Exhaust valve bore scoping

[MikeOH]

5 hours ago, N201MKTurbo said:

...That being said, once you take enough stuff off to pull one cylinder, it is easy to pull the rest.

A thought to consider...I believe Mike Busch doesn't recommend doing that; read up on his thoughts on cylinder work in general.  I think he views cylinder work as one of the riskiest maintenance operations.

https://www.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2014-06_cylinder-work-be-afraid.pdf

 

Edited April 1, 2020 by MikeOH

[N201MKTurbo]

9 minutes ago, MikeOH said:

A thought to consider...I believe Mike Busch doesn't recommend doing that; read up on his thoughts on cylinder work in general.  I think he views cylinder work as one of the riskiest maintenance operations.

https://www.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2014-06_cylinder-work-be-afraid.pdf

 

I would tend to agree with him. It is the most invasive thing you can do short of splitting the cases. 

Ive probably R&Red 50 cylinders in my life and so far no issues (knocking on wood). I’ve never been in a rush or trying to make a living at it. So I always took it slow and easy. There are a lot of opportunities to screw things up.

BTW sense I got my IA I’m being overwhelmed with requests to make a living at it....

There is just too much Missile work that needs done these days....

[MikeOH]

1 minute ago, N201MKTurbo said:

I would tend to agree with him. It is the most invasive thing you can do short of splitting the cases. 

Ive probably R&Red 50 cylinders in my life and so far no issues (knocking on wood). I’ve never been in a rush or trying to make a living at it. So I always took it slow and easy. There are a lot of opportunities to screw things up.

BTW sense I got my IA I’m being overwhelmed with requests to make a living at it....

There is just too much Missile work that needs done these days....

WARNING! Thread creep!

Question:

I believe one of the risks is moving the crank while cylinders are off and having a bearing shift/spin in the case (loss of clamping force when cylinder through bolts are removed) presumably resulting in a mis-aligned oil hole.  With auto engines the bearings have 'tabs' that lock them in place...it sounds like aircraft engines don't have them.  Why not?

[N201MKTurbo]

5 minutes ago, MikeOH said:

WARNING! Thread creep!

Question:

I believe one of the risks is moving the crank while cylinders are off and having a bearing shift/spin in the case (loss of clamping force when cylinder through bolts are removed) presumably resulting in a mis-aligned oil hole.  With auto engines the bearings have 'tabs' that lock them in place...it sounds like aircraft engines don't have them.  Why not?

Nonsense, all bearings have some anti rotation feature. Aircraft engines run the gamut. Even the same model varies over time. Some have tabs, some have pins. Sometimes the pins are the oil hole.

lets be realistic, sure the cases lose the clamping pressure, but the half’s don’t move but a few tenths. How is that going to allow the bearings to spin? The only way they are going to spin is if something was wrong in the first place.

Ive seen an engine with a spin bearing. It sheared the alignment pin clean off. Not sure what caused it. BTW that engine was still running pretty well.

 

 

 

 

[MikeOH]

6 minutes ago, N201MKTurbo said:

Nonsense, all bearings have some anti rotation feature. Aircraft engines run the gamut. Even the same model varies over time. Some have tabs, some have pins. Sometimes the pins are the oil hole.

Good to know; thanks.  So, is there a reason not to move the crank while a cylinder is off? Or, am I misinformed on that, as well?

[kmyfm20s]

10 hours ago, philiplane said:

Your photos above show beginnings of exhaust valve seat erosion. Note the clear areas where the valve meets the seat. 

Because the photo not super clear it’s hard to tell if it’s erosion or deposit buildup to me. Compression check and listening for air escaping out of the exhaust pipe would help determine. 

[N201MKTurbo]

Just now, MikeOH said:

Good to know; thanks.  So, is there a reason not to move the crank while a cylinder is off? Or, am I misinformed on that, as well?

You kind of have to, to get the pistons back on. It would be impossible to get the piston pin back in with the rod all the way in. The biggest problem is the rods banging on the cylinder mounting pads, they can dent the o ring surfaces.

[kmyfm20s]

25 minutes ago, N201MKTurbo said:

 

There is just too much Missile work that needs done these days....

Are you talking about the Missiles that go boom? Cool!

[N201MKTurbo]

1 minute ago, kmyfm20s said:

Are you talking about the Missiles that go boom? Cool!

I’ve never got to see one actually do that, but yes.

[Danb]

9 hours ago, kmyfm20s said:

Because the photo not super clear it’s hard to tell if it’s erosion or deposit buildup to me. Compression check and listening for air escaping out of the exhaust pipe would help determine. 

