Exhaust decisions / PowerFlow debate

[Oldguy]

  On 3/27/2019 at 8:45 PM, ArtVandelay said:

This is were my J is different I think:
Both cowl flaps are the type with contouring for the muffler, I obviously only have the muffler on the right side, so even with cowl flaps fully close, there is opening for airflow.

Anyone with a J have this?


Tom

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Now that is different. What S/N is your J? 

[ArtVandelay]

There was a change at 1615, but they don’t show the difference.


Tom

[KSMooniac]

Re: reversed air flow under the cowl...one time when I had the bracket at the back/top of the engine that supports the baffling loose, I neglected to tighten the nut and of course it leaked a little bit of oil. I didn't notice until enough came forward, out of the cowl, and onto the windscreen!

I never thought of using oil as a tell-tale for adjusting the cowl flaps, but now I think it might be a fun experiment...

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[Bob_Belville]

FWIW, I was by @AGL Aviationtoday. Lynn had a PFS exhaust disassembled on a worktable. He pointed out a small crack inside the junction of the headers. The PFS is off a flying school's C172 and has 2200 hours without any cost except inspections. The new part, which is essentially the whole guts of the system is $1200. (The headers are fine as is the tailpipe and heater shroud. I asked Lynn if he'd ever mic'd the wall thickness of the headers. "Yes, it is double that of conventional muffler systems.")

If that's typical, $1200 over 2200 hours, I suppose the PFS system is cost competitive with conventional systems without appeal to performance (speed/HP) or CO safety considerations.

[Prior owner]

I don’t think I ever saw a weight given for the PFS- anybody know?

[Bob_Belville]

  On 3/28/2019 at 3:31 AM, PilotCoyote said:

I don’t think I ever saw a weight given for the PFS- anybody know?

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Just checked the W&B calculation for my E. Old exhaust -17.0 pounds @ -5.5" arm; PFS +20.0 pounds @ -4.5" arm. 

[Culver LFA]

  On 3/27/2019 at 9:46 PM, Bob_Belville said:

He pointed out a small crack inside the junction of the headers. The PFS is off a flying school's C172 and has 2200 hours without any cost except inspections. The new part, which is essentially the whole guts of the system is $1200.

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2200 hrs is pretty good but let’s not be frivolous here, are they replacing the part rather than repairing/welding the crack?  Once repaired that system should be good for another 2000 hrs!

[orionflt]

my system has been on since 92, the baffles are gone and its time to replace it. I am bouncing back and forth between a knisley and power flow

Brian

[Culver LFA]

  On 3/28/2019 at 3:31 AM, PilotCoyote said:

I don’t think I ever saw a weight given for the PFS- anybody know?

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Weights from the installation manual for each version and optional equipment.

[Prior owner]

Thanks guys.

[DXB]

  On 3/28/2019 at 2:18 PM, orionflt said:

my system has been on since 92, the baffles are gone and its time to replace it. I am bouncing back and forth between a knisley and power flow

Brian

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My 21 year old 2000 hr knisley exhaust probably should be replaced in the next couple of years.  Can’t decide whether I want Knisley again vs powerflow - particularly given the  rumored performance gain of the knisley may negate the value added of switching to powerflow.  I’d be curious to hear of your experience, particularly if you go Knisley.

[orionflt]

  On 3/28/2019 at 5:46 PM, DXB said:

My 21 year old 2000 hr knisley exhaust probably should be replaced in the next couple of years.  Can’t decide whether I want Knisley again vs powerflow - particularly given the  rumored performance gain of the knisley may negate the value added of switching to powerflow.  I’d be curious to hear of your experience, particularly if you go Knisley.

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that is the same dilemma too, if knisley performs as well as powerflow, why spend the extra money. 

[ArtVandelay]

  On 3/28/2019 at 5:46 PM, DXB said:

My 21 year old 2000 hr knisley exhaust probably should be replaced in the next couple of years.  Can’t decide whether I want Knisley again vs powerflow - particularly given the  rumored performance gain of the knisley may negate the value added of switching to powerflow.  I’d be curious to hear of your experience, particularly if you go Knisley.

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Can you post a picture of your exhaust, especially the tailpipe?

[DXB]

 

 

@ArtVandelayNot a great pic, but here's the end of my tail pipe last year after it started to disintegrate and had to be replaced.

The full exhaust looks exactly like pictured on the Knisley website.

Edited March 28, 2019 by DXB

[Bob_Belville]

  On 3/28/2019 at 2:03 PM, Culver LFA said:

2200 hrs is pretty good but let’s not be frivolous here, are they replacing the part rather than repairing/welding the crack?  Once repaired that system should be good for another 2000 hrs!

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They replaced the part. I did not ask about whether welding is an option on the PFS. 

