e30 M3 minor rust repair.

[Beach Bum]

F5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5

[SimplyDope]

Sweet baby Jeebus. Amazing thread that I can't stop revisiting.

[xworks]

Next up "taper". What we're after here is that the walls of the cylinder are "straight"
and not tapered like in the diagram below........



Again I'm using a maximum tolerance of 0.0004", so any of the X measurements
or Y measurements in the same cylinder can't have a difference of greater then 0.0004".
Again looking at the figures I'm good to go, the largest taper figure I have is in cylinder 4
on the Y measurements, Top Y = 3.6950" Bottom Y = 3.6953" a taper of 0.0003".

There was one other thing I wanted to check at this stage and that was the viability
of a "torque plate". In the picture below you can see the ten bolt holes that the
head bolts screw down into to secure the cylinder head to the block. These head
bolts take a fairly good squeeze to fully tighten them and what can happen on some
engines is that the metal around these bolt holes in the block can distort a little.
Depending on how close those bolt holes are to the cylinder bores this can sometimes
lead to the cylinders getting a little distorted. After you've just seen the tolerances we've
measured the bores to, you can see how this could be a problem......



so, how to check, well it mightn't be the most accurate way but it'll do for me.
Old head gasket fitted.......



Old cylinder head fitted and torqued down to the right torque........



and then flip the block over stick the bore gauge back in again to see if it made
much difference to the figures taken earlier........



The answer is I couldn't measure a big enough change in the figures taken earlier
to justify the cost of a torque plate. A torque plate by the way is a big slab of
aluminium that bolts down onto the block just like the cylinder head. Its job is to
distort the block just like the cylinder head might, the only difference being that the
torque plate has four big round holes in it allowing you to bore out the block while
it's fitted.......



typing finger sore, more to follow as the week goes on..........

[xworks]

The gauge on top has only a very small range of movement, this specific one only reads
50 thou from fully out to fully retracted, so you've got to choose the right
attachment (anvil) to put you in the ball park for the hole your measuring.
The cylinders on my block were all bored to 3.6950", so the correct anvil is
chosen and a micrometer is set up in the bench vise with a gap of 3.6950"
like so.......



and then the tips of the bore gauge is placed between the jaws
of the micrometer and the dial gauge is moved up or down in the tool
to get the needle zero'd on this measurment........



there's more appropriate setting block's out there to make it easier to
set the bore gauge up to a certain measurement and it's on the long list
of things to buy, right after a better f**king camera (don't hold your breath).
So, with the bore gauge zero'd on 3.6950" it's placed into the bore and rocked
left and right like so.........



Basically, you keep an eye on the needle and read off the lowest number it
shows while your rocking it at that point. The lowest number will be when the
gauge is straight and perpendicular in the bore, and thats the measurement of the
bore at that point. If the gauge read's 0, then the bore is bang on 3.6950", if it
will only drop as low as +05 then the bore is 3.6955" (3.6950"+ 0.0005") or if the
needle drops to the other side of zero, like -05 then your bore at that point is
3.6945" (3.6950" - 0.0005").
I know, I know, clear as mud isn't it? The only thing I'll say is when you have the tool
in your hand it's a damn sight easier to understand than what you've just read.

When your done you should have 6 measurements for each cylinder (3 X's and 3 Y's)
giving you a total of 24 measurements for the block, which should look a little something
like this......




So what the hell do I now do what all this crap you may ask?
Well I'm glad you did ask, because I just spent the last 30 minutes fighting this bloody computer
to get that Excel graph small enough so you don't have to be an orbiting astronaut to read it.
The answer is your now going to check these figures for cylinder bore "out of round" and "taper".

When you start to assemble your nice clean engine your going to fit a
nice round piston into each cylinder, and that piston will need to have a clearance between it
and the cylinder walls, too tight and when the aluminium piston starts to expand with heat it'll
scuff the bore or worse seize, too loose and the rings will struggle to seal against the walls of the
bore and you end up loosing compression and with it, power.
In an ideal world, you'd leave your block in and have it bored to 3.6950" and no matter where
you measured it you'd get 3.6950". Well, take a look at that list of measurements up there and you'll
realise thats not how the real world works.

So, your given tolerances and if your figures falls within these tolerances then everything should work
out ok. The first tolerance is for "out of round". Basically this is how oval your bore can be at any given
height and still be acceptable.
So, remember those X and Y measurements we took.......



If the cylinder was perfectly round both X and Y would be the same, however
the max "out of round" tolerance figure I'm using for this engine build is 0.0004".
That means the biggest difference between any of the 12 X and Y readings listed
above can only be 0.0004". I've a couple that are right on that limit of 0.0004"
but none over it, so I'm good to go.

