# sidevalve flat twin



## ownthesky2010 (Jul 26, 2015)

Hi All
Here is my second project.
Its a sidevalve twin of my own design.
Still a lot of tweaking and tuning to do but Im planning on putting it in a model plane and flying it.
[ame]https://www.youtube.com/watch?v=MBsCQWOtNkY[/ame]


----------



## Herbiev (Jul 26, 2015)

That runs great. Thanks for sharing.


----------



## Hopper (Jul 26, 2015)

Wonderful work. Sounds like a real goer!
What combustion chamber design did you use in the end?


----------



## kadora (Jul 27, 2015)

Hello
Very very nice work
What capacity and compression ratio has your engine?
what kind of glow plugs do you use?
Did you machine caruretor or it is some factory RC carb.


----------



## ownthesky2010 (Jul 27, 2015)

Thanks for the kind words.
Hopper, I will attach a pic of the head and some other bits.
kadora, the capacity is 22cc. Im not 100% sure of the compression ratio, I think its 8:1
Im using hobbyking no3 plugs but Im going to get Os f plugs to try. Its losing a bit of rpm when you take the driver off.
The carb is the same one I used for my single cylinder version, its a model car carb. I am going to change it to twin carbs soon but i will make them myself.
http://www.homemodelenginemachinist.com/showpost.php?p=261197&postcount=78


----------



## Hopper (Jul 27, 2015)

Nice. Looks just as lovely on the inside as it does running.  Looks like plenty of breathing space between the valve area and the bore area, which is more critical on a SV than the compression ratio that it costs. Will be interested to hear how it performs compared with a similar weight ohv engine in a plane.


----------



## Billitmotors (Jul 28, 2015)

G,day Ownthesky
Nice engine.and lovely machining job.
Back in 1990 I made a 20cc twin using the same single throw configuration. 
At the time I was teaching eccentric turning to a class and when driving home from work I used to see an old BMW motor bike with the eliptical cylinders and rocker box, with the pushrods coming up through the back of the cylinder fins. When I had first started the engine it had round cylinders and a single cam shaft on the top of the crankcase, after noticing the BMW I scrapped the original engine and made the eliptical version with the pushrods in the rear of the cylinder  and now twin camshafts in a conical back plate and engine mount. It runs well on the carburetta that I made but really performs on the second hand OS 60 carburetta that I bought from a mate.
If you are interested I will post a photo.


----------



## ownthesky2010 (Jul 28, 2015)

Thanks guys
Billitmotors, please post pics of your engine. I love to see how other people have done it.
Its interesting that you had the best results with a purchased carb. I had the same issue with the single I built.
When I tried running it with a home-made air-bleed type carb it wouldn't go past 7000pm, with a model car carb I got 9700rpm in the end.
Hopper, I am looking forward to getting it in tune and seeing how it stacks up. I will post numbers when I have them.
I did my usual trick of letting my excitement get the better of me and rushing the final assembly.
Now that the dust has settled I have done a bit of much needed inspection and found that one exhaust cam is out by 2 teeth, I'm losing compression in one cylinder due to a combination of the cam follower guides being a little too high thus preventing the cylinder from seating and the head o-ring groove not being deep enough allowing compression loss down the bolt holes as well as finding that my valve clearance is more than 0.2mm which has reduced the valve duration from 270 degrees to 240 degrees.
I have also got a bit of work to do on balancing the crankshaft. 
So all in all Im pretty sure there is more performance to be had


----------



## petertha (Jul 28, 2015)

Very nice looking (and running!) engine. May I ask a few questions about materials etc.?

- what is the cylinder liner made from?
- are valve seats cut direct in the aluminum head, I cant quite see if there are seat inserts
- did you make your own rings? If so any special method or the popular Trimble-like method of heat setting on a dowel pin?
- what material for crankshaft?


----------



## Billitmotors (Jul 29, 2015)

Gday Ownthesky
       Here are some pictures of my twin it looks a bit grubby these days it was finished in 1990, the same year my eldest son was borne. Hence its name Little Pete. After that it sat in a cupboard for a very long time, but now with my three kids have grown up I get a bit more time to work on my other engines. It has had a lot of running and runs very smoothly and powerfully.
Rob.


----------



## ownthesky2010 (Jul 29, 2015)

Hi Peterha, I cheated and bought the rings and liners from hobbyking. They are for an ASP.60 and so cheap its not worth the time to make when there are more important things to build.
There are no seperate valve seats or guides, the valves seat directly on the aluminium cylinder. Both engines I have built had marginal compression when assembled and very strong compression after a couple of mins of running after things start settling in.
I have read that you can gently bash the valves to seat them in aluminium and I think I prefer the idea to any kind of lapping compound but thankfully i have not needed either.
The crankshaft is turned from an 8.8 bolt. I have built a couple of single throw cranks and I have found old bolts to be a good source.
There is much less stock removal and they are so easy to get. If 8.8 isn't strong enough there are high tensile options.
The crankpin is the same material and pressed in.
Billitmotors, thats a great looking engine. I like the fins on the crankcase. Did you ever put it in a model plane?


----------



## Billitmotors (Jul 31, 2015)

G'day Ownthesky
It has mainly been run on the bench but it has had about a half hour in the air, until dumb thumbs took over and the model didn't survive.
I started to build a new one but got side tracked with other things. I will have to get too and finish it as there isn't much to do.
Rob.


----------



## toolznthings (Sep 7, 2015)

Congratulations !! Very nice !  Sounds great, too.

Brian


----------

