# Elmer's Comber Rotary Engine



## Inky Engines (Sep 5, 2012)

After a partial rebuild during the last week I'm now happy with the way this engine runs.

To me this was always an engine that should run fast.  As originally built, it ran, but lost lots of air through the front bearing - I tried fitting carefully sized bronze bearing bushes, but to no avail - it still needed lots of air to run reasonably fast (10 - 40 psi), and still lost lots of air through the front bearing. I was convinced that the piston, conrod and bearing fits were reasonable and the airways were clear, but the engine as built was clearly not efficient.  I noted that on arnoldb's second build of this engine he 'seriously' increased the bore - I did not wish to rebuild the engine to this extent, but found that I could increase the bore diameter by 2mm, giving approximately 50% increase in piston loading with the same size cylinder block - I also increased the diameter of the airways slightly.  The improvement was amazing - the engine now ticks over on as little as 2 psi - at 40 psi it screams round at 1800 + rpm with very little air loss through the bearing.







[ame]http://youtu.be/IhpozqRRgx4[/ame]

So next I'm intending to have a go at Elmer's Geared Engine - that's after a brief intermission to get some 'jobs' done around the house and garden!

Kind regards

Geoff at Inky Engines


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## rhitee93 (Sep 5, 2012)

That is pretty slick looking Geoff.  Nice work


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## nemoc (Sep 5, 2012)

Geoff,  That's a beautiful engine and a great runner!

Craig


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## Swift752 (Jan 21, 2013)

Hi Geoff:  My Comber BARELY runs. And I do mean barely. Tell me.  They say to make the rollers touch  the cam but at which position?  Vertical or horizontal?  If touching at vertical then there is slop at horizontal. LOTS of slop. If touching at horizontal, then it won't turn as at it locks up in the vertical.  I guess that means my cam isn't right?    Please help.  And also, is the bore increase REALLY needed?  What bore did you use? I see you threaded the cam followers onto the conrod ends.  I used 2-56 set screws and plan to then solder once the correct adjustment is found. Thoughts? THANKS! Really appreciate the help.  Swift752  (Bob)


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## vascon2196 (Jan 21, 2013)

Inky Engines said:


> After a partial rebuild during the last week I'm now happy with the way this engine runs.
> 
> To me this was always an engine that should run fast.  As originally built, it ran, but lost lots of air through the front bearing - I tried fitting carefully sized bronze bearing bushes, but to no avail - it still needed lots of air to run reasonably fast (10 - 40 psi), and still lost lots of air through the front bearing. I was convinced that the piston, conrod and bearing fits were reasonable and the airways were clear, but the engine as built was clearly not efficient.  I noted that on arnoldb's second build of this engine he 'seriously' increased the bore - I did not wish to rebuild the engine to this extent, but found that I could increase the bore diameter by 2mm, giving approximately 50% increase in piston loading with the same size cylinder block - I also increased the diameter of the airways slightly.  The improvement was amazing - the engine now ticks over on as little as 2 psi - at 40 psi it screams round at 1800 + rpm with very little air loss through the bearing.
> 
> ...


 
Geoff..thanks for sharing this. This engine is on my list! I'm going to try this engine per the original plans first to see how it goes...I built the geared engine a few years back...to this day it still draws a crowd at engines shows. Anyway..Elmers Engines are awesome.


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## lensman57 (Jan 21, 2013)

Hi Geoff,

Great looking and great running engine, thanks for sharing.


Regards,

A.G


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## GailInNM (Jan 21, 2013)

Swift752,
Two things that I know of could cause your problem. One of course is the cam is cut incorrectly as you know. The other is that the cam is mounted too low compared to the cylinder bearing.  As designed, the cam ring is offset 0.25 inch so if you measure from the bearing center to both the top of the cam and the bottom of the cam there should be 1/2 inch difference.  If you are using the plan dimensions you should measure 1.063 from the bearing center to the bottom of the cam and 1.563 from the bearing center to the top of the cam.
Gail in NM


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## Inky Engines (Jan 24, 2013)

Bob

Sorry to hear of your difficulty with the Comber engine.

