MG Maintenance 101 Tech Day
June 5-6, 2004 - Streamwood, Illinois

An interresting but seldom seen standard part. Notice the banjo bolt on the oil filter mount. This is securing the output end of a steel oil supply pipe which was fitted to inverted spin-on oil filter mounts when an oil cooler was not fitted. An inverted canister (not spin-on) was fitted from 1968 to mid 1970. An inverted spin-on filter was used starting mid 1970. For 1971-1974 models either the inverted spin-on or offset hanging spin-on mounts were used, but the hanging filter mount used a different supply pipe. For 1975-1980 models a flex hose was used. So this model of steel supply pipe was only fitted from 1968 to late 1970 with no oil cooler, and for 1971-1974 cars with the inverted spin-on filter and no oil cooler. The inverted oil filters were not very popular, and many have since been changed to hanging type mounts, so this particular type of supply pipe is rather rare. (And yes, we know the distributor drive is misaligned).

Click for BIGGER pictures, average 35K.

One of the stickiest problems was a non-functioning TCSA (Transmission Control Spark Advance) circuit. This was fitted to MGB starting about 5000 cars into the 1977 model year in late 1976. This can involve the inertia switch, overdrive gear TCSA switch (when fitted), TCSA micro switch, and the TCSA solenoid valve. This circuit is intended to inhibit ignition vacuum advance except in 4th gear, but when it doesn't work you never get vacuum advance, and the engine will have very poor power in top gear. First picture at left is checking the TCSA solenoid valve, which would function okay if it had power. Groveling around underneath the car the problem was finally traced to a bad switch on the transmission. Even in the later cars with the larger tunnel this is no joy trying to get to the switch on top of the gearbox.

The next "funky"problem involved a late model MGB running hot. This was caused by low coolant level. While topping off the cooling system it was discovered (the hard way) that the coolant fill plug in the top of the thermostat housing was a plastic part (as fitted to 1977-1980 model years) with a crack in it. This part promptly broke with only finger torque during reassembly. After some searching an earlier style brass plug was found for replacement. Let owners of 1977-1980 model MGBs be aware of this, and recommend that a brass plug be fitted.

The most serious problem of the day came with a car that had to be rescued from a parking lot where it "expired" en route to the tech session. Two years (but no so many miles) earlier a pro shop who shall remain nameless (unless someone should ask) did some work on the carburetors. This is a late model MGB which has been converted to dual carburetors. Pancake air filters (very restrictive) had been fitted to clear the brake booster. The filter base plates had been attached to the carburetors with coarse threaded bolts and no lock washers. For the front carb the coarse threaded bolts were screwed (wrenched and jamed in place) into the fine threaded bracket for the choke cable. For the rear carb the threaded bracket was omitted and hex nuts were used, but no lockwashers. The rear hex nut vibrated loose and fell off, found on top of the chassis rail in front of the firewall. The hex head bolt then dropped inside the air cleaner and was subsequently sucked into the carburetor throat. First picture above shows retrieval of the bolt from the disassembled carburetor. Second picture shows bolts with no lock washers.

First report was that it ran badly with poor power and backfiring under throttle. We surmise that the bolt was then caught under the dashpot air float and holding it up, which would kill the venturi vacuum and cause it to run very lean. Next report was that the engine was racing and would not idle below 3000 rpm, which is when it was parked. This is when the bolt was sucked farther into the carburetor and was stuck in the throttle butterfly valve holding it open. Good thing the car was parked at that time, because it could have been only seconds away from injesting the bolt through an intake valve and causing serious internal engine damage. This was a 10 minute on the spot diagnostic and repair, but only after the inconvenience of finding a ride and summoning the mechanic. This is one problem that never should have happened if the pro shop had exercised appropriate care during initial assembly. DO NOT EVER LEAVE A LOOSE FASTENER INSIDE THE AIR CLEANER.