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Overhaulin'

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jindoguy(at)gmail.com
Guest

Posted: Sun Dec 10, 2006 3:18 pm Post subject: Overhaulin'

I was presented with this philosophy about Rotax overhauls at the repairman maintenance class I took this summer. It opened my eyes to a new way of looking at the subject. The A & P who offered it has been in ultralights for over 20 years, is a Quicksilver dealer, and used to have a clean room for doing Rotax overhauls. He no longer does them and advises his clientele to do the following. 

Set your engine up per Rotax, warm it properly before flying, use good oil, perform the normal maintenance per Rotax, and keep good engine logs. Fly it for 400 hours, then put it up for sale, while you are still flying it, for half the price of a new engine. There will always be somebody looking for a bargain engine and you should have no problem selling it at that price (that's the complete engine, gearbox, carbs, exhaust,  i.e. the works). Take that money and the cost of an overhaul (including new crank, as per Rotax) and buy a new engine.

Brian used the example of a 582. New engine (check falling dollar value to be correct) $7,000 USD. Cost to overhaul, with new crank, $3500, or half the cost of a new engine. Voila', you just bought a NEW engine for the cost of an overhaul.  

And the guy who bought your old engine? If he treats it the same way you did, it goes at least another 400 hours. The average guy flies 50 hours a year, so he gets eight years of service from the engine at $450 a year (approx) or $9 an hour. AND the engine still has value at the end of that time. 

One of the fellows in the class runs a towing operation in FL just like the fellow who commented on engine longevity. When presented with this idea, he ran the numbers for his business that night and told me the next day he had just done his last engine overhaul, too. 

Now there are some important considerations to this philosophy. 

Number one is you can't scrimp or cheat. You have to embrace the philosophy in its totality. Two things, that are free to you are selling while the engine is still on your aircraft. The potential buyer gets to see it run, it's not under a bench covered by a blanket. It's a living, breathing, honest to goodness aircraft engine, not a bench weight of unknown condition. Number two, keep good logs. If you are familiar with TC aircraft you know that the logs themselves have value, even without an engine attached. Their value to you is that it shows you are an above average owner, in the ultralight universe, and this impression is passed on to your prospective buyer. 

As I said, I didn't invent this philosophy, I only present it for your consideration.



Rick

-- 

Rick Girard

"Ya'll drop on in"

takes on a whole new meaning

when you live at the airport.   [quote][b]

herbgh

Joined: 10 Jan 2006
Posts: 145

Posted: Sun Dec 10, 2006 3:40 pm Post subject: Overhaulin'

Rick

  

   Or buy a Hirth with factory suggested overhaul of 1000  hours...   I am assuming that the main reason for a 300 hour  overhaul has to do with big end rod bearing wear?  Anyone know the  difference.  Nickasil cylinders on the Hirth..    Herb  

  

  

  

 On Sun, 10 Dec 2006 17:17:37 -0600 "Richard Girard" <jindoguy(at)gmail.com (jindoguy(at)gmail.com)> writes:

 [quote]   I was presented with this philosophy about Rotax overhauls at the    repairman maintenance class I took this summer. It opened my eyes to a new way    of looking at the subject. The A & P who offered it has been in    ultralights for over 20 years, is a Quicksilver dealer, and used to have a    clean room for doing Rotax overhauls. He no longer does them and advises his    clientele to do the following. 

Set your engine up per Rotax, warm it    properly before flying, use good oil, perform the normal maintenance per    Rotax, and keep good engine logs. Fly it for 400 hours, then put it up for    sale, while you are still flying it, for half the price of a new engine. There    will always be somebody looking for a bargain engine and you should have no    problem selling it at that price (that's the complete engine, gearbox, carbs,    exhaust, i.e. the works). Take that money and the cost of an overhaul    (including new crank, as per Rotax) and buy a new engine.

Brian used the    example of a 582. New engine (check falling dollar value to be correct) $7,000    USD. Cost to overhaul, with new crank, $3500, or half the cost of a new    engine. Voila', you just bought a NEW engine for the cost of an overhaul.    