I can only agree with Gail re the probable cause of the problem - the roller/cam ring clearance should be constant in any position.   How did you mark out/cut the cam ring?  

As to the bore diameter, for me increasing the bore from 9.5 to 11.5 mm brought about a significant improvement in performance - I believe others have made the engine work well using the original spec.

One of the followers on my engine is silver soldered to the Conrod - the other is threaded as you note - I'll solder this too in due course.

Good luck with the build - this engine is one of my favourites.

Kind regards

Geoff at Inky Engines.


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## Swift752 (Jan 25, 2013)

Geoff:


I glued the drawing to some hard thin cardboard and using a #11 Xacto blade to carefully cut it out after I'd glued it to the metal.  The blade left a mark to follow. I put the metal in a 4 jaw and after boring a large hole in the center, I used a boring bar to get close to the marks then used an oscillating drum sander to get the final shape. Frankly, I couldn't make much sense of the directions and me with a major in math! Ideas? Thanks. Swift752. Bob


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## Brian Rupnow (Jan 25, 2013)

The engine build is superb. Congratulations!!! I really liked the background music. Do you know what the name of the music is and the artist performing it?---Brian


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## GailInNM (Jan 25, 2013)

Bob,
The problem may be in your printer/copier that you used to make your drawing that you cut out.  The  X and Y scaling on most printers that use inkjet technology is seldom that same.  On early printers and copier it could vary by up to 5 percent. Modern ones still vary up to 2 percent in some cases.

The Coomber cam only has a difference of 1.8 percent in the 2 axis so it is quite possible that cam is incorrect.  You should be able to check your cam by measuring the inside dimensions in both the horizontal and vertical directions.  The vertical dimension should be 2.625 inches and the horizontal dimension should be 3.675, a difference of about 0.050.   The absolute dimensions are not as important as long as they are close, but the difference is important.

Once we find where your problem is, then we can solve it.

If we get into methods of making cams or other things we should probably start a new thread and let Geoff have his thread back.

Gail in NM


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## Inky Engines (Jan 26, 2013)

Bob...

Again, I can only agree with Gail, I strongly suspect that inaccuracy has crept in in the glued template method of producing the cam profile.  I considered marking the cam out in the way described by Elmer, but was not convinced that I could ensure the necessary accuracy - I eventually milled the profile on a rotary table using calculated longitudinal table movements at each point of rotation - a little laborious (with my choice of 180 2° increments), but it did produce a smooth, and I believe accurate profile.


Brian...

I'm pleased you like the video music - its called Shetland and is from the Apple iLife jingles folder.

Kind regards

Geoff at Inky Engines


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## Swift752 (Jan 28, 2013)

Geoff:

I checked my printer made drawings against the shown dimensions. They were good.  I redid the cam in the same way.  Glued the print to the metal and finished w/ a half round file this time.  I think its better but very difficult to say with certainty.  A place to start. If you used the 11.5mm piston did you do it in the original dimensioned block?  It seems that would be VERY tight especially with respect to the passages.  Bigger block? How much? I appreciarte all the help you and Gail are giving.  I've done two cylinder reversing tug boat engines, Atkinson Cycle and Hit and Miss but this one is tough.  Swift752   Bob


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## Inky Engines (Jan 29, 2013)

Bob

You certainly didn't waste any time in remaking the cam!  I presume that you don't have access to a milling machine and rotary table.

I did squeeze the 11.5 mm bore into the original block size, it is tight and the passages do need to be repositioned, but it will fit - the idea came from the excellent 'another Comber' build log of arnoldb on this forum - although he increased the bore to 16mm which obviously did require a resize of the cylinder block.  

