1.6L, 104K, very early 1990.
I ran a compression test a while back, showing very low dry
compression in cylinders 2 and 3, with OK dry compression in 1 and 4.
Review, as follows:
1: 146/182 (+36) [front]
2: 126/152 (+36)
3: 112/134 (+22)
4: 155/192 (+37) [rear]
2 and 3 are below Mazda spec. After getting good help from you all,
and learning about this as I went along, I resigned myself to having
ring trouble. I was not looking forward to the rebuild task, to say
But now that I have time to tackle a rebuild, I borrowed a full-on
90/100 psi 20 gallon air compressor rig and did a real deal leakdown
test to pinpoint the problem before I started.
I found this...
All 4 cylinders leaked fairly substantial air out the exhaust, with
the middle two quite a bit more. No bubbles in the radiator. No air
from the PCV. No air from the intake. No air from the dipstick.
The crank was replaced at about 70k due to the infamous nose failure.
I do not know if the main seals were replaced, nor any bearings down
there, but I have to assume the rebuild was competent and at least the
seals were replaced. It was done for the previous owner. So I safely
count the lower end as solid.
The engine overheated at 95k due to a radiator failure. The stock
exhaust manifold is cracked at the 4 to 1 joint, fairly significantly.
Gas mileage is below avg, about 21 in town, 26 highway. Engine noise
is above average.
The exhaust valves are shot. Question is, how do these things fail
when overheated, if that is the cause? If not the overheating, are
these known to wear prematurely for some other reason? Is it possible
the head has more damage that simple valve seats or the valves
themselves? Should I go ahead and have all the springs replaced? (ie,
are they compromised when overheated?)
The compression will go up after the valve job. Based on the halfway
decent numbers of 1 and 4, am I likely to see 170 across the board?
That would represent very good numbers for a 104k engine and make me a
While I've got the head off, what else should I consider doing? I
have the enthusiast manual in the mail, so I'm relying on the group
and sites for my info now. I do plan the cooling reroute mod and will
work to correct my low heater output I asked about a few days ago.
I'll polish the intake manifold and work up some kind of CAI. As for
the valve seats, I'm debating single and 3 angle. I depends on the
cost. I'd like to either polish or chrome the valve cover.
- posted 16 years ago