--> Europa-List message posted by: "Area-51" <goldsteinindustrial@gmail.com>
Job done; my fingers are sore again... ready to box up swap out the 80hp.
This unit scrubbed up great in the end; as good as new, with 700hrs and 4years
TBO remaining. Now just have to replace the few throttle arms and spark plug
caps I raided off a while back for the 80hp in 181.
What was learnt through this process:
The rotax 912ULS-S2 will benefit greatly with a cylinder head service at
1000hrs. Which will prevent the exhaust valves having to be binned at 2000hrs
TBO, and return the unit to full compression.
Inlet valve stem seals provide inadequate sealing of oil ingress into the inlet
port at 1300hrs, causing carbon build up upon the inlet valve and combustion
chamber. The symptom of this is seen via low compression on one cylinder during
burping as loose bits get trapped under the valve seat. It blows out upon
startup but is indicative inlet valve stem seals are failing.
Rear two cylinders of the 912 ULS-S2 run hotter than the front two cylinders.
This shows up as minor evidence of detonation erosion on the piston crown and
combustion chamber.
For reasons unknown #4 cylinder has had a Sodium "Inlet" Valve fitted.
All four exhaust valves exhibited pitted seats (same as recent 914 job)
indicating either hot lean mixtures or acid chemical erosion. The valves are
softer than the seats.
The pistons crowns in the 912 are very soft material. A head nut dropped from
the barrel stud and fell onto the crown leaving a small indentation; very soft
material.
Now that You have read all that nominal stuff I can discuss cleaning methods...
Firstly you will need "high end laboratory tools" like in the attached
pictures. Secondly, expect to end the task with really sore fingers by the end
from using some of the high end laboratory equipment. The secret to achieving
the look achieved is knowing what materials to use; I will go on...
Ultrasonic cleaning bin; I have 5L and 25L units... This is great, but not that
great for alloy motor bits; darkens the metal. I need to try sewing machine oil
or sulphuric acid and see what the results are. So caustic alkaline fluids are
no good for zinc, or zinc alloys.
Scotch pad; industrial grade "grey"; available in a roll at your local paint
panel trade supplier... I use this with diluted sugar soap to "finish" clean
everything before spray and wipe off with Wurth Rostoff. You will have tired
and sore fingers afterwards if you scrub an entire engine.
Brass brush... used to descale corrosion off the engine exterior.
Tooth brush... used to scrub exterior of engine
Stainless brush... used to scrub bits i should be using the brass brush for.
215 or 225 Aluminium sheet. I use this to create some of the high end
laboratory equipment. It is used to scrape off the piston crown, head ports,
combustion chambers and cylinder wall, and is softer than the piston crown. The
edges need to be kept dressed as you work scraping off the crap. You will have
sore fingers by the end from scraping... Any piece of metal softer than the
piston crown will do the job but you will struggle with lead; mercury would be
totally useless though...
Threaded brass pipe. I use this on the exhaust valve stem as a rasp to get the
tough shit off quickly.
A piece of flat 0.125" 2030 carbon steel. I use this on the exhaust valve to
scrape off the really tough shit.
An oyster shucker. I use this to get the "nothing else will budge it" stuff out
of the exhaust port. Its a delicate light handed job because the oyster shucker
is hardened steel and will ruin a valve seat and slice through a finger
instantly without taking any prisoners.
A piece of TIG welding rod, hammered flat and bent 90deg at one end. This is
one of my favourite tools and is used to extract hydraulic lifters to check
their face condition.
(When lifting the cylinder barrels you may notice three numbers felt tipped
onto the barrel; record these numbers. They are your bore dimensions taken at
the factory during engine assembly)
3D printer. Used to print the valve spring compressor.
A vacuum cleaner with a high end laboratory attachment such as repurposed piece
of washing machine drainage pipe. Used to extract all the crap from the
cylinder and ring lands, and valve ports as you go and keeps the work area
clean. Wife will scream and be unhappy for a while, but its only momentary...
Air compressor. To blow out any thread bores before bolting up.
(x4) 2" sections of 3/8 fuel hose.. I use this to seal off the cylinder studs
and hold the barrels in place as I work. Screw down two head nuts and you can
roll the motor over while head is off. They can be fun to remove afterwards; i
use pointed pliers to lift them up and off.
Wurth Rostoff... I use this to wash off the scotch brite residue when cleaning
completed. I also skirt a bit into the valve port together with some oil when
lapping in the valves. I use a cordless drill on the top of valve stem; much
quicker than old timer method.
Each head takes about four hours to process. You will have sore fingers by
about midway through the second cylinder onwards.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=515226#515226
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