And the guy who bought your old engine? If he treats it the same way you    did, it goes at least another 400 hours. The average guy flies 50 hours a    year, so he gets eight years of service from the engine at $450 a year    (approx) or $9 an hour. AND the engine still has value at the end of that    time. 

One of the fellows in the class runs a towing operation in FL just    like the fellow who commented on engine longevity. When presented with this    idea, he ran the numbers for his business that night and told me the next day    he had just done his last engine overhaul, too. 

Now there are some    important considerations to this philosophy. 

Number one is you can't    scrimp or cheat. You have to embrace the philosophy in its totality. Two    things, that are free to you are selling while the engine is still on your    aircraft. The potential buyer gets to see it run, it's not under a bench    covered by a blanket. It's a living, breathing, honest to goodness aircraft    engine, not a bench weight of unknown condition. Number two, keep good logs.    If you are familiar with TC aircraft you know that the logs themselves have    value, even without an engine attached. Their value to you is that it shows    you are an above average owner, in the ultralight universe, and this    impression is passed on to your prospective buyer. 

As I said, I didn't    invent this philosophy, I only present it for your    consideration.



Rick

-- 

Rick Girard

"Ya'll drop    on in"

takes on a whole new meaning

when you live at the airport. 

 	  Quote: 	
		  



aeroelectric.com

">www.buildersbooks.com

kitlog.com

homebuilthelp.com

.matronics.com/contribution

http://www.matronics.com/Navigator?Kolb-List



	
    

[b]

jindoguy(at)gmail.com
Guest

Posted: Sun Dec 10, 2006 5:20 pm Post subject: Overhaulin'

Herb, I can't tell you the reason that Rotax suggests the TBO that they do, but like the TBO of Lyc's and Conti's, there's no law that says you have to do an overhaul then. If the engine is within service limits and it doesn't put you over your personal comfort limits, fly on.  

As for the Hirth, has anyone ever taken one to TBO? Not to sound like an economist, but the market has spoken about Hirth. If the Hirth is such a long lived powerplant, where are they? 



Rick



 On 12/10/06, Herb Gayheart <herbgh(at)juno.com (herbgh(at)juno.com)> wrote:[quote]      Rick

  

   Or buy a Hirth with factory suggested overhaul of 1000  hours...   I am assuming that the main reason for a 300 hour  overhaul has to do with big end rod bearing wear?  Anyone know the  difference.  Nickasil cylinders on the Hirth..    Herb  

  

  

  

 On Sun, 10 Dec 2006 17:17:37 -0600 "Richard Girard" <jindoguy(at)gmail.com (jindoguy(at)gmail.com)> writes:

  	  Quote: 	
		     I was presented with this philosophy about Rotax overhauls at the    repairman maintenance class I took this summer. It opened my eyes to a new way    of looking at the subject. The A & P who offered it has been in    ultralights for over 20 years, is a Quicksilver dealer, and used to have a    clean room for doing Rotax overhauls. He no longer does them and advises his    clientele to do the following. 

Set your engine up per Rotax, warm it    properly before flying, use good oil, perform the normal maintenance per    Rotax, and keep good engine logs. Fly it for 400 hours, then put it up for    sale, while you are still flying it, for half the price of a new engine. There    will always be somebody looking for a bargain engine and you should have no    problem selling it at that price (that's the complete engine, gearbox, carbs,    exhaust, i.e. the works). Take that money and the cost of an overhaul    (including new crank, as per Rotax) and buy a new engine.

Brian used the    example of a 582. New engine (check falling dollar value to be correct) $7,000    USD. Cost to overhaul, with new crank, $3500, or half the cost of a new    engine. Voila', you just bought a NEW engine for the cost of an overhaul.    

And the guy who bought your old engine? If he treats it the same way you    did, it goes at least another 400 hours. The average guy flies 50 hours a    year, so he gets eight years of service from the engine at $450 a year    (approx) or $9 an hour. AND the engine still has value at the end of that    time. 

