Author Topic: Jeff builds a 1936 popular science Midget engine  (Read 569 times)

Offline jirvin_4505

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Jeff builds a 1936 popular science Midget engine
« on: September 22, 2022, 02:19:33 PM »
A little introduction

https://www.modelenginemaker.com/index.php/topic,11016.msg255582/topicseen.html#new

It all started when Emma sold me the castings for ETW Kiwi 11 described here….


The thought of messing it up was too much for me (I’ve messed up plenty!)

After dabbling with some of the Gingery home shop projects I really appreciate the diy approach to castings.

So after a crash coarse on learning fusion 360, doing some 3d printing and joining the gang at the local trades guild…

We have a casting  :cartwheel:

« Last Edit: September 22, 2022, 02:26:50 PM by jirvin_4505 »

Offline jirvin_4505

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #1 on: September 26, 2022, 05:01:11 AM »
Made the flywheel casting
Worried about having enough spare to have the mounting boss stand 3mm high of the inside rim



Results of using 3d print in green sand to produce flywheel for 1936 midget model engine. Cast at Old Petrie Town trades guild


Cheers jeff
Working to the closest CM

Offline jirvin_4505

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #2 on: September 26, 2022, 05:08:04 AM »
Cylinder head
This really pushed my beginner skills at using 360 fusion
Generating double draft on the rocker tower with rounded top almost broke me!  :killcomputer:
Kept thinking I should use a screw in tower similar to jasonB build and the kiwi11 plans, but I wanted to see what I could learn
I’m still tempted to simplify the pattern

Took 3 iterations before I was happy with draft, clearances and machining allowances


Ineteration of patterns as I print and measure and make allowances for green sand casting



Midget model motor cylinder head 1st casting = rough  :toilet_claw:


First pour. Initial pull from sand worked well (surprise!,) some troubles cutting gates so we replaced the pattern to stabilise the sand.. always a poor option however time pressure to get it poured (furnace was hot). Mainly a test ramming to see if the valve bosses would release from the rocker tower.

How am I doing….humble beginner :popcorn:

Cheers Jeff

working to closest CM


« Last Edit: September 26, 2022, 05:15:16 AM by jirvin_4505 »

Offline jirvin_4505

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #3 on: September 26, 2022, 05:48:33 AM »
Crankcase castings made
Having trouble calculating and allowing for shrink to get the gear spacing correct
I sourced aliexpress 1m 44 and 22 gears (just trying to ease the learning curve a touch)
Online calculators suggest 33mm as spacing - hope I did that correct

Another shaky table cam (wife will return in a few days = cleanup time)


Midget model engine crankcase halves from 3d prints

A few iterations to get the spacing correct for the gear train. Slightly smaller gears than the imperial ones


Cheers Jeff
Working to closest CM


Offline A7er

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #4 on: September 26, 2022, 08:35:05 AM »
Nice work Jeff! I don't know how I missed this thread, I am always interested in watching anything to do with casting and small engines. I will follow this one with interest.
Lee

Online Jasonb

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #5 on: September 26, 2022, 05:13:33 PM »
You'll soon have a full set of castings.

Yes 33mm ctrs is right for those two MOD1 gear

Offline bent

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #6 on: September 26, 2022, 06:39:58 PM »
They are solid and metal, not bad!   :)

I hope I can do as well with my first attempts at sand casting, at some future date...

