wild.blue(at)verizon.net
Guest
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 Posted: Sun Jan 17, 2010 11:54 am Post subject: Hydro lock |
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Gents--
Two weeks ago a friend went to fly a Grumman Avenger. Very experienced guy
and crew. Went through the usual pre-start drill, no problems. Fires the
engine, it turns about two blades (out of three) and comes to a very
definite sudden stop. Big heavy prop, lots of inertia, oops. What could be
The Problem? All pistons go up and down, as do valves, but though the
engine will rotate, it'll only turn about 300 degrees (both directions)
before coming to a very definite clank stop. They detect one piston not
going very high up the cylinder so decide to pull the jug. Sho 'nuff, one
very bent rod (as in fractured at the bend), ring below the skirt. Turns
out this had happened once before, but was "cleared" and had been flying
ever since. Not good. Maybe just as well that it came to a stop on startup
and not in the air. Avengers have Wright 2600's, a bit much to pull by hand
so the starter is used, but there's a clutch that's not supposed to force a
lock. Pappy?
Weather before the incident was usual Seattle 40's, not real cold, but not
warm, either. No preheat. As is well known, taildragger ground attitude is
conducive to gravity fed oil going into intake tubes undetected until start
when things suddenly go bad. So, I think Doug's query as to temps is on the
mark.
I've had lock on CJ's and -52's, nose and tailwheel, also Wilga. OTH, I
had a Broussard with R-985, both fuel and oil shutoff, ICO shutdown, never
had a problem. You couldn't turn the fuel on unless you also turned the oil
on. Worked great, no locks never, tho oil shutoff notwithstanding sometimes
it would puke oil aplenty during pre-start drill and startup, tho nothing
like a -14P. Have also heard of M-14's wicking (?) oil into the UPPER
rocker boxes resulting in UPPER cylinder locks. Had to drain the boxes to
clear the lock. Say what? Makes no sense. I've flown (stupidly and no
fun) both a CJ and -52 that upon further inspection had bent rods, one a
MASTER rod. Wooaah! A customer actually BROKE a rod in HS-6A, but it kept
on til he could land. Scary.
Be careful out there.
Jerry Painter
Wild Blue Aviation
425-876-0865
JP(at)FlyWBA.com
www.FlyWBA.com
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