One of the fellows in the class runs a towing operation in FL just    like the fellow who commented on engine longevity. When presented with this    idea, he ran the numbers for his business that night and told me the next day    he had just done his last engine overhaul, too. 

Now there are some    important considerations to this philosophy. 

Number one is you can't    scrimp or cheat. You have to embrace the philosophy in its totality. Two    things, that are free to you are selling while the engine is still on your    aircraft. The potential buyer gets to see it run, it's not under a bench    covered by a blanket. It's a living, breathing, honest to goodness aircraft    engine, not a bench weight of unknown condition. Number two, keep good logs.    If you are familiar with TC aircraft you know that the logs themselves have    value, even without an engine attached. Their value to you is that it shows    you are an above average owner, in the ultralight universe, and this    impression is passed on to your prospective buyer. 

As I said, I didn't    invent this philosophy, I only present it for your    consideration.



Rick

-- 

Rick Girard

"Ya'll drop    on in"

takes on a whole new meaning

when you live at the airport. 

 	  Quote: 	
		  



aeroelectric.com

">www.buildersbooks.com

kitlog.com

homebuilthelp.com

.matronics.com/contribution

http://www.matronics.com/Navigator?Kolb-List



	
    

	
    	  Quote: 	
		  [b]  www.aeroelectric.com www.buildersbooks.com www.kitlog.com www.homebuilthelp.com http://www.matronics.com/contribution http://www.matronics.com/Navigator?Kolb-List 	


-- 

Rick Girard

"Ya'll drop on in"

takes on a whole new meaning

when you live at the airport.  [quote][b]

slyck(at)frontiernet.net
Guest

Posted: Sun Dec 10, 2006 6:35 pm Post subject: Overhaulin'

Sounds like reasonable advice, especially the part about it showing it

running on your plane.

Even on a standard category airplane the logs are as important as the 

plane.

(never could figure why they sometimes "disappear" just like the owner's

manual in a used car you go to buy... WHY did they take it out?)

If that continental or lycoming was "overhauled" there should be a 

complete

list of new parts WITH part numbers in the engine log unless it was 

bought

yellow tag from someplace like mattituck or penn yan.  Plus the A&P

number and signature.

BB  do not archive

On 10, Dec 2006, at 6:17 PM, Richard Girard wrote:



 	  Quote: 	
		   I was presented with this philosophy about Rotax overhauls at the 

 repairman maintenance class I took this summer. It opened my eyes to a 

 new way of looking at the subject. The A & P who offered it has been 

 in ultralights for over 20 years, is a Quicksilver dealer, and used to 

 have a clean room for doing Rotax overhauls. He no longer does them 

 and advises his clientele to do the following.

 Set your engine up per Rotax, warm it properly before flying, use good 

 oil, perform the normal maintenance per Rotax, and keep good engine 

 logs. Fly it for 400 hours, then put it up for sale, while you are 

 still flying it, for half the price of a new engine. There will always 

 be somebody looking for a bargain engine and you should have no 

 problem selling it at that price (that's the complete engine, gearbox, 

 carbs, exhaust, i.e. the works). Take that money and the cost of an 

 overhaul (including new crank, as per Rotax) and buy a new engine.

 Brian used the example of a 582. New engine (check falling dollar 

 value to be correct) $7,000 USD. Cost to overhaul, with new crank, 

 $3500, or half the cost of a new engine. Voila', you just bought a NEW 

 engine for the cost of an overhaul.

 And the guy who bought your old engine? If he treats it the same way 

 you did, it goes at least another 400 hours. The average guy flies 50 

 hours a year, so he gets eight years of service from the engine at 

 $450 a year (approx) or $9 an hour. AND the engine still has value at 

 the end of that time.

 One of the fellows in the class runs a towing operation in FL just 

 like the fellow who commented on engine longevity. When presented with 

 this idea, he ran the numbers for his business that night and told me 

 the next day he had just done his last engine overhaul, too.