My compressions are between low of 73/80 high 76/80, the picture quality is lacking as was the operator, I’ve never done it before since I had plugs out for servicing I borrowed a scope looked and took a couple pix, since this thread I’ve been looking at valve you tube videos, reading articles and got AOPAs info on valves. Mike Busch has an engine book I’m ordering it’s tough for a 70+ year old CPA  to enter all this knowledge into a worn out head.

[larryb]

23 hours ago, N201MKTurbo said:

I remember back in the day, you would just replace the valve, seat and guide. A few hundred $ vs a few thousand $.

Is that possible today? I think I paid 16 hours at $120 for the cylinder R&R. So basically $2000 up front in labor alone. The factory new cylinder cost me $1700. The shop said they have not had a cylinder overhaul come back for less than $1000 in quite some time. So the $700, or less, premium for new vs. overhaul seems to be a good deal. Add in the significantly reduced down-time and replacing with new seemed a no-brainer.

[N201MKTurbo]

1 hour ago, larryb said:

Is that possible today? I think I paid 16 hours at $120 for the cylinder R&R. So basically $2000 up front in labor alone. The factory new cylinder cost me $1700. The shop said they have not had a cylinder overhaul come back for less than $1000 in quite some time. So the $700, or less, premium for new vs. overhaul seems to be a good deal. Add in the significantly reduced down-time and replacing with new seemed a no-brainer.

I'm not talking about overhauling the cylinder, just repairing it. There is a big difference. I'm pretty sure our local engine shop will repair cylinders. I don't think many people ask them to.

[smwash02]

1 minute ago, N201MKTurbo said:

I'm not talking about overhauling the cylinder, just repairing it. There is a big difference. I'm pretty sure our local engine shop will repair cylinders. I don't think many people ask them to.

I agree most don't ask, but in some cases it can be penny wise pound foolish. It comes down to the labor cost of the removal and re-installation and subsequent break in.

All up on the C this was nearly a 2 day affair. On a 172 it's probably a half a day.

Hopefully others have better luck, but I've had to warranty more than one O/H'd jug and am hesitant to do them anymore.

[larryb]

23 hours ago, N201MKTurbo said:

I'm not talking about overhauling the cylinder, just repairing it. There is a big difference. I'm pretty sure our local engine shop will repair cylinders. I don't think many people ask them to.

I think I was unclear in my post. When I said "is that possible today" I was referring to the cost "A few hundred $ vs a few thousand $"  I wasn't doubting that if I asked for a repair that I could get a repair. If R&R of a single cylinder costs $2000 you are already well above a few hundred $. With that R&R expense I want to minimize the chance of having to work on that cylinder again in the future. 

[N201MKTurbo]

Just now, larryb said:

I think I was unclear in my post. When I said "is that possible today" I was referring to the cost "A few hundred $ vs a few thousand $"  I wasn't doubting that if I asked for a repair that I could get a repair. If R&R of a single cylinder costs $2000 you are already well above a few hundred $. With that R&R expense I want to minimize the chance of having to work on that cylinder again in the future. 

I kind of live in a Utopian world. I haven't paid anyone to work on my plane for over 30 years. I have no idea how much it costs. It just costs time. The only money I spend is getting parts worked on. The last time I had a cylinder off (for other reasons), it had a broken valve spring. I took it to the engine shop to get a new valve spring. The nice lady who works on cylinders said she had no new springs. They were on back order. She asked if a used one with 100 hours on it would be OK, I said sure! It took her about a minute to change it. Didn't want to do the paperwork. Free cylinder repair!

[John Mininger]

Forgive me if someone else already posted this, but here’s the link to a poster AOPA did a few years ago: https://www.aopa.org/-/media/Files/AOPA/Home/Pilot-Resources/ASI/Valve-safety/14FN0000-ASI-Valve-Safey-Poster_Final.pdf

[Guest]

On 3/31/2020 at 9:58 PM, N201MKTurbo said:

Nonsense, all bearings have some anti rotation feature. Aircraft engines run the gamut. Even the same model varies over time. Some have tabs, some have pins. Sometimes the pins are the oil hole.

lets be realistic, sure the cases lose the clamping pressure, but the half’s don’t move but a few tenths. How is that going to allow the bearings to spin? The only way they are going to spin is if something was wrong in the first place.

Ive seen an engine with a spin bearing. It sheared the alignment pin clean off. Not sure what caused it. BTW that engine was still running pretty well.

 

 

 

 

Fear and lack of general knowledge seems to be a great promoter of Mike’s business.

Clarence

[mike_elliott]

On 3/31/2020 at 10:16 PM, N201MKTurbo said:

I’ve never got to see one actually do that, but yes.

AGM 86's?

[N201MKTurbo]

Just now, mike_elliott said:

AGM 86's?

I'm working on projects for a number of different programs.

Mostly precision motion systems for assembly and test.