Ron Colonna 1/4 Scale Offy

[mikemill]

Around 10 years ago I bought the build manual for the Offy, I am now considering to build this wonderful engine.

If any member has built the engine could they comment on the drawings or offer any advise, it would be appreciated.

Thanks

Mike

[petertha]

To augment any posts that may arise on this forum, FYI there is a very detailed build by Terry.M on HMEM

https://www.homemodelenginemachinist.com/threads/270-offy.31486/

[mikemill]

Petertha

Thanks for the link, just what I was looking for. The design of the block is suspect as the method of fixing the mid crank bearings requires tiny fingers.
A split block makes more sense, back to the drawing board!!

Mike

[uuu]

I'm interested to see the split block in the link uses bearing caps on the lower section.  I wonder if you could dispense with these and have the upper part of the bearing as part of the upper block - rather like Japanese motorcycles?

Wilf

[steamer]

Petertha

Thanks for the link, just what I was looking for. The design of the block is suspect as the method of fixing the mid crank bearings requires tiny fingers.
A split block makes more sense, back to the drawing board!!

Mike

Just FYI.   Ron made the block the way the real one was made which resulted in those "clover leaf" shaped bearing shells that drop in from below.   Yup it will be some work to get in there to screws in.     That said, will the option of a split block, you could go with a ball bearing main crank in place of the plain one.....You are the president of your model engine company.   

Ron has had his at 10000 rpm....and it has a nice howl to it.

Dave

[Art K]

Mike,
Ron's Offy is on my list of engines to build. This video is from 2012 NAMES.
<a href="https://www.youtube.com/watch?v=OXKV7ez2wEg" target="_blank">http://www.youtube.com/watch?v=OXKV7ez2wEg</a>
Ron used every book and detail he could find to make it as close to "as designed as possible" and still be possible to install all the internal bearing webs. I have the CAD over 90 percent complete but am not convinced that is the way I want to build it. I like Terry Mayhugh's split case, if you haven't read his build article on HMEM it's worth a look before you get to far along in the design process.
Art

[Mayhugh1]

I'm interested to see the split block in the link uses bearing caps on the lower section.  I wonder if you could dispense with these and have the upper part of the bearing as part of the upper block - rather like Japanese motorcycles?

Wilf

You could certainly make the upper half of the crankcase also be the upper half of the main bearings, but scraping them in becomes a hassle. - Terry