IO-470 Compressions

[Fearless Tower]

Doing the pre-buy on a B55 Baron right now. So far, airplane appears to be in excellent shape. Maintenance history is excellent. Engines are around 650 SMOH. Compressions are:

LH engine #1= 70/80, #2= 60/80, #3= 70/80, #4= 65/80, #5= 65/80, #6= 62/80

RH engine #1= 70/80, #2= 60/80, #3= 68/80, #4= 70/80, #5= 66/80, #6= 70/80

I was a little suprised to see some cylinders down around 60/80, but I have zero experience dealing with maintenance of -470s. My O-300 in the 170 still has compressions well in the 70's at around 400 SMOH.

Is this normal for IO-470s? Any concerns? I'll be doing oil analysis, but probably be a few days before I get that info.

It is a good airplane - I am mostly concerned with overpaying on the purchase if I am going to have to do a TOH within the next 5 years.

 

[poadeleted21]

Big bore contis don't have the same compressions as O320's

An expert will be along shortly to explain. There's a little controversy.

Those numbers look good to me;

 

[timwinters]

Did they use the proper technique and orifice? How much has it been flying? Was it flown hard right before taking compressions?

If it's anything like mine you can check it again tomorrow and they'll all be different.

But, I don't see anything alarming in those numbers.

 

[Clark1961]

How much has it been flying?

My compressions have been improving since I bought the aircraft. Engines need to be run. Run them at high power and fly frequently...

 

[Henning]

Did you listen to the exhaust pipe during the compression test? Leaking through the exhaust, not good, leaking through the breather, acceptable. Are they chrome cylinders?

 

[Fearless Tower]

Did they use the proper technique and orifice?

I assume so. The IA doing the pre-buy(annual inspection) used to work for Beech and has 1000 hrs in type flying company B55s around the country.

How much has it been flying?

Only about 50 hours per year the last two years. 75-100 hrs per year before that.

Was it flown hard right before taking compressions?

No - I believe just a ground run.

Overall, my IA didn't feel too concerned about the numbers, but when dealing with something I am new to, I like to get multiple opinions before I drop that kind of cash.

 

[Skylane81E]

I'd fly it (just based on that info of corse)

Was a check against the master orifice made?

 

[jtheune]

Doing the pre-buy on a B55 Baron right now. So far, airplane appears to be in excellent shape. Maintenance history is excellent. Engines are around 650 SMOH. Compressions are:

LH engine #1= 70/80, #2= 60/80, #3= 70/80, #4= 65/80, #5= 65/80, #6= 62/80

RH engine #1= 70/80, #2= 60/80, #3= 68/80, #4= 70/80, #5= 66/80, #6= 70/80

I was a little suprised to see some cylinders down around 60/80, but I have zero experience dealing with maintenance of -470s. My O-300 in the 170 still has compressions well in the 70's at around 400 SMOH.

Is this normal for IO-470s? Any concerns? I'll be doing oil analysis, but probably be a few days before I get that info.

It is a good airplane - I am mostly concerned with overpaying on the purchase if I am going to have to do a TOH within the next 5 years.

Don't be surprised if you need to do a top at 1000 hours. We had to do that on the 470 in our 182 and from what I heard that was not unsual.

 

[Fearless Tower]

We had to do that on the 470 in our 182 and from what I heard that was not unsual.

I have heard that about -470s as well. I guess I am wondering how much (if any) to make of it as a negotiating point.

Vref just based on engine time alone (not considering engine health specifics) is around $115-120k.

 

[Skylane81E]

I have heard that about -470s as well. I guess I am wondering how much (if any) to make of it as a negotiating point.

Vref just based on engine time alone (not considering engine health specifics) is around $115-120k.

Who knows, PO of my plane ripped the cylinders off at half time "because you have to"

Another 470 with similar hours to that Barron has all its compressions in the low 70s currently. The #2 spent the first couple hundred hours under my care in the 50s but jumped up with frequent flying.

But another one got almost topped one cylinder at a time, but the owner went through 6 cylinders before 4 had been replaced, kept cooking valves so do the math on that engine.

 

[Fearless Tower]

Who knows, PO of my plane ripped the cylinders off at half time "because you have to"

Another 470 with similar hours to that Barron has all its compressions in the low 70s currently. The #2 spent the first couple hundred hours under my care in the 50s but jumped up with frequent flying.

But another one got almost topped one cylinder at a time, but the owner went through 6 cylinders before 4 had been replaced, kept cooking valves so do the math on that engine.

I was just talking to the local engine shop owner and he mentioned that alot depends on where the leakage is. Apparently leakage past the rings is pretty common for -470s and is not usually a big issue. If the leakage is in the valves, then it is a bigger problem and will likely require rework sooner.

 

[Skylane81E]

I was just talking to the local engine shop owner and he mentioned that alot depends on where the leakage is. Apparently leakage past the rings is pretty common for -470s and is not usually a big issue. If the leakage is in the valves, then it is a bigger problem and will likely require rework sooner.

Agreed, If I have a questionable result the oil cap comes off, I listen there, at the tail pipe and the intake for leakage to determine the source.

 

[Henning]

I have heard that about -470s as well. I guess I am wondering how much (if any) to make of it as a negotiating point.

Vref just based on engine time alone (not considering engine health specifics) is around $115-120k.

Fly LOP and you can avoid doing the top.

 

[timwinters]

Don't be surprised if you need to do a top at 1000 hours. We had to do that on the 470 in our 182 and from what I heard that was not unsual.

I have over a 1000 hours on mine and compressions are all well over 70.

I've only touched two cylinders.

1. At about 500 hours #5 had a broken oil scraper ring. It was broken since day one because an engine that always burned a qt every 5 hours all of a sudden dropped to a quart every 12 to 15 after that cylinder was reworked. So that one wasn't the engine's fault. That was the overhauling mechanic. We overhauled that one cylinder.

2. Number 4 had a valve guide with excessive slop last year at annual so we overhauled that one cylinder.

There is no reason to "top" a 470 unless everything is going south.

 

[docmirror]

I also vote this is fine. The big Conti jugs of that vintage are fairly loose. I'd go fly it at high power for about an hour running lean, then come back and redo the test. Listen for where the air is going. Most likely out the oil filler. Exhaust valve leaks usually turn up readings in the 40s or so.

 

[Henning]

I also vote this is fine. The big Conti jugs of that vintage are fairly loose. I'd go fly it at high power for about an hour running lean, then come back and redo the test. Listen for where the air is going. Most likely out the oil filler. Exhaust valve leaks usually turn up readings in the 40s or so.

They start with a slow drop, by the time you hit 40s you have a burnt valve. You can take a borescope and look at the face of the exhaust valve. If the coloration on the valve is not symmetrical, you have valve concerns even if you don't see/hear a leak yet. LOP operations prevents most all these typical cylinder problems.

 

[Silvaire]

Nothing wrong with those numbers. If this is a typical Baron it's probably been sitting around unused or rarely used for the past few years and that's the worst thing for them. You need to take it out and flog it because if that doesn't fix it babying it definitely won't help.

 

[docmirror]

They start with a slow drop, by the time you hit 40s you have a burnt valve. You can take a borescope and look at the face of the exhaust valve. If the coloration on the valve is not symmetrical, you have valve concerns even if you don't see/hear a leak yet. LOP operations prevents most all these typical cylinder problems.

Trust me, I know how to look at them very well. And I run so lean at 60% power that I'm getting gas back in my tank. Now that's lean running.