Yes, Pietenpols do need 5th Bearings..


Dan Weseman was speaking to a guy who wanted to build a Corvair powered Pietenpol.  He told Dan that it didn’t need a 5th Bearing. Dan told him he was not correct about that, that is was our joint policy that Pietenpols do need 5th bearings on their Corvairs.


Funny thing happens next: Guy who has never built a Corvair, nor a Pietenpol, tells Dan, a guy who has about 1,000 hours of Corvair time in 10 or 12 different Corvair powered planes, works with this stuff every day, is the closest of friends with me, and has his finger on the pulse of the Corvair world, that Dan is wrong, he doesn’t know what he is talking about.


I don’t have the imagination to understand how a guy with essentially no experience, tells the guy with 15 years of hardcore experience and full access to all I know after 28 years, that he is wrong. That is beyond my comprehension. So just sticking with the direct question: Yes, Pietenpols do need 5th bearings, period.



Above, Bob Lester with his Corvair powered Pietenpol at CC #39 in Barnwell SC. The plane is now approaching 900 hours. Ever since hour #1, the plane has had a 5th bearing on it. Before this plane, Bob had a Corvair powered KR-2, and experienced a crank break in it before the advent of 5th bearings. When it came to his Piet, he was not going to gamble nor rationalize; It has a first class 2,700cc Corvair with a 5th bearing. The plane has modest instrumentation and an ‘industrial’ finish.  Bob understood that actually managing risk effectively means a solid motor comes before paint and radios. 


I’m not sure who is promoting the idea that some Corvair powered aircraft really don’t need a 5Th bearing, but let me be really clear: Every Corvair powered plane needs one, period.


I have heard a lot of rationalizations on why Pietenpol do not, but these opinions are mostly based on very old experience, and I can easily name 4 Corvairs without a 5th bearing on Pietenpol that have fractured a crankshaft. Fortunately, no aircraft were destroyed nor anyone seriously hurt, but no one should gamble that he can become the 5th guy on that list, because he could easily become the 1st guy on a different list, a title  which is posthumously awarded.


Here is something of a wake up: I go to Colleges to teach people how to build the best motors possible, and how to exercise good judgement. I do this for free. When I drive there, I take a 31 year old truck, worth about $1,500. The 3,000cc Corvair in my plane cost  5 times this amount of money to build. Although my work earns me a “McDonalds assistant Manager” level of income, I don’t cut corners on aircraft engines to save money.  Just like a Pietenpol, my plane has a passenger seat, and the person getting in it can read the FAA mandated sticker saying that the plane does not conform to certified standards, but the passenger has a rational expectation that the builder and pilot was intelegent enough to make a $1,050 investment in safety.


When a guy comes to a College driving a pickup truck that litterally is worth thirty five times as much as mine, and he wants to cry poverty about the $1,050 cost of a 5th bearing, I may look like I’m paitently discussing it with him, but that is just an illusion provided by my first class anger management training. In reality, I think he is making a very poor decision. In my experience, there is no correlation between ability and willingness to pay.  I have seen an awful lot of people who drive $50,000 vehicles and live in $500,000 houses claim a $1,050 5th bearing is too expensive. Perhaps these people need to look into the rising cost of final expenses to understand what they can’t afford.


Lots of people say “BHP didn’t have one” or “No one had one before 2003” My response: Great, go back to the first chapter of my book and read the sentance that says “I reserve the right to get smarter.” Look at it this way: Does anyone think at the FAA will accept an anual inspection on a certified plane that didn’t comply with any AD written since 2003 because the owner says “It was considered airworthy in 2002 before that AD was issued.” Really, run that past your FSDO and let me know how that works.


In the greater Pietenpol community, theyre are many people who like old wives tales and don’t like airworthlyness. At Brodhead, the Pietenpol gathjering, I had one of them actually stand up and say to me that I was “Ruining Pietepols” by teaching people about CG issues on them. He stated “Some people just want to fly low and slow and not worry about that stuff.”  I told him he had just publicly advocated running out of altitude, airspeed and ideas all at once.


I can’t help people like that. I can’t help people who think that a $2,000 paint job comes before a 5th bearing. I can’t help people who spend $1,500 on wire wheels but say things like “it will be alright.” In the words of the most famous guy from my Florida town; “Say you will be alright come tomorrow, but tomorrow might not be here for you.”



Are you listening? Oshkosh 2016: Lynn Knoll, flanked by his sons, brought his 2700 cc Corvair/Pietenpol to Airventure. The plane took 12 years to build. It had 60 hours on it, and it did not have a 5th bearing.  After congratulating them on completion, I took them aside and flatly and plainly told them they needed to go diretly home and install a $1,050 Weseman Gen I 5th bearing. It would take one weekend. His sons thanked me for this and said they were certianly going to do this.


