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So where to next. The 360 build is largely finished, needs a lot of tuning time and I guess a bit of fetteling as per most of my projects. So not finished but Im already thinking what next. 

Find a set of YZ 125 cases and copy cast a set to allow for a 61mm stroke, 60mm bore cylinder, 175cc. A side project perhaps

Make a rotary valve 175 along the lines of the 360, only smaller and perhaps a little less complicated but still a standard loop scavenge twostroke.

Or make a twin piston, single cylinder 175 uniflow twostroke. Two times 48 x 48 bore and stroke. No need for a balance shaft, no cylinder heads, possibly even stick to ( hated ) carburetors. And still have less fuel loss out the exhaust than an injected twostroke by way of splitting the inlet and exhaust ports up, a ring of ports at each end of the cylinder, in one end, out the other.

Fundamentally I want 175cc. 

 

 

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3 hours ago, uniflow said:

Or make a twin piston, single cylinder 175 uniflow twostroke.

I like this one.

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12 hours ago, redrider144 said:

I like this one.

Me too. 

Its a project that will produce results, I know enough about crank case charged uniflow engines now with my previous work to produce something I can do trail rides on, my measure of success. 

And its just a bit different, with a useful twist, efficiency. 

I have a new, never been used before scavenging system and a new style of combustion chamber, the two key elements to uniflow success.  

Self isolation may have its benefits. 

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Be careful what you wish for. NZ is in total lock down now for four weeks, my pattern shop is well stocked so might be intetesting to see what develops. 

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These cases are to suit a KE 175, a reasonably robust  looking gearbox but best of all, its free. 

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Posted (edited)

For those unfamiliar with the two piston per cylinfer uniflow, this is one I built years ago. Nearly 25. 

This is a crank case charged twin cylinder, four piston twostroke uniflow engine. See the four sparkplugs in the center of the engine, two per side. This was the first start up. 

And under load in the boat, first time under load too. Best at approx 5 min mark. 9200 rpm. 

 

Edited by uniflow
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This supposed YZ 175 X is a 250F frame with this single cylinder, two piston uniflow twostroke, rotary dis valve induction. 2 x 48 x 48 bore and stroke, head to head. 

No cylinder heads needed, no counter balance shaft needed as each crank offsets the other, counter rotation.

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Posted (edited)

The reason for the lugs, machining the case old school, boring and facing head in the manual mill. Busy pitching out all the holes and bearing centers. 

Nice alloy to machine, CC601, heat treated to T6. Case cast at home. 

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Edited by uniflow
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Very interesting project! I wish I lived within driving distance from you. I’d love to come help and learn. The machining I could handle but I’d love to learn some about casting and engine design. Nice Wohlhaupter boring / facing head by the way. Thanks for sharing! Clay

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Posted (edited)

inside of the first case machined, second case in the mill. Slow but sure.

Clay, the casting is the easy part, relatively, the pattern making in the first place is where all the thought effort goes in although I do enjoy pattern making, Its therapy, working with wood, glue and bondifill. If you make a mistake, who cares just glue / bondi it up and start again. 

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Edited by uniflow

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Here is some pattern making for the YZ250 TPI throttle body, drum type.

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Some more, using something called Armorboard, glued together.

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White stuff is casting resin, especially for pattern making = expensive. 

Adding wall thickness

Finished pattern.

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Posted (edited)

The finished product fitted and ready to do its job, TPS runs off to the drum shaft,  drum runs on small ball bearing, almost friction less. 

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Edited by uniflow
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Dude. Your craftsmanship is amazing. I love threads like this! 

One question though. What made you choose a barrel type throttle body over a butterfly type? Is it an intake length/TB placement thing or just a preference? I know they were common on ultra high revving F1 engines before profiled butterfly TB types made an appearance. 

I’ll leave it at one question. I have about 100 others I could ask but I will be glued to this thread to track your progress. 

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Butterflies are for the garden. I wanted an inlet that when it was wide open, no restrictions, no butterfly valve, no needle, no slots, nothing just a clean smooth hole. Drum valve is that. (never mind the reed valve restriction just down the line😆)

Drum itself was machined from solid in my CNC, 'shelled', so it had a 2mm wall thickness all around. So its extreemly light. And yes I could have just CNC machined the housing but I like making patterns the old way. Casting still has its place. Its cheaper if you want to make a few of them. Ill see if I can find some pictures of my 350 Kawasaki TPI throttle body, its different again. 

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