Engine problem - Seneca II

[BDS[_2_]]

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

[Darkwing]

"BDS" > wrote in message
. net...
> 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
>
>

I'm assuming that turbos on planes have a popoff boost valve. Ever had those
checked to make sure they hold pressure properly? Maybe they are getting hot
and losing their resistance. I really only have experience with turbos in
cars, I've never flown a turbo charged plane or seen how the system works on
them (if they are even different).

-------------------------------------
DW

[Capt.Doug]

>"Darkwing" wrote in message
> I'm assuming that turbos on planes have a popoff boost valve.

You know what they say about assuming....

The stock Seneca 2 does not have automatic wastegates.

D.

[Capt.Doug]

>"BDS" wrote in message
> 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.

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.

D.

[Darkwing]

"Capt.Doug" > wrote in message
...
> >"Darkwing" wrote in message
>> I'm assuming that turbos on planes have a popoff boost valve.
>
> You know what they say about assuming....
>
> The stock Seneca 2 does not have automatic wastegates.
>
> D.
>
>

That is why I stuck the disclaimer in there. So what happens on a turbo
plane if you pull the power back real fast without a wastegate? On a car if
the wastegate fails you can damage the engine.

I have had the distinct pleasure of driving a Lingenfelter Twin Turbo 01'
vette on more than one occasion, 650hp, 6 speed, BAD BAD BAD!!!

--------------------------------------
DW

[Scott Skylane]

Capt.Doug wrote:


> You know what they say about assuming....
>
> The stock Seneca 2 does not have automatic wastegates.
>
> D.
>
>
That's correct, but it *does* have pop-off boost valves.

Happy Flying!
Scott Skylane

[BDS[_2_]]

"Darkwing" <theducksmail"AT"yahoo.com> wrote in message
...

> I'm assuming that turbos on planes have a popoff boost valve. Ever had
those
> checked to make sure they hold pressure properly? Maybe they are getting
hot
> and losing their resistance.

Thanks - I can't say for certain whether that has been considered or checked
at this point. We have mainly suspected that there is some coking despite
being careful about allowing proper spin down time.

BDS

[BDS[_2_]]

"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

[Friedrich Ostertag]

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

[Kingfish]

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?

[Capt.Doug]

>"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]

>"Darkwing" wrote in message > So what happens on a turbo
> plane if you pull the power back real fast without a wastegate? On a car
if
> the wastegate fails you can damage the engine.

The cylinders shock cool and crack with a strong pssibility of the heads
seperating from the barrels and/or seizure from the barrels shrinking around
the pistons.

> I have had the distinct pleasure of driving a Lingenfelter Twin Turbo 01'
> vette on more than one occasion, 650hp, 6 speed, BAD BAD BAD!!!

Sweeetttt!!!!

D.

[Capt.Doug]

>"Scott Skylane" wrote in message > That's correct, but it *does* have
pop-off boost valves.

So... I can firewall the throttle levers without overboosting the engines
on a Seneca 2?

D. (stock- as in from the factory)

[Scott Skylane]

Capt.Doug wrote:

>>"Scott Skylane" wrote in message > That's correct, but it *does* have
>
> pop-off boost valves.
>
> So... I can firewall the throttle levers without overboosting the engines
> on a Seneca 2?
>
> D. (stock- as in from the factory)
>
>
Doug,

Doing so would exceed max rated M.P. by about 1". The Pop-offs are
designed to be last chance protection against overboost, and are not to
be relied upon in normal operation. See:

http://www.kellyaerospace.com/articles/Turbocharging.pdf

Look at the section titled "How do you spell relief" on page 8.

Happy Flying!
Scott Skylane

[Capt.Doug]

>"Scott Skylane" wrote in message
> Doing so would exceed max rated M.P. by about 1". The Pop-offs are
> designed to be last chance protection against overboost, and are not to
> be relied upon in normal operation. See:

I remember 2 little lights in the upper middle of the instrument panel that
illuminate when overboosting. Are they activated by the PRV?

D.

[Scott Skylane]

Capt.Doug wrote:

> I remember 2 little lights in the upper middle of the instrument panel that
> illuminate when overboosting. Are they activated by the PRV?
>
> D.

No, the P.R.V.'s (Pop-Offs) are purely mechanical in nature. They have
no electrical function.

Happy Flying!
Scott Skylane

[BDS[_2_]]

"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[_2_]]

"Scott Skylane" > wrote in message
...

> > So... I can firewall the throttle levers without overboosting the
engines
> > on a Seneca 2?
>
> Doing so would exceed max rated M.P. by about 1". The Pop-offs are
> designed to be last chance protection against overboost, and are not to
> be relied upon in normal operation. See:
>
> http://www.kellyaerospace.com/articles/Turbocharging.pdf
>
> Look at the section titled "How do you spell relief" on page 8.

I think our overboost lights come on at just over 40 inches. I am pretty
sure you can go up to 42 for short periods, but I haven't tried. The
throttles on a stock Seneca II are quite sensitive - at sea level ours will
reach 40 in mp at about 75% of throw and you can get +/- 2 in by just
breathing on the throttles. Most of the time with the load and the runway
available I do not need to use more than 35 in so I don't even approach max
boost.

[BDS[_2_]]

"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

[Capt.Doug]

>"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.

[Morgans[_2_]]

"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.

[Blueskies]

"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...

;-)

[BDS[_2_]]

"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.