e30 M3 minor rust repair.

[CorvallisBMW]

You're using the stock crankshaft, correct? And the h-beam rods you bought were the same size as the stock pieces? So why wouldn't your CR be the same as it was from the factory? Was there a need to measure it?

[xworks]

After doing all the calculations we found that, if fitted, the standard pistons would have given this
engine a compression ratio of 10.5 : 1 , and after flogging the last few remaining brain cells I have to
withing an inch of their life, I then managed to figure out that the new pistons would require a dish of
of just 7.5cc to raise the compression ratio to 11.0 : 1 . By this stage we'd finalised all the dimensions
for the new pistons, and were ready to place the order. We had decided to go with JE Pistons and instead
of going straight to JE themselves with the order we were going to use one of their agents as the price was
going to work out much the same and it gave us the opportunity to have a second set of eye's, as it were,
to look over the spec's and make sure they'd result in what we wanted.

So just to recap, standard pistons look like this..........



new pistons would look fairly similar as the only adjustments being made were the
valve cut outs being deepened and enlarged a little and the dish in the piston being
made a little shallower. So, the order was placed and we waited for the pistons to
arrive so the build could continue.
Eventually the package arrived, and just like a little kid does at christmas the box was ripped
asunder to get a first look at those four little expensive aluminium pots of goodness........



The essence of the moment can be neatly summed up in one short word,
BOLLOCKS.

Jesus H f*cking Christ, what the hell are these? There's a f*cking pyramid in
the middle of me new pistons. The valve relief's were deep enough to house
a small family of elephants, with weight disorders. In short, the pistons were
totally useless to me........



I'm not going to go into details here of what happened as the outcome is still ongoing,
all I will say is that there was a monumental cock up and it wasn't at my end.
The end result of all this at the time was I was severely out of pocket
and severely pissed off with the whole build.

I closed the door on the garage that evening and didn't return to it for quite a while.

[xworks]

This engine is being built to power a day to day road car as opposed to a "balls to the wall" all out race motor.
And as such I've decided to shoot for a compression ratio of 11 : 1, which should be well enough inside the
"safe zone" that detonation won't become an issue, but still provide a little bump in hp over the 10.5 :1 compression
ratio the engine originally left the factory with.

So with the target set at 11 : 1 the first thing we needed to do was find out what compression ratio the standard
pistons would give us, and then hopefully from this we could figure out what modifications to make to the new pistons
to arrive at 11 : 1.
To do this we first need to know the volume of that dish on top of the standard piston,
so the piston is assembled onto a conrod and instead of fitting a piston ring
we use some rubber o-rings to seal the piston in the bore..........







then the piston and rod are fitted into the cylinder and bolted up to the crank.......



As we're going to be using fluid to measure the volume of the dish in the piston crown
the next step is the same as what was done on the cylinder head earlier. Get it all 100% level.........







with everything level the next step was to drop the piston down the bore a known
amount. To do this we set up a dial gauge and zero it on the deck surface of the
block...........



Then move the needle onto the raised circumference of the piston (not in the dish),
and rotate the crank till the piston drops down 3.00mm from the surface of the deck.........



From our bore measurements taken earlier we know that the diameter of the bore is
exactly 3.6950" or 93.85mm, so now we can figure out the exact volume of the space
between the top of the piston and the surface of the deck (the red area below)..........



using the formula for the volume of a cylinder, pi x radius squared x height, the volume
of the red area in the diagram above comes out at 20.7cc.
So what the hell did we do all that crap for?
Well when we fill up the hole with fluid in a minute, we now know that it takes exactly
20.7cc to fill up the red area and anything over this must be the volume of the dish in
the piston..........



So, with the nail rig in place to indicate when the holes full, the burette is again filled
and the tap opened........



When the fluid reached the tip of the nail, the tap was shut and we read off how much
fluid it took to fill the hole. Which was 29.3 cc. So subtracting the 20.7cc (red area) from earlier
the 8.6cc we're left with is the volume of the dish in the piston.

