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ROMCO Manufacturing
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#24 Can you "Convert" my "Six Bolt" drive hub to "Single Bolt"

Yes we can, it is one of the Coolest Set-Ups you will ever see.  Please hang with us for the next couple of pages, this is not a simple situation, there is a lot to talk about.

There are only a couple of reasons to be talking about doing a Single Bolt Conversion to your existing engine.  It is not about saving money it is about problems, problems with vibration or problems with the hassles of drilling and changing props. 

We have all experienced the hassles of messing around with the Six Bolt prop mounting system, both at home in the shop and out at the flying field on a nice pretty spring day.  This system works and would appear to be a heavy duty set up, but in fact it is about the worst situation possible and it is obvious if you really analyze the situation.

The one main ingredient that is missing in most six-bolt set-ups is the "Pilot" to guide your prop and spinner on centerline of the crankshaft.  The 3-W engine has a six-bolt drive hub and is the only engine on the market at this time that has the pilot for proper mounting.  The basic rule of geometry is to get everything running in perfect alignment so that it will not "Vibrate".

Six loose screws through a hand-drilled prop are not going to make things line up, it's only a "Fair" situation at best.  The next worst situation is an engine that uses a single Hex Head Bolt to hold the prop on, it is a lot less hassle but just about as bad.  One loose fitting bolt with no pilot guide for your prop or spinner is not a good situation on its best day.  We have seen these types of drive systems cause problems that even the user did not understand.

We are committed to "Precision Machine Work" here at Tru-Turn, so our opinions about engines and engine drive hubs are more than just an opinion, they are the result of experience.  We machined the very first one-piece single bolt conversion hub that was ever made, right here in 1986.  It was a result of trying to solve a problem with an A&M six bolt drive that was causing major vibration.  The six bolts were not concentric to the hub and the hub was not concentric to the crankshaft rotation.  This happened to be an engine that was to be used in the "Tournament Of Champions" that year.  The Single Bolt Conversion worked great and the airplane wound up in the Winners Circle.


The following sketch will show you the single bolt and how it is mounted.  It is an addition to your engine that requires some consideration due to the fact that these conversions can run from $ 59.95 up to several hundred dollars depending on your situation.  The single bolt conversion will not run true if it is mounted on something that is running out, so mounting it becomes "Very Important".











Some engines that use the six-bolt or hex bolt system have a considerable amount of run-out as mounted from the factory.  They do not hold close tolerances and they do not machine the drive hub after it is mounted to the crankshaft, therefore run-out occurs and vibration becomes a factor to the overall well being of your airplane.  When we machine your engine drive hub and mount a "Single Bolt Conversion Hub" on it, all of these things are no longer a factor.  You have a true running hub, a "Pilot" diameter to mount your prop and spinner on and you do not have all of the hassles of the multi-bolt drive.

The only bad news about this conversion is that in some cases you will have to send us your engine.  The drive hub must be prepared for the conversion hub, mainly because most drive hubs do not have a way to mount the hub or they do not run "Tru" enough. Most engines run around $ 45.00 for machine work and the conversion hubs run $ 59.95 for the small 3/8" type up to $ 99.95 for the big, extra long " hubs for the big engines.  They are available in short or long shaft and in 10mm diameter as well as the more popular 3/8", it all depends on what you are trying to do and what you are trying to do it with.

You will see these conversions on "Unlimited Racing Planes", I.M.A.C. Planes, T.O.C. planes as well as just every day sport flyer's airplanes.  Sometimes you will see single bolt conversion hubs made by "Other" companies, but you will never see any other brand made as well as a Tru-Turn Hub.  Tru-Turn Hubs are machined from 17-4 PH Stainless Steel in the H-1075 Heat-Treated condition for maximum strength, absolute concentricity and corrosion resistance for use around any type of fuel or cleaner. They are 100%  C.N.C. machined to exacting tolerances of less than .001 inch, unlike other "Look-Alikes".

You will not find better "Quality" or "Service" anywhere! Just give us a call and we will walk you through the details, give you a firm price, and get you going quickly.

If you have more questions or do not see what you are looking for, just "Call" or "E-Mail" us and we will do everything we can to help you.

 Fly Safely, It's More Fun!

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