Debate about Mark Langford's 3rd crank failure

Ross,

I have no idea how long it has been since you held a Corvair head in your hands, or how many you worked with, but coincidental to the discussion, I spent all weekend prepping 16 pairs of heavy cast 66-67 110 heads for processing, starting with removing the seats and guides, milling off the carb flanges, and cleaning them. I have about 100 heads in my hangar right now. I don't have to rely on memory, I work in the hangar 10 feet from my house every day.

In your writing you make reference to you having built all types of engines, and knowing them in some detail. Conversely, I have spent the last decade or two working almost exclusively on just one engine, in the single application of flight. Yes, I know that comparing the weight of heads isn't directly comparing their cooling potential, I was just making a rough point since they are both aluminum, and designed as air cooled heads, the comparison was good enough for the point, and a lot easier than figuring out the exact square inches of cooling area. Over the years I have learned a lot about much more important points, like how much detonation suppression you can get out of enrichment on takeoff with specific compression ratios, fuels, quench areas and ignition timing at various OAT's. I have seen countless heads with imbedded gaskets, and I can share why some engines can sustain 500F cht without damage, but another indents the gaskets on the take off with the cht indication below this. I know this one motor pretty well.

None of the stuff I share is intended to be confrontational or caustic, or even really an element of debate. Just trying to share some of the experience from working on different levels of this stuff personally for a long time. I shared the Lancair IVP pictures to say that I once worked on that end of aviation, but personally chose to use my time since then in pursuit of making learning and personal flight more accessible to people who represent the majority of the rank and file EAA members. Looking back at the photos, I can say a lot of spectators were impressed when we brought the Lancair to Oshkosh, but this doesn't compare to how I feel when we are packing up from a Corvair College where 15 or 20 new engines ran, built by the people who will fly them.

Ross, I don't know if you remember this, but I contacted you by email last year and offered to send a free copy of our 250 page new manual, as a courtesy, so your comments might better reflect what we are doing today. I never heard back. When you make a comment about my website saying I have never seen a cracked crank, perhaps you are looking at some dated material? Just typing "Cracked Crank" in the search box on the bottom of the front page produces this: Crankshafts 101 at www.FlyCorvair.com, a story about how we tore down a number of flying engines and tested all their cranks, and found some cracked. It is long, factual, frank and detailed........and it has been there every day for 10 years

In a previous post you said something about there being people who "knew a lot more about Corvairs" than I do. Having never met me, and not having read my book, I am not sure how you evaluated that, and If we were speaking of just flying Corvairs, I could disagree with you. You mention people, but not by name, don't say which shops are you are referencing. I don't really care, but for my own notes, I like to share names and photos when making statements like that. But lets just say you are right, there is some guy out there who has a gods eye view, knows everything and has an IQ twice mine, and he is even a nice person. OK, he wins the smartest Corvair guy award.....and this does what for the homebuilder who wanted to learn something, build and fly his own plane? If that guy doesn't share what he knows, have a name, website, teach seminars for free, test stuff and share the results, answer questions and make some parts, then what he knows is only good for winning the title of "smartest Corvair guy", and I am not seeing that by itself as the basis of a useful life. I only contend that I happen to be the most experienced accessible guy on Corvairs, and my work has brought a lot to grass roots homebuilders.-ww.

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Here are the actual CHT numbers we have observed on fly planes and the limits I recommend:
Corvair CHT, letters and notes. | flycorvair

For people who like data in formalized spreadsheets, a 6 cht / 6 egt 601XL
CHT info taken from test flight of 601XL | flycorvair

A comparison of why the spark plug is a poor spot to take CHT
Measuring Cylinder Head Temps on Corvairs. | flycorvair

More info to read, integrating inlet size with discussion
CHT part #3, Letters, notes, sources and inlets. | flycorvair

Another part of the same article
CHT Part #4 more notes | flycorvair

Spread sheet data taken from a 2850cc Zenith 750
CHT part #5, flight data from Zenith 750 | flycorvair

A Pegziar, 601XL and 701 from our hangar:
Corvair Cooling, Three 2007 examples from our hangar. | flycorvair

Something informative and slightly ironic
Cowling Inlet Area, marketing, accident stats, Darwin where are you? | flycorvair

An in depth study of a series of mistakes made on an eyebrow cooling arrangement on a Pietenpol
Pietenpol Engine Issue

Thank you, -ww.

 

Where is Rodney King [RIP] when we need him?


