Today's Message Index:
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1. 11:04 AM - Re: RotaxEngines-List Digest: 1 Msgs - 03/06/09 (Kitfoxkirk)
2. 12:22 PM - Rotax 921ULS rough running(420 hoursTSN) (Malcolm Ferguson)
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| Subject: | Re: RotaxEngines-List Digest: 1 Msgs - 03/06/09 |
I have inspected the inside of the intake manifolds on a Rotax 912UL and
found black soot like fine particulate in there. It does wipe off with a
rag, so it is not stuck on very hard. Has any other person experience this?
Thanks,
Kirk
On Sat, Mar 7, 2009 at 2:57 AM, RotaxEngines-List Digest Server <
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> Total Messages Posted Fri 03/06/09: 1
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> 1. 07:00 AM - 912 UL for sale (george.mueller@aurora.org)
>
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> ________________________________ Message 1
> _____________________________________
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>
> Time: 07:00:25 AM PST US
> Subject: RotaxEngines-List: 912 UL for sale
> From: george.mueller@aurora.org
>
> If anyone is looking at buying an engine, I have a Rotax 912 UL 60 hours
> total time since new, plus a Woodcomp Klassic three blade prop 30 hours
> total time since new, plus a Rieff rotax engine preheater for sale on
> Barnstormers for $14,900. The engine is currently being gone over at the
> rotax dealer to make sure it is perfect.
>
>
> George in Milwaukee
>
>
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| Subject: | Rotax 921ULS rough running(420 hoursTSN) |
Over a period of a couple of months the engine/plane has developed
significant vibration that was related to engine revs and was like it
was running on 3 and a half cylinders-not actually missing.
After much head scratching and all the usual things such as carby
balancing, plugs etc. a leak down test was performed with the following
results:
Cyl 1: 73/80
Cyl 2: 64/80
Cyl 3: 63/80
Cyl 4: 73/80
By listening I determined the intake valves in cyl. 2 and 3 were
leaking. Subsequently all 4 heads were removed and sent for service.
All 4 intake valves were too badly damaged on their valve seat mating
surfaces to be repaired. So 4 new valves. The Rotax mechanic had no
explanation for the damage. Have used mostly Mogas premium unleaded. The
mechanic said he would expect to see that damage on an engine that had
done 1200 hours exclusively on Avgas.
No damage to the valve seats in the heads. Talk of sending the valves
back to Rotax. I liked the lack of head gaskets. There would be good
heat transfer from the top of the cylinder barrels to the heads.
The mechanic also suggested that some people had vibration problems at
around 3000 revs that could not be cured. It was discovered that the nut
holding the small gear(gearbox) on the crankshaft was loose. This proved
to be the case on mine. It was well below the required 200nm(146 ft/lb).
The serrated bellville washer under the nut was badly worn and was
replaced. The nut is supposed to be put on with Loctite. On my engine it
appeared that Loctite had been applied after the nut was tensioned up
and had wicked in only a couple of threads. I was impressed with the
simplicity of the Rotax gearbox and its ease of disassembly. I loved the
use of bellville(cupped) washers and shims to get the required torsion
in the "dog clutch".
After carby disassembly 2 damaged O rings were found on the idle mixture
screws, after renewal the idle improved marginally.
Engine has always run much smoother on one mag than the other, although
rev drop difference between the two was only 30-40 revs at 4000, much
less than the roughness indicated.
Trigger coils checked and tested okay with an ohm meter. Trigger coil
plugs reversed at the ignition modules, but roughness stayed with the
same mag circuit eliminating the trigger coils. Then switched plugs
that connect the ignition modules to the coils(4 of) and voila the
problem changed mag circuits, indicating a problem with 2 coils or their
leads and plug caps. Both coils test okay, both primary and secondary
circuits. One spark plug cap tested okay until a slight tension was
applied, then went open circuit. It was replaced and engine test run.
Still the same problem. The ignition modules/coil pack are an absolute
dog's breakfast to get at, compact but a terrible design for access.
So the saga continues. I have found several major problems I would not
have found for a while. Have just priced a coil. Hard to imagine how a
tiny little coil could cost more than a set of tyres for my car or a
bottle of Australia's premier red wine-a bottle of Penfold Grange(over
$500). Incidentally, I priced an ignition module and I could get a one
way airline ticket to London for less. So I just need a few days to
pluck up the courage to order a new coil then try to work out which coil
is crook.
On a more serious note the ignition modules are supplied with power from
2 charging coils. The schematic shows 2 seperate wires from the charging
coils to the ignition modules. On my engine there is only one wire,
jumpered to each module. The failure of that wire at either end results
in the loss of both ignition systems, a very serious design flaw and one
I'm glad I found.
Malcolm Ferguson
Esqual, 912ULS, Rospeller CS
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