And Now for the Twin

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Mike Rometer
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And Now for the Twin

Post by Mike Rometer » Thu Apr 10, 2014 6:49 pm

Now after getting the hybrid single to run fairly well, my thoughts have turned to its cousin, the twin.
Block (1) (600 x 450).jpg
Block (1) (600 x 450).jpg (60.02 KiB) Viewed 3583 times
Unfortunately unlike the Hybrid there is only the block; nothing else at all, not a stitch! It has though, been basically machined, the top and bottom faces, valve port faces and the bores, so that at least is some help.

There are one or two things I'm not totally happy with, like the positioning of the ports, they are a bit far into the bores for my preference and seem to me to be wasting bore length.
Ports (1) (600 x 450).jpg
Ports (1) (600 x 450).jpg (52.6 KiB) Viewed 3583 times
The block is four inches tall but the positioning of the ports leaves only about two and a half inches available, assuming a piston of around an inch thick. I'm sure I can increase that fairly easily.

The other thing is the cast in ports on the end faces, whilst easily enough corrected, they leave a little bit to be desired.
Ports (2) (600 x 450).jpg
Ports (2) (600 x 450).jpg (51.8 KiB) Viewed 8698 times
In all probability the usual method of design will be employed (fag packet)!
Last edited by Mike Rometer on Tue Jan 01, 2019 3:53 pm, edited 3 times in total.
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DetroiTug
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Re: And Now for the Twin

Post by DetroiTug » Thu Apr 10, 2014 10:24 pm

On my twin there are two 1/4" rings with .125" in between. The rings at both ends travel right up to the port. That is the only way I could get 4" stroke out of it. The new Tiny Power cylinders - or all of these made since the early 60's have been 1/2" taller.

-Ron
Mike Rometer
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Re: And Now for the Twin

Post by Mike Rometer » Fri Apr 11, 2014 3:43 pm

Ron, I think I have a suitable solution, but I need to obtain two cylinder dry liners (sleeves) of an appropriate size, 2.5" X 4" (or one at 8" long). There is plenty enough material in the casting to bore out to take a liner, and then I can cut the ports down from the top edge. I should be able to get at least a 3" stroke and maybe a touch more with a slimmer piston. My next thought is whether to make patterns for covers and etc., or just go with M.S. stock. Looking promising!
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DetroiTug
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Re: And Now for the Twin

Post by DetroiTug » Sat Apr 12, 2014 2:43 am

Mike,

That's a good idea.

My buddy that builds the Uniflow engines, built one for his car that he has ran quite a bit so far. He's using stainless steel (303 I think) liners and bronze piston rings, it appears to be holding up quite well.

If you have access to a foundry, I'd have some castings made. It's not hard to do and they machine much easier than low carbon steels and they don't rust as easy and they hold oil as cast iron a bit porous. And it looks better.

-Ron
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Re: And Now for the Twin

Post by Mike Rometer » Sat Apr 12, 2014 8:14 am

As you say the pattern making is simple enough, just the foundry isn't too close, so I would need to be sure I was getting it all in one shot and not go running with odds and ends. I do agree cast looks a lot better, besides its other properties.

The idea of using cylinder liners was largely Pete-the-Pen's, I hadn't got quite that far with the thinking. (I'm getting slower with age ;) )
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Re: And Now for the Twin

Post by Mike Rometer » Thu May 15, 2014 9:26 pm

Having enjoyed a longish (3 weeks) holiday away from all things technical, I have made a start. After a rather fruitless search for suitable cylinder liners, most suppliers seem to be in India, and don't find it necessary to quote sizes or prices, I started to look for some spun cast pipe, but even that seems in short supply in these parts. I did happen upon some 75mm solid continuous cast bar, which came at a considerably cheaper price than any dry-liner that I did manage to trace, so I got a length of that and have started to the long arduous job of turning that into liners. Suffice to say, there will be a bucket load (or two) of swarf! :roll:
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Re: And Now for the Twin

Post by Mike Rometer » Fri May 16, 2014 5:17 pm

Liners  (5) (600 x 450).jpg
Liners (5) (600 x 450).jpg (70.91 KiB) Viewed 8469 times
A long 'boring' job, and that's only one. Now out to 2.25" (finish size 2.5"), and then ditto repeato from the other end. The outside dia. can be reduced some, but how much, will be decided when I've bored the block out. While waiting for the cut to finish I've checked the block and found that the bottom face is slightly warped so that will need a light skim which I will probably leave till the liners are in and need trimming off, meaning they will be fitted from the bottom. No biggy!!!
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Re: And Now for the Twin

Post by Mike Rometer » Thu May 22, 2014 5:36 pm

Having bored both ends to the middle, I tried parting the liners, but a lack of rigidity, even with the fixed steady meant recourse to the saw. No problem, as there was plenty of extra length for re-trueing.
Liners (6) (600 x 450).jpg
Liners (6) (600 x 450).jpg (57.99 KiB) Viewed 8412 times
The first setup for boring proved a touch too shallow to allow adjustment of the boring head from below,
Block Boring Settup (1) (600 x 450).jpg
Block Boring Settup (1) (600 x 450).jpg (76.04 KiB) Viewed 8412 times
so setup with setup two I decided on belt and braces,
Block Boring Settup (3) (600 x 450).jpg
Block Boring Settup (3) (600 x 450).jpg (76.94 KiB) Viewed 8412 times
four clamps. Two would probably have been adequate but why take a risk with a one-off casting? Now ready for the first 'right upper-cut'!
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Re: And Now for the Twin

Post by Mike Rometer » Thu May 22, 2014 5:38 pm

After a lot of handle turning (I've no power feed to the miller knee), the second bore is completed. The difference between both bores is less than 0.0005". Good enough for me!
Block Boring Settup (4) (600 x 450).jpg
Block Boring Settup (4) (600 x 450).jpg (76.73 KiB) Viewed 8412 times
One problem was because the cut was slow and the 40ish turns of the handle for each cut, cramp set in in both hands, so a slight mod was required for the 'knee' handle.
Handle Mod (600 x 450).jpg
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Lopez Mike
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Re: And Now for the Twin

Post by Lopez Mike » Fri May 23, 2014 5:25 am

Some thoughts for your piston.

I suspect you could get by with one ring. Or if two, make them relatively narrow and close together. Or have them share a common groove. Two L shaped or Dykes rings back to back in a common groove would certainly work. I cannot think of any scheme that would take up less stroke.

To gain stroke length, make the piston quite thin and cone shaped. This is common in full sized practice. Since you haven't designed either cylinder head, you can have them cone shaped to match the piston, a male cone on one end and a female on the other. Minimize the dead space as much as possible.

The conical shape makes the piston very stiff. I'd bet you could make it an eighth of an inch thick for most of it's area with a boss for the piston rod and a thicker ring at the edge for the ring grooves.
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