BJC

 

You are the go to guy for how to prep a DD Corvair for aircraft- we got it.

I am not disputing your intimate knowledge of Corvairs converted for flight, hard won over a couple of decades of experimentation with many examples. My point was about others having been working on Corvairs in the competition world for as long or longer and testing the limits of the design to a much greater degree. In the race world, weakness is usually uncovered quickly. Likewise, experience with many different engine designs helps one see different solutions to similar issues. You seem to act like all the knowledge on your site is somehow newly discovered. Hardly. Lots of others like Sam Elliott, Bob Sutcliffe, Ray Sedman and myself have known most of this since the the late '70s/ early '80s. We saw all the same broken stuff back then and had fixes for it. These guys are all very modest but smart engine guys and I don't say that casually about too many.

I've been reading your site since circa 2002 as well as Mark's since I had fond memories of working on these engines way back and building several road racing versions and had designed my aircraft around one. I personally found Mark's site more succinct, easier to read and more informative. I won't swing to your extreme comparing IQs. I am just saying that lots of other people know lots about the Corvair engine. In some areas, you might know more, in others you might not. I am just saying keep an open mind. It's fine to be proud of your passions and accomplishments but infromation is always taken to heart more readily when a smigeon of humbleness comes with it.

From my perspective, the Corvair was a pretty well designed production engine- light, innovative, reliable and it shouldn't be hard to convert it for aircraft use and have it last at 3000ish rpm and 120hp for 500-1000 hours. Kudos that you have many examples flying to prove it but is does not impress me as much as some of the race development projects others have done in years past. BTW, I am currently involved with an EFI project on very radical 300+ hp atmo Corvair so I still have my hand in there among many other projects.

With regards to the cooling comments, I wasn't sure what your point was. Mass has nothing to do with heat rejection rates, only the time to reach thermal equilibrium. I was being polite in how I formatted my response. In your article on CHTs, you've told us you have adopted almost identical limits to Lycoming so, like I said, no magic there since they both have aluminum heads and similar structural concerns.

So, in the end, getting back to the thread title, do you have a theory on what caused Mark's 3rd crankshaft failure?

 

Honestly, as a bystander, this thread has made me dizzy... like being pecked to death by chickens... I wish i could use the Corvair engine but it won't work on my plane, if I could I'd be going to the Corvair College... but since I can't I'm kinda glad I'm going with a VW. IMO :ermm:

 

OT but what was the cause of the Subaru Engine failure on this crash? N.J. man, 73, survives small plane crash - NY Daily News

 

Speaking of the title of this thread:

The distinguishing characteristics of Marks engine were

8409 GM crank
3100cc
Rear starter
Belt driven rear alternator
ww 5th bearing.

This version of the motor went 450 hours in Mark's KR-2s before the break. For comparison, the closest other plane in the Corvair fleet belongs to Mark's close friend Joe Horton. You can see Joe's plane here: Coast to Coast and back in Corvair powered KR-2S | flycorvair

and you can see a photo of Mark Joe and Dan at Corvair College 31 here:
The Cherry Grove Trophy, 2014 | flycorvair

I bring this up because Joe's plane now has about 1,000 hours on a nearly identical set up, in the same airframe, operated in much the same fashion. Joe and Mark are close friends and shared a lot of operational notes and styles. two planes is a tiny sample to make any conclusion from, but it does serve to illustrate a point.

Joe actually did about 400 hr with no 5th bearing, and then installed a Weseman Gen 1, which he has flown since. The difference in 5th bearings is the only large difference in the engines. My bearing has a regular straight bearing in the Corvairs#1 bearing position, which is normally occupied by a double sided thrust bearing, the position closest to the rear of the engine.

Perspective: if a crank breaks in 20-50 hours, I believe that it had an undetected flaw or previous damage, or a stress riser that was significant enough that nearly every crankshaft revolution, not just the high G stuff, was working it.

Conversely, if it gets to say 300-400 hours of typical operation, and then breaks, it seems that one of 2 things could have happened: Only a small fraction of the operations could have been in overload conditions, and these accumulated, or there was an event , like a prop strike , that initiated the break there after.

Marks contention was that it is not TV, it was bending loads from combustion working against the Corvairs very small fillets. He doesn't think the rear starter plays a role nor having the balancer and ring gear come off the engine in flight 100 hours earlier.

