Our C90 is having a mid-life crisis.
It's done around 700 hours since a complete, professional rebuild, about 6 years ago. It has been mostly brilliant since then, great starting and smooth running. It gets run throughout the year, very rarely more than 4 weeks between use and usually several times a week.
Lately (over the last say 3 months, maybe 20 hours) it's been sounding just a little rough when cold.
Today I noticed a slight misfire on short final (not much time to take notice, I was busy landing) and on taxy I noticed the oil pressure was lower than usual. Checked the oil level, and some oil had gone during the flight (more than I would have expected).
Came to restart, and it wouldn't. Pulling the prop through it feels as if at least one cylinder compression is down, maybe two. We noticed a good deal of oil vapour exiting the breather during starting attempts.
Eventually, it started, and I made a short flight, and the oil pressure is seriously down, and power is reduced - maybe 2300 rpm in climb instead of the usual 2400.
I've truncated events and observations a bit here for the sake of brevity.
I have now drained the oil and examined the inside of the oil filter. as far as I can see with the naked eye, there are is no metal debris in the oil.
Tentative diagnosis at this stage is, one or more broken piston rings. We will do a full compression test this week.
What I need to know from those of you with more experience of these engines is, what could explain the drop in oil pressure? It does appear that there was a steep loss of oil during the flight, but the level never went low enough to result in a drop for that reason. The oil temperature remained at the normal level.
The oil filter is a screw on type, and although it was coming up to replacement at 100 hours, it wasn't overdue.
Is there anything else except knackered bearings (shudder) that might cause a fairly sudden drop in oil pressure?
Can anyone think of a connection between a (likely) loss of compression and drop in oil pressure?
Many thanks
C90 wisdom needed
Moderators: John Dean, Moderator
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mike newall
- Posts: 331
- Joined: Mon Jan 28, 2008 2:56 pm
- Location: N Yorkshire
Well, here is a few thoughts - Hardaker - please come in as your experience is welcome.
If you have changed the oil and filter, do a compression check.
If 1 or 2 are down, don't panic......... yet.
Whip the rocker covers off and spike the valves - i.e hit them with a soft ish item such as a rubber or plastic mallet.
This may eliminate problems such as low compression, it will not restore oil pressure.
If it is acceptable to fly, put some Redex or Marvel in the fuel and do a hard, full power 20 mins assuming the oil pressure remains acceptable.
After that, if there is no improvement, you are into more investigation.
If you want to do it stage by stage, remove the sump, check the contents.
If your find bits.............. Don't panic.
If that is the case, you are into a probable top overhaul - rings etc etc.
800 hrs on a C-90 isn't bad, I would expect a quick tickle at about this time unless you have been doing oil changes at no more that 25 hrs/4 months.
If there are no bits of debris, then it may, I say may be the oil regulator or oil pump - unlikely though.
At this stage, you would need professional hopefully through a LAA inspector with good engine experience and with an ability to split a crankcase - then you can do your overhaul yourself at minimal cost compared to sending it to an overhaul shop.
To all you overhaullers - sorry - this is an LAA Maintenance site - we are here to help and encourage chaps to get stuck in and do this very straightforward stuff themselves and learn in the process.
If you have changed the oil and filter, do a compression check.
If 1 or 2 are down, don't panic......... yet.
Whip the rocker covers off and spike the valves - i.e hit them with a soft ish item such as a rubber or plastic mallet.
This may eliminate problems such as low compression, it will not restore oil pressure.
If it is acceptable to fly, put some Redex or Marvel in the fuel and do a hard, full power 20 mins assuming the oil pressure remains acceptable.
After that, if there is no improvement, you are into more investigation.
If you want to do it stage by stage, remove the sump, check the contents.
If your find bits.............. Don't panic.
If that is the case, you are into a probable top overhaul - rings etc etc.
800 hrs on a C-90 isn't bad, I would expect a quick tickle at about this time unless you have been doing oil changes at no more that 25 hrs/4 months.