 Now there are some important considerations to this philosophy.

 Number one is you can't scrimp or cheat. You have to embrace the 

 philosophy in its totality. Two things, that are free to you are 

 selling while the engine is still on your aircraft. The potential 

 buyer gets to see it run, it's not under a bench covered by a blanket. 

 It's a living, breathing, honest to goodness aircraft engine, not a 

 bench weight of unknown condition. Number two, keep good logs. If you 

 are familiar with TC aircraft you know that the logs themselves have 

 value, even without an engine attached. Their value to you is that it 

 shows you are an above average owner, in the ultralight universe, and 

 this impression is passed on to your prospective buyer.

 As I said, I didn't invent this philosophy, I only present it for your 

 consideration.



 Rick



 -- 

 Rick Girard

 "Ya'll drop on in"

 takes on a whole new meaning

 when you live at the airport.

d-m-hague(at)comcast.net
Guest

Posted: Mon Dec 11, 2006 9:21 pm Post subject: Overhaulin'

At 09:34 PM 12/10/2006, robert bean wrote:



 	  Quote: 	
		  Even on a standard category airplane the logs are as important as the plane.

(never could figure why they sometimes "disappear" just like the owner's

manual in a used car you go to buy... WHY did they take it out?)...


	


Not always the owner's fault... I had a T-Craft some 20 years ago.  Took it 

in for annual.  They did some engine work, took a jug off (I forget why), 

then said a piston was cracked (I have reason to believe they dropped 

it).  I got a NOS piston from a surplus parts guy in the next town, they 

put it back together, then found some corroded longerons.. said they didn't 

want to work on it any more, and since they didn't complete the job I 

didn't owe them anything.  OK, I flew it back home (it wasn't that bad) so 

an A&P friend could do the welding for me.  I asked for the logs back, they 

said they couldn't find them, and on top of that they sent me a bill.  I 

never got the logs back... and they never got any money.



Less than a year later, the shop was out of business.



                                 -Dana



--

--

A computer lets you make more mistakes faster than any invention in

human history... with the possible exception of handguns and tequila.

rlaird

Joined: 10 Jan 2006
Posts: 373
Location: Houston

Posted: Wed Dec 13, 2006 6:41 am Post subject: Overhaulin'

Can someone explain to me why it is Rotax can't make 2-stroke bearings

and/or crankshaft components that last longer than 300 hours

(notwithstanding those that go well over that time limit)?  I mean, is

it a matter of cost/materials, or is it a "no material known to man

can withstand the stresses involved" kind of thing?



  -- Robert

On 12/10/06, Richard Girard <jindoguy(at)gmail.com> wrote:

 	  Quote: 	
		   I was presented with this philosophy about Rotax overhauls at the repairman

 maintenance class I took this summer. It opened my eyes to a new way of

 looking at the subject. The A & P who offered it has been in ultralights for

 over 20 years, is a Quicksilver dealer, and used to have a clean room for

 doing Rotax overhauls. He no longer does them and advises his clientele to

 do the following.

 Set your engine up per Rotax, warm it properly before flying, use good oil,

 perform the normal maintenance per Rotax, and keep good engine logs. Fly it

 for 400 hours, then put it up for sale, while you are still flying it, for

 half the price of a new engine. There will always be somebody looking for a

 bargain engine and you should have no problem selling it at that price

 (that's the complete engine, gearbox, carbs, exhaust, i.e. the works). Take

 that money and the cost of an overhaul (including new crank, as per Rotax)

 and buy a new engine.

 Brian used the example of a 582. New engine (check falling dollar value to

 be correct) $7,000 USD. Cost to overhaul, with new crank, $3500, or half the

 cost of a new engine. Voila', you just bought a NEW engine for the cost of

 an overhaul.

 And the guy who bought your old engine? If he treats it the same way you

 did, it goes at least another 400 hours. The average guy flies 50 hours a

 year, so he gets eight years of service from the engine at $450 a year

 (approx) or $9 an hour. AND the engine still has value at the end of that

 time.

