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Chicagoland MG Club: Driveline
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  Chicagoland MG Club:Driveline
Just a Simple Wrench

by Jake &Ann Snyder

Night Sounds

We knew the guys at the quick lube had nothing to do with the engine miss. Every so often we take one of the MGs, usually the 72 GT, to recycle five gallons of used motor oil, and, incidentally, have the oil and filter changed. Needless to say, some of the amenities, such as checking the battery electrolyte level, are predicated on the guys finding the battery and knowing how to get to it, but we do this regularly ourselves, anyway. The whole point of the commercial oil change is to get rid of a few laundry detergent jugs of used oil before we reach the point where the last container left empty of used motor oil is the big soup tureen. A few commercial oil changes a year gets rid of all the oil from all the gearboxes and engines for all three of our MGs. And we had a pleasant chat with a young fellow who fondly remembered his dad's MGB and hopes to have one himself one day.

The miss got worse and louder the further we traveled in the suburban area in which we had a few errands and light shopping to do. The miss got so bad that we stopped once just to check that the oil level and coolant were okay. We have hung around tracks enough in the last few years to appreciate the good signs when the oil is where the oil should be and the coolant is where the coolant should be, and every thing was fine (except the miss) so far. Finally, the last bit of shopping was done, and the car was now making heavy exhaust noises from the engine compartment while taking a full half minute to build up to thirty from a stop light. The coolant temperature had started to rise, and with the very poor acceleration, the interstate seemed a better choice than stoplights. The third means home, on the hook of a tow truck, was also a very real consideration, but the car still showed eighty pounds oil pressure, and giving up seemed too easy. After a full mile accelerating as best the engine could, we were very happy to tuck in behind a semi and make the next six or seven miles at fifty-five mph in overdrive. The two miles from the interstate to home were nerve-wracking, but uneventful.

We had been convinced from the first that the manifold gasket had blown out around one of the carburetters, as clearly had happened at the front exhaust port. The SU HIFs were quickly removed, revealing perfect gasket surfaces around the intake ports. Bad luck, this, as the next (and some will argue, the most likely) possibility was the head gasket itself. Prior to removing the head, the plugs were removed and the compression checked. Cylinders one and two showed about 150 psi, but the gauge said that cylinders three and four were completely lost. Not wishing to trust a single measurement of a not very expensive compression gauge, we noted that a thumb placed over either of the first two cylinders got pushed off, but a thumb over cylinder three gave a spray of air from the spark plug hole of cylinder four. So the coolant was drained to spare the new oil, and, needless to say, there was no thrill of surprise when the head was removed to reveal a head gasket with no substance remaining for most of the area separating the back two cylinder bores. The good thing was that the destruction of the gasket had stopped a little short of a water passage, otherwise the option of calling a tow truck would not have been an option.

The studs were removed, and the deck was massaged with a hard white stone and a little WD40 until everything was clean and shiny. The burned area between cylinders three and four cleaned up nicely. The pistons in bores one, two and three had heavy deposits of carbon. Grease was pressed into the edge around each piston before the carbon was removed, and the tops of the piston were then polished with a plastic kitchen scouring pad. The old head looked perfectly flat, but a fresh one was on the shelf for just such happenings. The question of what kind of gasket to use was not much of a question, as we had only one of the newer silver kind instead of the copper laminated type that had failed. Later, after questioning club members with greater knowledge of materials and practices, we learned that the best head gaskets to use currently are the graphite and steel versions made by Payen. We will try one of these the next time we must replace a head gasket.

But the question remains, "Why did this gasket fail?" Was it because we have put about a half-million miles on our several MGs, and it was our turn? It certainly was not because we failed to retorque at recommended yearly intervals, or because we over-revved the engine. The Fel-Pro web site mentioned pre-detonation as a possibility, but we always use the highest octane fuel we can get at the pump, and the ignition is timed properly, at least at 1500 rpm.

Thinking back to months before the gasket failure reminded us of long night drives on heartland highways, with the wind noise blending with the sound of the engine, gearbox, exhaust and tires, when the total rush of sound is broken only by the occasional creak from the oft-welded monocoque. And there is the occasional tinkling on a curve as the hubs run out to the extent allowed by the bearing shim packs, and the rotors ever so slightly caress the brake pads. This strange menage-a-trois of two human beings and an MG is further ushered by a melancholy, musical whistling note that does not seem to change. WAIT A MINUTE. MGs do not have "melancholy, musical whistling notes". When daylight came, we checked for a frayed fan belt and bad alternator and water pump bearings. But we did not find the source of the whistling for months, until the distributor was removed. This first thing we do when handling a distributor is to attempt to blow through the vacuum advance mechanism. And the diaphragm was perforated, apparently just enough to give a whistling note as air was pulled though it into the intake manifold. Changing the vacuum advance device cured the whistling, but we had still driven the car at cruising speed for thousands of miles with the spark occurring at the wrong time with respect to the piston travel. Did this cause the gasket failure? Could be, as this was the first head gasket failure for us in the only whistling MG we ever hope to have.

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