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MG MGA - Pinging, How Noticeable?

I've made some changes to my 1800 installation. One piece side covers and a port and polish of the head. The engine sound has changed. some of the harshness of the exhaust note is diminishes and i'm hearing a very feint "tinkling" sound during very hard accelleration. Timing is slightly retarded and the onboard oxygen sensor indicates correct mixture. How loud is true detonation?
Thanks,
Doug
D Sjostrom

Your tinkling sound would seem to be pinking due to incorrect timing ( mixture will have little effect on this although a very lean mixture could butn out your valves)- it will not be very loud and the radio would drown it out - which is always an option. Try adjusting the distributor position little by little (or turning the adv/ret screw if you have one) and driving round the block each time until the pinking is eliminated - will save damage to your engine - cheers Cam
Cam Cunningham

You haven't got too many answers, hey Doug so I will have a go.
I would say Pinking is easily audible, well to me anyway. I ran an engine in a midget for a couple of years that was so near the limit it often pinked a little at 3.5K that I would back off the throttle slightly until I got the revs up to about 4.5 then I could give it evrything. So I know what it sounds like.
That said the B series, well all of mine anyway, is a rattly engine when revving. Thus it is worrying to know if it is simply valve train noise or detonation. I also have to disagree with Cam and say that a major cause of detonation is weak mixture so where Cam got that info is only known to Cam.

So to answer your question.

Detonation, (pinking) will occur at about 3.5K revs under heavy load! It ought to disappear at maybe 5K plus! It should also disappear if you back off the throttle slightly.

You should try and make the engine pink to know for sure what it sounds like. Advance the timing and find a good hill and see if you can cause it to pink and then be sure of the sound.
Bob (robert) yes I own an MG Dwarf!

As Bob says, weak mixture will cause pinking even if the timing is spot on. I cannot run 95 fuel in my car (pinks like mad under acceleration if I do). Pinking destroys engines fast, so don't leave it long to sort out.

A good way to sort out the timing / mixture balance is to adjust the mixture and carbs till they are right, then aadvance the timing till it pinks and back of gradually till it doesn't pink anymore - with modern fuels the optimum timing is nowhere near the original setting any more. Then take the car for a run, and if it pinks back off, if not advance till it does, and then back off etc. Then paint a very clear mark onto the casing of the distributor, and a corresponding mark on the retaining collar, and you will never have to repeat the excercise for that engine/fuel/carb setup.

There is an alternative from J&S to be used with electronic timing, and that does the whole thing in real time, per cylinder, automatically. Great piece of kit, but expensive at $300 (but a lot cheaper than a new engine)
dominic clancy

Robert,
Good advice. It's been so long since I've heard the real thing I'll purposely induce it to remove any doubt.

Dominic,
I'm intrigued by your description of the "J&S" product. Can you supply a web site address?

Thanks all,
Doug
D Sjostrom

Dominic's first paragraph sums my car up. It was probably Dominic who told me to run Shell Super (98+) octane. It got rid of all the pinking without having to touch the ignition. A couple of weeks ago I was forced to put in 95 (run out of super). Pinks like crazy as described by Bob in his ditty. Can't wait to get back onto 98 again.

Steve
Steve Gyles

http://www.jandssafeguard.com/safeguard.html
dominic clancy

Doug, what distributor do you run? What's the 5-digit number on the casting? If you have an emissions dizzy, it'll have way too much advance for a good performance engine. That'll cause the pinking.
Jeff Schlemmer

It's a Eurospec purchased from Brit Tech a few years ago before they became scarse. I've checked the advance with an adjustable timing light and am satisfied that the dizzy isn't at fault. I'll learn more after the intentional ping test. I'll probably need to wait for spring however as our salt and sand free balmy early winter seems to be about to abruptly depart.
Thanks,
Doug
D Sjostrom

This thread was discussed between 14/01/2007 and 15/01/2007

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