REFLECTOR: Reflector Digest, Vol 123, Issue 19
Grover McNair via Reflector
reflector at tvbf.org
Tue Jun 16 07:21:30 CDT 2015
I respectfully disagree that running lean of peak will damage an engine if it is at 75% power or greater.
Regardless what manifold pressure you set, the critical point is 50 degrees rich of peak. The key is to pass through this point quickly. This is where there is the highest risk of detonation which is not good for any engine. Running lean of peak at any power level does not damage engines.
Grover McNair
Sent from my iPhone
> On Jun 16, 2015, at 6:52 AM, Jones Nick via Reflector <reflector at tvbf.org> wrote:
>
> I would like to add a caveat to your quote from Mike Bush in regards to "They all also say you can't hurt an engine by running it too lean, provided you're too lean on the lean side of peak -- the engine just eventually flames out!" This is correct except that you want to be @ or below 75% power. Running lean of peak at full power WILL damage your engine. I would also have to take issue with the "little detonation is good for your engine", nothing good will come of trying to run your gas engine like a diesel.
>
> Nick and Connie Jones
> Velocity XL-RG
> N10CN
> -----Original Message-----
> From: Reflector [mailto:reflector-bounces at tvbf.org] On Behalf Of via Reflector
> Sent: Monday, June 15, 2015 17:56
> To: reflector at tvbf.org
> Subject: Reflector Digest, Vol 123, Issue 19
>
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> Today's Topics:
>
> 1. Re: Piston Crack -- Dye Penetrant Testing
> (Bob Jackson via Reflector)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 15 Jun 2015 17:56:10 -0400
> From: Bob Jackson via Reflector <reflector at tvbf.org>
> To: "'Velocity Aircraft Owners and Builders list'"
> <reflector at tvbf.org>
> Subject: Re: REFLECTOR: Piston Crack -- Dye Penetrant Testing
> Message-ID: <01a801d0a7b6$173e26e0$45ba74a0$@org>
> Content-Type: text/plain; charset="utf-8"
>
> Steve, Mike & Kerry,
>
>
>
> Thanks for your ideas and inputs. The engine only has 75 hours on it and no
> pre-ignition, but one short detonation 'event'. I do run LOP a lot, but LOP
> (and even some occasional light detonation are supposed to be good for an
> engine according to Busch and Deakin and Tornado Alley) in terms of keeping
> the carbon deposits down. They all also say you can't hurt an engine by
> running it too lean, provided you're too lean on the lean side of peak --
> the engine just eventually flames out!
>
>
>
> In the inspections I've done, I have not seI would like to add a caveat to your quote from Mike Bush in regards to "They all also say you can't hurt an engine by running it too lean, provided you're too lean on the lean side of peak -- the engine just eventually flames out!" This is correct except that you want to be @ or below 75% power. Running lean of peak at full power WILL damage your engine. I would also have to take issue with the "little detonation is good for your engine", nothing good will come of trying to run your gas engine like a diesel.
>
> Nick and Connie Jones
> Velocity XL-RG
> N10CN
> -----Original Message-----
> From: Reflector [mailto:reflector-bounces at tvbf.org] On Behalf Of via Reflector
> Sent: Monday, June 15, 2015 17:56
> To: reflector at tvbf.org
> Subject: Reflector Digest, Vol 123, Issue 19
>
> Send Reflector mailing list submissions to
> reflector at tvbf.org
>
> To subscribe or unsubscribe via the World Wide Web, visit
> http://www.tvbf.org/mailman/listinfo/reflector
> or, via email, send a message with subject or body 'help' to
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>
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>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of Reflector digest..."
>
>
> Today's Topics:
>
> 1. Re: Piston Crack -- Dye Penetrant Testing
> (Bob Jackson via Reflector)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 15 Jun 2015 17:56:10 -0400
> From: Bob Jackson via Reflector <reflector at tvbf.org>
> To: "'Velocity Aircraft Owners and Builders list'"
> <reflector at tvbf.org>
> Subject: Re: REFLECTOR: Piston Crack -- Dye Penetrant Testing
> Message-ID: <01a801d0a7b6$173e26e0$45ba74a0$@org>
> Content-Type: text/plain; charset="utf-8"
>
> Steve, Mike & Kerry,
>
>
>
> Thanks for your ideas and inputs. The engine only has 75 hours on it and no
> pre-ignition, but one short detonation 'event'. I do run LOP a lot, but LOP
> (and even some occasional light detonation are supposed to be good for an
> engine according to Busch and Deakin and Tornado Alley) in terms of keeping
> the carbon deposits down. They all also say you can't hurt an engine by
> running it too lean, provided you're too lean on the lean side of peak --
> the engine just eventually flames out!