My only point is that in the years since the event, many other Corvairs of equal power output and some of higher loads, have logged a lot of hours, with fillets not much different than Mark's photos. Joe Horton's arrangement is nearly identical and had twice the hours, but it didn't have the same event that Mark's site refers to, losing the 7 pounds of balancer and ring gear off the back of the engine in flight. I had some thought that as it came off it had a moment where it put large out of balance loads on the crank, but that is just a guess. You can also read Mark's site in detail, and he will casually mention having the engine detonate, even on some take offs. I have rabidly warned people not allow that to happen, but not everyone see it that way. Even Lycoming states that intermittent detonation was a factor in crank failures.

Only one other Corvair crank has broken in the same position as Mark's and it came on an engine that had flown about 300 hrs but had a prop strike at 200 or so. That motor kept running because It had a Weseman bearing with the stock GM thrust bearing and no rear starter, so the motion of the broken part was restricted. I was standing right there setting the timing on the engine furring a house call, and I could hear it in the engine before there was enough vibration from it to notice. I confirmed it by wiggling the prop tip and looking at the timing mark on the balancer. Even though the crank was broken, the noise and vibration were below what a pilot with 300hrs on a normal engine would notice from the cockpit, but I am sure it would have become noticeable in a few minutes at power.

The nature of the debate between Mark and I boiled down to his belief that we were going to see a lot more of these, particularly on the 3000 3100 engines, and my belief that his break would remain a one of a kind or a low very probability event. with 38 months of hindsight, the record says my prediction came true, not his.

Anyone who looks at all the radius pictures on Mark's site and doesn't like them has two options: Buy a Weseman billet crank, or fly some other engine. Seems like a pretty simple choice. We have plenty of examples of working GM cranks, and the Billet cranks have radiuses that look magnificent by comparison, so a reasonable person could see the issue as closed with a billet crank. But the majority of builders still think the 8409 works fine for their build.

Before anyone gets to concerned that I find the same GM crank that was in Mark's engine acceptable for ones I build, Consider that Mark runs the Corvaircraft discussion group, it has dozens of people on it flying a GM crank, including Joe Horton, Mark's close friend, and he is OK with these people doing this, and he offeres no further warning than his 3 year old webstory. Condsider that Dan Weseman, who sells the billet crank, is also the largest source of reworking GM cranks. If he thought flying one was stupid, he would just sell Billets, but in reality he sells 6 or 8 times as many reworked GM cranks.

Since the thread has been around for years, and it has had 200 posts about what it might have been, many from people who have never seen a Corvair, perhaps it is time to wind up this thread with a few people willing to say what they believe it was, not what it might have been?

Even if anyone has some specific factor the believe, it isn't going to have much effect because no one is building an engine in the configuration Mark was using, and myself and almost all of the Corvair builders with planes operate with the exact same perspective that Mr 'Monty' described in post #203 on this thread. -ww,

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Ross, your comment:
" You seem to act like all the knowledge on your site is somehow newly discovered. Hardly. Lots of others like Sam Elliott, Bob Sutcliffe, Ray Sedman and myself have known most of this since the the late '70s/ early '80s."
I have met, bought parts from, listened to and spent a lot of time in conversation with both Bob Sutcliffe and Ray Sedman, This includes hanging out at Bobs house with him and his wife in California in the 1990s. I also spent a lot of time with Jeff Ballard after Bob sold SC Performance to him in 2003. I have known lots of people from high end land based Corvairs, None of those guys told me that they already knew everying I did with planes, 10 years before I did it. So far, out of land based racing Corvair people, you are the only one who has told me that you knew all of this first. You might be a very smart guy, but if I need a lesson in humility, I strongly suspect you have no skills to share.

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Mr Proppastie:

One of the things I wanted to do here was find out if I could provide enough information on Mark's issue 3 years ago to finally let this thread die. I understand that there are apparently lots of commenters here but maybe the Subaru stuff should be in that section? I probably doesn't matter as I suspect that this thread will be kept alive no matter what. I have pretty good tracking on the links to the stories on my site, and comparing them to the total visits on this thread daily, I strongly suspect the thread isn't drawing a lot of actual Corvair builders, it may mostly be people tuning in for a little drama.

 

I have seen closed threads I do not know how that is done. It does seem we are beating a dead horse.

 

I would like to see evidence and explanation of the failed crankshaft.
Why would bending occur at such low power?

Is bending a common cause of crank failure at low rpm? How does someone diagnose that either bending or Torsional Vibration occurred by examination of the part?
From the photo, how would the "beach marks" be different with Torsional Vibration?

