Test for cracks in the case?
11-29-2011, 11:43 PM
#16
Rennlist Member
However, I think comparing an aluminum engine crankcase for an aircraft to an aluminum crankcase for a car is an apples to oranges comparison.
The aircraft crankcase must be much lighter. It is therefore thinner. Aircraft owners and operators expect to re-engine their aircraft at some point during the service life of the aircraft.
This is not the design philosophy of a car. The engine is more robust and expected to outlive the chassis. Since warranty costs and customer satisfaction are at stake, engine designs endure punishing testing to insure that they meet this goal.
11-30-2011, 11:49 AM
#18
Nordschleife Master
You think continental / lycoming would make , get approval for and sell cases that crack so they could save a few pounds ?
You think continental / lycoming would accept engine case failure for a few pounds ?
When the Porsche flat six was used as an aircraft motor it needed to be fixed up to be more robust and reliable for lives depended on it not failing in flight .
http://www.seqair.com/Other/PFM/PorschePFM.html
http://dedeporsche.posterous.com/fro...gines-that-fly
"The Porsche FlugMotoren (Porsche Aero Engines) was either sort of a disaster, or a total disaster, depending on who you ask."
"Under United States law, where most of the engines were used, Porsche was required to continue to supply parts and maintenance for the engines. Instead, they claimed to have destroyed all spare parts and refuse to support the very engines they put into the marketplace. The company has even gone so far as to try and render the planes worthless by claiming the engines need certain parts replaced after a number of flight hours and then refusing to provide technical information so such parts could be privately manufactured."
11-30-2011, 12:24 PM
#19
The Porsche Mooney, pretty much just came down to initial cost to build and maint. cost of ownership, so it didn't fly, pardon the pun.
There was more going on there under the radar and was some infighting about the whole project.
So Porsche did what Porsche does and took their football and went home when it doesn't go their way.
There was more going on there under the radar and was some infighting about the whole project.
So Porsche did what Porsche does and took their football and went home when it doesn't go their way.
11-30-2011, 01:25 PM
#20
Rennlist Member
http://www.lightplane-maintenance.com/LPM_LPM_0605.html
"While we will agree some cases seem more crack-prone than others, no engine is immune. Both Lycoming and Continental discuss crankcase cracking at length in service literature, understanding that it can happen and with some frequency.
Both publish guidelines for inspecting cases and offer advice on what is considered airworthy and what isn't. Some publications provide repair criteria to be used during overhaul that severely restrict where welding and re-machining of the case may be accomplished."
"Crankcases crack because aluminum castings do not like to flex and air-cooled engines equipped with opposing cylinders flex as a matter of operational functioning. The result is predictable as the case relieves normal and abnormal stresses."
My father was a prototype machinist for Hughes Aircraft , he tells me that every piece of metal is flawed from the get go and more so after it has been machined as most machining rips metal from metal . Every cut surface has micro cracks resulting from the cutting . He has told me that if you look close enough at any part you will find flaws , that the trick is knowing what flaws are acceptable and what flaws are not .
"While we will agree some cases seem more crack-prone than others, no engine is immune. Both Lycoming and Continental discuss crankcase cracking at length in service literature, understanding that it can happen and with some frequency.
Both publish guidelines for inspecting cases and offer advice on what is considered airworthy and what isn't. Some publications provide repair criteria to be used during overhaul that severely restrict where welding and re-machining of the case may be accomplished."
"Crankcases crack because aluminum castings do not like to flex and air-cooled engines equipped with opposing cylinders flex as a matter of operational functioning. The result is predictable as the case relieves normal and abnormal stresses."
My father was a prototype machinist for Hughes Aircraft , he tells me that every piece of metal is flawed from the get go and more so after it has been machined as most machining rips metal from metal . Every cut surface has micro cracks resulting from the cutting . He has told me that if you look close enough at any part you will find flaws , that the trick is knowing what flaws are acceptable and what flaws are not .
Established criteria is used to determine what is acceptable surface defect we also have to consider surface irregularities which are common in castings which may or may not have an impact. What is a stress riser depends on its application, alloy used and location of the indication to an outer edge or a highly stressed part of the casting.
My understanding of aluminum and magnesium castings is somewhat extensive and I can assure you odds are if his case is cracked it is more the result of bad practices from previous mechanics than it is from flexing.
