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HomeRC & Power✈️Aircraft🚁HelicopterEngines Plugs Mufflers Fuel › OS-91SZ (non-pumped) Hydraulic Lock Problem
07-24-2006 02:57 AM  14 years ago
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Danville, IN

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OS-91SZ (non-pumped) Hydraulic Lock Problem
Is there something I should do after each flight on my Vibe & Fury Extreme to prevent the SZ from hydra-lock the next time I try to start them? A friend of mine has the same problem on his Raptor 90 as well. We used to shut down using a switch on the transmitter but the thought was that there is still enough unburned residual fuel in the crankcase or fuel in the cylinder that drains back into the case and past the piston causing it to lock up. We then decided to clip off the line to the carb and let it purge itself versus Tx shutdown. Still, this doesn't help.

Some other factors that may help answer questions you might have.
1) We are using 3600mAh 14.4V Dynatron starter setup.
2) My machines both have MP2 mufflers, the Raptor uses a Century.
3) We are using header tanks on all 3 machines.
4) We are running Enya 3 and OS#8 plugs.
5) We are using the stock head shims that come with the SZ. We did not add the extra shims that come with the engine.
6) We are running YP-30 fuel.
7) One thing that may be a factor is that all 3 engines are very low time and we are running them rich. Maybe things will get better when we start leaning them out. Any suggestions on needle settings for all 3 needles on the carb?

Thanks for any help.
07-24-2006 08:16 AM  14 years ago


Middlesbrough, England

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We had a problem with one at our club. After running one tank through it it just would not turn over, no matter what. In the end we fitted the extra head shims and that solved it. Try the following methods....

1) Turn it over using 24v Dynatron.
2) Take out glo-plug and turn it over to remove all fuel from engine.
3) Lay heli on side (muffler down) whilst turning over so excess fuel 'falls' into the muffler.
4) Loosten the plug right off until it is only on one/two threads whilst trying to start. Then remove glo-clip and tighten with engine running.
5) Fit the extra head shims.
6) Always run it dry by pinching fuel line rather than cut switch.
7) Empty everything out of the tank after flying.
8) Clip fuel line to carb when finished flying or remove fuel line from carb.

Having said all that my 0S91SZ (non pumped) has been fine starting ever since I got it with the stock shims!

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07-24-2006 11:29 AM  14 years ago

rrElite Veteran

Johnston USA

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From my experience and others at the field, seems at least 14 cells are needed to turn the ninety over. ChrisChris
07-24-2006 12:04 PM  14 years ago
Dr Lodge

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Guildford, Surrey - UK

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I find a clip on the fuel line which is taken off only when you're ready to start the engine works wonders. For a troublesome engine, crank the engine over with the clip in place to ensure the engine will turn over ie its "dry", then remove clip and start.

To stop engine, clip fuel line then immediately shut off engine via the Tx switch.
Vibe 90, Vibe 50, Vigor CS x2,
Dyna-x, Knight 503D, Logo 10,
TRex 500, Furion, Gaui EP200
07-24-2006 01:58 PM  14 years ago

rrElite Veteran

Meridian, Mississippi

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💎Sustaining Member
-- Use 16 high current cells. 2, 7 cell 1500 mah packs don't get it.

-- Right after a flight, pinch the fuel line.
-- Fuel with the line pinched.
-- Start with the line pinched.
-- After the engine cranks, un-pinch line. Sometimes I can do this before the engine dies. Sometimes the engine dies and I un-pinch the line and have to re-crank.

Also, adding the two other shims will help and if you're running 20-30% nitro, you may have to add them for tuning reasons. I think most folks are running something around .016 to .024". The engine ships with .008". The other 2 shims will take you to .020"

Works every time.

Bill Vail
07-24-2006 02:30 PM  14 years ago
Paul Hinz


Oostburg, WI

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Also with the MP2 mufflers after you shut off the engine move the piston to top dead center. The oil that collects in the muffler tends to run back into the cylinder when sitting.

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07-24-2006 02:35 PM  14 years ago


Danville, IN

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Thanks for all the responses guys. I wasn't quite sure what the extra shims would do for my situation. I am at a point right now on my Extreme (engine out of heli) that I can take advantage of installing the shims. Just out of curiosity, what will the added shims do for engine tuning, i.e. needle valve settings?

There is a guy in the club that runs a YS91 in an Extreme that tips it on the side for starting purposes. I frequently have to pull the plug out to purge the residual fuel. That tends to be a pain but it works every time.

Again, thanks for your help.
07-24-2006 04:02 PM  14 years ago
Jerry Sudimick



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Adding headshims to aid in engine starting is silly. Shim changes should not be predicated on how easy your engine starts. The dynatron likes voltage. If you put a Torqmaster 180 side by side with a dynatron - with both on same voltage... the dynatron would seem less powerful. 2 six cell packs on a Dynatron will not cut it at all.

I shut my SZ's off via the transmitter cut switch then I clip the line. I then bring heli back to pits and hit it with starter for 3 seconds or so. Then I rotate it to top dead center.
My dynatron with 2 seven cell packs wasn't as peppy as my torqmaster with the same.I think like someone else said - go with more volts on the dynatron.

But don't be changing headshim because of starting issues.

07-24-2006 08:46 PM  14 years ago

rrKey Veteran

High Crompton, Manchester. UK

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With the Musclepipe you can also fit the header so it slopes away from the engine. Clamp the fuel line as soon as you can and depressurise the tank.

That's how I close down my YS, and Rick his C-Spec. Never have a problem on the restart.

BTW, only using 12V via a 40AH lead acid motor cycle battery. The C-Spec fights a bit with the first start of the day but after that its fine
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07-27-2006 01:13 PM  14 years ago


UK. Herts

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only using 12V via a 40AH lead acid motor cycle battery. The C-Spec fights a bit with the first start of the day but after that its fine
same here
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HomeRC & Power✈️Aircraft🚁HelicopterEngines Plugs Mufflers Fuel › OS-91SZ (non-pumped) Hydraulic Lock Problem

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