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Propeller/engine rotated backwards

 
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JonathanMilbank



Joined: 14 Apr 2012
Posts: 234
Location: Aberdeen area

PostPosted: Sun Nov 05, 2017 3:05 am    Post subject: Propeller/engine rotated backwards Reply with quote

What if someone's been turning my propeller/Rotax 912ULS backwards through several revolutions? I know in that case oil will be "sucked" out of the hydraulic tappets and damage would/could be caused to the valve train.

Would I hear clattering on engine start and would the noise continue? Or after initial clattering, would the tappets fill within a few minutes and the clattering disappear? The trouble is that someone else did the first start and he didn't report unusual noises.

The engine has subsequently run for two hours including four flights. Should I now undertake investigations for damage and if so, what should I be doing to put this worry behind me? Rocker covers off and look at valve spring caps? Check magnetic plug? Prime the oil system again to purge air out of the tappets?

Your advice would be very welcome, thanks.


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Roger Lee



Joined: 10 Jan 2006
Posts: 1452
Location: Tucson, Az.

PostPosted: Sun Nov 05, 2017 8:43 pm    Post subject: Re: Propeller/engine rotated backwards Reply with quote

If you keep doing that not only will oil be displaced, but you'll ruin the sprag clutch on the starter and that usually means pulling the engine. Removing the back end of the engine and replacing th4 sprag clutch. That will be expensive.

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JonathanMilbank



Joined: 14 Apr 2012
Posts: 234
Location: Aberdeen area

PostPosted: Mon Nov 06, 2017 2:34 am    Post subject: Re: Propeller/engine rotated backwards Reply with quote

As I said "someone's" possibly been doing it and it wasn't me. Regarding sprag clutches, if my propeller gets turned even slightly the wrong way then it can clearly be heard and felt that the starter motor is being driven backwards through the sprag clutch. There is an extra resistance to turning the propeller and a whirring sound.

Having already had the sprag clutch replaced when changing from the old style starter to the longer-bodied starter motor, I've seen and understand what's involved in that job. I removed and replaced the engine myself and don't wish to repeat that anytime soon!

So going back to my main concern, I'm keen to know if running the engine will get rid of air in the tappets, in which case that's already happened, or is bleeding the oil system the ONLY way to achieve this?


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gilles.thesee(at)free.fr
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PostPosted: Mon Nov 06, 2017 4:19 am    Post subject: Propeller/engine rotated backwards Reply with quote

Le 06/11/2017 à 11:34, jonathanmilbank a écrit :

Quote:
Quote:


So going back to my main concern, I'm keen to know if running the engine will get rid of air in the tappets, in which case that's already happened, or is bleeding the oil system the ONLY way to achieve this?

Jonathan,

Let's say it is the only way to achieve peace of mind Wink
SI-912-018 is really no big deal, if it were my airplane I'd perform it and clearly label my prop with a "never rotate backwards" sign.
And why not craft a prop cover with something preventing rotation of the prop -unless some harm to the engine is deliberately meant ?

FWIW
--
Best regards,
Gilles
http://contrails.free.fr
http://lapierre.skunkworks.free.fr


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JonathanMilbank



Joined: 14 Apr 2012
Posts: 234
Location: Aberdeen area

PostPosted: Mon Nov 06, 2017 5:04 am    Post subject: Re: Propeller/engine rotated backwards Reply with quote

Gilles, you've hit the nail on the head with "unless some harm to the engine is deliberately meant ?", but when a friend went flying in my aircraft after it had not flown for 4 weeks, he later told me that it started perfectly first time with no unusual noises. I only spoke to him after I started this topic, when I had also flown the aircraft and thought the engine was less smooth.

I have done SI-912-018 a couple of times previously, so I'll probably take your advice and do it again. However it would be useful to know from someone who has experienced it before, whether the engine makes noises caused by hydraulic tappets with air trapped inside. I imagine it would sound a bit like an old diesel engine, only quieter.

Perhaps I'm just being too suspicious of someone who is known to have done underhand things before, but not as serious as this!


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Roger Lee



Joined: 10 Jan 2006
Posts: 1452
Location: Tucson, Az.

PostPosted: Mon Nov 06, 2017 5:37 am    Post subject: Re: Propeller/engine rotated backwards Reply with quote

If you can actually hear the tappets because you have that much air in the system you are going to damage and bend things. These are hydraulic lifters and need oil to function properly.

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Roger Lee
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Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
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