Vibration on a Cessna 150...
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Vibration on a Cessna 150...
Hello all,
My problem Is regarding a vibration issue that I have been fighting for over a year. I purchased a Cessna 150 just over a year ago. I bought it because in 2010 the engine cylinders were replaced as the then purchaser flew the airplane but at annual the engine had a 20/80 compressions (flew fine amazingly). So he decided to due extensive work to the engine/airplane. The engine had roughly 400 SMOH and he installed 4 new Millenium cylinders, overhauled carb, new mags, spark plug leads. About $20K were spent in all (so I’m assuming no shortcuts were taken).
I purchased the plane early 2013 and all seemed fine. As part of the annual (one year ago, June) I had the prop dynamically balanced (CopaAir Services in Indiantown FL). At initial reading the vibration was very bad (off the chart and no reading could be taken) and they had to take the reading at a lower RPM setting (1.2 ips). They finally balanced the engine with the resultant numbers at .2 ips. After the annual I sensed the vibration was worse. At full power on takeoff was fine, but once I retarded the throttle to 2300-2400 RPM the floor seemed to shake, the instruments shook as well and the pitot tube. Speaking with CopaAir they stated that the vibration was difficult to minimize and possibly I should check the prop. I went ahead and had the prop overhauled.
The prop was installed and we removed the weights that were previously used to dynamically balance the engine. The engine seemed better. But I had them try to again dynamically balance the engine/prop again. When they went to measure the initial reading again it was very high. Using reduced RPMs we read ( 1.0 ips). We rotated the prop and took a new reading ( 1.1 ips).
The mechanic then flew the airplane to "feel" the vibration. He leveled off but kept full power (something I never do, I'm very easy on the engine). Vibration seemed fine but once the throttle was retarded for cruise it was bad. We landed and found a cracked spinner bulkhead (which I firmly believe was a recent occurance. The bulkhead was replaced and we tried to again dynamically balance the engine/prop. The readings at the front of the engine are 1.22 IPS @ 296deg. Vibration at the rear of the engine is .67 IPS @ 358deg
CopaAir took readings of the engine cylinders with the cowl off to question the combustions causing vibration.
At 1500RPM all cylinder temps were close but EGT on cylinder #2 was 140 deg cooler.
At WOT with RPMs at 2550, the temps were all in 350f except for #2 cylinder which was at 400f. EGTs were all 600 to 650 degs as measured at the exhaust using a laser infrared but #2 cylinder was 175degrees cooler at 475 degrees. They inquired with Don from Don’s Dream Machines and he stated that the temp difference would not cause such a big vibration. To be safe regarding #2 cylinder, they ruled out hydraulic lifters, induction leaks, bad spark plugs and compression was 77/80. Since engine makes full power the cylinder was deemed to be okay. I read on Harry Fenton's website that a .030 over pushrod could fix this issue.
So, the vibration, they said is most likely due to one piston that is heavy (or lighter, I guess). I have a hard time swallowing this as these were 4 new pistons that were all installed at the same time and there did not "seem" vibration before. I say seem cause possibly I have become more aware of it as I have owned it, flew it and generally became more familiar with it. But I’m no expert and it could be possible.
Any guidance would be GREATLY appreciated!
My problem Is regarding a vibration issue that I have been fighting for over a year. I purchased a Cessna 150 just over a year ago. I bought it because in 2010 the engine cylinders were replaced as the then purchaser flew the airplane but at annual the engine had a 20/80 compressions (flew fine amazingly). So he decided to due extensive work to the engine/airplane. The engine had roughly 400 SMOH and he installed 4 new Millenium cylinders, overhauled carb, new mags, spark plug leads. About $20K were spent in all (so I’m assuming no shortcuts were taken).
I purchased the plane early 2013 and all seemed fine. As part of the annual (one year ago, June) I had the prop dynamically balanced (CopaAir Services in Indiantown FL). At initial reading the vibration was very bad (off the chart and no reading could be taken) and they had to take the reading at a lower RPM setting (1.2 ips). They finally balanced the engine with the resultant numbers at .2 ips. After the annual I sensed the vibration was worse. At full power on takeoff was fine, but once I retarded the throttle to 2300-2400 RPM the floor seemed to shake, the instruments shook as well and the pitot tube. Speaking with CopaAir they stated that the vibration was difficult to minimize and possibly I should check the prop. I went ahead and had the prop overhauled.
