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YS170 Sudden Dead Stop from Fast Idle

Old 03-19-2020, 02:51 AM
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low701
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Default YS170 Sudden Dead Stop from Fast Idle

I was running my newly purchased second hand YS170 for the third time in the air-frame in preparation for a first flight.
I was setting up the existing throttle servo end points to match my RC system. Trying to get a stable idle ready for flight.
During the third engine run the motor suddenly stopped dead from a fast idle.

Anyone experienced this before?
There is now no compression, I haven't tried to restart. Suspect I need to strip down to find the problem.
There was a metallic clunk when the engine stopped, but carefully turning the engine over by hand does not make any odd noises.
Old 03-22-2020, 01:23 AM
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low701
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Further to my first post I used the wrong terminology. The engine stopped while on fast tickover while trying to set low throttle position on the servo.
Havent run the engine at WOT yet.
Old 03-28-2020, 02:30 PM
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speedracerntrixie
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If you haven't already done so, pull off the rocker cover, I have a feeling you will see a stuck valve.
Old 04-01-2020, 08:37 AM
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low701
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Whipped rocker cover off. Turned over by hand, Both valves working, decent compression.
Put my new starter on the front and gave it a spin.
Felt ok for 2 seconds then both valves stopped working.
Does not sound like anything broke, what could have occurred?

Would you advise I attempt a fix myself?
Old 04-03-2020, 07:49 PM
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Put your fingers on the rocker arms over the pushrods. Turn the engine by hand and feel if the pushrods are moving. If they are then the valves are sticking. Use a little head and some penetrating oil to lube the valve stems. If the valves are stuck it might be worth the trouble to remove the cylinder head. I have a 170 and it had a bent valve and a corresponding "dent" on the top of the piston. I'm not 100% sure if this is an interference engine or not. Maybe mine got over revved and the piston smacked the valve???
Ken
Old 04-03-2020, 11:48 PM
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low701
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Thanks Gents,
I still have not figured out why the engine stopped suddenly while on a fast tickover. I was setting the throttle end points at the time trying to achieve a reliable slow tick-over.
I wonder if it could have been running too rich causing a hydraulic lock?
As I mention below I’ve not found anything broken as yet.


Ive been very industrious while we are in lockdown here.
Partially stripped the engine down. Everything is in very good condition. Nothing sticking. These really are very good quality engines!
I was suspicious that the cam gear had lost a tooth. However, during the strip down I found the problem was the prop nut coming loose!! (Inexperience on my part!)

Im going to bench run the engine today, hopefully it will run!
Then I’ll try adjusting the mixture needles in a more controlled environment.
This engine is considerably more powerful than the others I own. It frightens the life out of me to be holding the air frame, even though it’s tethered, with the engine at even middle revs.

RC

Old 05-19-2020, 08:44 AM
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low701
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Quick update.
Thought I had learnt how to handle this engine now.
Previous problems all down to running too rich.

Tried to run it in the airframe today, first time with engine inverted. It’s now developed very high compression!
Starter will not turn it over. Tried to drain any fuel from the engine by removing pipes and plug to no avail.
Two steps forwards three steps back!!
Old 06-30-2020, 04:59 AM
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This is a DZ?
A condition I've seen with a stored engine is a stuck ring.
Excess fuel required to get it to fire and idles a bit, ring frees up a bit and goes rich and pops the prop.
Compression is higher and starter struggles. What are you using.
It does turn over by hand OK?
Personally I would bench mount to sort it - only knocking the airframe about while you get a handle on it.
The GP engines start up smoother with a PB switch in the GP lead - light the plug after getting the prop spinning,
avoids the occasional popping and banging/jerking on startup.
The prop must be kept tight, kept tight, kept tight, infinitum
Old 06-30-2020, 09:51 AM
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low701
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It is a DZ. problem above was my rebuilding the engine incorrectly!
lessons now learnt the engine has been fine ever since.
And yes following some other advice I have just made a switched glowplug lead. Haven’t tried it yet.
Im well impressed with the engine. It needed a new diaphragm and that was all.
As I have got used to it it’s become much more predictable and reliable.

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