why there are no 2S twin/multi cylinder engines?

HP has a twin, There were a few made by Ross (years ago). There are several gassers offered in twin and multi cyl configurations. Fox, DA, ZDZ and others.


ZB

Fox had a twin also. I think there have been a number of multi cylinder two strokes made over the years. But now if you are going to spend bucks on a multicylinder engine you might as go whole hog and buy a fourstroke.

Folks, if you re-read the first post, and remember there are several twin cylinder engines around 25cc, you have to realize he's asking about 0.25 cubic inch engines.

And the answer to his question is that there have been several small multi cylinder engines on the market, none have survived.

Biggest problem is cost, a two cylinder engine has to be more expensive to produce than a single. Next is mechanical loss, the more moving parts the more friction there will be, so (up to a limit) a single will be more powerful than a multi of the same size.

K&B/Allyn made an inline twin, it came in 0.09 cid and 0.15 cid sizes. They ran well when you could get one to start, and they looked good in a P-40 of the right size.

Once in a while you will find a small radial on "The auction site," can't remember the brand, but they were geared/coupled single cylinder engines. Again, hard to start, not a lot of power, and the gears wore out quickly.

If you go to the "1/2A and 1/8A forum, there are several threads about people making their own small multis, not only "Boxer" twins but some radials too.

Go look, and enjoy.

Bill.

Bill,

He read his post again and he asked about 2S engines (as in two stroke or 2 Stroke), not 25cc or .25.

ZB

Hi Bill.
The small multi, I think you were refering to was the G-mark .30 five cylinder radial, had one years ago , it ran quite well made wierd sort of noise with all those gears, never ran it long enough to wear the gears out......... Wish I had kept it , they seem to be making quite good money on Ebay.
Martin.

Martin:

Yes, I wasa thinking of the G-Mark.

Thanks.

And ZB:

Looking at it again I think you are right. And obviously there are so many two stroke twins (and fours) on the market I wonder why he even asked.

Bill.

Had both the Allyn Fury motors .09 had the carb between the cyls. One would run rich, the other lean, so it never ran right. The .15 ran fine on both cyls. Good power for its day.

Yes have one of them, It started on the first flip on the first start that I ever did on it. I guess that I was lucky. It ran well and was smooth with a neat mechanical whirring sound, idle was good and fuel consumption was really good for what it was, which was 5 G-Mark 061's geared together in a common casewith a single carb.
Power was it's downfall though. This motor didn't generate enough power to get out of it's own way. It was rated as a thirty with the power of a 10.
Same for the G-Mark 12 and 30 twins. Neat but not really practical. The 30 twin did fly a Cub though as it was not a demanding model power wise.
Dennis

MVVS makes a couple of 2-stroke glow twins.

The problem with two stroke twins or multis is that unless they are opposed or cylinders fire at exactly the same time, each cylinder needs its own crankcase( the G mark 5 cyl is an example) It is essentially five separate engines geared together. An opposed twin, ie. The G mark .30, has its ports open at the same time so the mixture from the crank can go to both cylinders at the same time. A twin inline like the HP 1.20 also has separate crancases.The end result is a very heavy engine for the power output.

Max

2 stroke twins are, as you say, opposed and fire at the same time. But they don't have seperate crank cases, that is why the fire at the same time. Someone once made a two stroke radial with something like 7 or 9 TD .051's. It had a common crankcase but had a blower to pump the fuel air mixture into the engines. Don't remember who, I don't even remember if it went into production.

How about this???

I meant that the only exception is opposed twins that fire at the same time as they can use a common crank. No other configuration can.

Max

P.S. here's two photos

what make is this?

The twin in my picture is a Ross .60, probably about 25 or 30 years old. I have had it almost as long, I got it from the original owner who could not get it to run satisfactory. I never really did anything with it until last year when the picture was taken. It ran great for me on Byron Super 18 fuel, Zingali 11X7.75 prop and OS #8 plugs. Very smooth, nice low idle, and remarkably quiet considering the exhaust is just hollow square stock. I ran it for probably 30 minutes or so and it never quit once, although the #2 cylinder would flame out if it idled more than 4 or 5 minutes. It also seemed to run quite cool, considering I did not add extra oil to the mix.