[xworks]

Another job that was carried out at the machine shop was the block was "crack tested".
Basically this involves the use of a strong electro magnet, some coloured metal dust and an
ultraviolet light. This process should show up any stress cracks in the block and
stop you spending any more money on preping it because it's most likely just
been relegated to boat anchor status. If your curious to see how the process works
look up "Magnaflux" on youtube.

Next up is the cylinders, the holes in which the pistons are to travel in. As could probably be
expected the bores on my block were fairly well worn from over a hundred
and seventy thousand miles of one careful owner and five wanabe Arton Senna's.
Usually on a high mileage rebuild like this the block will need
to be "re-bored", the reason being the bores are so worn that to refit the
same size pistons again would leave them wobbling around like a stick in a
welly boot. There are oversize piston sizes available from the main dealer to deal with
this situation
standard size is = 93.355mm/3.675"
first oversize is = 93.555mm/3.683"
second oversize is = 93.755mm/3.691"

Your job is to decide which piston will you need. Common logic dictates that you should only
go as large as you need and therefore try and leave one more oversize piston to "bore to"
down the line should the block need another rebore at a future rebuild. However, you may not
have the luxury of this choice if your cylinders are badly worn. A good machine shop should be able
to advise which size the block needs to be bored to, to remove all traces of wear and return the
cylinder to a factory fresh finish ready for new pistons. As mentioned previously, I had my block at the
machine shop a long time ago (in an effort to speed up the rebuild, seems funny now looking back)
and the resulting wear meant that I had to get my block bored out quite heavily to return it to a usable state.
However, there is one slight difference with my specific build, and that is I am intending to
use custom pistons. These would be made to my own stated sizes and so all I had to ask of
the machine shop was to rebore all 4 cylinders to a common size of there choice.
In an ideal world you would collect your block from the machine shop and take his word as to what the
new cylinder size was, however past experiences has taught me never to accept someone else's word
on important things like this. You've got to measure for yourself !

So, next step was to measure the cylinder bore so I could start to calculate what size pistons would be needed,
and also to check the quality of the rebore. In the pic below you can see the two axis that measurments were taken,
X and Y, and these pair of measurements were also taken at 3 different depths in each cylinder.
Depth A = about half an inch down from the top
Depth B = halfway down the cylinder
Depth C = about half an inch up from the bottom of the cylinder



To take these measurements we use whats called a bore gauge, which looks like
this.........



The gauge above comes with a range of different attachments to allow it to be
used in measuring a large range of different hole sizes. This specific one reads in
0.0001" increments and is fairly accurate. When it comes to buying tools for measuring
engine parts it really makes sense to try and buy the best you can afford, this is one item
where buying cheaply usually ends up costing you more money down the line as your
engine shits itself due to bad measurements made by cheap tools. (the down side is if
you have decent tools you've less things to blame it on when it all go's pear shaped.)

So, how does it work?

have a look at the picture of the gauge shown below. At the business end of the tool you
can see theres two ends (arrowed). Whats a little harder to see is that each of these ends has
a ball tip on it. The end marked purple is rigid and doesn't move. The end marked red does
move however, and as it is pushed inwards the needle on the dial gauge reads how much it's
retracting..........

[xworks]

The other two red circles above represent the similar metric sizes, a hundredth
of a mm and a thousandth of a millimetre.
In the following waffle I tend to favour Imperial measurements using Thou and
Ten Thousandths of an inch, however, it would appear I also switch over to
millimetres at times as well, because, just between you and me, my brain is
mush.
The reason I'm telling you this, is if your going to be using any of this info to
check your own engine parts (very brave) then you need to be careful of
what units are being used.
The following link is to an online converter to change between thou and
mm and can be quite handy to have....

http://www.alcula.com/conversion/length/thou-to-millimeter/

One other final link before we get started and thats to BMW's
Tolerance and Torque manual, all the data you'll need for figuring out
working clearances and so on can be found here.....

http://www.bmwtechinfo.com/repair/main/941en/index.htm

Click "Contents" then "engine" and then choose your weapon of choice.

Right, all that shite done with, it's on to the actual engine bits, starting with
the block. After the engine was stripped, the block was "hot tanked" and
steam cleaned in every orifice to remove all the gunk that had built up over
the previous 20 odd years........



next up was to check the flatness of the deck face. This is the surface the
headgasket has to seal against when it's sandwiched between the block and the
cylinderhead, and as such it needs to be perfectly flat and smooth.
To check this we use an engineers straight edge which is basically a very straight
piece of tool steel. This is placed across the deck and you check to see if a 1 thou
feeler blade will fit in anywhere underneath indicating that the surface isn't quite flat enough.......



