Remi and Jonathan,
Of course the early 912ULS were happier running backwards than forward.
If you have done all you say you have, the list gets pretty small and expen
sive.
Things which helped the kickback was most importantly, the soft start modul
e and the new ignition modules (six wire). Careful assembly of the pickups
on the electrics was also essential to assure the correct pickup went to t
he correct box. An early spark just as the valves close will kick right ba
ck. See your Rotax Heavy Mx manual. I have only seen this once on a very
early Rotax 912ULS where the A&P found some broken wires (another problem w
e all discussed before) and repaired the wires with new wires and didn=92t
quite get everything wired back up right. What a nightmare. We ended up g
oing to two new ignition boxes paying extreme attention to the pickup wirin
g and all was fine. I was chastised by Kerry at Lockwood for not changing
both boxes initially, as tinkering with one old box and putting only one ne
wer one initially with the old one, really made a mess. Note that the timi
ng controls changed as did the flywheel pickups in the early 2000s then aga
in around 2009. The new boxes even with the original flywheel really helpe
d this plane.
The high torque starter was also a help on some of these older engines with
soft start or with starting on one ignition technique. On a 912/914 low c
ompression, the low torque spins at about 300 RPM with a supercharged batte
ry or booster charger at 50 amps. The high torque starter spins at nearly
500 RPM on the 914. On the 912ULS I found the RPM still hit 400 plus which
is more than enough for quick starts. The Skytec starter is OK but I went
with the Rotax. I was impressed and you know what a cynic I am!
I would also check for a spun crank shaft or a valve timing problem. I do
n=92t do that in my shop. I pull the engine and go to Lockwood and have Ke
rry speck out the problem. A spun crank is nasty expensive and is usually
better to replace the entire short block. Really expensive. $14,000 min w
ith labor.
I had a sticky valve problem on two cylinders causing a problem which was j
ust that, sticky valves. We never could figure what actually caused it but
the kickback was spectacular. We redid the heads and that cleared up the
problem. Changed a slightly bent valve and a pushrod, lapped the valves, r
eplaced valve springs (Service bulletin) and checked the crank and ignition
modules which were OK. Heck of a thing. And only about $4300 which was a
bargain considering two guys for 3 days plus engine runs at Lockwood. I s
uspect that the engine was over revved and hit a valve as there were some t
ell tale signs on the piston carbon of the valves hitting.
I=92m in Florida so cold engine starts occur only one month of the year for
about 2 days. If the engine is really cold (below 0C) the cold oil and ti
ght oil pump can slow the engine crank some 50 RPM on even a semisynthetic
oil. Warm your engine with a blanket or something. I=92m not a fan of boc
k engine heaters that use the crankcase bolts however, they make heat pads
for the oil tank and crankcase that work if the cowl is wrapped fairly tigh
t outdoors or in a hangar. A 100 watt bulb in the intake works if you leav
e it for an hour and wrap the cowl tight. Mobile 1 MX4T or Motorcycle raci
ng full synthetic oil helps, but warmth is always nice for quicker starts.
Good luck. Remember you will find the problem. It is always the last plac
e you check.
Bud Yerly
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________________________________
From: owner-europa-list-server@matronics.com <owner-europa-list-server@matr
onics.com> on behalf of Remi Guerner <air.guerner@orange.fr>
Sent: Monday, March 4, 2019 12:27:46 PM
Subject: Europa-List: Re: I'm puzzled, again!
As an addition to my previous post regarding the kick-back problem, I belie
ve it is useful to add the following regarding the sprag clutch replacement
. After reviewing the different issues of the 912 IPC, from 2017 up to now,
I discovered that Rotax has made several changes in that area over the yea
rs. The sprag clutch itself has not been changed but the sprag clutch housi
ng was modified several times. Housing P/N 852405 was introduced in May 200
8 with the following comment: "new housing with expanded space for sprag cl
utch". Then in January 2017, P/N 852406 was introduced with the very same c
omment. I guess the changes were designed to improve the behaviour of the s
prag clutch.
My conclusion: when replacing the sprag clutch, it is critical to replace a
lso the housing and make sure the P/N is the last version.
Remi
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