On saturday I finally got round to changing the gearbox/overdrive oil on our
1978BGT. It was the first time I'd stuck the car up on ramps and had a good
nose underneath since buying it a year ago. We have always had problems with
the overdrive taking a long time to engage. It wouldn't even think about
coming in unless over 60mph and was taking up to a minute to engage and then
it wobbled in and out for a while. The gearbox was also excessively whiney.
I got up underneath and had a look at the various drain plugs. I seemed to
remember some of you on the list saying that the gearbox and overdrive
shared their oil and they needed 20W50 NOT gear oil. I couldn't remember if
it was 1 filler plug and 2 drains, or 2 fillers and 1 shared drain, so I
looked in Haynes and it said 1 filler and 1 drain...mmm...ok. So I carefully
got a bowl under the gearbox drain plug and undid it. About 1/2 a litre of
reddish brown thickish oil came out. Didn't look like 20W50. Looked more
like hydralic fluid or some sort of gear oil. Some of you had advised
removing the sump plate from the OD unit (a Laycock LH type) to clean the
filter gauze. Haynes said to remove it after the oil was drained, so I
happily undid the 6 bolts (which were not tight at all) and then got a face
full of oil. :-(
Cleaned up the gauze thing and bunged it back together, then decided to
re-fill the gearbox (and therefore OD too). Mmmm....how on earth am I going
to pour the oil into that hole on the side? I rigged up a hose up to the
engine bay and then carefully poured in some nice new 20W50. How much went
in?!! (looked in haynes....three and a half LITRES!!!). NO WONDER THE
OVERDRIVE TOOK AGES TO ENGAGE!!! Filled it up and replaced the side plug.
Did the engine oil and other bits and bobs. Fitted a new heater tap too (old
one sprang a leak). Went for a drive....MY GOD!!! How different?!?!?! The
OD now comes in *instantly* and also can be used from ~30mph upwards. The
whole engine and gearbox sounds a lot better too.
Now for the interesting thought. The OD seemed ok when we first bought the
car but then got worse and worse. Lately the car has been smoking a lot. Not
just the usual blue smoke when accelerating hard but clouds of white smoke
out the back. It only does this at speed on the motorway. I put this down to
the blow-by gases (the crankcase breather was dribbling oil onto the
exhaust, but ducting the vent back into the carbs made no difference to the
smoke which was odd), then I suddenly had a thought. It only smokes white
smoke at speed, WHEN THE OVERDRIVE IS USED, and white smoke = oil on a hot
surface not blue smoke from burning oil, and the oil has leaked out of the
overdrive (somehow, probably due to the finger tight bolts) and must have
gone onto the hot exhaust. The rear half of the exhaust looked quite black.
If this is all true then it is really good news. I was really thinking I
would pull the engine out this autumn. I have been pricing up engine hoists
etc and we were pretty much thinking of selling the MG and buying something
sensible. It's a great car, but the smoke etc made it awful to drive and no
good for longer journeys. I put the smoke down to worn piston rings (but the
compression was ok) and was planning to pull the engine and rebuild it.
Maybe now I don't have to lift it out after all.
The engine is quite rattly above about 3krpm so I would like to change the
big-end and main bearings if possible. I heard this was possible with the
engine in the car. Do I just pull the sump pan off and tuck in? The front
sump pan bolt heads look hard to get to. What about thrust bearings? The
revs drop by ~500rpm when the clutch is pressed so that signifies worn
thrusts. If the piston rings really are in need of renewal is it possible to
just pull the head, undo the big ends and then extract and refit the pistons
with the block in the car. Lifting that B series out looks like a nightmare
task.
One other thing, there are some rust bubbles rearing their heads just under
the silver strip above the front wheel on the wing. Is it easy to remove
this strip so that I can attack it with the sander and rust killer.
Scott
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