If there are no bits of debris, then it may, I say may be the oil regulator or oil pump - unlikely though.
At this stage, you would need professional hopefully through a LAA inspector with good engine experience and with an ability to split a crankcase - then you can do your overhaul yourself at minimal cost compared to sending it to an overhaul shop.
To all you overhaullers - sorry - this is an LAA Maintenance site - we are here to help and encourage chaps to get stuck in and do this very straightforward stuff themselves and learn in the process.
Could be any of the above. A compression check should give a good indication of what is happening in the cylinders. If air is leaking past a valve the gentle touch with a rubber hammer may work. The low oil pressure could be the relief valve not seating, pickup tube in the sump sucking air through a crack or split washer. I have just done a C85 with similar symptoms the low oil pressure was caused by a crack in the crankcase opening up when hot.
Good Luck
Alan
Good Luck
Alan
Thank you, both.
We will be checking the compressions this week, and anticipate one or more ring failures, though we will check the valves as you suggest, good call.
The oil pressure drop has been fairly sudden, and coincides exactly with the lack of compression - it all happened in one flight - which can't be good news I guess. Compressions were fine at the last annual, in October.
Our inspector has already been called and has come back with some useful ideas - he will hopefully be there for the compression test.
We will be checking the compressions this week, and anticipate one or more ring failures, though we will check the valves as you suggest, good call.
The oil pressure drop has been fairly sudden, and coincides exactly with the lack of compression - it all happened in one flight - which can't be good news I guess. Compressions were fine at the last annual, in October.
Our inspector has already been called and has come back with some useful ideas - he will hopefully be there for the compression test.
032561
I think that may have some coincidences here and they might not even be related.
Slight misfiring if not electrical can be the valve guide, one or more worn, allowing valve sticking or non seating. do a compression test and find which cylinder. Then drop the valve cover and push the valves by some means like a screwdriver under the rocker and feel if it is wobbly or sticky. if that is noticed, then time for a barrel off and a guide check, the valves can lift over the to the side of the seats and allow burning of both the valve and seat. 0-200 and C90 do not really like 100LL and after a time the lead can build up on the stem, face and seat losing compression, Exhaust Valves do bend and stick quite often and would need a new one, with a new guide,
When the low compression cylinder is at TDC put some pressure into the cylinder and listen to the breather pipe and a loud hissing means rings, from the exhaust pipe a leaking valve and from the carb , an inlet valve.
Make sure however that there is no way that the prop can turn or it will flick over and WILL hurt.
Low oil pressure can be the simple thing first, the gauge, a sudden drop is gauge first, then the pressure control valve, a drop over a longer time is bearing or oil pump related. Oil temperature is another check , was it high and the level low? If an seperate oil filter is fitted the screen should be out, check to see if it is and not blocked with detritous, because no one has checked for 800 hours, to see if it is actually there, thinking it gone.
Do the simple checks first then start worrying about the expensive ones like bearing, cracked crank, and broken case half on early C90s, without through bolts
Cheer up it might be simple.
Regards
Graham
Slight misfiring if not electrical can be the valve guide, one or more worn, allowing valve sticking or non seating. do a compression test and find which cylinder. Then drop the valve cover and push the valves by some means like a screwdriver under the rocker and feel if it is wobbly or sticky. if that is noticed, then time for a barrel off and a guide check, the valves can lift over the to the side of the seats and allow burning of both the valve and seat. 0-200 and C90 do not really like 100LL and after a time the lead can build up on the stem, face and seat losing compression, Exhaust Valves do bend and stick quite often and would need a new one, with a new guide,
When the low compression cylinder is at TDC put some pressure into the cylinder and listen to the breather pipe and a loud hissing means rings, from the exhaust pipe a leaking valve and from the carb , an inlet valve.
Make sure however that there is no way that the prop can turn or it will flick over and WILL hurt.
