Author Topic: Little '36 Midget Build  (Read 6466 times)

Offline Craig DeShong

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Re: Little '36 Midget Build
« Reply #15 on: October 24, 2019, 03:11:28 AM »
Outstanding Jason  :ThumbsUp:

I’m really enjoying following this build.
Craig
The destination motivates us toward excellence, the journey entertains us, and along the way we meet so many interesting people.

Offline mike mott

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Re: Little '36 Midget Build
« Reply #16 on: October 24, 2019, 03:17:14 PM »
Most interesting your SBS pictures were very informative thanks for taking the time.

Mike
If you can imagine it you can build it

Offline Jasonb

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Re: Little '36 Midget Build
« Reply #17 on: October 24, 2019, 05:08:07 PM »
Thank's for the interest guys.

As I mentioned in the previous post before doing the taper on the crankshaft the flywheel was machined. first job was to recess the sides of a slice of 80mm EN1A steel, by setting over the top slide 2 degrees some draft angle could be included on the outer edge while turning conventionally.



Then buy running in reverse and working on the rear side of the hub that could have the same taper and by noting the topslide handwheel setting it was easy to machine to the correct depth. A tool with a rounded end was used to again give the look of an internal fillet as found on castings.



I could now set my topslide to the correct angle for the crankshaft taper and then use that to gauge the depth of the flywheel's tapered bore all without altering the angle so both tapers match. Fine cuts were taken until the shaft entered the flywheel and left 0.5mm clearance between the assembled bearing and timing gear.



Without altering the topslide angle I also machined a tapered arbor and pushed the flywheel onto that using a block and the tailstock ctr to make sure it stayed in place which allowed me to skim the OD to a true finish relative to the bore and cut the recess for the starting cord.



The arbor did not go to waste, with it held at an angle in an ER Collet block a slot was cut so that it could be used as a bush when broaching the flywheel.





Offline Jasonb

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Re: Little '36 Midget Build
« Reply #18 on: October 25, 2019, 07:10:23 PM »
The two rocker arms were mostly done using the CNC, first roughing out the profile and contour and then using a corner radius cutter to refine the shape before drilling the pivot hole. After that they were sawn off the parent bar and held in some shaped aluminium jaws to shape the other side.

<a href="https://www.youtube.com/watch?v=kO9qIaB77vA" target="_blank">http://www.youtube.com/watch?v=kO9qIaB77vA</a>

The adjuster and oil holes were done on the manual mill, pivot hole reamed and some final needle file work soon had the contours blended in.



The rocker post started as a simple turned part.



Which was the milled and reamed before a bit more shaping was carried out.



The valves were fairly straight forward turning from stainless steel using tailstock support to prevent the 3mm shank deflecting, the DCGT tip helps with this and also allows you to get in close to the revolving ctr.



A 0.7mm carbide grooving insert was used to cut the groove for the spring retainer. After sawing off the main bar the head was faced to final thickness then the valve inserted into the collet from the back end so that the ctr hole could be turned off and the end slightly domed.



The cam blanks were turned from silver steel (drill rod) before making use of the CNC to cut the profile, so much easier than having to use a rotary table and keep adjusting the mill to a set of co-ordinates from the likes of Cam-Calc





After heat treating they were Loctited onto the 5mm shaft, I just used the indexer and a square to set the angles as the indexer was already on the mill.




Offline Jasonb

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Re: Little '36 Midget Build
« Reply #19 on: October 26, 2019, 07:02:57 PM »
The piston was turned from some 1" 6082 aluminium and a groove cut for a single Viton O ring.



I did all the hollowing out on the KX3 which was a lot easier and quicker at doing the "dogbone" shape than using the rotary table.



It was then just a case of cross drilling and reaming for the wrist pin before parting off and skimming the top.




The two halves of the conrod were taken down to overall size by flycutting the 2014 ali, the rod part was drilled and tapped, the cap drilled and counter bored for the screw heads. I made up a couple of sacrificial brass screws to hold the two parts together so that the CNC could do the outer profile in one without worrying about the screws. The big and little ends were done on the manual mill then a simple block with two tapped holes and a couple of tap hat bushes to holed the rod down and then press go.



<a href="https://www.youtube.com/watch?v=XGB7FHfdGsE" target="_blank">http://www.youtube.com/watch?v=XGB7FHfdGsE</a>




Offline kuhncw

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Re: Little '36 Midget Build
« Reply #20 on: October 27, 2019, 01:17:11 AM »

Jason,

Thank you for a very nice series of build photos.  I especially like your method for orientating cam lobes using your spin index and a square.  That is very simple and effective.