[Bob_Belville]

  On 3/28/2019 at 6:39 PM, DXB said:

 

 

@ArtVandelayNot a great pic, but here's the end of my tail pipe last year after it started to disintegrate and had to be replaced.

 

 

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That looks familiar. I left a big chunk of tailpipe somewhere between Atlanta and home a couple of months into ownership of the plane. The muffler guts were mostly missing as well and the flanges on the headers had been welded before.

That occasioned the new PFS.  

[AlexLev]

No PowerFlow for me:

[DXB]

  On 3/31/2019 at 4:06 PM, AlexLev said:

No PowerFlow for me:

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You might not want to use your Sensorcon monitor for a few months.  If it registers a few ppm CO after the replacement, the frustration might be difficult to handle 

[AlexLev]

  On 3/31/2019 at 4:45 PM, DXB said:

You might not want to use your Sensorcon monitor for a few months.  If it registers a few ppm CO after the replacement, the frustration might be difficult to handle 

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Checked it yesterday. 0ppm in cruise again.  

[AlexLev]

Embarrassing update: wanted to re-torque the bolts after the A&P bolted on the exhaust (after flying it) and instead of using 150 in lbs, used 150 ft lbs and broke off on the left rear exhaust stack/riser. Hope someone learns from my mistake.

@Shadrach or @M20Doc: curious if you have any ideas for how to work that out without damaging the cylinder? I'll be working with an A&P as well, but wondering if any of you have any experience on working that remaining stud out. I feel really dumb

See pics: 

[MARZ]

removing that exhaust riser may give you enough of the broken stud to remove successfully.  Luckily it wasn't the inboard stud.

consider one of these - DO NOT  give into the temptation to try a vice grips......

 

https://www.amazon.com/Powerbuilt-648639-Stud-Extractor/dp/B002INQORU

https://shop.advanceautoparts.com/p/kd-tools-studs-camshaft-style-stud-remover-1-4-to-3-4-kdt1708/22988109-P

https://www.grainger.com/product/36T852?gclid=Cj0KCQjw7YblBRDFARIsAKkK-dK8jtIH7yButDfQ1s2-8HfffLi-48GFWwo3SBzmNuhmsP7m2QlF2qsaAtpsEALw_wcB&cm_mmc=PPC:+Google+PLA&ef_id=Cj0KCQjw7YblBRDFARIsAKkK-dK8jtIH7yButDfQ1s2-8HfffLi-48GFWwo3SBzmNuhmsP7m2QlF2qsaAtpsEALw_wcB:G:s&s_kwcid=AL!2966!3!50916684477!!!g!66418499839!

As a last resort one can place a nut - oversize in some cases - and weld the nut to the stud.  But that's for someone who KNOWS how to weld.  Misplacement of the ground lead can be more damaging to the engine than the broken stud. 

 

 

[MIm20c]

If you gradually tightened the other ones in a star pattern well above the value you might want to change those as well. I admire your strength, I have to strain a fair bit to get my car lug nuts to 105 ft lbs. 

[AlexLev]

  On 4/2/2019 at 12:05 AM, MIm20c said:

If you gradually tightened the other ones in a star pattern well above the value you might want to change those as well. I admire your strength, I have to strain a fair bit to get my car lug nuts to 105 ft lbs. 

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Luckily, I didn't touch the other ones w/a torque wrench and they are not at all close. Thanks for the advice so far.

Edited April 2, 2019 by AlexLev

[Shadrach]

@AlexLev  I would have to agree with @MARZ that the best course of action is removing the riser and going after the stud.   Call your A&P and come clean...  He can help you tack weld a nut to to what's remaining of the stud as I don't think there's enough there to lock two nuts together. He'll likely take pity on you. You will need him for the re installation of the riser after the stud is replaced.

 

Edited April 2, 2019 by Shadrach

[Marauder]

  On 4/1/2019 at 11:42 PM, AlexLev said:

Embarrassing update: wanted to re-torque the bolts after the A&P bolted on the exhaust (after flying it) and instead of using 150 in lbs, used 150 ft lbs and broke off on the left rear exhaust stack/riser. Hope someone learns from my mistake.
[mention=8069]Shadrach[/mention] or [mention=12030]M20Doc[/mention]: curious if you have any ideas for how to work that out without damaging the cylinder? I'll be working with an A&P as well, but wondering if any of you have any experience on working that remaining stud out. I feel really dumb
See pics: 

What happened to that stud is exactly what happened to me. Except I wasn’t the guy who overtightened it but I was the guy sitting in the plane at 8000’ over low IMC when the stud finally cracked and the piece fell off.

With the stud/nut gone, it took about 2 minutes for the other nut to vibrate off and the entire riser to fall into the lower cowling. After completing an unscheduled landing, the field I landed at was able to get the remaining stud out.

Hopefully you only torqued this one this much.


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