Pawnee front seal leak

[Andy[_1_]]

Both Pawnees at the local glider club suffer from leaking front
crankshaft oil seals. One has had several oil seal changes and the
problem is not cured, the other started leaking within a few hundred
hours of a major overhaul. One is in original fixed prop
configuration and the other was converted to fixed pitch from constant
speed. Both engines will exceed oil pressure redline on a full power
takeoff when the oil temperature is above low red line (bottom end of
green range).

So a few questions for those with experience of operating or
maintaining Pawnees -

Is front seal leakage common and if so if there a known cure?

On your specific aircraft, at what oil temperature can full power be
applied on takeoff without exceeding oil pressure red line?

What do you consider a minimum oil temperature for full power takeoff?

Do you think oil seal leakage is associated with high oil pressure or
only influenced by crankcase pressure?

The guys that maintain the Pawnees are looking for some answers, and
I'm tired of flying with an oily windshield, so any help appreciated.

Andy

[lanebush]

On Sep 28, 3:23*pm, Andy > wrote:
> Both Pawnees at the local glider club suffer from leaking front
> crankshaft oil seals. *One has had several oil seal changes and the
> problem is not cured, the other started leaking within a few hundred
> hours of a major overhaul. *One is in original fixed prop
> configuration and the other was converted to fixed pitch from constant
> speed. *Both engines will exceed oil pressure redline on a full power
> takeoff when *the oil temperature is above low red line (bottom end of
> green range).
>
> So a few questions for those with experience of operating or
> maintaining Pawnees -
>
> Is front seal leakage common and if so if there a known cure?
>
> On your specific aircraft, at what oil temperature can full power be
> applied on takeoff without exceeding oil pressure red line?
>
> What do you consider a minimum oil temperature for full power takeoff?
>
> Do you think oil seal leakage is associated with high oil pressure or
> only influenced by crankcase pressure?
>
> The guys that maintain the Pawnees are looking for some answers, and
> I'm tired of flying with an oily windshield, so any help appreciated.
>
> Andy

If the crankcase breather tube is cut improperly on the bottom it will
cause case pressure or vacuum. Breather tube should be cut squarely
and not tapered like some are done. Front seals need to be installed
with the proper tool. Stretching them over the crankshaft flange with
a screw driver, pry bar, rags, rope etc. will damage them. A cracked
crankshaft can cause what looks to be a front seal leak. This is
probably info you have already gone over but good luck.

Lane

[T[_2_]]

On Sep 28, 12:23*pm, Andy > wrote:
> Both Pawnees at the local glider club suffer from leaking front
> crankshaft oil seals. *One has had several oil seal changes and the
> problem is not cured, the other started leaking within a few hundred
> hours of a major overhaul. *One is in original fixed prop
> configuration and the other was converted to fixed pitch from constant
> speed. *Both engines will exceed oil pressure redline on a full power
> takeoff when *the oil temperature is above low red line (bottom end of
> green range).
>
> So a few questions for those with experience of operating or
> maintaining Pawnees -
>
> Is front seal leakage common and if so if there a known cure?
>
> On your specific aircraft, at what oil temperature can full power be
> applied on takeoff without exceeding oil pressure red line?
>
> What do you consider a minimum oil temperature for full power takeoff?
>
> Do you think oil seal leakage is associated with high oil pressure or
> only influenced by crankcase pressure?
>
> The guys that maintain the Pawnees are looking for some answers, and
> I'm tired of flying with an oily windshield, so any help appreciated.
>
> Andy
We had a leaky crank seal about 800 SMOH that was replaced. Lyc O-540
engine. No problems since.
I have found that excessive oil pressure with full power at low
temperatures. Engine run up at 1800RPM with oil temp below 100F will
red line the oil pressure. For us it takes about 120F tobe. Able to
apply a full power takeoff.

High oil pressure could cause seal damage, we changed to steel braided
oil lines at overhaul so those are holding up well. We have had
problems with loose case bolts contributing to oil leaks and may have
also contributed to our leaky seal.

T

[Fred[_5_]]

Find a mechanic who knows how to replace the seals -- simple things
like bathing the seal in warm oil for 10 minutes before putting it on
will save you a lot of headaches. I had a problem with oil on the
windscreen and had the oil seal replaced twice, once with a special
oversize seal, before I found another mechanic who was a good
detective. Using spray-on chalk he discovered the leak was not the
seal, it was the accessory cover where the prop governor would go on a
constant speed installation. The cover itself (about 2" X 3") was
warped and when it warmed up it would leak. since this was above the
cooling baffles the pressure blew the oil forward onto the pulley,
then threw it out as if it was coming out of the crankshaft seal. We
couldn't find a replacement accessory cover in a hurry, so the
mechanic put it back on with a bunch of hi-temp sealant.

I tow out of Minden, 4700' MSL, so exceeding red line was not a
problem. I always wait for the oil temp to get into the yellow or
green before applying full power, even to check mags.

Hope this helps.

Fred

[aerodyne]

I agree with Fred, In our case, a CS prop converted to fixed, the
acessory cover on one of our Pawnees has leaked, and it behaved
exactly as he described..

As far as exceeding the oil pressure redline, we have this problem as
T described. Oil temp needs to be over 140 to allow full power. I
warm up 6-10 min, then partial power takoff ~2300 as part of the first
flight of the day check, by the time I land, the oil temp is up and
full power is possible without exceeding the pressure redline.

aerodyne

[[email protected][_2_]]

Here is a good trouble shooting guide for this problem from Sacromento Sky Ranch.
http://www.sacskyranch.com/eng3.htm

[[email protected][_2_]]

Here is a good trouble shooting guide for this problem from Sacromento Sky Ranch
http://www.sacskyranch.com/eng3.htm

[T[_2_]]

On Sep 28, 8:43*pm, Fred > wrote:
> Find a mechanic who knows how to replace the seals -- simple things
> like bathing the seal in warm oil for 10 minutes before putting it on
> will save you a lot of headaches. *I had a problem with oil on the
> windscreen and had the oil seal replaced twice, once with a special
> oversize seal, before I found another mechanic who was a good
> detective. *Using spray-on chalk he discovered the leak was not the
> seal, it was the accessory cover where the prop governor would go on a
> constant speed installation. *The cover itself (about 2" X 3") was
> warped and when it warmed up it would leak. *since this was above the
> cooling baffles the pressure blew the oil forward onto the pulley,
> then threw it out as if it was coming out of the crankshaft seal. *We
> couldn't find a replacement accessory cover in a hurry, so the
> mechanic put it back on with a bunch of hi-temp sealant.
>
> I tow out of Minden, 4700' MSL, so exceeding red line was not a
> problem. *I always wait for the oil temp to get into the yellow or
> green before applying full power, even to check mags.
>
> Hope this helps.
>
> Fred

We have also had a warped cover were the governor would be with or
fixed pitch prop. Our mech had another cover and gasket in stock. Lots
of oil from there.

T