Cylinder Low Comp/ Oil Consumption

D

Danny Dub

Pre-Flight
Joined
Feb 7, 2018
Messages
80
Display Name
Display name:
Danny Dub
Hi gang as always thanks for any insight you can offer.

We have a Cessna 175 with the beloved GO-300 motor. At annual the number 1 cylinder is showing low compression (20) and we are using oil about a quart an hour.

Our AP suggests replace cylinder and that should fix both issues. My co-owner preferrs the option of working on the valves to try to bring the cylinder into specs.

I am not particularity mechanically knowledgeable and I'm sure the mechanic is giving his best advice but he doesn't really have the tooling to do the work.

I guess my question is does it seem likely that one low compression cylinder could create that much oil loss or do we likely have multiple issues? The bottom of the plane does not show much oil so I don't think it is just blowing out the breather tube.

Thanks!
 
I would most likely change the cylinder with a reman. Cost to overhaul, remove and install will not be much less than just replacing, IMHO.

WHERE’S THE OIL GOING?
When troubleshooting an oil consumption
problem, the fi rst question to ask is always,
“Where’s the oil going?” There are only
three possibilities:

• The oil is exiting the engine through its
breather line.

• The oil is leaking out of the engine somewhere
else.

• The oil is getting into the combustion
chamber of one or more cylinders and
being “consumed” in combustion.

It’s usually not hard to fi gure out the
answer. If the oil is departing through the
breather, then there will be excessive oil on
the belly of the aircraft. If it’s leaking from
the engine, then there will be excessive oil
inside the engine compartment. If it’s being
consumed in combustion, then the inside of
the tailpipe(s) will be dark and oily instead
of being coated with the normal light powdery
residue.
 
Did this come up all of a sudden, or has oil consumption been gradually increasing? Has the cyl been borescoped? What color is the oil? Can you hear where the compression is leaking from, crankcase or exhaust pipe? Best case, it's happened before that as the piston rings turn in the lands, all the gaps get lined up and leak compression and use oil like crazy, though you'd see it on the belly, or dripping out the breather. Do you have an oil/air separator installed?
 
Plane was bought last year and has pretty much been going through oil at this rate for the 15 or so hours it has been flown by us.

A&P says it sounds like the pressure is escaping into the exhaust.

A little leaking on the engine but my gut tells be that most of this oil loss is in the combustion area.

No air oil separator that I know of.

Oil looks like normal engine oil to me.

No boroscope yet either.
 
No matter why the cylinder is bad, simply put a new one on it, playing with valves seldom works for long.

With my humble experience with the GO- 300 is you have broken a ring, which would ruin a cylinder.

Maybe the time to do the top with 6 new cylinders.. plus the GO cylinder has a different part number than the regular 0-300/0-200
 
Tom-D said:
No matter why the cylinder is bad, simply put a new one on it, playing with valves seldom works for long.

With my humble experience with the GO- 300 is you have broken a ring, which would ruin a cylinder.

Maybe the time to do the top with 6 new cylinders.. plus the GO cylinder has a different part number than the regular 0-300/0-200
Click to expand...
Wow
 
Tom,

forgive my ignorance but curious as to why not just replace the one bad cylinder?

If we replace one and figure out that the oil consumption is still bad, can the others be replaced and still call it a top overhaul?

Thanks!
 
Salty,

Do you have an alternate opinion of Tom or are you amazed by how spot on his advice was?

Thanks!
 
Danny Dub said:
Tom,

forgive my ignorance but curious as to why not just replace the one bad cylinder?

If we replace one and figure out that the oil consumption is still bad, can the others be replaced and still call it a top overhaul?

Thanks!
Click to expand...
Yes to your last question, cylinders can be replaced at any time.
can one be replaced at a time? that would in reality depend upon the condition of the other 5, I don't like any engine to go putt, putt, putt, putt, putt, bang. You may never feel it but your aircraft does as does all your instruments.
the GO-300-D was the smoothest running engine I've ever flown behind. I'd just prefer to keep it that way.
 
