Hi again! Just a quick update on my 79BGT. As I mentioned the other day, the
car has been garaged for 9 months with a bad smoking habit. Everytime it
went over 50mph it smoke screened the road. I found lots of things which
could cause smoke (leaking OD oil, leaking mech fuel blanking plate, oil
from crankcase breather going onto exhaust or into carbs, head gasket
problems, etc etc...and everytime I found something and thought "aha! that
must be it!" I'd drive it again and still it smoked. I just got so fed up we
bought another car and left the MG in the garage awaiting new piston rings
(lots of blowby) and new bearings (rattly as hell).
I have finally got round to doing some work on it. Last night I got the
cylinder head off. I am still puzzled as to whether it is the piston rings.
Case for the defence : Compression test gave 10-10-9-9 (150-150-130-130) so
no problems.
Case for the prosecution : Lots of blowby gas, milage = 110k, if gas goes
down past the rings oil must come up
Initially I turned my attention to the gearbox and OD, as it only smoked at
speed (OD on). I found the oil had been leaking onto the hot exhaust. It
would take about 10 minutes / 5 miles before it smoked, but this could be
the time it takes the exhaust to heat up. Once smokey it would continue to
smoke at most speeds until left to cool. I really thought I'd found the
cause with that oil leak, but after fixing it it still smoked, worse than
ever.
I got my girlfriend to drive it while I followed and most of the smoke was
coming out of the exhaust (but some was general under-car smoke). This
pointed at oil being burnt. The smoke wasn't particularly blue, more white.
Coolant level was not dropping and the head had been skimmed with a new
gasket.
Upon pulling the head last night I could see nothing obvious. The gasket was
fine. I poured some light oil onto each piston crown and all 4 held the oil
for a good 30 minutes or more. The bores are smooth and shiney, no scoring.
I am now wondering whether to bother doing the rings or not. (would you?)
Seeing as I need to do the big ends, and the head is off, I may as well. The
engine has done a lot of miles.
One thing I did find which I think may possibly be the cause of the smoke
are the tappet chest covers. One has the breather pipe and a gauze inside.
Both seemed to have been leaking oil out under the seal and the breather
cover didn't look like it was seated properly at all. The exhaust manifold
was a little dark, but no signs of major oil contact. Maybe it all burnt
off?
What I plan to do is acquire another non-breather cover plate (anyone in UK
got one for an 1800 B series? beer tokens await!) and fit two of these with
new seals. I will then vent from the rocker cover where there is less oil. I
don't think I'll plumb this back to the carbs, more likely just pipe it down
the back on the non-exhaust side of the gearbox.
Anyone got any comments or suggestions here?
thanks
Scott
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