REFLECTOR: Special O-Rings

[Bob Jackson]

Scott,

(My reply didn't seem to post properly the first time I tried -- here it is
again in case its of interest to you.  Bob):

Another possible source of oil leaks into the upper deck side of a
turbocharger plumbing can be the turbocharger itself -- especially when
they're new (and before the 'slug ring' that is created over time has been
created).  

When setting up our custom twin turbocharged IO-550N (on the ground) we had
A LOT of oil coming out both the turbo tail pipe and being sucked into the
upper deck tubing.  After talking with the Kelly people and a number of
other turbo experts, we learned that to minimize oil blow-by during initial
turbo set-up:

	*  minimize time on the ground at idle,
 and	*  if it's a manual wastegate -- keep it fully closed on the ground.

Once we started flying and got the engine broken in (you need to get the
turbochargers real hot), apparently the 'slug ring' they talk about formed,
and we now have no oil coming out of the turbo tail pipes or into the
induction system.  

Early on, we were getting tablespoons-full of oil in the induction piping.
Turbocharger oil rings are not very tight fitting.  The slug ring is created
over time as the turbos get very hot and small amounts of oil get burned,
with the deposits that remain forming a slug ring around the oil bearings to
help, especially statically, to seal the bearings.  Also, when you run at
high power settings, the increased pressures on both sides of the turbo oil
sealing rings helps minimize oil blow-by past the bearings.

Bob Jackson
Custom Twin Turbo IO-550N
50 hrs flight time now!
N2XF


-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Derrick
Sent: Thursday, January 22, 2009 10:06 AM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: Special O-Rings

Whilst attempting to tune the turbo/induction system on a TSIO520, I 
found out the wastegate controller was leaking oil into the upper deck 
pressure side of the unit.

I dissembled it and found the "O" rings needed replacement. not many 
hours on the unit but a lot of years.

The three large rings were a standard size but the small one is not. Its 
close to a -008 size O-ring(3/16x5/16x1/8) but with a width of 3/32 
instead of 1/8 of an inch.

I've searched and searched for an O-ring with a (3/16x5/16x3/32) but 
can't find one on line.

Any suggestions?

Scott
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