Low oil pressure can be the simple thing first, the gauge, a sudden drop is gauge first, then the pressure control valve, a drop over a longer time is bearing or oil pump related. Oil temperature is another check , was it high and the level low? If an seperate oil filter is fitted the screen should be out, check to see if it is and not blocked with detritous, because no one has checked for 800 hours, to see if it is actually there, thinking it gone.
Do the simple checks first then start worrying about the expensive ones like bearing, cracked crank, and broken case half on early C90s, without through bolts
Cheer up it might be simple.
Regards
Graham
Thanks Graham, all useful stuff.
The oil level dropped rapidly during the flight, likely because it was being blown out of the oil breather. Incidentally we recently fitted an Airworld breather system, so the outlet of it is now visible blow the firewall - and we did notice a lot of oil vapour puffing out when cranking the engine.
The oil pressure drop continues to be the main worrying issue. It took place during the same flight as when te compression dropped. The oil pressure settled to 2 pips below the green (sorry can't give the figure right now) which is far lower than we have ever seen before even on tickover. Even though the oil level dropped during the flight, oil temp did not rise significantly (it was a short flight of about 20 min.)
We will be checking compressions on Tuesday.
The oil level dropped rapidly during the flight, likely because it was being blown out of the oil breather. Incidentally we recently fitted an Airworld breather system, so the outlet of it is now visible blow the firewall - and we did notice a lot of oil vapour puffing out when cranking the engine.
The oil pressure drop continues to be the main worrying issue. It took place during the same flight as when te compression dropped. The oil pressure settled to 2 pips below the green (sorry can't give the figure right now) which is far lower than we have ever seen before even on tickover. Even though the oil level dropped during the flight, oil temp did not rise significantly (it was a short flight of about 20 min.)
We will be checking compressions on Tuesday.
032561
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Steve Brown
- Posts: 257
- Joined: Wed Jan 02, 2008 11:00 am
Good analytical advice to eliminate the simple issues first.
Minor point - ref 'When the low compression cylinder is at TDC' - do make sure it is at the top of its compression stroke (check with your thumb over the plug hole for building pressure - if no pressure rotate the prop 360 deg & try again) - otherwise both valves will be rocking open/closed and you'll think you've got a massive leak on both valves! I'd do the pressure test before removing the rocker covers.
Ref your first post / last question - Oil pressure is really totally unrelated to rings or valve issues. Yes, oil consumption may increase but not pressure (providing oil temp is in limits). The pistons & cylinders are fed by splash only with no link to the oil pressured gallery.
Pressure is a function of temperature / oil pick up tube / oil pump / filter / main & big end clearances / pressure relief valve & spring / gauge accuracy.
I'd check the pressure using a known accurate gauge with numbers rather than colours . TCM book figures are - hot tickover pressure is 'Above 10psi' , Cruise is 30 - 60 psi, my O-200 with new bearings etc runs at 42-47 in cruise.
A good point ref the screen. The oil pressure sensor is after the filter and so if the filter (does it have an internal bypass?) is getting progressively blocked by micro particles that have gone through the screen (if its there) , the oil pressure sensor ( and your crankshaft!) will see a lower pressure than the pressure output from the pump.
How often do you change the filter - I'd change at 50hrs tops. Have you run it since changing the filter - any pressure change?
Could the missing be electrical or some water in the float bowl?
Regards
Steve
Minor point - ref 'When the low compression cylinder is at TDC' - do make sure it is at the top of its compression stroke (check with your thumb over the plug hole for building pressure - if no pressure rotate the prop 360 deg & try again) - otherwise both valves will be rocking open/closed and you'll think you've got a massive leak on both valves! I'd do the pressure test before removing the rocker covers.
Ref your first post / last question - Oil pressure is really totally unrelated to rings or valve issues. Yes, oil consumption may increase but not pressure (providing oil temp is in limits). The pistons & cylinders are fed by splash only with no link to the oil pressured gallery.