 One of the fellows in the class runs a towing operation in FL just like the

 fellow who commented on engine longevity. When presented with this idea, he

 ran the numbers for his business that night and told me the next day he had

 just done his last engine overhaul, too.

 Now there are some important considerations to this philosophy.

 Number one is you can't scrimp or cheat. You have to embrace the philosophy

 in its totality. Two things, that are free to you are selling while the

 engine is still on your aircraft. The potential buyer gets to see it run,

 it's not under a bench covered by a blanket. It's a living, breathing,

 honest to goodness aircraft engine, not a bench weight of unknown condition.

 Number two, keep good logs. If you are familiar with TC aircraft you know

 that the logs themselves have value, even without an engine attached. Their

 value to you is that it shows you are an above average owner, in the

 ultralight universe, and this impression is passed on to your prospective

 buyer.

 As I said, I didn't invent this philosophy, I only present it for your

 consideration.



 Rick



 --

 Rick Girard

 "Ya'll drop on in"

 takes on a whole new meaning

 when you live at the airport.

_________________
~~~~~~~~~~~~~~~~~~~
Robert Laird
formerly: MkIIIc w/ 912ULS & Gyrobee
current: Autogyro Cavalon w/ 914ULS
Houston, TX area
http://www.Texas-Flyer.com

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Wed Dec 13, 2006 7:09 am Post subject: Overhaulin'

| Can someone explain to me why it is Rotax can't make 2-stroke 

bearings

| and/or crankshaft components that last longer than 300 hours

|

|  -- Robert

Robert:



I don't know, but will guess.



The environment the two stroke lives in might help contribute to its 

shorter life that the 4 stroke.  The 4 stroke crank shaft enjoys a 

life in an enclosed case with pressure fed oil and relatively small 

amounts of the outside environment.



The 2 stroke is trying to survive on oil that is mixed with the fuel 

charge.  All the intake air is routed through the crankcase.  Seems 

like a haphazard way to lubricate bearings, plus any inefficiency in 

the air filter allows dirty atmosphere to bath the crank, connecting 

rods, and their bearings.



Just a guess.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

jindoguy(at)gmail.com
Guest

Posted: Wed Dec 13, 2006 11:09 am Post subject: Overhaulin'

Add to that the Rotax crank is pressed together and not keyed in any way. From the perspective of being a machinist, well, hmmmm. The Germans and Austrians have a long history of pressed together cranks and they are able to make them work in their environment. 

In the early days of hotrodding VW's the hot crank was a German unit with ball bearing main and rod bearings. Worked great in road racing, not so good when you did a burn out.

The same is probably true of the Rotax. 

Another area of failure of the Rotax crank is corrosion. Engines laid up without proper precautions develop corrosion which leads to stress cracks.

Cold seizures can be very mild in terms of visible damage to the piston and cylinder, but the loads on the crank are very high. If the cranks slips slightly out of register the whole engine suffers. 

Last, a postulation. Rotax has been out there in the field for over 25 years, plenty of time for a lot of cranks to go through the system. Straightening a crank is an age old fix, ask any Harley mechanic. The tools and technique are well known. How many used cranks have been recycled as new and the resulting problems blamed on them pesky Rotax cranks? 



Rick



On 12/13/06, John Hauck <jhauck(at)elmore.rr.com (jhauck(at)elmore.rr.com)> wrote:[quote] --> Kolb-List message posted by: "John Hauck" <jhauck(at)elmore.rr.com (jhauck(at)elmore.rr.com)>



 | Can someone explain to me why it is Rotax can't make 2-stroke

bearings

| and/or crankshaft components that last longer than 300 hours 

|

|  -- Robert

Robert:



I don't know, but will guess.



The environment the two stroke lives in might help contribute to its

shorter life that the 4 stroke.  The 4 stroke crank shaft enjoys a 

