the little C-90

[Tom-D]

This week I started the overhaul of a C-90 off a Cessna 120. a few pictures.
Just getting started, the aircraft sets about 3 months at a time, then gets used for about 2 months then gets to set again. no preservation between idle periods.

 

[Ghery]

Any chance this experience will teach the owner of the folly of his ways?

 

[Mason]

Wow, definitely needs work.

 

[Tom-D]

Any chance this experience will teach the owner of the folly of his ways?

Naw,, he'll put nickel cylinders on it.

A guy must make a living.

 

[Tom-D]

Wow, definitely needs work.

4 cylinders anyway.

 

[Tom-D]

Did anyone notice the perfect flame propagation on the piston? all 4 were that way.

Ring grove is way wide, the rings are worn flat, cylinder bore is belled .015 over Why?

 

[jesse]

Was the engine installation and firewall that clean to begin with or did you clean the hell out of all that?

 

[Tom-D]

Was the engine installation and firewall that clean to begin with or did you clean the hell out of all that?

Nope, the whole aircraft is that way.

 

[Richard]

Did anyone notice the perfect flame propagation on the piston? all 4 were that way.

Ring grove is way wide, the rings are worn flat, cylinder bore is belled .015 over Why?

Eccentric action of crank which induces wobble which induces transient thrust. Eccentricity caused by worn bearings rods?

Sounds chaotic. Hence the name, rattle trap.

 

[Ted]

And here I was thinking you meant a King Air.

 

[Henning]

Did anyone notice the perfect flame propagation on the piston? all 4 were that way.

Ring grove is way wide, the rings are worn flat, cylinder bore is belled .015 over Why?

No air filter? That and rust.

 

[Greg Bockelman]

And here I was thinking you meant a King Air.

Hey! This is Tom we are talking about. Not sure he would even turn a wrench on one.

 

[Tom-D]

Hey! This is Tom we are talking about. Not sure he would even turn a wrench on one.

This is Soooo true.

 

[Tom-D]

No air filter? That and rust.

This A/C does have a Bracket air filter, and we fly in Puget sound where the air is washed most every day. so, that's not the problem.

But these are steel cylinders, and that iron oxide that was removed from those pits in the cylinder walls took the rings and pistons out.

 

[roncachamp]

Just getting started, the aircraft sets about 3 months at a time, then gets used for about 2 months then gets to set again. no preservation between idle periods.

Preservation is a good idea during the idle periods, none needed between them.

 

[Everskyward]

And here I was thinking you meant a King Air.

That is what I thought too when I opened this thread.

 

[3393RP]

Nope, the whole aircraft is that way.

That's a nice looking aircraft.

 

[Tom-D]

That's a nice looking aircraft.

That's a sweet aircraft, inside and out, but it didn't have any compression

 

[Tom-D]

That is what I thought too when I opened this thread.

Since when is a Beechcraft C-90 little. ?

 

[Everskyward]

Since when is a Beechcraft C-90 little. ?

Perspective. For a while the C-90 was the littlest aircraft in the fleet. Now it's gone and the the littlest aircraft is a BE-20.

 

[Greg Bockelman]

Since when is a Beechcraft C-90 little. ?

Well, when you fly a 777 for 17 and a half years, almost anything could be considered "little".

But as you know, my heart is in non corporate General Aviation, especially older GA, so my mind automatically knew what you meant when you were talking about a CONTINENTAL C-90.

 

[Richard]

Tom, are you saying rust caused the elongation (belled) of the cylinders? I don't understand that because that means the erosion of the walls was notable along one axis.

 

[timwinters]

That is what I thought too when I opened this thread.

Me three but probably because I spent a lot of time in one during one of my corporate lives.

 

[Henning]

Tom, are you saying rust caused the elongation (belled) of the cylinders? I don't understand that because that means the erosion of the walls was notable along one axis.

No, they erode in "dwell" conically. The end near the head gets larger and gets a step at the top to the ring.

 

[Tom-D]

Tom, are you saying rust caused the elongation (belled) of the cylinders? I don't understand that because that means the erosion of the walls was notable along one axis.

When you have a piston traveling in a cylinder where does the wear occur? add the factor of having the piston and rings loaded with a very good abrasive what would you expect?

 

[Tom-D]

No, they erode in "dwell" conically.

no. the cylinder actually becomes oval, the vertical measurement will be bigger than the horizontal, due to the crank pulling in one direction and pushing in the other.

and the center will be the largest.

 

[Clark1961]

No, they erode in "dwell" conically. The end near the head gets larger and gets a step at the top to the ring.

aircraft engines never get a step like automotive engines

 

[Tom-D]

aircraft engines never get a step like automotive engines

because they are made to wear the rings out first.

 

[Clark1961]

because they are made to wear the rings out first.

thanks, thought I'd have to argue on this one...the guys that taught me were very matter-of-fact about it

 

[Richard]

I was mostly going off Tom's 4th picture. In that picture it looks like the scuffing and wear pattern, etc is 'belled' in the middle of the stroke but also the cylinder is oval.

I guess that is the difference between automotive or even lawnmower engines and that of aircraft engines. I'd just never seen that wear profile even in 300,000 mile rebuilds.

 

[bnt83]

What is the date of the last major overhaul?

 

[bnt83]

Crank and rods are what? 50+ years old?

 

[Tom-D]

What is the date of the last major overhaul?

I didn't bother to look. It will be zero soon.

 

[Tom-D]

Crank and rods are what? 50+ years old?

who would know? we don't track time on internals.

And I only care if they pass inspection and are good enough to rework.

 

[roncachamp]

And here I was thinking you meant a King Air.

I was thinking of a Luscombe Model 8.

 

[bnt83]

Curious about what parts, if any, you find corroded and approximately how old they are.

I'd guess there is some parts well over 50 years old in it.

 

[Tom-D]

Curious about what parts, if any, you find corroded and approximately how old they are.

I'd guess there is some parts well over 50 years old in it.

As clean as this engine is inside, I doubt we find any.

 

[nrpetersen]

On 294025.jpg - What's that broken spark plug? Has there been detonation & resulting heat in addition to the corrosion? And do you usually see that much fretting under the cyl bases?

FWIW - My J4A C85 oil pump (with full flow oil filter mod) likes to loose its prime so I raise the tail for a few seconds before starting it.........

 

[Tom-D]

On 294025.jpg - What's that broken spark plug? Has there been detonation & resulting heat in addition to the corrosion? And do you usually see that much fretting under the cyl bases

I see no broken Spark plug, or fretting, the dark stuff on the cylinder base is sealer.

 

[Tom-D]

FWIW - My J4A C85 oil pump (with full flow oil filter mod) likes to loose its prime so I raise the tail for a few seconds before starting it.........

You need to get the pump fixed. It won't heal itself.