The prop was installed and we removed the weights that were previously used to dynamically balance the engine. The engine seemed better. But I had them try to again dynamically balance the engine/prop again. When they went to measure the initial reading again it was very high. Using reduced RPMs we read ( 1.0 ips). We rotated the prop and took a new reading ( 1.1 ips).
The mechanic then flew the airplane to "feel" the vibration. He leveled off but kept full power (something I never do, I'm very easy on the engine). Vibration seemed fine but once the throttle was retarded for cruise it was bad. We landed and found a cracked spinner bulkhead (which I firmly believe was a recent occurance. The bulkhead was replaced and we tried to again dynamically balance the engine/prop. The readings at the front of the engine are 1.22 IPS @ 296deg. Vibration at the rear of the engine is .67 IPS @ 358deg
CopaAir took readings of the engine cylinders with the cowl off to question the combustions causing vibration.
At 1500RPM all cylinder temps were close but EGT on cylinder #2 was 140 deg cooler.
At WOT with RPMs at 2550, the temps were all in 350f except for #2 cylinder which was at 400f. EGTs were all 600 to 650 degs as measured at the exhaust using a laser infrared but #2 cylinder was 175degrees cooler at 475 degrees. They inquired with Don from Don’s Dream Machines and he stated that the temp difference would not cause such a big vibration. To be safe regarding #2 cylinder, they ruled out hydraulic lifters, induction leaks, bad spark plugs and compression was 77/80. Since engine makes full power the cylinder was deemed to be okay. I read on Harry Fenton's website that a .030 over pushrod could fix this issue.
So, the vibration, they said is most likely due to one piston that is heavy (or lighter, I guess). I have a hard time swallowing this as these were 4 new pistons that were all installed at the same time and there did not "seem" vibration before. I say seem cause possibly I have become more aware of it as I have owned it, flew it and generally became more familiar with it. But I’m no expert and it could be possible.
Any guidance would be GREATLY appreciated!
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I think you'd be better posting this in the engineering and tech. area.
As # 2 seems dramatically different to the other cylinders, i'd be investigating this further.
I'd make a wild guess, based on the given info. that worn camshaft lobe (s) is/ are preventing this cylinder from "breathing properly....in fact, i'd say inlet!
If the engine and prop are mechanically balanced, then it must be down to differences in power-output (or friction-losses on the other 3 strokes).....Now! there's a thought!...has #2 had a partial-siezure?
it would not only give reduced output, but the tight piston would have a lot higher drag!.
I'm NOT an aircraft mechanic, the info is worth what you paid for it!
As # 2 seems dramatically different to the other cylinders, i'd be investigating this further.
I'd make a wild guess, based on the given info. that worn camshaft lobe (s) is/ are preventing this cylinder from "breathing properly....in fact, i'd say inlet!
If the engine and prop are mechanically balanced, then it must be down to differences in power-output (or friction-losses on the other 3 strokes).....Now! there's a thought!...has #2 had a partial-siezure?
it would not only give reduced output, but the tight piston would have a lot higher drag!.
I'm NOT an aircraft mechanic, the info is worth what you paid for it!
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Have you checked the engine mounting frame where it attaches to the firewall, engine mounting rubbers and tried mounting the prop at 180 degs to the current position.
The engine had roughly 400 SMOH and he installed 4 new Millenium cylinders, overhauled carb, new mags, spark plug leads.
Or was that the work done at the overhaul? That looks like a TOH. I'd be suspicious of someone saying it was a MOH.