life in an enclosed case with pressure fed oil and relatively small

amounts of the outside environment.



The 2 stroke is trying to survive on oil that is mixed with the fuel

charge.  All the intake air is routed through the crankcase.  Seems 

like a haphazard way to lubricate bearings, plus any inefficiency in

the air filter allows dirty atmosphere to bath the crank, connecting

rods, and their bearings.



Just a guess.



john h

mkIII

 

takes on a whole new meaning

when you live at the airport.  [quote][b]

NeilsenRM(at)comcast.net
Guest

Posted: Wed Dec 13, 2006 12:16 pm Post subject: Overhaulin'

Could it be that there is money to be made on new  engines and rebuilds???

  

 When you have the market all sown up you can get  all kinds of shit happening. In the heyday of Ford and GM there was a campaign  of reducing quality to keep their cars from lasting too long. I refuse to  believe that Rotax couldn't make their cranks last allot longer if they wanted  to. 

  

 We need to get some alternative engines flying so  that there is SOME competition for Rotax. 

  

 Do not archive

  

 Rick Neilsen

 Redrive VW powered MKIIIc

 [quote]   ---

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Wed Dec 13, 2006 3:07 pm Post subject: Overhaulin'

| Add to that the Rotax crank is pressed together and not keyed in any 

way.

| >From the perspective of being a machinist, well, hmmmm.

|

| Rick

Rick:



Lots of applications use the pressed crank with no problems.



One would be hard pressed to get a crank shaft to slip.  About the 

only way would be to have a blade strike with other than a Warp Drive 

or metal prop, or some other catastrophic seizure.



My Cuyuna and Rotax two strokes all had blade strikes, to total 

destruction, without causing a crank to slip.



The 912 and 914 series engines use pressed cranks.



Almost all motorcycles, ATVs, jet skiis, outboard motors, two and four 

stroke use pressed cranks.



Don't think slippage is one of their problems.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Dec 14, 2006 9:45 am Post subject: Overhaulin'

....Can someone explain to me why it is Rotax can't make 2-stroke 

bearings

       and/or crankshaft components that last longer than 300 hours

       (notwithstanding those that go well over that time limit)?  I 

mean, is

       it a matter of cost/materials, or is it a "no material known to 

man

       can withstand the stresses involved" kind of thing?.....



In addition to what John Hauck said, I would add the following. If my 

memory serves me correctly, the forces acting on reciprocating machine 

parts is proportional to the  4th power of the RPM. Jack Hart can 

probably confirm or correct this number. In other words, if the RPM 

goes up from 3000 to 6000 (doubling) then the reciprocating forces go 

up by a factor of 16 (2 to the 4th power).  So, if a 2 stroke engine 

normally runs at 6,000 rpm vs a 912 running at 5,000 rpm, the 2-stroker 

is running 20% faster in rpm which (if all other variables were held 

constant) would equate to a bit over twice the forces (1.2 ^ 4 = 

2.076). Any wonder why drag racing engines running at redline for a 1/4 

mile need rebuilding so frequently?



When I was flying an early FIrestar with 377 I normally cruised at 

around 5200 rpm. No signs of trouble at all with that engine at near 

500 hours on it when I sold the airplane.



Thom in Buffalo

do not archive

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

herbgh

Joined: 10 Jan 2006
Posts: 145

Posted: Thu Dec 14, 2006 11:03 am Post subject: Overhaulin'

The lower rpms of the Hirth engines might account for some of their

stated 1000 hour overhaul?  Herb 



 

On Thu, 14 Dec 2006 12:44:08 -0500 Thom Riddle <jtriddle(at)adelphia.net>

writes:

 	  Quote: 	
		   

 

 .....Can someone explain to me why it is Rotax can't make 2-stroke 

 bearings

        and/or crankshaft components that last longer than 300 hours

        (notwithstanding those that go well over that time limit)?  I 

 

 mean, is

        it a matter of cost/materials, or is it a "no material known 

 to 

 man

