The cylinder head.
All things being equal down below, it's generally up here where power
is gained or lost. As with everything else on an engine build, close attention to detail
can ensure that your raging horses don't end up clapped out nags.
This part of the process started for me a long time ago, back when the engine was first stripped and
the block was sent out for machine work at the beginning of the build, attention was turned to cleaning
up and inspecting the cylinder head...........
Unfortunately what we found at the time wasn't pretty. After cleaning up the combustion
chambers we found some cracks between the exhaust valve seats..........
The cracks were small and the engine had shown no signs of pressurising the coolant
system before coming asunder, which it would do if the crack had spread to the water gallery
and was allowing combustion pressure to leak into the cooling system.
Also the engine was compression tested shortly before it came asunder and while the figures
weren't great they weren't bad enough to suggest compression was being lost on a large scale.
So from all that we surmised that the crack was probably local and most likely didn't
extend all that far.
However when you placed a flat edge across the crack you could see that the surrounding
aluminium had started to shift...........
This was the nail in the coffin for this particular head, as the valve seats which are press fitted
into the head either side of the crack rely on everything in this area staying nice and
solid to stay put. With the aluminium starting to shift, however little, there was a real
possibility one of the valve seats could start to work it's way loose, should that happen
while the engine was running the resulting damage would be very, very, expensive.
There are repair options for this type of crack but they'd require both valve seats either side
of the crack to be cut out, the crack welded up and then the whole lot machined again
to refit new seats. But, this head was proudly displaying 3 cracks in total, all in the same places,
between the exhaust valve seats, in three different chambers, which meant this head was beyond
economical repair.
The other surprising discovery made on dismantling the head was the condition of the valves and valve
seats, they were in poor poor shape and can't have been sealing the combustion chamber that well.
This was most likely the reason behind the poor compression figures tested earlier on.
Actually it was a little surprising this engine drove as well as it did before coming asunder........
So after deciding that replacing the head would be the best option for the rebuild, the
search began. As this engine and car was built in 1986, that made this a 200hp version of the
S14 engine (195hp when fitted with a catalytic converter).
And a little later in it's life (around '89 I think) the S14 engine was available in an uprated form producing
215hp. Along with other changes one of the main differences in the 215hp engine was larger
inlet ports on the cylinder head. If I was going shopping for a cylinder head I decided I might
as well try and track down this larger port head, which would help in the search for a little more
horse power from this engine.
A quick call to the main dealer for prices on both the 195hp and 215hp heads let me know where
I stood,
should I happen to win the lottery,
twice!
195hp head pt. no. 11121309891 = €1220 -10% discount + 22% Irish Vat = €1340
215hp head pt. no. 11121312785 = €3035 -10% discount + 22% Irish Vat = €3330
So,
the search began for a good second hand head. And after a while ringing around and trawling
the interweb we came up lucky. A 215hp head overhauled and ready to go and the iceing on the cake,
the head came with uprated Schrick inlet and exhaust valves, springs and titanium retainers, and all for a good
bit less than the price of a bare 215hp head from the dealer. Excellent.........
Although not blindingly clear here in the photos, when the two heads are parked
beside each other (195hp and 215hp) the difference in inlet port size is quite obvious.......
From what I've read on the interweb it seems the diameter of the 195hp head
inlet port is 25.8mm and the 215hp ports are closer to 28mm. Below is a sectioned
picture of a 195hp head showing the port diameter........
(picture courtesy of Uwe on S14.net, thanks Uwe)
All things being equal down below, it's generally up here where power
is gained or lost. As with everything else on an engine build, close attention to detail
can ensure that your raging horses don't end up clapped out nags.
This part of the process started for me a long time ago, back when the engine was first stripped and
the block was sent out for machine work at the beginning of the build, attention was turned to cleaning
up and inspecting the cylinder head...........
Unfortunately what we found at the time wasn't pretty. After cleaning up the combustion
chambers we found some cracks between the exhaust valve seats..........
The cracks were small and the engine had shown no signs of pressurising the coolant
system before coming asunder, which it would do if the crack had spread to the water gallery
and was allowing combustion pressure to leak into the cooling system.
Also the engine was compression tested shortly before it came asunder and while the figures
weren't great they weren't bad enough to suggest compression was being lost on a large scale.
So from all that we surmised that the crack was probably local and most likely didn't
extend all that far.
However when you placed a flat edge across the crack you could see that the surrounding
aluminium had started to shift...........
This was the nail in the coffin for this particular head, as the valve seats which are press fitted
into the head either side of the crack rely on everything in this area staying nice and
solid to stay put. With the aluminium starting to shift, however little, there was a real
possibility one of the valve seats could start to work it's way loose, should that happen
while the engine was running the resulting damage would be very, very, expensive.
There are repair options for this type of crack but they'd require both valve seats either side
of the crack to be cut out, the crack welded up and then the whole lot machined again
to refit new seats. But, this head was proudly displaying 3 cracks in total, all in the same places,
between the exhaust valve seats, in three different chambers, which meant this head was beyond
economical repair.
The other surprising discovery made on dismantling the head was the condition of the valves and valve
seats, they were in poor poor shape and can't have been sealing the combustion chamber that well.
This was most likely the reason behind the poor compression figures tested earlier on.
Actually it was a little surprising this engine drove as well as it did before coming asunder........
So after deciding that replacing the head would be the best option for the rebuild, the
search began. As this engine and car was built in 1986, that made this a 200hp version of the
S14 engine (195hp when fitted with a catalytic converter).
And a little later in it's life (around '89 I think) the S14 engine was available in an uprated form producing
215hp. Along with other changes one of the main differences in the 215hp engine was larger
inlet ports on the cylinder head. If I was going shopping for a cylinder head I decided I might
as well try and track down this larger port head, which would help in the search for a little more
horse power from this engine.
A quick call to the main dealer for prices on both the 195hp and 215hp heads let me know where
I stood,
should I happen to win the lottery,
twice!
195hp head pt. no. 11121309891 = €1220 -10% discount + 22% Irish Vat = €1340
215hp head pt. no. 11121312785 = €3035 -10% discount + 22% Irish Vat = €3330
So,
the search began for a good second hand head. And after a while ringing around and trawling
the interweb we came up lucky. A 215hp head overhauled and ready to go and the iceing on the cake,
the head came with uprated Schrick inlet and exhaust valves, springs and titanium retainers, and all for a good
bit less than the price of a bare 215hp head from the dealer. Excellent.........
Although not blindingly clear here in the photos, when the two heads are parked
beside each other (195hp and 215hp) the difference in inlet port size is quite obvious.......
From what I've read on the interweb it seems the diameter of the 195hp head
inlet port is 25.8mm and the 215hp ports are closer to 28mm. Below is a sectioned
picture of a 195hp head showing the port diameter........
(picture courtesy of Uwe on S14.net, thanks Uwe)
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