Pressure is a function of temperature / oil pick up tube / oil pump / filter / main & big end clearances / pressure relief valve & spring / gauge accuracy.
I'd check the pressure using a known accurate gauge with numbers rather than colours . TCM book figures are - hot tickover pressure is 'Above 10psi' , Cruise is 30 - 60 psi, my O-200 with new bearings etc runs at 42-47 in cruise.
A good point ref the screen. The oil pressure sensor is after the filter and so if the filter (does it have an internal bypass?) is getting progressively blocked by micro particles that have gone through the screen (if its there) , the oil pressure sensor ( and your crankshaft!) will see a lower pressure than the pressure output from the pump.
How often do you change the filter - I'd change at 50hrs tops. Have you run it since changing the filter - any pressure change?
Could the missing be electrical or some water in the float bowl?
Regards
Steve
One point, on a small continental the gauge and relief valve are the last items in the oil chain and that is why the pressures look low compared to other makes. the pump supplies, or should, a deal more than arrives at the relief valve. I think you have a piston/ring problem if it is pumping into the crank.
Let us all know if anything is found.
graham
Let us all know if anything is found.
graham
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David Hardaker
- Posts: 70
- Joined: Fri Jan 04, 2008 6:18 pm
- Location: Yorkshire
C90 not well
FWIW I knew someone who had a C90 in a Jodel 120.
They had problems keeping the oil level at the normal 4 mark. They even put a vented oil filler cap on ! As soon as they topped up the oil level, the oil was lost all over the place.
It turned out the crankcase breather tube (plastic) had collapsed and kinked just after the elbow fitting in the crank-case, causing crank-case pressure.
Change tube, re-route slightly, problem solved !
TR's other probs sound to be a coincidence, the advice so far sounds OK to me .
Re the oil pressure gauge, I would think it's "live" system, ie you have a live oil line to the panel gauge. Especially on an Emeraude. My C90 only ever had an oil - light ! I'm not a fan of sender-driven clocks of any sort. Senders sometimes fail, but what do you believe ?
d
They had problems keeping the oil level at the normal 4 mark. They even put a vented oil filler cap on ! As soon as they topped up the oil level, the oil was lost all over the place.
It turned out the crankcase breather tube (plastic) had collapsed and kinked just after the elbow fitting in the crank-case, causing crank-case pressure.
Change tube, re-route slightly, problem solved !
TR's other probs sound to be a coincidence, the advice so far sounds OK to me .
Re the oil pressure gauge, I would think it's "live" system, ie you have a live oil line to the panel gauge. Especially on an Emeraude. My C90 only ever had an oil - light ! I'm not a fan of sender-driven clocks of any sort. Senders sometimes fail, but what do you believe ?
d
Last edited by David Hardaker on Mon Jun 01, 2009 9:42 pm, edited 1 time in total.
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Steve Brown
- Posts: 257
- Joined: Wed Jan 02, 2008 11:00 am
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mike newall
- Posts: 331
- Joined: Mon Jan 28, 2008 2:56 pm
- Location: N Yorkshire
Mike,
Colin Dix here, one of the share holders. Is it possible for us to rebuild the engine under supervision of our Inspector? We have the experience in the grpoup to do this?
Does anyone know the best place for spares,
Cost of a Cylinder, Piston, ring sett, gaskets etc.
Mant thanks for a really helpfull thread.
Cheers,
Colin
Colin Dix here, one of the share holders. Is it possible for us to rebuild the engine under supervision of our Inspector? We have the experience in the grpoup to do this?
Does anyone know the best place for spares,
Cost of a Cylinder, Piston, ring sett, gaskets etc.
Mant thanks for a really helpfull thread.
Cheers,
Colin
mike newall wrote:Well, here is a few thoughts - Hardaker - please come in as your experience is welcome.
If you have changed the oil and filter, do a compression check.
If 1 or 2 are down, don't panic......... yet.
Whip the rocker covers off and spike the valves - i.e hit them with a soft ish item such as a rubber or plastic mallet.