In other words, I ask for evidence and proper debate about the cause, instead of debating who is smarter.

 

REPLY: WW, while I'm an avid reader of the things you write and have a lot of respect for your knowledge, I do feel that you are often somewhat unnecessarily abrasive with your replies. I find myself doing the same thing sometimes and often rewrite what I am saying....because I really don't mean to sound that way. While I'm sure Ross can defend himself, personally I consider him to be a wealth of knowledge and experience........just as I consider you to be. I'll tell you a little personal story if you are interested......use it or discard it as you will.

Once upon a time a fellow I worked with was a project manager who wanted a promotion to a higher grade. When the company refused to accomodate him, he took another job within the company (US Govt) and tried to call their
hand and force a promotion and return to his original job. Instead, I was promoted to the same level he was and given the job. This was at a time when our company was undergoing a major change in our computer operating system.
The job was as a Project Manager over spare parts and assemblies for weapon systems we produced. The spares were built by the same people who were building the complete systems and I had to rely heavily on integrating my needs
into their schedules. To keep this brief, suffice it to say that the fellow who left the job wanted it back and was going behind my back trying to discredit me and show that only he was capable of running the program. He set up a meeting
with his supervisor,my asst dept head, and myself. At the meeting he started talking down to me and when I rebuffed his language he was forced to apologize. Then he got into the meat of his accusations about something I had done.
After listening to his misassessment of my actions, I explained the need for my actions and the fact that they not only created no problem within the system,but actually solved a problem.....and the most embarassing point was that had
he looked at the particular +ERC coding on the new bills of material, it should have been obvious that their was no problem created. He left the meeting with his tail between his legs. Where am I going with all of this........
After the meeting my dept head took me aside and said that he was impressed that whenever challenged I always had my information together and was able to defend my actions.....but he thought it might be wiser to tone my rebuttals
down and allow people to save some face rather than me just "blowing them out of the water". To that I replied that "He called this Fxxxing meeting to try to discredit me and my attempts to improve this program because he wants this job
back and you can bet it'll be a cold day in hell before he ever tries it again". Looking back on that pearl of wisdom from my asst dept head........maybe he was right. I'm not saying there aren't times when someone needs a little
smack, but a lot more is to be gained if you choose your battles rather than try to defoliate the whole jungle. Sometimes the best thing to be said is nothing. I like what you write and hope you continue to be a force for Corvair aviation.
Dispeling the misinformation is important and we need the inside up-to-date stuff you can provide, so please take this in the positive vein it was meant to be.

 

Thank you for sharing your personal experience. There is a good message in there for engineers who think that being correct trumps everything else in business.

Been there, done that too many times before finally learning.


BJC

 

Usually it's fairly effective to just ignore the what and get all the why's on the table. If you meet too many people (excluding customers and suppliers) who ignore arguments and just have an opinion, time to find a job where your professional judgement is more appreciated.

Bets are often a great way to solve disputes in a reasonably amical way.

I haven't bought a bottle of Scotch for years, yet drink it every now and then

 

.Back to the thread....I broke a crank back in 2005 or so...non nitrided stock crank. I have been flying hundreds of hours since with my IFB front bearing design and no harmonic balancer ( reason for that) with no failure to date. I used to fly VWs where cracked and broken cranks were common. I trust my corvair conversion as much as any certified aircraft engine....enough to know they are mechanical and can fail. Last month inspected an 0360 that had less than 100 hours since 0 time leaking oil.....through a five inch crack in the case...hard to spot but had to be removed and torn down and replace the case. No guarantee that one won't crack either ....just saying. Do good maintenance and be a prepared pilot. That's my advise.

 

My understanding is that P-Factor is the biggest cause of auto crank failures in aircraft. P-Factor can bend a spinning crank until it fails.

The following is my opinion:

Aircraft engines need two bearings slightly apart to isolate the crank from bending forces imposed by the prop's P-Factor. Even if a prop hub is bolted on and an additional bearing is utilized, you have to wonder if the bolt location becomes a pivot point for a bending motion. Additionally, does the drive boss on the crank end wobble with P-Factor due to a solid bolt connection? Only a "captured" prop hub integral to the crank can mitigate the P-Factor to acceptable levels.

Dave P.

 

The last previous post made on this thread was two years ago. Here is an exerpt from one of the early posters who apparently had good intentions but poor communication skills. Putting aside any personality issues in the post (#36), the factual(?) statements are what I would like to address. I came across this while researching info for another current thread I started on Crankshafts.