Offline jirvin_4505

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #7 on: September 27, 2022, 01:11:02 AM »
I had a request to post my drawings
These are per the pattern measurements in the original article

front crankcase
Note this would be improved with fillets added to improve sand cast
It was the first part I modelled  thus was very early in the learning curve

https://a360.co/3xUqRV9


Rear crankcase  The oil boss is a nod to the original.  The oil boss that Jason has drawn is much simpler and probably would work well in a pattern
(Edit. Will need to upload a later version of this rear link- just turn canvas off to hide drawing)

https://a360.co/3UDQ3J8

Cylinder head version 3  has modification to rocker tower to improve pattern release from sand
Let me know if you want the earlier versions

https://a360.co/3xXrRrA


flywheel pattern
https://a360.co/3LJo5rk


Will post the stl when I learn how

Cheers Jeff
Working to closest CM
« Last Edit: September 27, 2022, 02:41:54 PM by jirvin_4505 »

Online Jasonb

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #8 on: September 27, 2022, 09:34:39 AM »
I notice that my link to the assembled engine does not allow the file to be opened in F360 so shout if there are any parts you want the file for. Are you using the free or paid for version?

Following on from the cast iron cylinder thread what di you intend to do about the valve seats and guides in your aluminium head as the valves can't really run in that like they would if it were an iron casting.
« Last Edit: September 27, 2022, 09:38:32 AM by Jasonb »

Offline jirvin_4505

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #9 on: September 27, 2022, 10:24:01 AM »
I notice that my link to the assembled engine does not allow the file to be opened in F360 so shout if there are any parts you want the file for. Are you using the free or paid for version?

Following on from the cast iron cylinder thread what di you intend to do about the valve seats and guides in your aluminium head as the valves can't really run in that like they would if it were an iron casting.

Fusion is education version about to expire. My wife (teacher is about to become a fusion user😂)
Not sure how I got education account - must have been easier before changes

I did notice I couldn’t download your link

Would like access to cylinder carburettor and points mount(looks a simple CnC)

From my probing around 360 I think all you need to do is reexport (share link) the engine and mark the download box (you can add password)

Also sharing link for separate parts is very useful

Valves
I was going to follow Westbury kiwiii directions. The valve seats are cut direct into the head (nervous one shot go!!)

Another simple engine on the forum used valve cages with Honda 25cc valves 12mm - already sourced from China

Haven’t given it too much thought .. for cages I may need to change the diameter of the valve stems

Found a local model engine supplies and a stick of cast iron for cylinder is on way - going with aluminium cylinder like kiwi 11. Interesting it wasn’t much cheaper than ordering it off UK eBay!

Cheers Jeff


Online Jasonb

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #10 on: September 27, 2022, 10:48:07 AM »
Just seen there is another box to click to "allow downloads" unfortunately not active for the free non commercial one, I used to have educational and it worked then

Try the attached step file for the bracket and if that works I'll export the rest as step files from Alibre as I only do the ones that I want to use F360's CAM for, remember mine are smaller approx 1mm =1/16

You could also think about separate cages Loctited into the head to provide a bronze seat and guide
« Last Edit: September 27, 2022, 10:53:40 AM by Jasonb »

Offline ettingtonliam

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #11 on: September 27, 2022, 02:26:03 PM »
Would loctite stand the tenperature in a cylinder head?

Offline jirvin_4505

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #12 on: September 27, 2022, 02:57:39 PM »

Try the attached step file for the bracket and if that works I'll export the rest as step files from Alibre as I only do the ones that I want to use F360's CAM for, remember mine are smaller approx 1mm =1/16

You could also think about separate cages Loctited into the head to provide a bronze seat and guide

STL works perfectly.. responds to modify>scale

Thanks for idea on valve cage > add it to the list of possibilities

cheers Jeff


Online Jasonb

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #13 on: September 27, 2022, 03:14:03 PM »
That engine has a light press fit and the Loctite 648 (high temp) is as much a sealant as a retainer

Online Jasonb

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Re: Jeff builds a 1936 popular science Midget engine
« Reply #14 on: September 27, 2022, 06:49:21 PM »
Try this STEP file of the whole engine and see if you can separate the individual parts if not I'll do some individual ones.

You should be able to open the file in F360 and then click on a part name down the side and save as then it can be opened as an individual part, there may be a simpler way but I don't know it.

EDIT See PM as file is too large to attach >:(