Roo Man

My Feedback: (1)

Just a foot note:
I have two MDS 68's that run very well. I found that the MDS is a high compression engine and can easily run without nitro. I used 5% nitro and as I said they run great. Mine have the newest carb, I am sure that helps.

Calvinman

Oops sorry Tim, I reread your post and noticed you wanted the ID of the carb, it is about 10mm down to 7mm. It does appear to be the machined carb and it did run well at first on the ground but as soon as it took to the air in a nose up full throttle climb it would flame out. That's when I did some reading and found that the MDS's needed an extended run in time.

Calvi

1QwkSport2.5r

Law enforcement doesn't have my prints. I've never been arrested or incarcerated. I don't take selfies either, so I have nothing to worry about!

1QwkSport2.5r

New engines need richer fuel mixtures too - especially in flight. Richen up that needle a bit more and you should be fine. ABC engines don't need a lot of break-in time, however they do benefit as do most other engines to be set a bit richer than normal during that first gallon of fuel.

As to the carb size - when selecting a different carburetor, if necessary, choose one about the same as stock. Slightly bigger carb's will often make a little more power, however fuel draw can suffer some. I've been busy installing and finishing a wood floor in my basement, so I haven't had time to dig through my parts box. I will say that the 14mm neck and 6-7mm carb choke is on-par with a 7.5cc size engine.

blw

My Feedback: (3)

That's already been done, Pope. It's a good bet they have yours too, or the links and passwords to get them.

1QwkSport2.5r

The SuperTigre GS45 carb would fit. 14mm neck and 9mm choke. I would get more time on the engine and evaluate the carb later - that is if it runs reliably and throttles good now. Set it richer and see how it goes.

jaka

Hi!
All ABC ABN and AAC engines should be run in at full throttle and nearly at max rpm, appr 500 rpm down from full speed , adjusting the rpm with the full speed needle; Never with the throttle lever !! In case of the MDS .48 a 10x7, 11x6 prop should be used. Preferably APC ,RAM or Graupner G-Sonic as those are the best props on the market performance wise.
MDS engines are like any other ABC engine and does not require any prolonged running in!
AS Mr COX says the colored band is just a part of the piston that is turned a little smaller diameter to avoid the piston getting stuck in the cylinder at high temperatures.
The MDS engines all run good on no or 5% nitro as they are high compression engines. Therefore when using 15% nitro the engine will quit when giving full throttle and it will be impossible to set the high speed needle.
Nothing wrong with the carb!

Calvinman

Hi Jaka, I did read the MDS engines need a lower percent nitro to run properly I was thinking of adding a shim to the head so I don't have to carry two different fuels with me to the field. I generally use 10 nitro. Would you or anyone else know a good starting point for shim thickness to lower the compression so I could run at 10 to 15% nitro?

Calvi

1QwkSport2.5r

Measure the current head spacing to get an idea of where it is first. Then shim accordingly. Too loose of a head clearance loses power. .012" is a strong minimum, but .015"-.020" is common. Some are beyond that. You would need to try it and experiment as you go, but adding .005" at a time from the base head spacing would be a good start I think. You would need a dial indicator to accurately measure the head spacing. https://youtu.be/fIpyYRMJ1eI

Im not one of those guys that just throws stuff at an engine to make it run right. I like to know where I am in the beginning and Where I end up. This way you know what didn't work and what does and what variable made it work.

Sometimes taking videos of the engine running can give other clues as to what's going on also after watching it back. Some "tells" are harder to hear when you're right next to the engine.

Calvinman

Hi Tim, thanks for the info, I think I am getting ahead of myself though. I think I will pick up some 5% and see if I can get it running on that first, I'm going to go over the engine this weekend and maybe try to run it.

Calvi

1QwkSport2.5r

It sounds more complicated than it is..

I don't think it would be a bad thing to try some 5% fuel like you mentioned before taking the head off. Then you could get a baseline on how the engine runs and have something to compare to if you do decide to shim the head up. Another thought - If you end up getting more engines that require lower nitro fuels, just run your fleet on 5% instead of 10%. There's really only about a 200rpm difference between 5% and 10% nitro.

Mr Cox

One shim about 0.15mm thick (around .005-.006") should do the trick. Aluminium from a soda can is a little thinner than that, but it's better than nothing.

If you want ot measure the deck height you can insert a piece of solder-wire through the glow pug whole and then gently turn the the engine over TDC to squeeze the solder flat at the squish-band. Measure the flattened portion of the wire for the deck height.