With this info and a few more little measurements we could now figure out what the compression
ratio would be with these standard pistons fitted. I'm not going to get into the formula's and
calculations end of working out the compression ratio here, as, well, it's boring. And with porn only
ever a click of a mouse away I reckon there'd be an echo in here after a short while.
What I will say before we move on though is I came across a great bit of software to help
with the calculations if you ever find yourself doing something similar. Its by a crowd called
Performance Trends and is downloadable here http://performancetrends.com/download.htm#crc

[xworks]

Chapter 52: Custom Pistons and the road to financial ruin.
In this exciting episode we'll be revealing the closely guarded secrets of how to f*ck up a
custom piston order, quickly followed with a "how to" guide on using a kitchen bread knife
to remove a kidney with a view to selling it on ebay.
But, before we get to that, it's probably best we deal with question of why we wanted custom
pistons in the first place. Below is a picture of a Mahle standard piston for the S14 M3 engine.
If you should happen to wander in to your local dealer with a pot of gold large enough,
four of these little carefully machined slugs of aluminium can be obtained...........



So, why didn't I use these? Three main reasons really, increase the valve relief's,
changing the engine's compression ratio, and reducing piston weight, and of course not forgetting the most
important of all, my seemingly unavoidable irritating habit of complicating everything.

Valve relief's.
Due to the design of the S14 engine, the valves come in quite close proximity
to the top of the pistons while the engine is running and as such the top of the
piston has 4 little valve relief notches cut out of it to avoid any disastrous contact
between the two..........



When running standard diameter valves and standard lift camshafts all this works
as it was designed too. However, when (like I am) you change to oversize valves and
higher lift camshafts, these relief's cut in to the top of the standard pistons are usually
insufficient to offer the proper clearance any more. The Schrick 284 degree inlet and 276 degree
cams being used in this build can be considered relatively mild in the large scope of whats available
out there for this engine, and as such seem to be right on the border of being usable with standard
valve relief's.
As a guide Schrick recommend a minimum of 1.5mm clearance between valve and piston at their
tightest point. I'm not 100% sure that you'd run into trouble if you were just running the higher lift cams
mentioned with standard diameter valves. Some folk report no issues with running them,
while others report problems when the valve to piston clearance is measured upon assembly.
What is probably clear from that is you should at least take the time to measure the clearance when assembling,
as the "f*ck it, it'll be grand" approach could end up being expensive down the line should the pistons and
valves take a notion that they'd both like to occupy the same space at the same time.

I had no such worries however as when you add in the larger valves I'm running I was pretty confident that
the end result would be mass suicide should I have tried to use the standard pistons.
So, reason number 1 for custom pistons = larger valve relief's.

Raising the compression ratio.
In the last section we touched briefly on the subject of compression
ratio when we balanced the volumes of the combustion chambers in the cylinder head.
The piston, or more precisely, the top of the piston, has a dish in it (coloured red below).
With a custom piston you can alter the volume of this dish and as such change the compression
ratio of the engine............



I find myself ideally suited to offer a simple explanation of what compression ratio is,
as I haven't half a f*cking clue myself. But, since that small fact hasn't seemed to stop me
anywhere else in this thread I shall now continue the fine tradition.
Static Compression Ratio, at it's simplest, is the ratio of all the volume in the chamber
when the piston is at the bottom of it's stroke (all the area you see as green below).........



compared to the volume of what it all gets squashed into when the piston
comes to the top of it's stroke........



If the volume of the green area in the top picture were 300 cubic centimetres (cc) and the volume
of the area it all gets squashed into in the second picture was 30cc, then you'd have a
compression ratio of 300 : 30 or simplified down, 10 : 1.
As a very general rule of thumb, the tighter you pack that volume when the piston squashes it,
the bigger the bang you'll get, thus, the higher the compression ratio the better the power output
from the engine. Everything thing else being equal, an engine with 11 : 1 compression ratio will
normally produce more power than an engine with 10 : 1 and so on.

