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Engine History
Before:
The car in question is a
1987 Toyota MR2 Supercharger imported into the UK from Japan. It was
purchased by me in 2001 for £2000, it was known to be a bit rough around
the edges but generally sound, it was however known to be clocked. Most likely
this was done in Japan before purchase by the previous owner who imported
it. Estimated mileage was over 100,000 miles
The engine was known to be
good although it did burn a bit of oil on start-up. Other than that it was
good and reliable.
Two weeks preceding the track day
i had fitted a Blitz Pulley and was generating around 12psi for the most
part.
On track:
I had the first session
out on track for 20mins, engine felt good and expected no problems. In fact
i was just starting to enjoy the car for the first time since i'd purchased
it as i'd been working on improving the car considerably as a lot of parts
needed replacing (brakes, springs, bushings, steering rack, ball joints
etc.)
During this
session i heard detonation and i also remember hearing what i'm sure was
the sound of the pistons tapping on the head. Although the sounds where worrying
there was nothing during the session to suggest there was anything wrong.
Aftermath:
As i warmed
the engine up for the next session i noticed large quantities of smoke
from the exhaust, it was at this point we knew something was wrong. At
first we thought that the head gasket had was failing, but also considered
rings and maybe valve stem oil seals. Due
to some very annoying circumstances we had to drive the car back from
Elvington to Macclesfield (about 100 miles). Still thinking the head
gasket was the most likely cause (the sounds of the detonation wouldn't
really ring home until i watched the video back the next day) we decided
to drive back after buying 8 litres of oil from a local garage so we could
keep topping her up. Strangely as the engine warmed up the clouds of smoke
almost disappeared, adding more to the confusion. Oil consumption was
still bad, using a few litres on the drive back alone. The
problems didn't appear to be getting any worse as we drove so we continued
at a steady speed limiting it to 3000 rpm. We arrived home late Saturday
night. The
next day we went out to inspect the engine in detail to decide if we
should think head gasket, in which case we would have left the engine in
place and just removed the head, or to consider a complete tear-down. Compression
test where confusing, which where very very high (over 200psi). We knew
this was from the oil, so surmised that this could only be from three
things; 1, head gasket failing. 2, ring damage of some sorts or 3, valve
oil seals. The head gasket was discounted as there was no gasses present
in the oil and no contamination of the water. Valve oil seals where
discounted because the high compression and oil was present on all four
cylinders. So
it was decided the damage was to the pistons/rings or cylinder bore. As
this meant accessing the bottom end of the engine it meant engine removal
was the only option. A
few weeks later and the sun was out on a gorgeous Saturday , with help
from a friend the engine was extracted.
On Sunday the engine was stripped and we found the problems.
Diagnosis:
It was
clear from what we where looking at that we'd suffered from detonation
across all four cylinders, most likely from a fuel shortage or failure of
the Knock Sensor. The
pistons where black with sooty oily deposits on
the crown with a small area burned clean, the outer edge of the piston had
warped upwards on the intake side, raising the piston above the deck to
make contact with the head. There was extensive pitting around the top
edge of the piston and ring lands. Because the piston was warped the rings
when when cold would be jammed into the land (this is what caused the oil
consumption that cleared when the engine warmed).
Next
Steps:
Ok, we knew
the block, pistons & rings where screwed. The decision to rebuild the
engine was not complicated. The fact that i could use a 2nd hand 4A-GZE
engine for around £500 was appealing, it also had its downside. It was an
unknown quantity, i would have no idea of the engine condition and could
quite likely have problems in the future with it. Given
i had not built an engine before and i like the idea of making a 'as new'
engine that should be as reliable as the day it left Toyota i budgeted
£1500 to rebuild the damaged one.
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