Ok, so the poster made several declaritive statements. You would have to go back and read the whole thing (s) that he wrote, so I'm going to summarize.

1. He said that the fillet radii made no difference as a contributing factor in the crank failures.

2. He said that it basically made no difference what the composition of the metal was because the modulus of elasticity was about equal.

3. He said that a fifth bearing was insufficient to eliminate bending and only prolonged the failure timeline.

4. He said that the propeller blades needed to be properly clocked. (Is that accepted practice now )

5. He said that the billet crankshafts (with larger fillets) should not be purchased.


It is now two years after the fact. What is current thinking and historical use of these products telling us ?

 

I am pretty curious myself. I'm at the point of installing my prop on my Corvair and asked the same clocking questions. The current word from WW/Weseman is the prop indexing doesn't matter because we aren't going to hand prop it. They don't discuss a proper index due to vibration or bending loads. Is this because they tested and found no difference, or because they just don't know? I figure if their advice is to just randomly install the prop, then there's no harm in clocking the prop like the guy above suggests.

 

I pretty sure that there hasn't been a Corvair crank failure using the billet cranks and fifth bearing. As often, don't believe all you read from internet experts.

 

Like you, I don't know how "not hand propping" would relate to the bending during flight. Maybe they just mistook the reason for the question. I don't see how indexing could be worse than randomly attaching the prop, but wondered if others were following that mantra. Some times when people don't like the messenger they ignore something that might have some value. Not saying thats the case here, but I have to wonder if its a helpful idea or not.

As far as I am aware, the billet cranks and fifth bearings are doing the job.

 

My advice is index for hand proping even if you never intend to. There may come a day when you have no choice. I landed at a forrest service strip (Cessna 170) and decided to walk down to the lake (Billy Chinnok) for a swim. When I returned I discovered a dead battery (I Left the master on and those old rotating beacons ate a lot of power.) No human around for miles and before cell service. Training in a T-Craft saved the day.
I have seen one or two very scary situations where the pilot left the master on and had a dead battery. Tricycle gear and the prop coming up on compression at a horizontal attitude requiring leaning into the prop to get the needed leverage. Coupled with a throttle that was more than cracked, he fell out of the way as the engine roared to life. He got up,chased the plane down and manage to close the throttle Very scary. Oh, did I mention his kid was in the plane? Mouth agape I watched that one.
This one is somebody I knew. It was so close to a decapitation that the pilot now has a scar similar to a hare lip surgery except it takes in bottom of his nose.

 

Bingo....everything is balanced so I am not sure I understand the idea that prop position makes a difference, except for hand proping.

 

Without getting too deep into the woods on this and starting a spitting contest I will offer a bit of my thoughts on the matter of prop indexing. Some may be surprised to learn of my take on this.

First ... I have no plans to ever try to hand prop my Corvair. Can it be done? Likely it can be but it is an electrically dependant engine (both points & electronic ignition) so if the battery is dead, hand proping is not an option. Even if the battery has enough power to run the engine hand propping with the short 54" blade & the firing pulses so close together (120º) seems like an injury waiting to happen. Still ... if it had to be hand propped it doesn't have to be set on number one cylinder as there isn't an impulse coupler and the ignition advance doesn't retard for starting. So there are a few options as to where the prop could be spun from.

On Dan Weseman's site he gives a few things that one can do to help the crank live a long life. No he doesn't mention indexing but he does list these (https://flywithspa.com/product/corvairbilletcrank/)

• If the crank had been Nitrided
• Crank has been reground with attention to detail and as large a radius as possible
• If the crank has a 5th bearing installed
• The engine setup for a front starter
• Wood prop dynamically balanced
• Ignition timing set below 30 degrees , use 100 ll only, and a good known carburetor set up (MA-3, Stromberg and Possibly Ellison) to eliminate any chance of detonation

I do use a mix of 100LL & Mogas at times but other than that I follow all of these recommendaions. To this I added smooth flight i.e. no snatching the plane about when yanking and banking, and indexing the prop 90º to the front crankshaft (#6) throw. There are a few posts earlier in this thread that mention the effect that the uneven pull of the prop will have on the front throw if the prop is aligned with the "U" shape of it. Do I believe all of this? Truth is I don't know if it does make a difference but it didn't cost me any money to index the prop and it seems really smooth. It has been the way from the beginning so I have no idea how it would feel if it wasn't indexed.

So put me down as an indexer ...

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
143.7 hours / Status - Flying