So, just wack up the compression ratio and we're good to go? Well, unfortunately it's not quite
that simple. When you reduce the space that the piston squeezes all the mixture into, the fuel/air
mixture obviously now gets compressed a lot more. The side effect of this is the more you compress
the mixture the hotter it gets. If you go too high with the compression ratio, and compress the mixture too
much, the temperature in here gets so high it can spontaneously explode before the spark plug even
has a chance to light the fire.
At this stage your into the wonderful world of detonation (also known as "knock"), the results of which,
if severe enough, can destroy engines in seconds.
So, the trick seems to be, raise the compression ratio as high as you can to reap the rewards of bigger
horse power, while trying not to go too high where the dreaded detonation becomes an issue.

If you look at the (fantastically detailed) diagram below you can see the area the mixture gets squashed into
is made up of the combustion chamber in the cylinder head,
some of the head gasket volume(the brown bit)
and then the dish in the piston makes up the final piece of space.......



By making the dish in the piston smaller we can reduce the space the mixture gets squashed into,
and, as such, compress it a little tighter which will raise the compression ratio.
But before we could start figuring out what volume dish we wanted in our new pistons
we first had a few decisions to make.

[ray325e]

damn I'm amazed !

[bmwmech1]

Now this takes me back to when I was engine building in high school... good stuff, ahhh the memories, lol!

Garey

[Conrad311]

my god man.
ive managed to miss the last few updates. (Thank you MSN for locking my email you douche bags)
and i just saw this and got all giggly inside.
Was not disappointed :)

[Cabriolet]

When you were grinding out the material in combustion chamber. How did you protect the bottom face of head, from getting nicked on accident?

[xworks]

the chamber is now exactly full of fluid........



and when we checked the graduations on the burette we could see exactly
how much fluid it took to fill the chamber. And hey presto, you now have the volume of
one combustion chamber.
(Now that was some fancy shit wasn't it? While I'd love to take the credit for thinking up this
stuff myself, I have to thank Jake over on S14.net for that method. The way I used to do it
took a lot longer and was a lot messier.)
One little thing to be careful of before we go on is about reading the burette.
When you fill it up originally the fluid doesn't lie flat in the tube, but rather
curves up at the edges. You need to be sure your reading the level either from the
top of the "curve" or the bottom when you fill it and the same again when checking how much has come
out afterwards.........



the test is done 3 times on each chamber and then an average reading taken for
each for each to avoid fu*k ups, sorry, "inaccuracies", making sure the chamber is totally
dried out between each test..........



One other thing thats worth keeping an eye on while doing this
is the fact that you shouldn't see any fluid leaking past the valves and out the ports
during any of this. If you do, you need to check your valve's and their seats, as, if
they just been freshly cut and lapped in, then they should be sealing against
any fluid leaking past......



With all the combustion chambers checked, the average figures came out
at:
cylinder 1 - 42.7cc
cylinder 2 - 43.0cc
cylinder 3 - 43.0cc
cylinder 4 - 42.8cc

Only a difference of 0.3cc between chambers.
Now a normal person would be happy with this as most cylinder head tech
articles advise balancing to within 0.5cc. But, if you've been reading this thread
long enough you already know whats coming next.

The "drip" beside the 1 euro coin below is an example of what 0.3cc volume looks like,
this is roughly what I'd to remove from two of the chambers to get all three balanced to
43.0cc.......



head surface gets masked up with some heavy foil tape to protect it from
any c*ck-eyed blows from the Dremel grinder...........



some old valves are loosely fitted to protect the freshly cut valve seats from damage
and the areas to be "buffed" get shaded a nice shade of blue.......



head is set up at a comfortable angle to work the Dremel......



and then the blue areas are lightly ground with a 120 grit disc.....



before being finished with 400grit.......



a few hours grinding and remeasuring had all four chambers reading 43.0cc.....





theres a good chance, even if you lead a long life, that'll you'll never witness a better
example of Obsessive Compulsive Disorder, I'll do well to finish this build without ending
up with a nervous twitch..........