        can withstand the stresses involved" kind of thing?.....

 

 In addition to what John Hauck said, I would add the following. If 

 my 

 memory serves me correctly, the forces acting on reciprocating 

 machine 

 parts is proportional to the  4th power of the RPM. Jack Hart can 

 probably confirm or correct this number. In other words, if the RPM 

 

 goes up from 3000 to 6000 (doubling) then the reciprocating forces 

 go 

 up by a factor of 16 (2 to the 4th power).  So, if a 2 stroke engine 

 

 normally runs at 6,000 rpm vs a 912 running at 5,000 rpm, the 

 2-stroker 

 is running 20% faster in rpm which (if all other variables were held 

 

 constant) would equate to a bit over twice the forces (1.2 ^ 4 = 

 2.076). Any wonder why drag racing engines running at redline for a 

 1/4 

 mile need rebuilding so frequently?

 

 When I was flying an early FIrestar with 377 I normally cruised at 

 around 5200 rpm. No signs of trouble at all with that engine at near 

 

 500 hours on it when I sold the airplane.

 

 Thom in Buffalo

 do not archive

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Thu Dec 14, 2006 12:56 pm Post subject: Overhaulin'

| The lower rpms of the Hirth engines might account for some of their

| stated 1000 hour overhaul?  Herb 

 

Herb:



Isn't operational rpm a design factor?



Running an engine too slow can be as harmful to it as over speeding.



 john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

jbhart(at)onlyinternet.ne
Guest

Posted: Thu Dec 14, 2006 2:07 pm Post subject: Overhaulin'

At 12:44 PM 12/14/06 -0500, Thom Riddle wrote:

 	  Quote: 	
		  



.....Can someone explain to me why it is Rotax can't make 2-stroke 

bearings

       and/or crankshaft components that last longer than 300 hours

       (notwithstanding those that go well over that time limit)?  I 

mean, is

       it a matter of cost/materials, or is it a "no material known to 

man

       can withstand the stresses involved" kind of thing?.....




	


Kolbers,



It has to do with the fact that roller and ball bearings are used in a low 

oil environment.  Ball and roller bearings do not have a large surface area 

supported by an oil cushion as do slipper bearings.  The ball has almost 

point contact and the roller line contact so that as the load comes on and 

off of them they are stressed through the center of the ball and roller.  

Actual surface deformation takes place as the load comes on and off the 

bearing.  If the loads are low enough so that the deformation does not go 

beyond the elastic limit, the bearing should hold up forever.  But due to 

material and surface imperfections, a bit of the ball, roller or bearing 

race surface spalls and leaves a little pit.  Then over time additional 

material will fail next to the original pit etc until the bearing fails.  

Higher loads accelerate this process.



 	  Quote: 	
		  From Timken:


	


    * Doubling load reduces life to one tenth. Reducing load by one half 

increases life by ten,

    * Doubling speed reduces life by one half. Reducing speed by one half 

doubles life.



Check out:



http://www.timken.com/products/bearings/fundamen/calculate.asp



The above assumes constant load at constant rpm.  But for an internal 

combustion engine, the dynamic bearing load varies with crank position and 

rises dramatically as rpm increases in a crank, connecting rod and piston 

system.  This why the engine explodes if it is over rev'ed.



I assume what engine manufacturers gamble on is that the bearings will hold 

up to the selected TBO.  In most cases they do and will go much further 

depending upon how the engine has been treated and if the engine initially 

received a very good set of bearings.  So they pick a TBO time that they 

believe is attainable for a high percentage of their engines.  If there are 

no failures in the field they may raise the TBO.  No one wants the 

reputation for engines that self destruct.  It is better to have a re 

buildable carcass.



Once you purchase your engine, you can make the choice of how you are going 

to run your engine.  I am not saying to never run your engine up to the 

