Bar Humbug (oz13687)


Bar Humbug (oz13687) by Ron Chernich - plan thumbnail

About this Plan

Bar Humbug. Model aero engine.

For either Diesel or Glow. Capacity .09 ci (1.48 cc).

Designed by Ron Chernich. CAD by Mike Rehmus. Published by MBI (Motor Boys International).

For more details, see

Quote: "Mention of bar-stock engines brings to mind a design I did four years back at the request of Mike Rehmus of Model Engine Builder magazine. The design drew on the observations arrising from the review of Beginner engine designs series that ran here some years ago. Basically, I wanted no milling, no thread cutting, no engineering at watch-making scale, and piston aside, one that required no close fits over a deep bore length. Then I also wanted an engine that was not unattractive, yet did not look like a Midge, or Little Dragon clone.

Mike added to the restrictions, requesting (more like demanding, actually) that all machining should be capable of being performed on table top machines like the excellent little Sherline lathe. This (pun alert) turned out to be remarkably difficult. Three prototypes were made and anything that I had to devote more than casual precision to was redesigned (which is why the published version appears slightly different to the prototypes).

The MEN style CAD drawings were handed over to Mike who re-drafted them in 3D CAD. The plans and first part of a serialization showing detailed construction have now appeared in issue 21 of Model Engine Builder.

At the time, I made arrangements with my pal, Roger Schroeder, to have castings made for the crankcase and backplate for those who wanted a more 'traditional' engine. Roger looked at the three head bolts and proposed a triangular Reuleaux head, just to be different. We dubbed the result the Custom Humbug. There is some not entirely tongue-in-cheek justification for the head shape. The front of a model engine cylinder receives more cooling than the rear due to the prop blast and turbulent flow behind the head. High performance engine designers worry about distortion cause by differential thermal expansion, and hence increased friction this causes..."

Direct submission to Outerzone.

Quote: " I am very fortunate to have had both a diesel and glow example built by Ron Chernich, given to me when I bought some motors off David Owen many years ago. I gave the glow version to one of the original Motor Boys International – Ken Croft. The diesel I made a reed valve for and used a Mills venturi, and it ran superbly. Ed,"


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Bar Humbug (oz13687) by Ron Chernich - model pic

  • (oz13687)
    Bar Humbug
    by Ron Chernich
    from Motor Boys International
    0.09 cu in
    Engine Diesel Glow
    clean :)
    complete :)
  • Submitted: 08/03/2022
    Filesize: 356KB
    Format: • PDFbitmap
    Credit*: EdHolly
    Downloads: 837

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User comments

Hi there having just down loaded the set of plans for the humbug I.E. RCBS1 i have discovered there are two sheets of the plans missing from the download which are sheets 7 and 8 which is a bit of a disappointment, as i was hoping to build this one and without those two sheets makes things awkward
Nigel Bujna - 29/10/2022
I can se no width dimension for the con rod
Roy Popejoy - 01/08/2023
I see it on sheet 2 because it has a circular section. pit
pit - 01/08/2023
Ten months on and the two missing sheets are still missing, I wanted to build this engine, won’t be able to now.
Baz - 20/09/2023
This is all we have. In the last ten months, we have not added any more pages. Neither indeed have you. Just saying.
SteveWMD - 20/09/2023
Download Motor Boys planbooks - there are only 2 freely available as far as I know. Neither book contains RC BS-1 or Bar Humbug but in total there are approximately 25 to 30 or more plan sets on vectorized pdf "pages" which can be imported into a cad program and worked with.
I did a quick scan of the plan set - parts shown appear to be sufficient to build the diesel version.
You are right in that there are one or more missing sheets - however they are probably for the carburetor and associated details required for the 2-stroke version which is implied by the glow plug detail shown on the general arrangement.
If so they would be redundant for the diesel version.
Too many guesses - go to the Motor Boys website and ask them which end is up - asking Outerzone is not appropriate at this point - go sideways grasshopper.
KW - 21/09/2023
My Bad - I just noticed the carburetor mounted on the engine back plate for a diesel version of this engine.
So - Plan A - adopt a carb from another engine plan set.
or - Plan B - email Motor Boys and ask for clarification.
or - Plan C - do both Plan A and B in coordination with each other.
Again - Outerzone is not the place to query this plan set - go after Motor Boys or find a credible knowledge source or wing it on your own - your choice.
KW - 21/09/2023
A good resource and starting point is the Model Engine News website
The site is up, but frozen in time. As far as I know, the Motor Boys, themselves, are all deceased.
Jan Novick - 21/09/2023
When I ran the diesel variant made by Ron Chernish - I used a MILLS venturi and needle valve assembly - that arrangement is available on the MILLS 1.3 plan. It fitted perfectly. Sorry to not add this before - but just seen the comments now ... regards .. Ed Holly
Ed Holly - 25/10/2023
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