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a continental O-200 is a beautiful engine. and being a horizontally opposed flat 4 it is inherently balanced. it should run like a sewing machine.
balance is a subtle thing.
starting at the spinner. are all the screws in the spinner the same length? having screws of different lengths and with different washers under the heads will throw out the balance.
are the engine mount rubbers (lord mounts) in good condition? there are two rubbers in each of the 4 mount points. your top rubbers can be quite serviceable and easily seen. the bottom rubbers can be totally stuffed and you wouldn't know it. they are only about $15 each so they are the cheapest you can get in the 150.
the rubbers won't affect balance but they will transmit lots of vibration.
the prop has been to a shop. but is it balanced??? you can check this yourself with a few spacers on a shaft on some blocks on the dining room table.
is the spinner symmetrical and balanced?
go and buy 8 new spark plugs. they are about $40 each. roughly $320 in total.
don't drop them and install them with care. spark plugs that are failing will cause uneven combustion and make some cylinders seem like duds.
are the magnetos in good condition? I had a failing oil seal in the bottom of one of mine and the uneven combustion it caused in the engine made it seem as though the engine was totally clapped out.
are the plug leads in good condition? if these are shorting or breaking down you engine will run roughly.
Are your magneto P leads in good condition. one of these leads intermittently shorting to earth will cause your engine all sorts of rough running.
is your engine oil screen nice and clean? a failing component will often lodge parts of itself in the screen. do some detective work.
are the bolts holding your propeller in good condition? a broken or stretched bolt can give the illusion of all sorts of vibrational problems. equally a set of loose prop bolts can cause all sorts of vibrational illusions. do you have identical numbers of washers under each bolt? ( i even use identical length lock wire between bolts)
get a dial gauge. firmly attach it to the engine and check the propeller flange.
when you turn over the engine by hand does the flange track true?
if it doesn't then you have a bent crankshaft.
with the engine ticking over at idle look at the prop tip arc. is it tracking true?
a prop mounted on crooked will give all sorts of trouble with blade angle of attack being different each side.
ok if all of that checks out then you need to look inside the engine.
the easiest first point of checking is to take off the oil sump, the "football".
with the sump off you can look up into the interior of the engine with a powerful spotlight. can you see any damage? can you see anything that doesn't look to be in the right place?
turn over the engine and check out the big end bolts on each each conrod.
are these all tight and secure? is there any corrosion evident?
putting the football back on will mean a new gasket and new oil.
are all the sections above the carburettor all tight and secure. no air leaks evident in the induction system or looseness introducing mixture changes randomly?
if everything so far checks out then the cylinders need to come off for checking such things as broken rings, cracked pistons, identically sized combustion chambers, valve seating and the like.
if you do this bit yourself you must make sure that as the cylinder is taken off the piston doesn't drop down and put a dent in the conrod. dent a conrod and you've stuffed it.
there is lots of other stuff that can be checked internally in the engine. basically you are looking for damage or out of tolerance setup.
if you don't have them already get yourself a copy of these two manuals.
Continental Aircraft Engine Overhaul Manual for models C75,C85,C90 and O-200. the identification on mine is Form X-30010.
Continental Aircrat Engines Series C-75, 85, 90 & O-200 Service parts catalogue. the identification on mine is Form X-30011. this gives exploded views of what is present in each assembly.
now the caveat here is that I am not a qualified mechanic. I am a private owner of an O-200 engined aircraft and I have been sitting here thinking "what would I check if I had this problem." I've been maintaining my own aeroplane for about a decade.
so your mileage may vary.
get your hands greasy and use a strong light.
balance is a subtle thing.
starting at the spinner. are all the screws in the spinner the same length? having screws of different lengths and with different washers under the heads will throw out the balance.
are the engine mount rubbers (lord mounts) in good condition? there are two rubbers in each of the 4 mount points. your top rubbers can be quite serviceable and easily seen. the bottom rubbers can be totally stuffed and you wouldn't know it. they are only about $15 each so they are the cheapest you can get in the 150.
the rubbers won't affect balance but they will transmit lots of vibration.
the prop has been to a shop. but is it balanced??? you can check this yourself with a few spacers on a shaft on some blocks on the dining room table.
is the spinner symmetrical and balanced?
go and buy 8 new spark plugs. they are about $40 each. roughly $320 in total.
don't drop them and install them with care. spark plugs that are failing will cause uneven combustion and make some cylinders seem like duds.
are the magnetos in good condition? I had a failing oil seal in the bottom of one of mine and the uneven combustion it caused in the engine made it seem as though the engine was totally clapped out.
are the plug leads in good condition? if these are shorting or breaking down you engine will run roughly.
