MVVS 120 boxer engine
 

Has anyone information on the 120 boxer engine.
I beleive it was purchased about 7 years ago.

I can find petrol boxers but no nitro run MVVS 120 boxer or twin.0

RE: MVVS 120 boxer engine
 

I found this post where you asked about this engine 2 years ago...
http://www.rcuniverse.com/forum/m_75...tm.htm#7584165

Still having problems with it?

Here's more:
http://www.rcuniverse.com/forum/m_29...tm.htm#2962066

I still have mine...still sits in the box...waiting...(I didn't have much luck with it either )

RE: MVVS 120 boxer engine
 

Sparky,


Please stop using this foolish term...

It is not a 'nitro engine', but a glow engine, or a methanol engine...


This engine specifically was designed for 20/80 fuel, without any nitro at all.
All other engines here can use nitro, but only as an additive...


It is at most a minor component of the fuel...


And why do you think you must yell at us?!

RE: MVVS 120 boxer engine
 

I don,t know who you are but I guess you are the RCU police .Ha Ha

I thought we only had fools like you in Canada.

The bold letters were a mistake
However with dumb Trollers lioke your self what can I say. You obvisously have no freinds or hobbies other than trolling.
Oh by the way I have been modeling 60 years and still and always will call then nitro
Put that in your pipe and smoke

RE: MVVS 120 boxer engine
 

lol funny stuff by you both

RE: MVVS 120 boxer engine
 

I think Sparkey has no idea how to behave when writing in public. Maybe he is ignorant of forum rules in general as well.
FYI Sparkey: Dar provides better support on glow engines than most of us here. Those 60 years of you mean nothing if you do not know how to manage a simple twin.
Use 80/20 fuel, and fit a glow carb on her. The methanol probably has hardened the membranes inside the carby, so it will never run well.
Even with a membrane set, the walbro is not the best choice.

RE: MVVS 120 boxer engine
 

Hi!
The twin did not work properly! That's why MVVS discontiued the 20 and 23,4cc twins after some years.

RE: MVVS 120 boxer engine
 

Where did my post go!
I provided an answer how to make it work properly!!!

RE: MVVS 120 boxer engine
 

checking

RE: MVVS 120 boxer engine
 

pe reivers
One of my post were deleted also.

Could you repost the information on the 120 boxer.
Thanks

RE: MVVS 120 boxer engine
 

Methanol and Walbro membranes are not the best friends. The diaphragms harden, and carb performance goes down the drain.
I have tried running glow engines with a walbro carb, but found the throttle response on glow fuel very lacking.
Some people have had very good results by changing the Walbro carb to a glow carb.
Like Dar said in his post, use low nitro fuel. MVVS engines of that time were designed for zero nitro operation. I would suggest to use 2% max. If you want to run more nitro, the heads need to be shimmed to lower the compression ratio.

RE: MVVS 120 boxer engine
 

I thought large MVVS glow engines were to be run with no nitro? So don't call it a nitro engine.

RE: MVVS 120 boxer engine
 

Hello Pe,

Did it take a extreme amount of time and effort to get the engine to behave? There is a new 1.20 listed on RCU at the moment. I proabably shouldn't ask but what would be a fair price to pay for this engine?

RE: MVVS 120 boxer engine
 

Hi!
Sorry Pe! But I have tried a standard MVVS 7mm glow carb on the twin but it did not improve things!

RE: MVVS 120 boxer engine
 

Jan, I have had reports that said the engine did run well with a 10cc glow carb (8mm). At least as well as an opposed twin can run. Do not expect them to run as well as a single cylinder, especially in midrange. I have no experience with the engine myself, but did test the walbro carb on a 23cc single cylinder glow engine.

@ RCdude,
Indeed, you should not ask. Whatever it is worth to you. The engine is not produced any more.

RE: MVVS 120 boxer engine
 

Thanks Pe, I have no idea what to offer......

I have been pretty good at getting engines to run where others fail, but if this engine design is flawed to the point where it cannot be made to run well without serious machine work, then I guess its value will only be nothing more than that of a pretty paper weight.

RE: MVVS 120 boxer engine
 

Who said the design is flawed?

RE: MVVS 120 boxer engine
 

I believe Jaka did just that...

RE: MVVS 120 boxer engine
 

No, Jaka did not.
He said he had no luck with the glow carb. Others did have good results.