Regards,

Chuck

Offline Jasonb

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Re: Little '36 Midget Build
« Reply #21 on: October 27, 2019, 05:44:43 PM »
Thanks Chuck

The carb body was carved from a length of 20mm 6082 aluminium, after facing off and drilling the ctr hole it was over to the  CNC using that to cut the elliptical flange and drill the two mounting holes under size.



I then tapped the holes so that a piece of 1.5mm thick stainless steel could be held and cut to a similar shape, this was used as the mounting flange for the exhaust.



It was then back to the lathe to complete the turning of the long central section which was done with a 1.0mm radius grooving tool as I wanted a fillet in the two internal corners.



Then with the part reversed in the chuck the same tool was used to form the inlet spigot.



The remaining 20mm dia section was then milled down to a 12mm square and a hole reamed through it for the carb's barrel to rotate in. The rough looking area at the upper far side of the hole is a tapped hole for the slow speed adjustment screw.



Not the best photo of the barrel which has been cross drilled for the airway and a flat milled at right angles for the above mentioned slow speed adjusting screw to bear on



The rest of the parts were fairly straight forward turning jobs so no photos taken. From a while I have wanted to use a jam jar for a fuel tank as a lot of trawling through e-bay finally found some suitable jars that could be built into the design. The throttle is controlled by twisting the jar rather than having a separate arm though one could easily be added.








Offline Jasonb

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Re: Little '36 Midget Build
« Reply #22 on: October 28, 2019, 07:02:05 PM »
The last major part to be made was the ignition timing bracket which was hacked to shape on the CNC

<a href="https://www.youtube.com/watch?v=cZrL3pbNxis" target="_blank">http://www.youtube.com/watch?v=cZrL3pbNxis</a>



A few holes and a bit of filing and it was done.



Some brass hardware was turned and a steel screw to allow the clamp to be adjusted so the timing could be advanced or retarded and a couple of Corian insulators completed that assembly.



A piece of 8mm copper tube was bent to a pleasing shape and silver soldered to the previously machined flange to complete the exhaust.



In keeping with the age of the engine some slotted filester head screws were made up in M3, M2.5 plus and M2 one with an additional straight knurl for adjusting the carb slow running position. A single large but flat headed one was made to seal the oil level hole.





Not a bad collection of bits, 58 parts and 32 fixings.




Offline Jasonb

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Re: Little '36 Midget Build
« Reply #23 on: October 29, 2019, 04:58:04 PM »
After a quick test run to see if everything work the engine was stripped down again and a bit of colour added, in this case Dodge Orange VHT paint and some satin black stove paint for the exhaust. I also made the stands to display it on from a couple of bits of 1/4" thick aluminium angle that were pocketed out on the CNC.











With the photos out of the way I could run a few tank fulls through it and have a play.

<a href="https://www.youtube.com/watch?v=v1WTcKEt--s" target="_blank">http://www.youtube.com/watch?v=v1WTcKEt--s</a>


Offline Flyboy Jim

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Re: Little '36 Midget Build
« Reply #24 on: October 29, 2019, 05:09:19 PM »
That is a fantastic looking engine Jason. Runs really nice as well.  :ThumbsUp:

I saw some of your shop in the background. It would be nice to have a shop tour sometime.

Jim
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Sherline 5400 Mill
"You can do small things on big machines, but you can do small things on small machines".

Offline mike mott

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Re: Little '36 Midget Build
« Reply #25 on: October 29, 2019, 05:48:42 PM »
Jason the engine sounded great. I am curious about your twisting the glass fuel bulb?

Mike
If you can imagine it you can build it

Offline awake

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Re: Little '36 Midget Build
« Reply #26 on: October 29, 2019, 06:14:11 PM »
Lovely work and an outstanding result!
Andy

Offline Chipmaster

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Re: Little '36 Midget Build
« Reply #27 on: October 29, 2019, 07:06:37 PM »
That’s a beautiful engine Jason, excellent.
Andy

Offline Jasonb

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Re: Little '36 Midget Build
« Reply #28 on: October 29, 2019, 07:14:35 PM »
Thank's chaps

The jam jar is connected to the throttle barrel so I turn that rather than the usual lever. There is not that much throttle response unless I lean it out a bit more but then it soon gets hot with no air movement so I was running it a bit rich and tweaking the advance/retard to get the slow lumpy tickover I wanted.

Did not show the workshop as I thought Jo may be offended by the sight of those couple of useless far eastern machines that keep on making these engines :LittleDevil:

Offline Laurentic

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Re: Little '36 Midget Build
« Reply #29 on: October 29, 2019, 10:20:04 PM »
Lovely engine Jason, looks a beaut, really stunning!

Just out of interest, roughly how many hours did it take to build, rough ball-park figure?  Takes me ages to do the smallest bit, lacking the experience to plough on like you do guys do, you guys seem to make it look so easy and like in no time at all it's done!!

Chris

 

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