The following spring, they called to say the plane now had 200 hours on it, they never put the bearing on, and now it had a broken crank. Besides the fact it now had $3,000 worth of internal engine damage, their dad flying the plane had just barely made it back to the airport. It had been a very close call. One of the son’s said to me “You were right” casually. He offered that his dad didn’t want to spend the money, and it was his plane. I wasn’t intrested in his addmision that I was right, that was evident enough, and I really wasn’t intrested in the rationalizations. I my book, you get one dad in this life, and if he is too cheap to take care of himself, you do it for him.


Think that was the last time I’d have that discussion? At Corvair College #41, Keith Goff had his new Corvair Powered Piet on hand. It did not have a 5th bearing. I privately said to him that he needed to correct this, Dan and Rachel were right there, and he could directly order it on the spot. When he offered “It was on his priority list” I shared the story of the Knoll Pietenpol, and told him that he was in the process of making the exact same mistake.


Standing beside me when I said this was Pietenpol builder Terry Hand. I pointed out to Keith that in the last 18 months, both Terry and I had lost our fathers, so neither one of us was casual about people taking unnecessary risks, particularly if it involved someones dad flying a plane, or someone like him, who is a dad.  I said that either Terry or I would have taken anyones serious advice to protect our fathers, and I didn’t understand anyone who was going to ignore what I had to say about this to save $1,050.


Please read: “If only someone had told him……”



14 Replies to “Yes, Pietenpols do need 5th Bearings..”

  1. Great stories William, and thanks (again). Incidentally, my wife Vicky (non-pilot and non-aviation person who for years worked as a secretary in the Environmental Health and Safety Department of Texas Tech University) is a big fan of yours, to the extent that even SHE has no clue why so many people are impervious to the risk management doctrine and procedures that you consistently and repeatedly insist upon. Dig it man- She doesn’t even fly yet she gets it! As for me (and I’m far from being any kind of shrink), though I’ve learned a few things from the little bit of reading I’ve done on Personality Disorders in the last year, I’m still drawing a blank on what’s going on in these folk’s brains. I’m just thankful that I DO get it, you know? (Vicky thanks you for the hearing protectors you let her use during my engine run on 11/12 by the way.) Take care William. See you next time

  2. William what about Pat Green’s Pietenpol? Been flying for 40 years now without the 5th bearing. As you know him very well and your visit with him to add some of your parts basically to have a starter not a 5th bearing.
    Any comments?

    1. Dennis,
      The plane has been flying 40 years but not the engine. I don’t know how many hours the engine has on it, but it was redone, so it may not even have the same crank in it.

      Pat is a good cat, and I was glad to make the house call, but that was many years ago. Just because I look at a persons plane, it doesn’t mean I offering an endorsement of their entire flying program.
      There were a number of original corvair powered poets that flew a long time without 5th bearings, but the track record of cranks that were later reground by “Race Car” shops is very poor by comparison. An implication that because his plane got its airworthiness cert in 1977, that it is safe today is a false conclusion.

  3. Yes, but rather than only admonishing such people, why not provide a good technical explanation as to how a plain crank with no 5th bearing would/could fail? The kind of explanation that Mike Bush provides in a respectful and understandable style would be great. That would be refreshing and much appreciated, especially if one doesn’t spend the time going through all of the archives to extract the information if it is in there?
    Thanks for the articles, they at least provide a prod for we poor creatures to research.

  4. Mike, mr Bush is a paid expert witness for sale to scum liability lawyers, it says this on the first page of his website. I suggest that you find another place to complement him.

    We have been telling people fro 12 years to use a 5th bearing because it takes the propeller bending loads off the crank. My website has countless articles on this and I spent 10 years covering it. If you want to read about it search crank issues on my page.

    I explained it in detail, I said it nice for 10 years, I’m done being super polite to people who will not spend a small fraction of their budget on a safety item. It’s like people who buy an expensive motorcycle but budget nothing for a helmet.

    If you want to reply, please include your last name, it is respectful if everyone gets to know my name than I should know yours.

    1. Yes, my name is Michael W. McKosky.
      We have talked before as you may recall.

      When I mentioned Bush I had in mind his explanation, in a recent article of his, of the nature of plain versus roller-element bearings in engine crankshafts. As I recall he pointed out that the plain bearing would best distribute the impact loads of the pistons, and that the rolling element bearings would have point or line loads and be more stressful to the bearing surfaces.
      His explanation did not suggest that someone who did not know was a moron, but maybe ignorant.
      His explanation was, in that sense, respectful.

      I have no idea of Bush’s relationship to legal matters. This may be of great interest and concern to someone who has been confronted with legal issues, and perhaps has developed a paranoid stance to such things.
      I am not in that position, so I prefer to accept Bush’s attempts to educate.

      Yes, it is my impression that the 5th bearing handles the bending loads off of the 4th bearing, the loads probably due to P-factor, amongst others.
      I did not get that technical insight from your writings, but from other sources. However, the comments made in your writings did elevate my awareness about the use of a 5th bearing.
      I do not have hands-on experience with engines, and having a “book-learning” understanding is not in itself enough. So, your experience provides, to some extent, that missing element for such as I.

