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Old 11-20-2020, 12:35 AM   #1
RICHARD PAINE
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MAP3 2.5 Russian diesel engine


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I have this old ?? Russian control line / free flight MAP3 2.5 diesel engine. I freed it up & ran it, but the moveable cylinder/ head that is adjusted for compression refuses to move & be adjustable when assembled. It is very free when disassembled. I suspect this is not a quality engine & parts bind when tightened,
Does any one have experience or knowledge of this odd ball engine?
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Old 11-20-2020, 09:19 AM   #2
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Re: MAP3 2.5 Russian diesel engine

Hi Richard
The screw in the top of the head turns free and that is normal. That screw pushes against a device called the contra piston which is a little short piston affair that fits very tight into the top of the bore. This is how the compression is adjusted. Compression will force the device up and the screw stops it. These things get stuck in the bore. Complete disassembly would be required to get it out, NOTE: do not remove it out the top of the bore, push it out the bottom..
I have cheated though, run the engine and use the mixture screw to vary the rpm, lean it until peak, let it run here for a few seconds and then richen the needle a turn or 2, be sure the comp screw is loose, with luck the contra will snap up into place. Use an 8x4 prop.

Edit: The reason for the ultra rich mixture is twofold, first it cools the engine down quickly and second the rich mixture is harder to compress and hopefully shoves the contra piston up. Contra pistons are usually made of cast iron and will expand and shrink at a different rate than the liner.
OR, if you determine the compression is actually low than I have used pliers to turn that comp screw in. Go slow as the finned muff is aluminum.
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Last edited by Frank Klenk; 11-20-2020 at 12:05 PM.
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Old 11-20-2020, 09:20 AM   #3
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Re: MAP3 2.5 Russian diesel engine

Contact this fellow.
https://www.adriansmodelaeroengines....php?cat_id=201
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Old 11-20-2020, 12:07 PM   #4
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Re: MAP3 2.5 Russian diesel engine

Was there not an O-ring between the contra piston and the cylinder head or was it just an interference fit ?
The Russians and Czeck’s made some very good motors . The outside may have appeared rough on some but the inside machining was something again.
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Old 11-20-2020, 12:34 PM   #5
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Re: MAP3 2.5 Russian diesel engine

Marz Map3 2.5cc diesel engine.
http://sceptreflight.com/Model%20Eng...rz%202.5D.html
http://sceptreflight.com/Model%20Eng...%20Review.html

The write up in the first link mentions the tendency for the contra piston to stick.
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Old 11-20-2020, 12:47 PM   #6
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Re: MAP3 2.5 Russian diesel engine

Thanks for the good advice, I am obviously not a "Diesel " man but things went better today. I was wrong in thinking the whole cylinder was adjusted up & down with the compression screw. I did disassemble the cylinder assembly & found the contra piston is separate from the cylinder. No, there is no O ring, it appears to be an interference fit. I was able to heat the assembly with a covering heat gun & tap the contra piston loose. If I had waited for Franks advice I may have saved myself some time. However, I crocus clothed the contra piston, reassembled the motor & it runs well on a 9x6 wood. I am trying to find a 8x4 as suggested. When the motor was running, the compression screw had tension when moved in either direction but when shut off & cooled the compression does not force the contra piston up. I assume that is normal ?
Now to mount it in a 60 year old Jr Flight Streak & have some fun !
Thanks again
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Old 11-20-2020, 12:52 PM   #7
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Re: MAP3 2.5 Russian diesel engine

Quote:
Originally Posted by stegl View Post
Was there not an O-ring between the contra piston and the cylinder head or was it just an interference fit ?
The Russians and Czeck’s made some very good motors . The outside may have appeared rough on some but the inside machining was something again.
There will not be an o-ring, the contra piston is usually a tight lapped fit, like a piston that goes in under a bit of protest. The force from compression normally does move them as mentioned, unless the engine is gummed beyond reason.

Original (prior to US import/distribution) MDS glow engines are another good example of the outside/inside thing - gross, grainy and rough on the outside with crappy slot head screws with the slot cut sorta towards the middle somewhere. But shiny and clean machining inside and gobs of high-compression low nitro practical Euro engine power if the carburetor behaves.
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Old 11-20-2020, 12:58 PM   #8
RICHARD PAINE
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Re: MAP3 2.5 Russian diesel engine

Thanks for the links, I looked all over the web for info on this motor. Good reading
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Old 11-20-2020, 07:19 PM   #9
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Re: MAP3 2.5 Russian diesel engine

Quote:
Originally Posted by RICHARD PAINE View Post
Thanks for the good advice, I am obviously not a "Diesel " man but things went better today. I was wrong in thinking the whole cylinder was adjusted up & down with the compression screw. I did disassemble the cylinder assembly & found the contra piston is separate from the cylinder. No, there is no O ring, it appears to be an interference fit. I was able to heat the assembly with a covering heat gun & tap the contra piston loose. If I had waited for Franks advice I may have saved myself some time. However, I crocus clothed the contra piston, reassembled the motor & it runs well on a 9x6 wood. I am trying to find a 8x4 as suggested. When the motor was running, the compression screw had tension when moved in either direction but when shut off & cooled the compression does not force the contra piston up. I assume that is normal ?
Now to mount it in a 60 year old Jr Flight Streak & have some fun !
Thanks again
Hi Richard, compression wont snap the contra up when its not running, normal. Does yours have the muffler ring or straight exhaust?
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Old 11-20-2020, 07:42 PM   #10
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Re: MAP3 2.5 Russian diesel engine

Quote:
Originally Posted by MJD View Post
There will not be an o-ring, the contra piston is usually a tight lapped fit, like a piston that goes in under a bit of protest. The force from compression normally does move them as mentioned, unless the engine is gummed beyond reason.

Original (prior to US import/distribution) MDS glow engines are another good example of the outside/inside thing - gross, grainy and rough on the outside with crappy slot head screws with the slot cut sorta towards the middle somewhere. But shiny and clean machining inside and gobs of high-compression low nitro practical Euro engine power if the carburetor behaves.
The O-ring was just a thought. Another Russian glow engine we called the MAC ... the letter A was in fact a Russian symbol that looked like the letter A ; although In fact the Russian symbol was the letter “D”. When I sold the MAC (MDS) engines I replaced all the slot head screw with socket head bolts. The only thing with the carbs I found was if a single particle of sand got caught up between the barrel and carb body it would cause the carb barrel to stop moving (bind). If that happened in the air , you had to fly until an empty tank and then dead stick. Here is an explanation of the two engines which we were one of the same . Later on the engines were cast with the letters MDS . Check out #12 below

https://www.rcgroups.com/forums/show...engine-history

Last edited by stegl; 11-20-2020 at 07:58 PM.
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