And, thats about all for tonight. Next on the menu is custom pistons and why I chose to
abandon the money tree's and go straight to printing my own counterfeit money.
Till then..............

[xworks]

The head was dispatched to have the work done and we waited for it to return.
And waited.
And waited.
2 months later the head returned, thankfully the quality of the work was a lot better
than the customer service........



With the head now back we could continue playing with it, and next up on the
fun and games list was balancing the combustion chambers.
Who, what, where, when, why???
Simply put, the combustion chamber is the dish you see in the pic below.....



It's the area the piston squashes all the fuel and air mixture up into as it rises to
the top of the cylinder. When all the mixture is fully squashed in here the spark
plug gives it's little spark and starts the explosion, the resulting expanding gas
pushes the piston down.
(I know, this is pure Stephen Hawking quality shit here, ground breaking, but bare with me.)
Depending on how tight you pack the mixture in here effects how much of
an explosion you get. Simply put, the tighter the squeeze the bigger the bang.
What we're doing next is measuring the 4 combustion chambers in the cylinder
head to make sure they're all the same size. The reason we want them all the same
size is, if one is a little smaller than it's neighbour, then the mixture squashed into that
chamber is going to give a slightly bigger bang than the cylinder next door.
What we want is a nice balanced smooth engine with all four cylinders "banging" identical to
each other.
(It's probably worth mentioning at this stage that unless your building a highly strung, high compression
ratio engine, which I am not, the following process isn't 100 percent necessary. But since I hadn't a pot to piss
in at this stage thanks to the amount of money I'd blown on engine parts, it seamed like a good
way to pass the time till the money trees sprouted some more branches.)

So, aim of the game is to measure the volume of the compression chambers and then
make them all the same.
First up we gotta reassemble some valves back into the bare head and for this
we'll be using "test" springs as opposed to the real valve springs........



reason being it's a lot quicker and handier to assemble the valve gear with the
test springs as you can squash them with your hand whilst fitting the collets,
whereas with the much stronger real valve springs you need to clamp each one
with a valve spring compressor to get the collets in.
So, 2 inlet and 2 exhaust valves were fitted with the test springs to keep them shut
tight against their seats........





next up was to screw 3 long bolts into the top face of the cylinder head
(red arrow M10 x 100mm, purple arrows M6 x 100mm)..........



and then flip the head over, screwing the bolts in or out of the head to get
it perfectly level end to end.......



and across.....



With the head perfectly level we pull out the burette.......



Those of you who took science classes in school and haven't killed your
brain since then with drugs and alcohol will know what this is.
For rest of us, it's a graduated perspex tube with a little tap on the end of it.........



We filled this burette with paraffin/kerosene........





next item required is this highly expensive precision tool. It's a piece of a large exhaust
clap with a sharpened 6 inch nail rigged into it (them money tree's were taking there time)........



this "rig" is placed on a flat piece of the head and when we were happy that it
sat perfectly flat and didn't rock, the nail is adjusted down till it just touches the head
surface..........



then, it's placed over the combustion chamber and the tap on the burette is
opened to allow the fluid to start filling the chamber. The idea is that the nail
acts as a guide, when the fluid reaches it, the chamber is full. You watch the
fluid slowly filling up and watch the reflection of the nail in the fluid getting closer
to the actual nail, giving you a guide of when to get ready to shut the tap........



and then, just as the fluid touches the very tip of the nail, the tap is shut..........

[xworks]

So with the head issues dealt with, the cylinder head was tucked away safely
at the time and concentration returned to stripping the rest of the car. Finally, a few months
ago, the head came back out of hibernation along with the rest of the engine hardware to
start this preping for assembly. First job was to strip the head down and give it the once over
to make sure it was as "good to go" as was advertised.
Valves, springs and retainers were pulled so we could get a good look at the valve seats and
check their condition. What we found looked good, all the seats looked to be freshly cut and
their respective valves had been lapped in..........



right up until we got to inlet valve seat number 6..........