The block needs to be checked in all the following directions......



As you can see above my deck face looks suspiciously clean and flat and
thats because when disassembled at the very start of this restoration the
surface was found to be a bit uneven and as a result I had the local machine shop
surface grind the deck 0.002" to flatten it out. Unfortunately this was so long ago
that cameras weren't invented and I don't have any before pictures to show you.

[xworks]

Well, how are ya? Good? Excellent! It's been a while since we last talked
and I've a pile of shite here to bore you with. Believe it or not I still haven't
managed to bolt together this bloody engine. However, I have just finished
all the prep work and need to empty all this crap out of the camera before
it bursts at the seams. So...... how the hell have I managed to spend the last
six months at this and still not built a simple engine? Well, it would appear I
possess a rare talent, the ability to drag out each and every task to its absolute
maximum length, however, in my defence, as this story unfolds you'll see
this river hasn't run smoothly.....

If you can remember all the way back to the time when Jesus was a young boy and I started
the bodywork on this restoration, you may remember that the preparation phase of the
bodywork took a lot longer than the actual spraying part, well, engine building is much
the same. While you could probably assemble an engine in a fairly short space of time
if you have all the parts in front of you, checking, measuring, cleaning and preping the parts
beforehand takes a great deal longer. But, just like the bodywork, if you don't spend
the time on the prep work the end result will almost always suffer.

One small point before we go any further, I'm not going to go into the minute details of
engine building in this thread for two simple reasons.....
a) theres a wealth of knowledge and fantasticly detailed build threads out there of how
to choose the right cams, pistons, valves etc. for your specific engine build and I'm far too dumb
to try and add to that knowledge.
b) what does seem to be scarce out there is some explanations of the simpler
stuff for people who may never have built an engine before,
like what to check to see if parts like the block, crankshafts, conrods etc are fit
to be reused again. If you've built your share of engines in the past then it's unlikely
you'll pick up anything useful here, however, if you've never built an engine before
then hopefully........ you'll fail to realise that most of whats to follow is,
as usual,
probably wrong!

First up, a quick word on measuring. When your looking up spec's for wear tolerances
or shopping for measuring tools then you'll most likley come across the two different
units of measurement common in the trade. Metric and Imperial.
Things usually tend to be a little less confusing if you choose one type and stick to it
for all your measuring. In this regard the various overhaul manuals from BMW for our
cars are well laid out and almost always give all important measurements and
tolerances in both millimetres and thousands of an inch.

Below you can see a little diagram of how each of the units of measure relate to each other.
The large blue circle on the left represents 1 thousandth of an Inch (1 thou) or 0.001" as you'll
usually see it written. To try and give some perspective to this measurement, the average human
hair is 2 thou thick. For most of the tighter tolerances in this engine build we'll be measuring
down to ten thousandths of an inch, 0.0001", thats 20 times smaller than that hair you just plucked
and it's represented below by the smaller of the two blue circles.........

[Cabriolet]

Is she back together yet?

[bmwmech1]

I'm as excited as an 18 year old HS chick the day before prom

I am as well... as Thomas Dolby wrote, "little rivers of anticipation are running down my inseam", Lol!

Garey

[CorvallisBMW]

I'm as excited as an 18 year old HS chick the day before prom

[xworks]

Thank you for the kind words, much appreciated.
I'm currently sorting through the pictures and uploading
them to the interweb for the next update, should be done
within a week if my typing finger holds up. ;)

[bmwmech1]

I've read this restoration thread on s14 at least a dozen times... I did not think to look for it here on r3v, but I'm glad it's here, as well. As many have said prior to this post, this is absolutely brilliant! Probably the single most informative and thorough thread ever written and your writing style is as real as it gets. I read and imagine standing next to you as you re-tell the story of having a friend's hand to use instead of your own hand while re-assembling the diff, so as not to smash your own, Lol! Well done my friend and I look forward to reading more, as soon as you are ready to inform us some more! Too bad we live an impossible distance apart, I'd love to drink a pint with you and see your work in person!!!

Cheers,

Garey

[dirtywhite89]

wow...:crazy:

Amazing thread.

What's going on with it now?

[Holland]

Nothing to add except my own amazement at the thoroughness of this project, and at the incredible documentation that has been shared with us.

This thread should be automatically subscribed for every E30 owner. It's that good.

Thank you for doing this.

This is one of the best first posts, I doubt you will need to ask about anything now.

[unome]

Amazing

Nothing to add except my own amazement at the thoroughness of this project, and at the incredible documentation that has been shared with us.

This thread should be automatically subscribed for every E30 owner. It's that good.

Thank you for doing this.