It would pay an old geezer to get his old cylinder tools out and dust them off.
 
Danny Dub said:
Salty,

Do you have an alternate opinion of Tom or are you amazed by how spot on his advice was?

Thanks!
Click to expand...
I’m amazed by the fact that tom can contradict himself so completely so often. I’m starting to think it can’t possibly be coincidence. Just last week or maybe this, tom insisted that pulling a cylinder was a complete waste of time.
 
Salty said:
I’m amazed by the fact that tom can contradict himself so completely so often. I’m starting to think it can’t possibly be coincidence. Just last week or maybe this, tom insisted that pulling a cylinder was a complete waste of time.
Click to expand...
Simply amazing that you can't tell the difference between one post/subject and another.
 
Salty said:
I’m amazed by the fact that tom can contradict himself so completely so often. I’m starting to think it can’t possibly be coincidence. Just last week or maybe this, tom insisted that pulling a cylinder was a complete waste of time.
Click to expand...
depends who's paying....and how much. :D
 
A typical compression test will identify where the compression is going. If it's leaking into the crankcase? Rings and bore require attention. Overhaul the cylinder. That'll include some valve love, too. If the valves are leaking that explains compression but not oil consumption.
 
Wait a sec...compression leaking into exhaust, oil looking normal ( not inky black), belly clean. How do you get broken ring from this?

Scope it, with particular attention to cyl wall, valves and valve seats. Look for wetness from oil, any pooling at the bottom of the jug? I'd be inclined to go with the OP's wrench on this. All the other compressions and jugs scope good? A full top is pretty excessive.
 
Chip Sylverne said:
Wait a sec...compression leaking into exhaust, oil looking normal ( not inky black), belly clean. How do you get broken ring from this?

Scope it, with particular attention to cyl wall, valves and valve seats. Look for wetness from oil, any pooling at the bottom of the jug? I'd be inclined to go with the OP's wrench on this. All the other compressions and jugs scope good? A full top is pretty excessive.
Click to expand...
The valve issue won't cause oil burn. A broken ring certainly can. Having both in one cylinder certainly isn't rare. (I actually had our O300 jugs bored oversize, as there was little time, but a bit of corrosion.)
 
Salty said:
I’m amazed by the fact that tom can contradict himself so completely so often. I’m starting to think it can’t possibly be coincidence. Just last week or maybe this, tom insisted that pulling a cylinder was a complete waste of time.
Click to expand...

Thread drift!
 
Kenny Phillips said:
The valve issue won't cause oil burn. A broken ring certainly can. Having both in one cylinder certainly isn't rare. (I actually had our O300 jugs bored oversize, as there was little time, but a bit of corrosion.)
Click to expand...

My experience has been if there was a broken ring allowing that much blowby, the oil would turn real black real quick, and you'd hear leakage in the case.. Now if there were a cracked valve seat and boss, it could conceivably go through oil pretty good too. Concede that having both isn't out of the question. In any event, it all means new jug.
 
Did you State the engine hours and years since overhaul or new? Seems to me with a 20 psi cylinder it needs work, I would look to a replacement.

Back in the day I had an O-320 that had a cylinder lose compression due to valve issues. I paid to get a new one & flew without problems until I sold the plane.
 
Seems to me that if you are using 1 qt/hr there should be some wet plugs in one or more cylinders. If the oil darkens quickly that would clinch a strong suspicion of blowby for me. Maybe a broken oil control ring, or loss of ring temper is common enough. BTDT over the years. A compression of 20/80 means you are replacing or repairing that cylinder anyway, so why not just fix it and see if the oil consumption improves? I wouldn't replace other cylinders until they have demonstrable issues.
 
flyingbrit said:
Seems they were a lot cheaper before Continental bought out ECI...
Click to expand...
Every thing was a lot cheaper years ago, It was so bad most small shops quit doing cylinders. but all in all I doubting one can overhaul a cylinder and do the complete job for less.
and overhauled cylinders are as good as who did it.
 