F.U.C.K.!!
The seat was very badly damaged. In the pic below you can just about see the nice
3 angle cut on the surrounding seats, while the seat in the centre of the picture looks
as if the valve had tried to "jack hammer" it's way clean out through the roof of the cylinder
head..........



This little "discovery" meant I was going to have to find some more cash to
spend on this head before it was ready to bolt on.
After chatting things over with the Samaratins I decided the best course of action would
be to send the head away and have the damaged valve seat cut out and replaced.
The thinking behind this was as follows.
As you might have seen in the previous pictures the valve seats have 3 angles cut into
them as shown in the diagram below..........



The middle angle is for the valve to seal against when it's shut, while the ones either side of it are
to smooth out the path for the incoming air as it rushes in when the valve starts to open.
The damage on my valve seat meant that if I tried to have these 3 angles recut into it, the valve
would end up sunk fairly deep into the head. This would almost certainly have a negative effect
on the airflow entering the chamber by this valve.
So, a new seat with freshly cut angles was the only real option.
Before the head could be sent off to have this done however, we needed to check everything
else to make sure this was the only work the head needed done.
First check was the valve guides......



These are the little bronze guides that are pressed
into the head. Their purpose, as their name suggests, is to guide the valves as the camshaft pushes
them open and springs pull them closed.......





Over time these can get worn, so they need to be checked.
To check them the valve is placed down into it's guide just far enough so that the
tip of the valve stem is level with the top of the guide, and then a dial gauge is set up
as shown below resting against the head of the valve.........



The valve is then "rocked" over and back in the guide whilst you check how much movement
it registers on the dial gauge.........



Maximum movement for the intake guides is 0.65mm and the exhausts is
0.80mm
After that the head had it's surface checked for flatness. Exact same test as was
done earlier on the block face. Engineers straight edge, feeler blade, blah, blah, blah.
Any unevenness or pitting from corrosion and the head will need skimming to return it
to a silky smooth flat surface. Finally, moving onto the final check, pressure testing the
head. For this test all the water ports are blocked off on the head.......





leaving one small port open.......



the head then has a large rubber block strapped over the remaining open water
ports on the face of the head and the whole lot is submerged in an 80degree tub of
warm water.
Pressurised air is fed in the one remaining open port shown in the pic above
and then you check for bubbles. With the water galleries all blocked off the appearance of any
bubbles is usually bad news as it normally means the head has cracked somewhere.
The reason warm water is used is sometimes small cracks don't open up till the head is at operating
temperature.

Thankfully this head passed all these checks, so all that needed doing to return it to active
duty was that valve seat. But, as is the nature of these things, I can't leave well enough alone,
so I was also going to have some mild port work done and change the 38mm oversized Shrick inlet
valves for some 38.5mm Supertech valves.
To have the work completed the head was going to have to go on a wee journey by courier.
We've had a few poor experiences in the past with cylinder heads getting damaged in transit
and this led to the construction of "the coffin"......







designed to withstand a stray ballistic missile strike.

[xworks]

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)

[xworks]

any thoughts on end balancing the rods?

Thankfully these rods came already pre-balanced which was handy as
I didn't like the idea of having to grind them after they had been shot peened.
A local machine shop has balanced my rods for me in the past as a
decent rig for weighing them end to end is still unfortunately way down the
list of things I need to buy.
Some day.
For anyone that mightn't be familiar with the process of balancing rods end to end
this video more or less lays it out..........

http://youtu.be/QLpiF0E0EJU

[nando]

seriously though, I'll be coming back to this thread when I build my next engine :D

any thoughts on end balancing the rods?

[KennyT]

I'm saving this thread to build engines by in the future.