I found simply lapping the exhaust into the head cured the issues with the
exhaust
leaks at the cylinder head. Attention to detail is essential as I covered
in my troubleshooting document.
The exhaust leak issues were normally with the 912S. The development woes of
the
912S and its shaking, kickback, harmonic problems and cracking of the block
were well covered up (probably a poor choice of words, more like "development
issues") and many individual owners suffered (and still do) as Rotax blamed
propellors,
fuel, carb balancing etc. rather than just fixing the engine. By 2005
Rotax silently (in my opinion again) fixed most of these issues and after
reinforcing the block, changing timing, carb mixture and stronger starters, we
now have a well reinforced and timed 912S being produced. Those soldiering on
with the older 912S engines have had to rebuild or replace the short block,
gearbox, sprag clutch and other issues. The newer 912S is still not perfect but
is an acceptable engine in my opinion as Rotax did address nearly all the
original
issues. I'm still not a fan of the 912iS or the big bores so don't ask
. Time will tell on that. The 912 and 914 do not have near head leak issues
as the 912S (pre-2006) but are not full proof either. Early models of the 912
and 914 had their issues also.
Lapping of the exhaust down pipe to the head has to be done at the angle and
orientation
the final fit will be, so alignment marking is essential as is patience
holding pressure and slightly rotating the downpipe during the lapping process.
It helps to have strong wrists or a helper to push while the other pushes
and pulls on the downpipe. We used valve lapping compound at Custom Flight,
and in about 20 minutes of work we had a good fit curing the leak around the
offending conical exhaust fittings used on most of the 912S exhausts supplied
for the Europa. I found the lapping method to be superior to trying copper or
asbestos exhaust gaskets. Just make it fit properly! Aluminum is soft and
easily
"machined by hand" with the lapping compound.
The large cone to cylinder mating surface is ideal for lapping. Some have
issues
with the studs coming off with the nut. Remove the corroded nut, clean the
stud or get a new one, and Loctite the stud back in and allow to cure. (Yes,
the Loctite will fail with heat, but it will allow fitting and proper torque
during cold installation.) PUT ON NEW NUTS as they are worth it. Don't be
cheap
or too quick to try Band-Aids as Aera 51 commented.
The muffler ball joints on the muffler originally did not have a proper seal
either.
I had to use exhaust sealing paste on the older CKT mufflers as a Band-Aid
(pre 2010). Later Robin at CKT redesigned his downpipe to muffler joint and
I find the new exhaust to be nearly full proof as the cup and ball seal works
very well, especially with a little exhaust paste. CKT also found that the
exhaust springs were best to be made from stainless spring material and they
did extensive work on the cause of spring failure as well as securing the
tooling
needed for smooth, nick free spring manufacture which greatly improved the
spring life. Hence you see nearly all the LSA aircraft using his exhaust or
a copy. I know that motorcycle springs are cheaper, but they also do not have
proper hooks in most cases. Again, don't be cheap, even motorcycles have issues
and quality springs are not used due to cost. If they cost more, they don't
sell but they last longer. Flying is not cheap unless you like a lot of
downtime
or excitement in flight. As my old friend Walter Hudson said: You know
what keeps an airplane airborne, MONEY. It costs time and or money to fly a
well maintained airplane.
Personally, I don't like springs on exhaust joints, so I also run .041 safety
wire
through my springs to the hooks to assure a broken spring did not become a
FOD hazard. Plus, the exhaust stays together if a spring corrodes or fails
because
you chose cheap steel springs. To prevent spring harmonic resonation
on the 912S I also run a thick bead of high temp silicone down one side of the
spring which dampens the vibration increasing spring life.
Note: Any 912S maintainer should change all the springs at the 5-year point in
my opinion. The springs will be heat cycled many times by then, and although
looking OK, will eventually fail. Corroded springs should be replaced period.
Finally, exhaust manifolds and mufflers are not forever pieces of equipment.
They
endure extreme heat, vibration and are often abused with poor mounting on
any internal combustion engine. Inspect your exhaust often and repair properly
as an ill-fitting exhaust not only leaks, but it also causes harmonics of its
own that contribute to fatigue around the heads. It is money in the bank if
you have an original troublesome exhaust to simply "drop a thou" and replace
the exhaust. (Engines don't last forever either. If your engine is excessively
shaky, consider a short or long block overhaul if it is one of the early 912S
engines. Maybe even a new replacement as even engines at or near 1000 hours
are due serious maintenance, just like those dinosaur Lycoming and
Continentals.)
My "Rotax Engine Troubleshooting and Maintenance from Experience" paper is
still on the Europa Club website and my website
(www.customflightcreations.com). It was updated last in November of 2021 and
is still current. It has many of my maintenance techniques over the last 20
plus years maintaining the Rotax, including the exhaust.
Just my thoughts,
Bud Yerly
Custom Flight Creations
-----Original Message-----
From: owner-europa-list-server@matronics.com
<owner-europa-list-server@matronics.com>
On Behalf Of Area-51
Sent: Friday, January 05, 2024 10:59 PM
Subject: Europa-List: Re: Slight exhaust leak at cylinder head manifold joint
Several possibilities; all treated differently.
The cylinder head sealing contact surface itself could require lapping. Best way
to affect this is removal and bench lapping with 240g paper glued onto the
exhaust
header with contact cement; some kerosene as lubricant and rotate header
back n forth about 50deg for a bit, then lift and rotate 30-70deg and repeat
several times Not much pressure required. Easiest to clamp header pointing up
and rotate head upon it; makes cleanup easier... can use valve grinding past
as well... soot or bearing blue at the start and end can be used to check
sealing
surface for gaps. Sealing surface only requires 1mm cross section.
The 914 has part of the header extending into exhaust port; it is a very firm
fit
when new; long term slop flogs out this area in the head casting and requires
sleeving insert to prevent leakage.
Copper compress rings can be used as mentioned and should be set centered and
tensioned
again when hot. This is a bandaid approach to rotax factory sealing method
and may work totally fine. Have found copper rings on some engines.
Heat expansion of the header pipe may be causing movement at the sealing point
and returning to normal once cooled down. Stainless steel pipes grow a fair bit
when heated up. Some stainless steel exhaust systems on cars can grow up to
30mm... Try loosening off header at cylinder head and collector; give the header
a few light taps with hide hammer and retighten just under spec and again once
cooled down. Observe for outcome.
Check the clamping collar when tensioned; there needs to be a gap between the
collar
and the head; the collars bend quite easily when over tensioned.
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http://forums.matronics.com/viewtopic.php?p=513027#513027
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