Scratch built Holt 75 engine

[gbritnell]

About a year and a half ago I started building a scratch Holt engine. The reason for this project is because I ordered a set of drawings from Coles to see what was involved. After going over the drawings I saw how hard it was going to be to machine the crankcase the way it was designed so I redesigned it to be split along the bearing centerline allowing for a more accurate build and better access to the main bearings. After I started on the crankcase I decided to scratch the whole thing, except for the manifolds and flywheels. Come on now, I'm not that much of a masochist!! Anyway, I have just finished the engine. Hopefully this week I'll get it started and work out all of the initial bugs, leaks, adjustments etc. I will post 2 pictures of it and include the link to my Photobucket account where you can see most of the entire build from start to finish. For those of you not familiar with Photobucket just go to the index on the left side and pick out the album you would like to see.
gbritnell
http://smg.photobucket.com/albums/v43/gbritnell/

 

[ksouers]

Wow! Beautiful example of craftsmanship, gbritnell. And dedication.

Hope it runs as well as it looks.

Of course you will have to post the obligatory video of it running...

 

[Mcgyver]

that looks great - wonderful work.

that is a very interesting looking engine - a governer on the camshaft?? how does that work?

I bet there are many parts of this engine where a detailed build explanation would be of great interest - one i'd like to learn more about is the radiator and the embossed emblem - very impressive!

 

[rangerssteamtoys]

A great engine. I have the coles power models catalog and love staring at the pics.

 

[bretk]

Wow,Nice engine!

I too am interested in the governor design, do you have any additional info you can post?

-Bret

 

[chuck foster]

i have been watching this build on another website and it is truly amazing to see what this man can do :bow: :bow:

i had the castings for the holt but i didn't like them at all so i got rid of them ...but never thought of building it from scratch

you stated "Hopefully this week I'll get it started and work out all of the initial bugs, leaks, adjustments etc."
like this engine will have any of those problems!!!!

chuck

 

[gbritnell]

Thank you gentlemen for your kind remarks. To answer a couple of your questions, the governor is the typical flyball type that in fact runs on the end of the camshaft. When I was making the parts I made the loading spring as per the drawing but when I got the engine to the point that I was spinning it over in the lathe to run in the parts I found that the print spring was way too strong so I progressively reduced the wire size till I got it to activate about 1500 rpm's. Upon movement of the governor it moves the linkage back to the carburetor. I have scratched 2 light lines on the throttle barrel to reference closed and wide open. I have it set somewhere in the middle for now but am sure it will need fine tuning as the engine starts to run. The radiator is based on the Jerry Howell design. I narrowed it and made it an inch longer to more fit this particular engine. As far as the Holt logo on the front of the tank I did that with the poor man's CNC. I'll explain. I drew the logo up in AutoCad and figured out what size cutter I was going to use and then offset the dimensions by the radius of the cutter. I then made a datum dimensioned drawing so I could step off the points to create the logo. After machining all the straight lines I turned my vise to the proper angle to get the remaining angular edges and cut them from the points I had already machined. I then took the tank and with my Magnavisor and Dremel and small files I cleaned everthing up. If someone would like the point drawing to replicate it please let me know and I'll send it to you.
gbritnell

 

[Bookmaker]

Hello gbritnell,
Fantastic job!! What a great model. I had the same idea with Ron Colonna's offy. I split the case and made split bearings with ball bearings front and back. It really simplified the assembly.

Best regards,
Roger

 

[octopus80]

Hello I see that you have build the motor whitout casting pieces do you have drawing of the engine? maybe you have made them in auto cad are inventor?
is there a posibilty that you can chair the drawing this is a project that I like to do also.
Greetings Benny

 

[10K Pete]

Beautiful engine George! I've always like the Holt but it just seems too
much for me to actually build one.

Can't wait to see it run!

Pete

OMG, just realized the date of your build!!

 

[gbritnell]

Hi Benny,
I have some of the parts, block, heads, cylinders etc. drawn in Solidworks. I never drew up the other parts because they were machined from the original drawings. If the solid model parts would help you out you're more than welcome to them.
gbritnell

 

[octopus80]

Hello Gbritnell
At the moment I don't have buy the drawing from the Holt 75 engine so I like to make the parts on a CNC machine so drawing that are made on computer good to postprosseor for the G code voor my milling, turning and EDM wire machine.
So what do you use for the the Inch are metric size on the drawings?
in what extention can you send me the drawings? this is that I can read them? are in what extension do Solid works write you the drawing away.

Greetings Benny

 

[gbritnell]

Hi Benny,
The drawings for the original engine are done in inches so that's what I used for drawing the models. Solidworks files are .sldprt files but can be exported in many different formats, .dwg, .dxf. but these are 2D files.
gbritnell

 

[octopus80]

Hello Gbritnell

so it may not be a problem to read the sldprt files you may send them to my email adress [email protected]

Greetings Benny

 

[kvom]

Of course version differences in SW part formats may cause problems. If Benny's version is newer than George's I expect it will work. Vise versa not so sure.

 

[octopus80]

I work in Inventor 2016 and I don't think that it gone be a problem I hope that this is good enoug.

 

[CFLBob]

I realize the last posts here were over 3 years ago, but since Coles is gone and the copyright is meaningless does anyone have drawings of the Holt 75? I did some web searches and haven't found a source.

I found a picture and short video I took of someone's engine at Cabin Fever in April '15, not knowing what it was, and I'd like to find plans.

I have a homebuilt CNC mill, and can handle most formats.

 

[LorenOtto]

The loss of Coles has really made a difference in our hobby. It has made people become more imaginative and to use newer tools and techniques.

 

[johnmcc69]

I too would be interested in knowing if any of these drawings existed (from Coles or otherwise..) in the "Free" domain. I really like this engine & would like to CAD model it up.

John

 

[Brian Rupnow]

If you save Solidworks parts or assemblies as parasolids (x_t) files or as .step files (.step), then the upward or downward compatibility between different years is no longer a problem, and modern cnc machines can work directly off the 3D files. If you export a Solidworks drawing as a .dxf file, the older version cnc machines can work from that.---Brian