>
>
>
> In the inspections I've done, I have not seen a 'sand blasted' look, just
> relatively clean surfaces. I did the this inspection because of the one
> detonation event, but that was only with this one cylinder. None of the
> other cylinders detonated and the valves and pistons look just like this
> one.
>
>
>
> Also, several of the other cylinders have similar dark colored 'track' lines
> on the pistons that also look like cracks. We're going to try to do a dye
> penetrant test, but it won't be easy through the spark plug holes.
>
>
>
> I'm still thinking these dark lines must be some kind of oil 'tracks'
> because after my test flight, the oil 'crack' didn't re-appear, but there
> was a new similar dark line in another area of the piston top, where there
> were no lines the flight before.
>
>
>
> My MAIN QUESTION is: has anyone else ever noticed dark 'track' lines (as in
> my photos below) that look like cracks on their piston tops before???
>
>
>
> Thanks,
>
> Bob
>
>
>
> From: steve korney [mailto:s_korney at hotmail.com]
> Sent: Monday, June 15, 2015 11:02 AM
> To: Bob Jackson
> Subject: RE: REFLECTOR: Piston Crack -- Dye Penetrant Testing
>
>
>
> Hi Bob...
>
> IMHO...... Your running that cylinder too lean... The carbon on the top of
> the piston has been eaten away by the excessive heat... After you cleaned
> the piston and went out to fly again the carbon has all but burned off...
> Looks like the pistons and the valves have been sand blasted... Detonation
> and pre-ignition cause that...
>
>
> Steve
>
> _____
>
> To: reflector at tvbf.org
> Date: Mon, 15 Jun 2015 10:12:46 -0400
> CC: bobj at computer.org
> Subject: REFLECTOR: Piston Crack -- Dye Penetrant Testing
> From: reflector at tvbf.org
>
> While checking the valves (with my new eBay Dental camera 'borescope'), I
> happened to rotate it 180 degrees and noticed what appeared to be a crack in
> the top of the #3 piston. The valves looked great, but a piston crack is
> scary. The engine only has 75 hours on it and has not been abused
> operationally. The cylinders and pistons were brand new from Continental
> (for our TNIO-550N).
>
>
>
> Cyl-3_Piston_Before-2.jpg
>
>
>
> Cyl-3_Piston_Before-4.jpg Cyl-3_Piston_Before-5.jpg
>
>
>
> The lighter gray marks between the crack and piston part # in the photo is
> where the top of the (plastic) dental camera hit the piston top when I was
> looking at the valves. Here's the #3 exhaust and intake valves.
>
>
>
> Cyl-3_ExhaustValve-4.jpg Cyl-3_ IntakeValve-1.jpg
>
>
>
> After a few days of head scratching and worry, we used a small wire brush
> and some AVGAS to clean off the top of the piston along the 'crack' line --
> then took it out for an hour long flight (overhead the field at 6000'). I
> wanted to see if the crack line would re-appear in the exact same spot or
> not. But after looking again after the test flight, there was no evidence
> of any line in the 'after' video -- the top of the piston looked smooth and
> clean where the stain/crack had been before.
>
>
>
> My questions are:
>
> . has anyone seen similar 'crack's or 'oil tracks' on the tops of
> pistons?
>
> . could it be a splash or 'seep' line of oil or fuel that appears
> possibly just as the engine is shutting down?
>
> . has anyone ever done dye penetrant testing of pistons before
> through the spark plug holes?
>
> . would the dye penetrant residuals likely damage anything or
> contaminate the oil?
>
>
>
> We're trying to gather some data and perspective before talking to
> Continental and the rebuilder and would appreciate your comments or
> suggestions.
>
>
>
> Thanks,
>
> Bob Jackson
>
> Velocity XL/RG/XC
>
> TNIO-550N
>
> 1000 hrs
>
> N2XF
>
>
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