Calvinman

Good tip Mr Cox, I seem to remember that you can buy some kind of a plastic rod that once flattened it either tells you on the rod or you line up the now thicker rod with a chart to give you thickness(incase you dont have a mic?)

Any way I am going to try getting it running on 5% before I start changing even more variables. I am going to measure up the carbs on my other engines and see what will fit, but the motor seems to have run so well at first with the stock carb I will start with it.

hsukaria

I've seen you running that OS engine!!! You weren't arrested for that yet?

1QwkSport2.5r

LOL. I have a few OS engines... My only crime is paying actual dollars for one of them. The rest were free. Better send the model engine police to my door.

I committed model engine sacrilege when I put that MDS .40 P/L into my old POS Fox .50. I remember a fellow belittling me about that one... It still runs.

hsukaria

I know I tend to be extreme about some things, but if I were you, I would run most of that 5% gallon through it before considering a carb change or adding shims. JMHO.

hsukaria

You can call it Detente, putting Russian parts in an American engine. That's good diplomacy. Maybe you should call Trump, he might put you to work!!!

The only OS engine I ever bought new had the liner peel on it. All the other OS engines I bought used and have had no trouble with any yet.

I had an MDS 1.48 briefly from a swap but never ran it before selling it (I wish I hadn't). It had incredible compression (ringed). That for sure would have run on 0% nitro.

1QwkSport2.5r

I look at it as taking two otherwise junk engines (the MDS was in a crash due to radio failure and the case was not able to be salvaged) and made one running engine. We made our own wristpin to fit the Fox conrod and wristpin retainers and we made some head buttons.

I'm going to see if I can force a liner to peel in an OS. As soon as weather permits, I'm going to test run my LA .25 to see what it does before I hack it to bits. I will be swapping carb's on that engine for sure.

Sorry for the thread hijack. Back to the MDS. I wouldn't spend a ton of time bench running an ABC engine for break-in purposes. Maybe a few tanks on a small prop set rich and then fly it. Set it 500rpm rich of peak and put a gallon through it that way. The only parts seating in an ABC engine that need break-in time is the conrod bushings. Bearings and the piston/liner find their own place with time - no special attention needed here. Just run it warm, rich, and fast initially.

hsukaria

Do the MDS engines require castor in the fuel?

1QwkSport2.5r

Castor isn't "required" for any engine, but it sure does make them run a bit better and last a bit longer IMO.

hsukaria

I meant like the manufacturer requirement also. I know that engines without conrod bushings (old and small engines) really need castor. I also finally understand why the Norvel (NV Engines) require castor based on a good explanation in the gas engine thread (has to do with the ceramic coated cylinder). But I guess an engine without those features could be run without castor if the user really wants to.

I sometimes wonder if my OS 55AX liner pealing could have been avoided if I had castor in the fuel. At the time, I was using it in an Ultimate biplane that has very high wing loading and cannot handle a deadstick. I was happily flying it when suddenly the engine started running lean. I found out later that some dirt clogged up the carb jet, causing the engine to lean out. I did not kill the engine to save the airframe. I did manage to save the airframe at least. I suppose an ABC engine might have survived that lean run?

Calvinman

No worries about hi jacking the thread Tim, I'm along for the ride, any info is good info as far as I'm concerned. I run Omega fuel that has some Castor oil in it and I always add 2 ounces to every gallon for good measure. I have already run close to a gallon through the engine with a very rich setting. Now I can't get the thing to run over half throttle .

I am going to grab some more 5% and try again and also get my castor oil smoke fix, cause up here in Canada its been to cold for me to even consider going to the field. Luckily for me I have a heated area to run it in. If I can't find anything wrong with the carb or any sign of a leak anywhere else and it wont run for me I'll put a different carb on it(if one of my other carbs will fit that is.

hsukaria

You might have done this already, but did you check if the carb is partially clogged. That is what happened to my OS 55AX. If did not matter how rich the needle was, the engine would not get more fuel.

1QwkSport2.5r

If they plated the liners correctly, it shouldn't peel. Look at a Thunder Tiger - their aircraft engines are ABN and you rarely hear of one peeling. Brass is far more resilient than Nickel by a long shot. Nickel can work well and last a long time until it's over-stressed. A piped pylon engine wouldn't last long with a nickel liner. Chrome liners don't really wear out... The piston does. Fit a new piston and you're good to go for a long time.

1QwkSport2.5r

Calvin - just fire the engine up on a 10x6, get it up to WOT (use glow heat if necessary) and lean the needle until it says, then Richen maybe 1/4 turn and then set the idle. If shouldn't take more than a tank to get it dialed in. Running in the cold sucks though, so I get it. I don't want to run engines even if it's 40F out.