RE: MVVS 120 boxer engine
 

Okay, it must be my poor english then, but " The twin did not work properly! " does not translate into "a great design with minor carburator problems" to me... :eek:

RE: MVVS 120 boxer engine
 

Hi!
All MVVS twin engines I have seen and run myself have the same design flaws. They are impossible to set rich despite open the needle all there is...

However...they are very easy to start, and throttle fairly well as long as you use glow power.
As soon as you remove glow power and throttle down and run the engine at low rpm...and then apply full throttle...one of the cylinders will cut out! I have tried many many different glow plugs and also used the 7mm and 8mm glow carb...all in vain!

Another design flaw is that if you want to use silencers instead of mini pipes...one of the silencers will be in the way when you try to adjust the high speed needle.

RE: MVVS 120 boxer engine
 

Jan, you call it desigh flaws. I would not! Saito twin engines are/were also known for cylinders cutting out. So are Seidel radials. Design flaws or user ignorance? Sometimes all it take is using different plugs L/R. My OS15 4S also needed glow support near idle. Design flaw? Come on and give me a break!

After the take-over into private hands MVVS assembled these engines as long as parts were available. With all parts gone they stopped selling them because they were not part of their new ideology in which there was no room for niche market engines.

RE: MVVS 120 boxer engine
 

Hi!

Pe ! If not possible to reach the high speed needle when using silencers is not a design flaw ...tell me what isn't a design flaw!

RE: MVVS 120 boxer engine
 

rotate the cylinders so the carb is on top?

RE: MVVS 120 boxer engine
 

Ok, I'm new here.
Seems to be an old thread, maybe someone still monitors it?
I recently aquired a brand new MVVS 120 Twin, installed it in a Drastik 120.
A 16x6 two blade prop gives me about 8500 RPM.
A 14x7 three blade gives me about 10000 RPM.
I'm using OS no 8 glowplugs, 10% nitro, 20% oil.(50/50 castor&Klotz)

I have absolutely no complaints about the power, 1/2 throttle it climbs vertical.
On the 16x6.
I do however also get the low throttle cutout at idle.

I have designed and built a PIC circuit to maintain glow at low throttle settings(not installed yet),
and can live with that solution.

Main questions, am I in the ballpark with the prop, fuel, and glowplug setup?

Oh, some pictures...

RE: MVVS 120 boxer engine
 

your rpm are ball park figures. about 8000 to 9000 rpm static should be fine.
The carb in downdraught configuration helps a lot.

RE: MVVS 120 boxer engine
 

Hi!
Try a 17x6 or 18x6 instead! Prefearbly a APC or RAM! The APC clone (JXF) that you now use in the picture is not particularly good!

RE: MVVS 120 boxer engine
 

As far as I can tell, the two cycle boxer twin engine designs all seem to have the same issues when you run them.
One issue is air fuel flow isn't balanced or even between the two cylinders (or four or six for that matter). So you have to compromise the adjustments to work with two cylinders. You can't quite lean it out all the way as the right cylinder would run too lean whereas the left cylinder tends to run too rich. The air fuel flow characteristics tend to cause the left cylinder to run more rich and more cool than the right cylinder. You can take athermometer and measure the cylinderhead temperatures to see the difference between them. Also the left cylinder has a unnatural air fuel flow through it in comparison to the right cylinder. This tends to cause the air fuel to not atomize as well and thus it leads to a tendency to drown out the glow plug when you lower the throttle from WOT to idle. Usually the left cylinder tends to be the one that flames out on you.

Now a MVVS twin uses a common crankcase for both cylinders with the single carb on it. This means you always have to set the carb mixture settings for the leanest cylinder. So it is always a compromise then. With the Fox twin cylinder engines, the two halves are offset and separated and each has its own carb, and the imbalance between the two cylinders is more easy to compensate for, but you still have to adjust everything for the leanest cylinder still. The left cylinder still runs more rich and cooler than the right cylinder does. The Fox Twin still fires both cylinders at the same time, just like the MVVS engine, and although both cylinders have their own carn, they are still connected with each other as the center bearing is a unsealed open bearing. The inline twins don't have this problem though, such as the HP 1.20 twins. They run fine without the weird flameout issues the boxer twins would have,

I once accidentally did a experiment with a Fox Eagle III .60 engine years ago. Where I took the cylinder and rotated it so the exhaust was on the left instead of the right. I also mounted the engine horizontally on the left too. I was going to use it in a twin engine plane at the time. That was when I discovered it had the same flameout issues that the Fox twin did in that same situation. When you study it some you can see how the air fuel as it flows through the engine is flowing in a opposite direction on the left versus the right, plus the crankshaft and piston causes a difference in the flow and interference too. The air fuel just doesn't like going inthat direction much at all.

