# 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/


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## 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...


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## 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!


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## rangerssteamtoys

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


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## bretk

Wow,Nice engine!

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

-Bret


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## 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


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## 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


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## 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


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## 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


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## 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!!


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## 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


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## 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


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## 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


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## 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


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## 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.


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## octopus80

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


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## 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.


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## 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.


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## 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


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## 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


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## CFLBob

Brian Rupnow said:


> 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



Hi, again, Brian,

My problem is getting the Solidworks files.  I did a couple of web searches and never found anything.  


Bob


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## stevehuckss396

johnmcc69 said:


> 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



I doubt you will find anything. Even tho coles is gone, the rights to the drawings and ability to produce castings for sale still belongs to the previous owner and should not be copied without his or her permission. If you find files on the internet they will most likely be illegal copies. One of the things I like about the model engineering community is there respect for copyrights of drawings created by other engineers. If we don't respect others work, most won't offer it for sale and we will have nothing to build.


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## johnmcc69

I totally agree with everything you said Steve. I think my post came across with the wrong message. I would never "pirate" copyrighted material or publish drawings without the original owners permission. I never had the intention of profiting off any of the plans I've posted & most likely never will.

 John


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## stevehuckss396

johnmcc69 said:


> I totally agree with everything you said Steve. I think my post came across with the wrong message. I would never "pirate" copyrighted material or publish drawings without the original owners permission. I never had the intention of profiting off any of the plans I've posted & most likely never will.
> 
> John



To be honest John I really didn't feel that you were asking for "pirate copies" of a any kind. I guess I was just trying to explain why they might not be found and it turned into an effort to educate the membership here a little bit. For instance I saw mention of "solidworks files" being looked for. If 3D files were found on one of the 3D file sites like GrabCad, the files are still illegal copies because the were created using the original drawings and are not original work. You cant take someones work and put it in another format (2D drawing to 3D model) and consider it "your" work and profit from it or just start giving it away for free. If I see those files on 3D file sharing sites I personally wont get them. I know how hard it is to find cool stuff to build and I don't want to discourage someone from publishing plans for sale thinking they will just get pirated. Again I said that that is one of the things I like about the "modeling community". I think the vast majority of the members here and modelers everywhere respect each others work and have no interest in that sort of activity. This is a great bunch of people and that includes you John. Sorry if I made you feel any less than that.


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## CFLBob

As probably the guy Steve's referring to, perhaps I should explain myself.  

My background is that I'm not a lawyer, but I have a patent under my name.  That patent was assigned to my employer at the time per our employment agreement.  I have also written a very large piece of electronic design software on my own (that is, at home) that I give away the executable form but not the source code.  I want to keep the copyright so that someone else doesn't release it under their name.  

What I was told was that patents and copyrights work essentially the same way.  US patent/copyright law is based on harm to the patent/copyright holder, and that means taking sales away by selling copies.   If I buy a book and want to copy it for my own use, I can do that as long as I never sell it to someone else.  I've copied pages out of books to use in the shop so that when they get oil on them, my expensive book doesn't get damaged. I believe that's fully legal under "fair use". 

When I copy a few pages out of a book I bought, have I hurt the company that holds the copyright?  It's possible if I had my book in the shop, I might have damaged it and bought a second copy.  I also might have said, "oh, well, now it has oil on it" and not replaced the book.  Our legal system typically considers the losses from not selling a single copy to be negligible.   

Since nobody is selling the prints now, how could copying them harm the copyright holder?  There's a swamp of legalese between copyright holders dying, or going out of business or just being unidentifiable.  This could be under the law of "Orphan Works" or it could be that the copyright was assigned to someone and they aren't tracking use or don't care about it at all.  

If someone knows if there's a copyright holder and if they intend to sell that to someone else, that would be a great answer.


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## johnmcc69

No worries Steve. It's because of the ethical morals of the members here that make this a pretty cool place.

 Always something new to see & learn. George did a great job on the Holt, as well as every other project he puts his hands on.

 Cheers gentlemen!

 John


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## stevehuckss396

"Since nobody is selling the prints now, how could copying them harm the copyright holder?"

Two things come to mind. One, the person who owns them may just be restructuring the business and intends to resume sale of the drawings. Two, the person may be retired because of age and is trying to find someone to purchase the design. If the internet is flooded with the design offered for free the "rights" would be worthless.

Again i'm not judging anyone or telling anyone what to do. How about we just let it go as to not muddy up Georges thread any further. George, my apologies.


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## CFLBob

stevehuckss396 said:


> ...
> 
> Two things come to mind. One, the person who owns them may just be restructuring the business and intends to resume sale of the drawings. Two, the person may be retired because of age and is trying to find someone to purchase the design. If the internet is flooded with the design offered for free the "rights" would be worthless.



This is primarily what I'm trying to find out.  Given my abilities (or lack thereof) I'd like to see what's entailed.  It might be so far over my head that the question is meaningless and will be for years. 



stevehuckss396 said:


> Again i'm not judging anyone or telling anyone what to do. How about we just let it go as to not muddy up Georges thread any further. George, my apologies.



Agreed, and my apologies, too, George.


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## rac37

I have a set of plans and instructions that I purchased from Coles a number of years ago. Thought I might get a set of 
castings to build that engine but never worked out. Would be glad to share, loan or gift to someone if they are interested.
Not sure how well they would copy but that may not be proper anyway.

Bob


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## Modelman

I completed my Holt several years ago. I also didn't like the crankcase procedure so I ordered an extra one from Coles when they were still Ventura for $30. Split them both and made one bolt together. Worked out very well. Much better. I too am sorry that Coles went extinct.      Larry


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