Engine problem - Seneca II

"Capt.Doug" wrote in message
...

I would suspect that the turbocharger bearings are lightly coked up and
squeeze the shaft when they expand from heat. This can happen even with
proper operation and cool down.

This is what we have suspected as well, although it hasn't gotten any better
or worse in the last several years.

The first time it happened I was on a trip from the east coast out to
Colorado and had it looked at while I was in the Denver area. The mechanics
at the time suggested that coking might be the problem but that the only fix
was to replace the turbo to the tune of $900 plus labor.

I wonder if the bearings could be changed out as opposed to replacing the
entire turbo.

BDS

BDS wrote:

I wonder if the bearings could be changed out as opposed to replacing
the entire turbo.

For automotive turbochargers specialized companies or the manufacturer
itself used to do this, they were then sold again as "reworked" for the
aftermarket. With mass production of turbocharged (mainly diesel-)engines I
don't think it's worth the labour any more for the automotive market. But
for aviation turbochargers, it might be an option, maybe best to check with
the manufacturer of the t/c directly. Though I don't know for sure for
aviation engines, I strongly doubt the local AP would be able to change
bearings on a t/c. The main obstacle would be to re-balance the rotor after
reassembly.

regards,
Friedrich

"BDS" wrote in message
I wonder if the bearings could be changed out as opposed to replacing the
entire turbo.

Yes, along with the seals. However, when you pull the compressor off the
shaft to slide the bearings off, you disturb the balance. Balance is
critical at 130k rpm. Then there is that pesky FAA thing about engine
accessories having to be overhauled at a repair facility.

Do you use Marvel Mystery Oil?

D.

"Capt.Doug" wrote in message
...
"BDS" wrote in message
I wonder if the bearings could be changed out as opposed to replacing
the
entire turbo.

Yes, along with the seals. However, when you pull the compressor off the
shaft to slide the bearings off, you disturb the balance. Balance is
critical at 130k rpm. Then there is that pesky FAA thing about engine
accessories having to be overhauled at a repair facility.

Do you use Marvel Mystery Oil?

Not in this aircraft as of yet but I have used it in other non-turboed acft
in the past. Can it handle the heat of the turbo and do you think it might
help clean the bearings?

BDS

"BDS" wrote in message
Not in this aircraft as of yet but I have used it in other non-turboed
acft
in the past. Can it handle the heat of the turbo and do you think it
might
help clean the bearings?

Don't know about turbocharged engines. I used it religiously in supercharged
R-985s, but that was to prevent sticking valves.

D.

"BDS" wrote

I wonder if the bearings could be changed out as opposed to replacing the
entire turbo.

At what point do you say that it is time for an overhaul of the turbo?

I would think that when the bearings need to be replaced would be a very
good time.

What would be redone on a rebuilt turbo? Cooked out, bead blasted, oil
ports cleaned or reamed, or whatever you do to clean out the gunk, new
shaft, reface the inlet and outlet flanges, and rebalance the whole thing.

It just seems to me that if the bearings need to be replaced, it would be a
shame to do that, then have something else go wrong.

I don't know specifically about aircraft turbos, but from a sound mechanical
preventative maintenance background, it seems to me that this is an
important decision, and one that should be talked around to various A & P's,
and other owners that have had work done on their turbo, just to make sure
that you are not throwing good money after bad.

"BDS" wrote in message . net...
:...
:
: I wonder if the bearings could be changed out as opposed to replacing the
: entire turbo.
:
: BDS
:
:

I'm sure the bearings could be changed out for no more than twice the cost of new turbos...

;-)

"Blueskies" wrote in message
...

"BDS" wrote in message
. net...
:...
:
: I wonder if the bearings could be changed out as opposed to replacing
the
: entire turbo.
:
: BDS
:
:

I'm sure the bearings could be changed out for no more than twice the cost
of new turbos...

Yep, sounds about right.

BDS wrote:
We've been having a problem with the engines on our Seneca II for awhile now
and I wonder if anyone else has any experience with it. The engines are
TSIO-360s and if we lean at cruise with about 75% power (typically around
32-in MP) or less to anything over about 1400 EGT (which is still ROP), the
manifold pressure will begin to drop off after awhile - sometimes after only
5 minutes or so, sometimes after 30 minutes or more.

It drops eventually to what would appear to be ambient pressure, as if the
turbo suddenly stopped providing boost. If the mixture is richened up the
MP will eventually return to normal - usually you have to go to full rich
until things return to normal and then lean back but not as far. Fuel flow
rates at the mixture setting that keeps this from happening are well over
what the book says they should be - as an example at 8,000 feet and 2300 rpm
with 32-in MP we need about 14 gph to stay below 1400 EGT. Lean the mixture
to below 14 gph, even to 13.5 and allow the EGT to rise to 1425, and the
problem will show up. The engines run fine when this happens - no
roughness, etc.

We have tried lots of adjusting and changing of parts in the fuel system -
about the only thing we haven't tried is changing the turbos because that is
prohibitively expensive - and we have always allowed 3 min of turbo spin
down time before shutdown. At first only one engine was doing this but now
both do it and have been for the last 1,000 hrs or so. Both engines are
still healthy with good compression in all cyls, so whatever this is it does
not seem to be causing any damage.

Anyone else ever seen anything like this?

BDS

There were a few good suggestions from others already - Turbo bearing
coking does make sense, but you clearly know to let the turbo unspool
before shutdown so that might not be as likely. (IIRC there is a way to
clean up the turbo bearings without turbo removal if that's what it
turns out to be) My guess would be the fuel control unit gone wonky;
the fact that power returns after richening the mixture might back up
that theory, but what are the chances of both acting up simultaneously?
Maybe the alternate air diverter is partially open? Out of curiousity,
what CHTs are you seeing at 1425 EGT?

"Kingfish" wrote in message
oups.com...

There were a few good suggestions from others already - Turbo bearing
coking does make sense, but you clearly know to let the turbo unspool
before shutdown so that might not be as likely. (IIRC there is a way to
clean up the turbo bearings without turbo removal if that's what it
turns out to be) My guess would be the fuel control unit gone wonky;
the fact that power returns after richening the mixture might back up
that theory, but what are the chances of both acting up simultaneously?
Maybe the alternate air diverter is partially open? Out of curiousity,
what CHTs are you seeing at 1425 EGT?


I know the fuel controls were double checked and adjusted when the problem
first came up. That doesn't mean they aren't the culprit, but they seem to
act normally when tested.

CHTs never get out of the green arc and typically remain at about 75% of the
scale.

BDS