D

dick seiders

Well Known Member
Checked plugs after 50 hrs and found all perfect (nice tan color) except for number 1 cyl. which were carbon coated and looking rich burning. Interesting in that the number 3 cyl which is serviced by the same carb and air filter looks fine. Any thoughts on this?
Secondly a friend was nearby when I shut down the engine on Sat. and he said "what was that squeak I heard at the shut off?" Since I have never heard that and won't with headsets and engine noise what is it?
Thanks for feedback.
Dick Seiders
 
Dick, what engine RPM are you shutting down at?

Try the 3 step shut down method. With the engine idling around 2,000RPM,
1. Pull the throttle back to low idle (around 1400RPM, but don't run the engine this low on the ground, final approach is okay),
2. While the engine RPM is decreasing to 1600 RPM click off the left mag.
3. Click off the right mag about 1/2 second later.
All this is done is about 2-3 seconds.

The idea is to keep the momentum of the engine, gear box, and prop all slowing down until it stops. Just shutting off the mags works, but it is not the best proceedure.

While the squeaking is not a huge problem, it may be a sign of improper engine shut down, IMHO.

Try it and see if that helps.
 
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Thanks Joe, and Larry. I checked the earlier posts threads and the info is very helpful. I will try the 1600 rpm shutdown. Only question I have is why not kill both mags simultaneously? I had been shutting down at 2000-2200 killing master , then a, then b as quickly as I could move fingers from switch to switch. Lower rpms makes sense.
On the sooty plugs up front I usually have a long taxi back to hanger so likely am stuck with that. Would it help to run up to 3500 or so for a bit just prior to shutdown, or isn't the soot worth worrying about?
Dick Seiders
 
dick seiders said:
Thanks Joe, and Larry. I checked the earlier posts threads and the info is very helpful. I will try the 1600 rpm shutdown. Only question I have is why not kill both mags simultaneously? I had been shutting down at 2000-2200 killing master , then a, then b as quickly as I could move fingers from switch to switch. Lower rpms makes sense.
On the sooty plugs up front I usually have a long taxi back to hanger so likely am stuck with that. Would it help to run up to 3500 or so for a bit just prior to shutdown, or isn't the soot worth worrying about?
Dick Seiders
Click to expand...

FWIW, there was a long fight on here a while back about the squeak and shutdown procedure, you can probably find it in the archives of the list.

In short, the squeak is normal. Most 912's equipped with the overload clutch squeak loud right as the engine comes to a stop, it's nothing to worry about. As for the shutdown procedure, there's also nothing wrong with what you're doing now so no need to change it if you don't want to.

As for the sooty plugs, that seems to be very common. I have found the stock 1.5 turns out setting on the idle mixture to be a little bit rich, however. I live at a high altitude (about 6300' MSL) and my idle screws ended up at about 3/4 turn out from closed the last time I did my carb service and pneumatic sync. So it might be worth it one day if you're out tinkering to adjust the idle mixture (EGT's seem to be around 1050 at idle when the mixture is 'on the knee').

The Bings as factory jetted have a rich spot in the 2200 to 3500 rpm range, so if you spend a lot of time in there you'll get a fair bit of soot buildup. But as long as you're sufficiently lean at high power (EGT's in the 1300-1400 F range) you shouldn't have any problem (the soot will burn off the plugs too). What I'd suggest is leaning the idle mix out (i.e. lean until engine just starts to get rough, then back off about 1/4 turn) and avoiding more than about 2000 rpm while taxiing. Won't do any harm to run in the rich spot, but it'll keep the soot buildup down.

LS
 
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I'd confirm the info in the post above. Our instrumented testing showed AFRs richer than 11.1 to 1 from 2250 to 3000 rpm so this is not the range you want to run in continuously. AFRs are back into the mid 12's by 3500.
 