11-30-2011, 01:58 PM
#21
Rennlist Member
Nah, I meant "with." I gleaned from porschefan's other postings that he was getting a 4-5 inch puddle per day, spreading to a two foot puddle after a few days. It seemed to me that a miniscule crack that noone has been able to locate wouldn't be big enough to leak that much oil and that the oil leak is probably coming from somewhere else.
Sorry if my words were confusing! I was just making a case for the simplest solution usually being the right solution as per Occam's Razor.
Sorry if my words were confusing! I was just making a case for the simplest solution usually being the right solution as per Occam's Razor.
11-30-2011, 06:44 PM
#23
Rennlist Member
Well that's a convincing argument!
Yes they would.
To make something lighter you have to remove mass.
Aircraft manufacturers go to obsessive lengths to save weight. Special lightweight upholstery and 3 phase power are two good examples of this. Product design and manufacturing are full of trade-offs. Some durability had to be traded for weight.
Well, that's why aircraft have to be inspected at set intervals and engines overhauled on a schedule too. Think of what it would be like if airplanes were maintained like cars?
Interpretation: Porsche had excess manufacturing capacity for 911 engines. Some suit in Wiessach got the bright idea to engineer and build 911 aircraft engines. The due diligence wasn't performed up front and down the road Porsche got a nasty surprise. They found out they had to supply parts long after they were accustomed to doing and that there are a ton of third party manufacturers and re-manufacturers, not to mention repair/overhaul businesses they would have to be responsible for. In the end, it was a big money loser so Porsche pulled out.
To make something lighter you have to remove mass.
Aircraft manufacturers go to obsessive lengths to save weight. Special lightweight upholstery and 3 phase power are two good examples of this. Product design and manufacturing are full of trade-offs. Some durability had to be traded for weight.
When the Porsche flat six was used as an aircraft motor it needed to be fixed up to be more robust and reliable for lives depended on it not failing in flight .
http://dedeporsche.posterous.com/fro...gines-that-fly
"The Porsche FlugMotoren (Porsche Aero Engines) was either sort of a disaster, or a total disaster, depending on who you ask."
"Under United States law, where most of the engines were used, Porsche was required to continue to supply parts and maintenance for the engines. Instead, they claimed to have destroyed all spare parts and refuse to support the very engines they put into the marketplace. The company has even gone so far as to try and render the planes worthless by claiming the engines need certain parts replaced after a number of flight hours and then refusing to provide technical information so such parts could be privately manufactured."
http://dedeporsche.posterous.com/fro...gines-that-fly
"The Porsche FlugMotoren (Porsche Aero Engines) was either sort of a disaster, or a total disaster, depending on who you ask."
"Under United States law, where most of the engines were used, Porsche was required to continue to supply parts and maintenance for the engines. Instead, they claimed to have destroyed all spare parts and refuse to support the very engines they put into the marketplace. The company has even gone so far as to try and render the planes worthless by claiming the engines need certain parts replaced after a number of flight hours and then refusing to provide technical information so such parts could be privately manufactured."
11-30-2011, 07:03 PM
#24
Rennlist Member
With the engine now out of the car, I have a suggestion on how to possibly locating porosity/crack in the case. This method is used in large tanks where it's not possible to put a hydro test on a small repair on a steel bulkhead. A vacuum is applied to the area by the use of a "vacuum box" that has a window to see the weld repair ( that's been soaped up) to be tested. To do an engine case, all you would need to do is clean the area, then use the same vacuum bagging techniques used in boat and surfboard construction to apply a deep vacuum on the suspected area. Let stand for awhile, then remove vac bag to see if there's oil residual drawn out of the casing. Unless the crack is in the vicinity of an oil passage where the pressure differential is 5bar, a vacuum should be sufficient to draw oil from a crack that normally leaks at static pressure.
Unless you prove your mechanic wrong, you won't have piece of mind until you replace the casing.......
As an aside, in the past, did you jack the car by lifting on the engine seam?
Unless you prove your mechanic wrong, you won't have piece of mind until you replace the casing.......
As an aside, in the past, did you jack the car by lifting on the engine seam?
12-01-2011, 10:28 AM
#25
Rennlist Member
I am curious to see what the results are and if and where they determined a crack to be.
01-15-2012, 05:54 PM
#26
Nordschleife Master
Kevin Cameron has a great article "Casting Chronicles" about casting cases .
Page 24 Cycle World , Feb 2012 .
He also has a great article "Hot Metal" about heat flow in an air cooled heads
Page 38 May 2011
Page 24 Cycle World , Feb 2012 .
He also has a great article "Hot Metal" about heat flow in an air cooled heads
Page 38 May 2011
