, then the rear carb. It's fairly easy to gauge how fast to pour, too fast and the engine will sputter too much. I was pouring fast enough that the water had an audible effect on the engine, but not nearly enough to choke it out. My reasoning was that too little water would probably not have a dramatic enough effect to really clean the head. Obviously you don't want to kill the engine with water, and I suppose if you had suspect rings an excess of water could make its way into the oil. Other than that I don't see too much danger to the engine.
Mark J Michalak

This thread was discussed between 14/05/2008 and 17/05/2008

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