Clarence Lee did a review of the Fox twin years ago, and to solve the problem he simply flipped the cylinder base gasket over 180 degrees to block off the boost ports on the engine. This is the big port opposite the exhaust port on the cylinder sleeve. This results in a loss of 200 to 300 RPMs, but that isn't much considering how much power the engine develops. Mr Fox himself suggested making a balsa plug to do the same thing, but I think the gasket method works good. Another method is to simply use a on board glow ignitor and program it to come on below 1/4 to 1/3 throttle too.

Anyway, I think if one did this same thing to the MVVS twin engine they would have success in using it as well. As it would have the same problem as the Fox twins I have been using in this area. Either block off the boost ports or use a on board glow ignitor program to come on at lower throttle settings.

One other thought is to mount the left cylinder so that the exhaust flows up. But then the engine becomes assymetrical and might look odd like that. I have also seen that method used with some homebiult twin engines as well.
Also what might work better is to mount both cylinders to face to the rear like some of the ROSS engines did years ago. Some people have setup their Fox Twins to be rear exhaust and those engines ran fine and didn't have the flamout issue on the left cylinder.

One thing is the Fox 1.20 twin was designed to run in the 12,000 to 14,000 rpm range wheras the MVVS 1.20 twin runs upwards of maybe around 8,000 rpms. So one has to prop accordingly for them.

Here is a pic of a MORIN from 1949 that used the assymetrical cylinder setup too.

http://static.rcgroups.net/forums/at...-morin%204.jpg</p>

RE: MVVS 120 boxer engine
 

You just nailed it earl.

A diverter to direct the flow towards the "lazy" cylinder also works to get balance.

RE: MVVS 120 boxer engine
 

Thanks for the tip, but I already have too little clearance on the prop tipshttp://www.rcuniverse.com/forum/js/f.../sad_smile.gif
I have installed my PIC circuit and a 1S 4000 mAh battery, and two heli glow plug connectors.
It is effectively a Y-Lead on the throttle output, and anything much below 1/4 throttle, the glow plugs come on.
Haven't had a flame out since. And I don't need Glow Drivers http://www.rcuniverse.com/forum/js/f...eeth_smile.gif
The carburator is now giving problems, two flights, and the diaphragm valves start curling up.
Leave the engine alone for two weeks, and they lie as flat as new.
I run the engine completely dry after the last flight of the day, maybe I should do that after every flight ?
Going to a local Walbro supplier tomorrow, see what he has in the line of alcohol resistant kits.

And to give credit where credit's due, a very easy starting engine, and actually does sound different from a single.
And much less vibration !

RE: MVVS 120 boxer engine
 

Current D10WAT carb kits have a blue mylar membrane that is alcohol resistant. The regulating diaphragm has limited resistance. Running the carb dry  will accelerate the rubber hardening, but running coleman fuel (or equivalent) after a flight day will preserve the carb quite well.

RE: MVVS 120 boxer engine
 

Well, just an update.
I found out the hard way that this engine is at it's happiest with 20%castor, 80 %methanol.
NO nitro !
I'm still using the low throttle on board glow driver, and on startup keep my hand on the RH cylinder, to feel when it fires up, and starts giving power.
Once hot and running, this motor pulls a Drastik 120 vertical.
Main needle almost fully screwed out, low needle set up for a slightly rich idle.
Last flight of the day, I pull the fuel tube, and let the engine run dry.
This motor isn't too particular about glow plug types.
Prime it 6 turns with fully open throttle, close to idle, pretty much starts on first or second flip.
Only flame-out I had, was when the fuel tank was empty !

RE: MVVS 120 boxer engine
 

When they are treated well, and given what the manufacturer specifies, provided the carb is in good shape, these engines are beasts.

RE: MVVS 120 boxer engine
 

Hi!
Sorry! But they are not! And that's why MVVS stopped manufacturing them after a very short period.

RE: MVVS 120 boxer engine
 

http://www.youtube.com/watch?v=nV0tLu7NflQ

Some have great success. Not for the beginner though.