      It is simply, in my estimation, a damn good idea to install a 5th bearing, and worth the several thousand dollars investment.
      But only after having acquired some insight as to why.

      So, why did the smaller non-aerobatic aircraft suffer crankshaft failures?
      What was the failure mechanism?
      What is the insight?
      Are the loads from the propeller enough to snap a crankshaft on a small aircraft? Or are there other more likely reasons?

      The matter of respect to the audience seems to me to be important.
      In my few discussions with Dan Weseman of SPA, I always got the impression that he was sincere in wanting to convey technical information and support to his customers.
      At no time did he bad-mouth anyone, nor did he confuse the issue with personal problems or air grudges. He just straightforwardly tried to serve his customers, of which I am one.
      He is a professional and an adult. He certainly gets my respect.

      Mike McKosky

      1. This is Mike McKosky, again.
        Got to thinking about why a Pietenpol aircraft, or any non-aerobatic plane etc., might need a 5th bearing anyway:

        The engine/crankshaft/prop doesn’t care if the plane is non-aerobatic, or if the pilot is a mild-mannered church-going conservative; if the pitch angle is non-zero and held steady, the prop can still go through one hell of a beating as the blades passing on either side undergo relative pitch changes.
        The shaft would experience bending forces every revolution! The shaft may not break right away but fatique would take it’s toll after awhile, eh?

        If this is not correct, or if further insight is available, please share.

      2. Mike McKosky, again,
        I just read Langford’s work, and he does mention P-factor and several other causes, and gives some good insight into various details, especially radius dimensions and condition, and nitriding, etc. Since I have not gotten around yet to installing the crank I will be able to look at my crank in somewhat more detail.
        Quite a nice piece, will re-read and try to digest it.

      3. Mike, if your crank was processed by Dan Weseman, it has all of those issues already accounted for. Mark Langford’s comments are not new issues or anything ‘discovered’

  5. Thanks for the article. I was under the mistaken impression that Pietenpols might not need a 5th bearing because of the slower speed of the plane: that the broken cranks occurred when Corvairs were put on faster planes. I should have listened closer when I attended my last Corvair college and read closer about stress risers.

    A 5th bearing truly is a matter of risk management and cheap insurance against broken cranks, so a plane keeps flying under power and keeps one’s butt safe.

  6. I didn’t know the 5th bearing thing was even a discussion point anymore. I figured it was a given –
    and not just from you and Dan, but every respected voice that knows Corvair. Not sure why someone wouldn’t want an engine they they are building to be as reliable as possible. I seriously doubt someone buying an off-the-shelf product powerplant would be ok with manufacturer having a selling point like this:

    “It doesn’t have the latest improvements in reliability, but it will save you some bucks. There has been a correlation between this configuration and broken cranks, but chances are that it’ll be fine. Just don’t push it too hard.”

    I don’t think the technical explanation for a potential crank break without the 5th bearing needs to be repeated here again – is not hard to find. But Mark Langford’s page hits some of the highlights regarding 5th bearing and other considerations. His an independent voice and bases his conclusions on his own experience and observations:

    1. Kevin,
      Thanks for your perspective. The only footnote I’d like to add on the link to Mark Langfords notes is they are as you mention, based on his personal experience, which wasn’t indicative on more mainstream planes and operations. He stopped flying Corvairs six years ago and at the time predicted that there would be a rash of crank failures on Corvairs with 5th bearings. This never happened, his prediction was based on seeing things through his lens, not the bigger picture that Dan and I see every day.

  7. I’m commenting too much today….I know. But you need to have a simple safety test, multiple choice will work, that includes these basic things you’ve very generously drummed into the heads of anyone who opens all your emails, reads, thinks, and then files them for future reference, buys your manuals (I admit I bought ed. 1 and 2, but not yet 3 until I actually start doing something). Typical subjects of questions: 5th bearings, owning and using a timing light, owning, reading and re-reading the manuals, pulling head out of bowel hole, carb heat, crank shafts, forged pistons, correct spark plugs, flex lines for header tanks, US calibrated torque wrenches, properly applied crank extensions, cam gears, proper crank washer and orientation, pre-oiling, never start w/out a prop, build checklist and log, leave the studs in the case if they aren’t rusty or have tool marks on ’em, don’t bead cases because the sealing surfaces will be ruined, Rotella oil, gentle and precise install of pushrod tubes/0-rings, proper OP relief valve installation and adjustment, ARP rod bolts, AN fittings for all lines, SPA carbs rebuilt by specialists – eschewing all slide types, your latest distributor, oil pan, oil cooler, recommended alternator, and starter…..this is just residual info in my head without consulting the files or manuals….just common reading retention of your emails…You’ve made it so it is NOT rocket science….no more excuses for any of us, experienced or not. Should be mandatory before College acceptance and maybe parts purchase, except for manual. Seriously. Definition of ignorant out here in the country is that you’re putting at least 80% of your energy into not learning the valid information under your nose. On purpose.

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