This may eliminate problems such as low compression, it will not restore oil pressure.
If it is acceptable to fly, put some Redex or Marvel in the fuel and do a hard, full power 20 mins assuming the oil pressure remains acceptable.
After that, if there is no improvement, you are into more investigation.
If you want to do it stage by stage, remove the sump, check the contents.
If your find bits.............. Don't panic.
If that is the case, you are into a probable top overhaul - rings etc etc.
800 hrs on a C-90 isn't bad, I would expect a quick tickle at about this time unless you have been doing oil changes at no more that 25 hrs/4 months.
If there are no bits of debris, then it may, I say may be the oil regulator or oil pump - unlikely though.
At this stage, you would need professional hopefully through a LAA inspector with good engine experience and with an ability to split a crankcase - then you can do your overhaul yourself at minimal cost compared to sending it to an overhaul shop.
To all you overhaullers - sorry - this is an LAA Maintenance site - we are here to help and encourage chaps to get stuck in and do this very straightforward stuff themselves and learn in the process.
-
Steve Brown
- Posts: 257
- Joined: Wed Jan 02, 2008 11:00 am
Yes you can - if you don't split the crankcase and the Inspector has 'Engines' approval.
I understand that if you want to split the C/C, the 'Engines' Inspector has to get approval from LAA Engineering to do so. Your inspector will know the full details/rules.
A TCM overhaul manual and parts list are essential
Go to Log In at TCM & register at Aviator Services at www.tcmlink.com ( or direct at http://tcmlink.com/aviator/index.cfm )
And TCM / Mattituck at www.mattituck.com
Fantastic source of Service Bulletins & Letters, rebuild tips, operating tips and TCM approved sealants etc for rebuild etc
Multiflight are very helpful - 0113 238 7151 (Parts) - good stock of parts & very friendly.
Regards
Steve
I understand that if you want to split the C/C, the 'Engines' Inspector has to get approval from LAA Engineering to do so. Your inspector will know the full details/rules.
A TCM overhaul manual and parts list are essential
Go to Log In at TCM & register at Aviator Services at www.tcmlink.com ( or direct at http://tcmlink.com/aviator/index.cfm )
And TCM / Mattituck at www.mattituck.com
Fantastic source of Service Bulletins & Letters, rebuild tips, operating tips and TCM approved sealants etc for rebuild etc
Multiflight are very helpful - 0113 238 7151 (Parts) - good stock of parts & very friendly.
Regards
Steve
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Geoff. Collins
- Posts: 13
- Joined: Fri Jan 04, 2008 2:10 pm
- Location: East Midlands
oil consumption
A common cause of "fairly sudden" low compression, coupled with high crankcase pressure and oil from the breather, is when the piston ring gaps line up. With the fairly generous clearances on these engines, the rings although correct when assembled, can eventually migrate round the piston and line up. Once like this, they do not "rearrange" themselves as the gas blowing through the lined up gaps keeps them there. If the gaps are on the bottom,some neat oil will often come out if the lower spark plug is removed.
Geoff.
Geoff.
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mike newall
- Posts: 331
- Joined: Mon Jan 28, 2008 2:56 pm
- Location: N Yorkshire
Getting the approval to do the crankcase split isn't a big deal - We have done a Lycoming IO-360 and Lycoming O-235 under our inspector's supervision. The guys in the States do this all the time and provided you follow the manuals and get good supervision, there really isn't a big deal about it - only the ingrained British backward attitude to aviation 
Main thing is - get a very sturdy bench to work off - we made one from 4 x 3 and 3 x 2 about 30" cube with double 18mm MDF top. This enabled us to bolt the engines upright and disassemble and rebuild easily.
Main thing is - get a very sturdy bench to work off - we made one from 4 x 3 and 3 x 2 about 30" cube with double 18mm MDF top. This enabled us to bolt the engines upright and disassemble and rebuild easily.