Lucien, and Ross, Thanks for the feedback. I will be considering all the inputs I've received in tweaking the squeaking, and booting the sooting in order to optimize the running of this fine engine.
Dick Seiders
 
dick seiders said:
Lucien, and Ross, Thanks for the feedback. I will be considering all the inputs I've received in tweaking the squeaking, and booting the sooting in order to optimize the running of this fine engine.
Dick Seiders
Click to expand...

Well I'll reiterate my position very briefly which will hopefully save you some trouble (and money):
- don't try to do anything about the squeak, basically follow a policy of 'fly more, worry less'. It ain't broke so don't try to fix it - the sensenitch prop is surely well within the MOI limits of the 912 gearbox also so there's nothing to fix. The 912 gearbox is a very good design with lots of self-safety built into it with the clutch and dog hub system.

- Also don't get bent out of shape about shutting the engine down. It's perfectly ok to shut if off the way you're doing it (killing the mags instantly from your normal idle speed) and any other procedure like the one-mag-wait-a-bit-then-the-other won't really buy you anything. It'll go to TBO just fine with your procedure. If you read the other threads, the fight broke out about the potential hazards the 'staged shutdown' method can introduce, so I won't go into that again.

Basically, don't worry about either of these. There's nothing wrong with your motor, nothing to see here folks ;). Enjoy your 912, it's a great engine!

LS
 
This was specifically addressed in a 2009 RVator...

In one of the threads referenced above, there was a fair bit of discussion (I didn't find it to be a 'fight'...but perhaps I'm less sensitive than some) on whether the 'dropping RPM/shutdown' technique solved the 'squeak issue' (not resolved) but also in fact was potentially a detrimental practice.

What was missing from that discussion was that there was a specific recommendation from Ken or Vans own proto shop folks who completed the Rotax courses (I forget which) on how to shut down the Rotax engine properly. FWIW their specific directions were to begin pulling back the throttle from ~1800 rpm and, as the rpms dropped, shutting down first one mag and then the other.

For anyone still interested in why that method might be preferred and/or whether it's potentially risky, I'd suggest following up with the Vans guys and hear what they have to say...not that further discussion here can't be useful as well.

Jack
 
Jack Tyler said:
In one of the threads referenced above, there was a fair bit of discussion (I didn't find it to be a 'fight'...but perhaps I'm less sensitive than some) on whether the 'dropping RPM/shutdown' technique solved the 'squeak issue' (not resolved) but also in fact was potentially a detrimental practice.

What was missing from that discussion was that there was a specific recommendation from Ken or Vans own proto shop folks who completed the Rotax courses (I forget which) on how to shut down the Rotax engine properly. FWIW their specific directions were to begin pulling back the throttle from ~1800 rpm and, as the rpms dropped, shutting down first one mag and then the other.

For anyone still interested in why that method might be preferred and/or whether it's potentially risky, I'd suggest following up with the Vans guys and hear what they have to say...not that further discussion here can't be useful as well.

Jack
Click to expand...

I'll simply restate my position on that and won't comment on it further (to spare the list another tussle about it):

- this staged shutdown won't affect the squeak on way or the other; the sqeaking happens at a _very_ low RPM, right as the engine comes to a stop, well below any sustainable idle RPM. The squeak isn't a problem to begin with so this is a solution to a problem that doesn't exist.

- the hazard is, if it's not done as described, the engine could be allowed to run, if only for a moment, below the minimum permitted idle RPM. With the sensenitch prop it's probably not terribly harmful, but it certainly wouldn't do any good either. The engine goes to TBO and beyond with the simpler method anyway, so I don't see how it's a bad practice.

So IMO, all this stuff does is just shorten the walk to the rubber room for the owner/op and offers no visible benefits to the engine. The engine will be enjoyed much more with these two non-problems crossed off the list of concerns carried around in the pilot's mind during flight.

That's my story, I'm stickin' to it, ;), and shan't mention or follow up on it again ;)

LS
 
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