Making a custom bike engine

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Mitchg95

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May 18, 2014
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Lakewood Colorado
Thanks for the measurement Theon :)
I got home this afternoon and discovered what bob Ross would describe as a happy little accident. The package arrived, and upon opening it I found the company I ordered from also completed the complete head and piston assembly. I had only ordered the rod and cylinder!
Got some more designing done. This is not the final drawing as there are still some changes I want to make to the part, but here is a crank disk. There will be nine of them total

How would I go about calculating the 1.3:1 ratio that was described for the crankcase volume?
I'm still thinking about have this case with reeds instead of the carb being hooked up to the cylinder
 
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Theon

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Jan 20, 2014
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Now that's a little more tricky, you need to fill as much as you can of the case with the flywheel discs your designing, See "full circle crank".
But volume of case with transfer ports, reed box(minus reeds), also minus complete crank assembly ect will want to be made as small as possible.
 
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Mitchg95

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May 18, 2014
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Lakewood Colorado
What is the stroke for the 48cc motor?
I'll go with the full circle crank. I'm still deciding if I'm going to make it be reed valve or just go with the stock option.
 
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Theon

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Jan 20, 2014
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3 carbs are going to be easier to tune than 6!
You ever tried tuning an Alpha Romeo Boxer with twin double barrel carbs?, and that's only 4 cylinder.
I thought the stroke of the 48cc was 40mm but not sure.
 
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Mitchg95

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May 18, 2014
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Lakewood Colorado
I went ahead and naught a lathe yesterday, I did not have a lot so I got the harbor freight 7x10 metal lathe made by central machinery.
I am fairly happy with the results of the lathe so far, It seems to be able to hold a reasonable tolerance .
So
I started experimenting on some parts for the engine, so I started with the crank pins. I was just trying to determine my final pin diameter. 10mm is equal to .629" so I turned some aluminum to .630" and the bearing and rod slipped on for a nearly perfect fit. I might make the next actual pin at .631" or .632 to get a better fit. The first was made out of 6061-t6 aluminum just to determine the size I needed. So, as soon as I get some steel about .750 in diameter I'll make the actual pins.
 
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Mitchg95

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May 18, 2014
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Lakewood Colorado
I consulted a friend of mine to see if he could do the grinding for me and he said that generally the finish is not as good as a general turned finish. We will see.
I'm thinking it would be cool to have a suicide shifter on the bike to mimick the older 1920's motorcycles.
I'm out of town in pueblo now so I can't really design much but I am thinking of how I'm going to make this thing.
I'm going to start pricing out materials from different suppliers then see what I can find at the scrap yards around my town.
Mitch
 
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Mitchg95

New Member
May 18, 2014
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Lakewood Colorado
That would be awesome!
Right now I'm starting to price out material. I'm going to make the crank pins out of 303 stainless, which has a feild strength of 40,000 psi and a tensile strength of 95,000 psi. A 3/4" rod that is 12" long is coming out at about $15 before shipping.
I might start ordering material for the crank pins in the next couple of days :)
Production should not be to far off!
dnut
Mitch
 
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Mitchg95

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May 18, 2014
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Lakewood Colorado
I'm looking into this more, if I make the disks and pins out of 1144, which from this company comes turned, ground, and polished. It is much cheaper than the 303 and is much stronger. I might just make the shaft parts out of this material
 
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Mitchg95

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May 18, 2014
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Lakewood Colorado
Thought out the crankshaft and timing today, the shaft will be made from multiple parts that are press together, ie: shaft segments, crank disks, and crank pins. I will make the parts a tight press fit and will cross pin the parts together with 1/4 inch pins. For the timing I am thinking of using a "wasted spark ignition." This ignition system is well suited to boxer type engines. This system is a distributerless ignition system using a double ended coil firing both Sparta plugs on each revolution, that is, on both the compression stroke and the exhaust stroke. This system only requires a single contact breaker and single coil to run the cylinders. Another advantage of this design is that it cuts the number of parts needed in half.
What are your guys ideas?
 
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Mitchg95

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May 18, 2014
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Lakewood Colorado
Is there a calculator that could help me figure out what size fly wheel I might need?
I'm looking at material and 15 pounds seems a little heavy, but I have no idea. Can some one help me?
 
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Theon

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Jan 20, 2014
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Although more familiar with metric 15 lb's does sound heavy. The bike engines have the bearings recessed into the crank discs, eliminating a fair amount of weight.
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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The crank firing layout will determine how much counterweight you will need. There are several ways to time the firing and this affects crank design. I have no clue where to find the formula but you absolutely need to include this in your planning if you expect success.
I'd pick the smoothest layout and try to reduce mass as much as possible for quick response and snappy revving.
Google the different V-8 styles for some idea how this parameter affects engine power and useability.
Be sure to check out flat crank v8's with 180 degree headers.
The sound will make you howl at the moon.
Or this: https://www.youtube.com/watch?v=DcMtMdFYHyM
 
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Theon

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Jan 20, 2014
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In a 6V there are two different firing orders, odd and even. odd gives a lumpier sounding motor, even is more common for the same reason, it gives a smoother idle.
Looking it up there are two. 145 235.
and the Porshe uses 162 435.
The crank discs need to give max primary compression, and as, If they are split cases?, that gives problems to recessing the crank for seals and bearings.
if bolt together segments, crank discs could be recessed as a bike engine crank is.
 
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Mitchg95

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May 18, 2014
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Lakewood Colorado
Thank you guys for all the tips. I'm taking all of them into consideration.
I've determined from research that in my engine the crank pins will be offset by 60 degree's relative to one another.
I've also thought out the crankshaft some more and changed how it will assembled. In my previous design, I was going to make every part as an individual part that get pressed and pinned together. I've changed my design in that, 4 of the crank disks will be made with the crank shaft as on piece instead of two with my previous design. Then there be two female crank disks that are bored through for the male end of the opposing crank disk/ shaft combo. These female ends will be have the shafts pressed into them, and have a screw that is a slip fit though the shaft and half the disk, then the screw will engage the threads in the other half of the female crank disk.
I hope i explained that we'll enough. But here is a photo of my drawing to help understand what my design is, currently.

I'm looking into the bearing idea. But I'm not sure if I'm going to go with bronze bushings or a bearing.
 
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Mitchg95

New Member
May 18, 2014
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Lakewood Colorado
xct2im getting ready to re-draw my cases, I drew them around the 66cc jugs. So since I'm going with 48cc jugs, can someone tell me what the crank shaft center to the bottom go the jug distance is?
 
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