Notwithstanding the above, I don't believe that your described problem would be solved just by increasing the bore diameter - my engine did run at the original bore size, it just felt inefficient demanding much more air than any of my other Elmer engines, even after being well run in.  I think success lies in producing an accurate cam profile and mounting it accurately and squarely in relation to the cylinder so that there is no binding of the cam and followers.

Good luck

Kind regards

Geoff at Inky Engines.


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## Swift752 (Feb 3, 2013)

Geoff and Eric:  Thanks for all the help w/ the Comber.  I remade the cam by pasting the printout on the metal (after I assured it was accurate in size) and CAREFULLY hand filed it.  It runs now.  Boy does it need a LOT of air!  Nowhere as efficient as say the Elmer #49, which I love. But it does run at 20 PSI and on high pressure really tears.  I'll  have to put a tach on  it. Funny little engine. I did increase bore by 20% and the next size up drill from 1/16" for the passages which I'm sure had to help.  It's easy to see why it never became popular.  While I certainly don't know, I'd suspect that it simply could not produce much usable torque in a bigger size, but that's just a guess. Again thanks guys.  Much appreciated.  Oh Geoff, to answer your questuion.  I do have a mill and a rotary table but I have NO idea how to go about it. I could see CNC as a real way to do it, but alas I'm just a self-taught amateur so no way. Just me and my trusty old large half-round file and a LOT of patience for sure.  Take it easy guys. Swift752   Bob


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## Swift752 (Feb 14, 2013)

Geoff and Gail:

I thought I had posted a thanks for the help but I don't sdee it.  Sorry for the delay.  I got her running after a very painfully slow hand filed cam was made.  She goes fine now.  Thanks for all the help.  Very much appreciated. Swift752  Bob


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## GailInNM (Feb 14, 2013)

Bob,
W understand.  The excitement of  a new runner makes me forget things too.  Congratulations.  On to bigger and better things.
Gail in NM


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## Lou Costello (Apr 21, 2019)

Hi I’m just getting started with my comber engine,I can’t figure out that cam,is there a more practical way of doing it with a rotary table and digital readout? This is my third engine,a single cylinder and a twin cylinder double acting,for some reason I can’t get my head around that cam drawing from Elmer, Any ideas? Thanks


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## Swift752 (Apr 21, 2019)

Lou:  Bet you get lots of "problems" wrt ur name. Anyway, my Comber runs like a scalded cat!! If u read all my posts you'll see how I did it.  Too much to type.  Call me at 937 272 3579 any time.  Retired and I'll do all I can to help. I've built 50 engines!  All run. Also  a Hit and Miss and an Atkinson gas engine.  Be glad to talk and send photos.   The Comber isn't for beginners. Esp if not a professional machinist.  I'm self taught all the way.    Just yell.  Even now wud be fine.  Bob


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## Lou Costello (Apr 21, 2019)

Swift752 said:


> Lou:  Bet you get lots of "problems" wrt ur name. Anyway, my Comber runs like a scalded cat!! If u read all my posts you'll see how I did it.  Too much to type.  Call me at 937 272 3579 any time.  Retired and I'll do all I can to help. I've built 50 engines!  All run. Also  a Hit and Miss and an Atkinson gas engine.  Be glad to talk and send photos.   The Comber isn't for beginners. Esp if not a professional machinist.  I'm self taught all the way.    Just yell.  Even now wud be fine.  Bob



Thanks Bob,the Comber will be my third engine,I’m a retired toolmaker (10yrs now)who mainly restores vintage British motorcycles.So this is kind of a neat hobby,I have a Bridgeport with dro,and rotary table ,a 14x 36 lathe and most tooling to go with them. I’ve made two wobblers so far ,a single and an opposed twin,double acting,I’ll definitely be in touch.



Cheers Lou


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## kvom (Apr 21, 2019)

I had problems with mine until I replaced the rollers with small ball bearings.


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