chemgeek said:
Seems to me that if you are using 1 qt/hr there should be some wet plugs in one or more cylinders. If the oil darkens quickly that would clinch a strong suspicion of blowby for me. Maybe a broken oil control ring, or loss of ring temper is common enough. BTDT over the years. A compression of 20/80 means you are replacing or repairing that cylinder anyway, so why not just fix it and see if the oil consumption improves? I wouldn't replace other cylinders until they have demonstrable issues.
Click to expand...
Well that's just it,,, we don't know if they do or don't. but he did say the other compressions were good.
 
Sounds like more research/ troubleshooting is in order. I didn't know that a valve issue is separate from oil consumption. The oil did turn dark quickly after an oil change but I assumed that was just gunk in the case that didn't come out with the old oil. Are you all thinking possibly bad valves and bad rings? If we had bad rings on other cylinders would the compression be ok?

This is great info by the way. Thanks for using small words too!
 
This engine has about 800 hours since an overhaul in the early 90s I think. The last owner had done some cylinder work recently but it is not clear how well or thorough the work was...
 
Blow-by (compression leaking past rings) dirties oil very quickly. A low compression cylinder bore also consumes oil.
 
Danny Dub said:
S If we had bad rings on other cylinders would the compression be ok?
Click to expand...
if the compression rings are good, you'll have good compression, when the oil control ring is bad you'll have high oil consumption. and visa versa
 
Stewartb said:
Blow-by (compression leaking past rings) dirties oil very quickly. A low compression cylinder bore also consumes oil.
Click to expand...
so will hot valve guides, oil coking in the cylinder heads.
 
Danny Dub said:
Sounds like more research/ troubleshooting is in order. I didn't know that a valve issue is separate from oil consumption. The oil did turn dark quickly after an oil change but I assumed that was just gunk in the case that didn't come out with the old oil. Are you all thinking possibly bad valves and bad rings? If we had bad rings on other cylinders would the compression be ok?

This is great info by the way. Thanks for using small words too!
Click to expand...

There's an expression "when you hear hoof beats, think horses, not zebras", meaning go with the simplest explanation first. Don't make trouble where none exists.

You've got one last long-shot. Could just be carbon in the ring lands. Do a ring wash procedure on the low jug. Remove the top plug, bring the piston up to 15 or so deg btdc on the compression stroke, fill the jug with MMO, replace the plug and gently rock the piston, compressing the MMO into the rings, and leave it overnight. Drain the MMO, replace the plug and fly it like you stole it for a few hours. If the Gods are on your side, the rings will free up in the lands and you'll see rising compression. If not, you haven't lost anything. Can't hurt, might help. Won't do a thing for valves, may not do anything at all. But I have had good results a couple times.

MMO is Marvel Mystery Oil, a solvent.
 
Chip Sylverne said:
There's an expression "when you hear hoof beats, think horses, not zebras", meaning go with the simplest explanation first. Don't make trouble where none exists.

You've got one last long-shot. Could just be carbon in the ring lands. Do a ring wash procedure on the low jug. Remove the top plug, bring the piston up to 15 or so deg btdc on the compression stroke, fill the jug with MMO, replace the plug and gently rock the piston, compressing the MMO into the rings, and leave it overnight. Drain the MMO, replace the plug and fly it like you stole it for a few hours. If the Gods are on your side, the rings will free up in the lands and you'll see rising compression. If not, you haven't lost anything. Can't hurt, might help. Won't do a thing for valves, may not do anything at all. But I have had good results a couple times.

MMO is Marvel Mystery Oil, a solvent.
Click to expand...
good idea, if he has a leaking valve he'll find t soon enough. :)
 
Tom-D said:
Simply amazing that you can't tell the difference between one post/subject and another.
Click to expand...
It’s the fact that you post so authoritatively on airplanes you’ve never even seen with few facts that is the problem. I don’t discount your knowledge, it’s your judgement that I just can’t trust based on your history. I’d bet you’re a great mechanic, just not so great at the internet thing.