Are your magneto P leads in good condition. one of these leads intermittently shorting to earth will cause your engine all sorts of rough running.
is your engine oil screen nice and clean? a failing component will often lodge parts of itself in the screen. do some detective work.
are the bolts holding your propeller in good condition? a broken or stretched bolt can give the illusion of all sorts of vibrational problems. equally a set of loose prop bolts can cause all sorts of vibrational illusions. do you have identical numbers of washers under each bolt? ( i even use identical length lock wire between bolts)
get a dial gauge. firmly attach it to the engine and check the propeller flange.
when you turn over the engine by hand does the flange track true?
if it doesn't then you have a bent crankshaft.
with the engine ticking over at idle look at the prop tip arc. is it tracking true?
a prop mounted on crooked will give all sorts of trouble with blade angle of attack being different each side.
ok if all of that checks out then you need to look inside the engine.
the easiest first point of checking is to take off the oil sump, the "football".
with the sump off you can look up into the interior of the engine with a powerful spotlight. can you see any damage? can you see anything that doesn't look to be in the right place?
turn over the engine and check out the big end bolts on each each conrod.
are these all tight and secure? is there any corrosion evident?
putting the football back on will mean a new gasket and new oil.
are all the sections above the carburettor all tight and secure. no air leaks evident in the induction system or looseness introducing mixture changes randomly?
if everything so far checks out then the cylinders need to come off for checking such things as broken rings, cracked pistons, identically sized combustion chambers, valve seating and the like.
if you do this bit yourself you must make sure that as the cylinder is taken off the piston doesn't drop down and put a dent in the conrod. dent a conrod and you've stuffed it.
there is lots of other stuff that can be checked internally in the engine. basically you are looking for damage or out of tolerance setup.
if you don't have them already get yourself a copy of these two manuals.
Continental Aircraft Engine Overhaul Manual for models C75,C85,C90 and O-200. the identification on mine is Form X-30010.
Continental Aircrat Engines Series C-75, 85, 90 & O-200 Service parts catalogue. the identification on mine is Form X-30011. this gives exploded views of what is present in each assembly.
now the caveat here is that I am not a qualified mechanic. I am a private owner of an O-200 engined aircraft and I have been sitting here thinking "what would I check if I had this problem." I've been maintaining my own aeroplane for about a decade.
so your mileage may vary.
get your hands greasy and use a strong light.
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Found the problem
So,
after 2 years of searching for the problem, here was the issue.
We opened the engine and checked for worn cam lobes, heavier pistons, all that jazz... The carb was rebuilt. Engine mounts replaced. other stuff I cant even remember...
In the end, I went to flip the propeller on another Cessna 150 and noticed that the impulse coupling fired with the prop at 1 o'clock and 7 o'clock looking aft. Mine fired at 3 and 9 o'clock. Well folks that's all I needed. Reinstalled the prop correctly and its a new engine.
The funny part is - I had two certified mechanics tell me that the prop was installed correctly a year ago...
Just wanted to relay the info after 2 years of searching this horror story.
Happy Flying
after 2 years of searching for the problem, here was the issue.
We opened the engine and checked for worn cam lobes, heavier pistons, all that jazz... The carb was rebuilt. Engine mounts replaced. other stuff I cant even remember...
In the end, I went to flip the propeller on another Cessna 150 and noticed that the impulse coupling fired with the prop at 1 o'clock and 7 o'clock looking aft. Mine fired at 3 and 9 o'clock. Well folks that's all I needed. Reinstalled the prop correctly and its a new engine.
The funny part is - I had two certified mechanics tell me that the prop was installed correctly a year ago...
Just wanted to relay the info after 2 years of searching this horror story.
Happy Flying