operating limit.  But I am saying yes run it up there for take off, but 

bring it on back a bit for cruise.  It will be much easier on the bearings, 

and the chances of making to TBO are increased.



Jack B. Hart FF004

Winchester, IN

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Thu Dec 14, 2006 8:51 pm Post subject: Overhaulin'

If you are lugging the engine, yes. If the engine is not being lugged, no. 

Jack Hart in his post on this subject gave an excellent analysis on the 

situation, as the crank load goes up expotentially as the rpm's increase, & 

the crank life is greatly extended by cruising at lower rpm's.



That is why I am still in pursuit of streamlining & cleaning up the MKIII so 

that it becomes possible to attain acceptable cruise speeds at minimal 582 

cruise rpm's.  Right now I am able to cruise at 65-70 mph at around 5300 

rpm's, and the bird is currently in the garage awaiting more streamlining so 

that it will (hopefully) become even more efficient. Don't know if I will 

accomplish anything or not, but the goal is to cruise at 65-70 at 5200 rpm 

or less. Not to mention that at this rpm the fuel burn is just slightly 

above 3 gph. And it is comparitively very quiet.

Richard Pike

MKIII N420P (420ldPoops)

---

_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

ul15rhb(at)juno.com
Guest

Posted: Fri Dec 15, 2006 10:00 am Post subject: Overhaulin'

I have been running my 447 at 5000 RPM in cruise, 450 hours. The 

slower RPM should extend the TBO of the engine and so far it's 

working. I have peered through the exhaust ports and it looks very 

good. I'm using 50:1 synthetic Koltz oil and give it S*****m 

treatments (that's a dirty word here). I think I can get many more 

hours out of it.



Ralph

Original Firestar, 20 years flying it



-- "Richard Pike" <richard(at)bcchapel.org> wrote:




If you are lugging the engine, yes. If the engine is not being 

lugged, no. 

Jack Hart in his post on this subject gave an excellent analysis on 

the 

situation, as the crank load goes up expotentially as the rpm's 

increase, & 

the crank life is greatly extended by cruising at lower rpm's.



That is why I am still in pursuit of streamlining & cleaning up the 

MKIII so 

that it becomes possible to attain acceptable cruise speeds at 

minimal 582 

cruise rpm's.  Right now I am able to cruise at 65-70 mph at around 

5300 

rpm's, and the bird is currently in the garage awaiting more 

streamlining so 

that it will (hopefully) become even more efficient. Don't know if I 

will 

accomplish anything or not, but the goal is to cruise at 65-70 at 

5200 rpm 

or less. Not to mention that at this rpm the fuel burn is just 

slightly 

above 3 gph. And it is comparitively very quiet.

Richard Pike

MKIII N420P (420ldPoops)

---

David.Lehman

Joined: 10 Jan 2006
Posts: 265
Location: "Lovely" Fresno CA

Posted: Fri Dec 15, 2006 10:18 am Post subject: Overhaulin'

Ralph...

  

 What's your indicated airspeed at 5K RPM?...  Does it feel like the airplane is "plowing" or "on the step" at that RPM...  My original Firestar with a 503 feels more like it's "plowing" at that RPM and I think the indicated is around 50...  At 5800 RPM, I indicate 60-63 mph, but I burn a lot of fuel...  May be partly because of my draggy 850x6 tires... 

  

 DVD



 

 On 12/15/06, Ralph <ul15rhb(at)juno.com (ul15rhb(at)juno.com)> wrote: [quote]--> Kolb-List message posted by: "Ralph" <ul15rhb(at)juno.com  (ul15rhb(at)juno.com)>



I have been running my 447 at 5000 RPM in cruise, 450 hours. The

slower RPM should extend the TBO of the engine and so far it's

working. I have peered through the exhaust ports and it looks very

good. I'm using 50:1 synthetic Koltz oil and give it S*****m 

treatments (that's a dirty word here). I think I can get many more

hours out of it.



Ralph

Original Firestar, 20 years flying it

[b]

_________________
ô¿ô

"Both optimists and pessimists contribute to the society. The optimist invents the aeroplane, the pessimist the parachute."

--- George Bernard Shaw

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