I will grant you that this is different in that it’s burning oil, but that’s largely a subjective thing. To be so sure in the other thread that they should never pull the cylinder, but in this one you're sure they should. All based on a few lines of description by someone that may be totally naive to what they are saying for all you know.

Bottom line, I’ll admit my criticism was too harsh on this one. you seem, in general, to be very passionate but not very consistent to me, but a lot of that is because you don’t say things straight, you often hold back in the “whys” of your logic, and come across very wish-washy. To be clear, I think it’s your communication style that trips me up more than your mechanical knowledge.

There’s just something about your style that I can’t resist busting your chops. But I apologize on this one.
 
Chip Sylverne said:
Wait a sec...compression leaking into exhaust, oil looking normal ( not inky black), belly clean. How do you get broken ring from this?
Click to expand...
Did you know that almost every one of these old GO-300-D's has a Pesko wet vac pump and an oil recovery system, that turned the oil black in 5 hours anyway, and none of it went out the case vent.
 
Last edited:
Salty said:
It’s the fact that you post so authoritatively on airplanes you’ve never even seen with few facts that is the problem. I don’t discount your knowledge, it’s your judgement that I just can’t trust based on your history. I’d bet you’re a great mechanic, just not so great at the internet thing.

I will grant you that this is different in that it’s burning oil, but that’s largely a subjective thing. To be so sure in the other thread that they should never pull the cylinder, but in this one you're sure they should. All based on a few lines of description by someone that may be totally naive to what they are saying for all you know.

Bottom line, I’ll admit my criticism was too harsh on this one. you seem, in general, to be very passionate but not very consistent to me, but a lot of that is because you don’t say things straight, you often hold back in the “whys” of your logic, and come across very wish-washy. To be clear, I think it’s your communication style that trips me up more than your mechanical knowledge.

There’s just something about your style that I can’t resist busting your chops. But I apologize on this one.
Click to expand...

No sweat Salty,,, we know this is the internet.

We also know that there are many here that read into a post what ain't there, over active imagination I guess.
 
Salty said:
just not so great at the internet thing.

yak - yak clip
I think it’s your communication style that trips me up more than your mechanical knowledge.
Click to expand...

Gotta remember I'm an old mech, not some introverted English major.

 
OBTW,, back in the day when we worked on GO-300-D almost every day, broken rings were pretty common, when the pilots would lug the engine which over boosted the cylinder. the piston could not travel down the cylinder fast enough to drop the combustion pressure (BMEP) to levels that were designed for the 0-300/ 0-200.

remember cylinder problems is why the GO-300-D got a bad name.
pilots simply would not operate them properly.
 
Chip Sylverne said:
There's an expression "when you hear hoof beats, think horses, not zebras", meaning go with the simplest explanation first. Don't make trouble where none exists.

You've got one last long-shot. Could just be carbon in the ring lands. Do a ring wash procedure on the low jug. Remove the top plug, bring the piston up to 15 or so deg btdc on the compression stroke, fill the jug with MMO, replace the plug and gently rock the piston, compressing the MMO into the rings, and leave it overnight. Drain the MMO, replace the plug and fly it like you stole it for a few hours. If the Gods are on your side, the rings will free up in the lands and you'll see rising compression. If not, you haven't lost anything. Can't hurt, might help. Won't do a thing for valves, may not do anything at all. But I have had good results a couple times.

MMO is Marvel Mystery Oil, a solvent.
Click to expand...

Fill the jug completely? Seems like it would leak past the rings and end up in the oil. I am all in on trying this procedure just want to understand. I'm guessing you drain it from the lower plug the next day? What would be the remedy if the MMO leaked into the crank case?

Thanks guys for all the comments.
 
You must log in or register to reply here.
Back
Top