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Monday, October 28, 2013

Webra .61 Blackhead & Silverline R/C

ModelWebra 60 R / C "Black Head"
ManufacturerWebra-Fein-Modelltechnik, Berlin, Germany
DistributedWebra-Fein-Modelltechnik, Berlin, Germany
Series / Serial No.12124
Year of manufacture1975
Displacement9.95 cc (0.613 cu. In.)
Diameter24 mm. (0.949 in.)
Career22 mm. (0.866 in.)
Power classGlow
Type of carburetorDimmable (with speed control)
InductionFront rotary valve (crankshaft)
Inner bearingIf
Outdoor BearingIf
Crankshaft to crankcaseIf
Crankshaft on bronzeNA
FuelMethanol / Oil
CommentsTwin Brother Webra 40, but usually known as "Black Haed". Stresses its piston with a ring and sweep flow deflector as well as the crankshaft with oversized intake passage and ball bearings. Carburetor TN with minimal regulation. One of the popular engines of the modern era of acrobatics.

This is one of those hard to find engines that seem to grow on you more and more as you continue to use it over the years. I currently possess two of these fine engines: one I had bought new in the mid 80's when I was in search of an engine for my then new airplane project, a Stirling PT 17 Stearman. The engine has been half buried in the nose of that airplane continually without removal or adjustments every since that time. I regularly fly that combination still and remark to myself what a wonderful engine the Webra 61 is: reliable service; easy to start; plenty of power for the job regardless of weather conditions; never requiring of maintenance except for an occasional tweaking of the needle valve setting or freeing of the throttle valve with a shot of WD40 after sitting untouched for a long time.
For all those years I have been mistakenly referring to it as my Webra Blackhead: it was not until I started this article that I discovered that it is actually a Webra 61 Silverline. An updated version  of the old Blackhead with a silver head and its own muffler, replacing the movable baffle of the old Blackhead. I now recall the popular myth that prevailed back in 1969 when the Blackhead first appeared on the scene: that model engines could not tolerate the back pressure caused by mufflers. But since that time internal changes in the area of porting and scavenging have resulted in an engine that produces even more power when run with a muffler attached.
The engine that I ran to make this article is an old used and abused Blackhead that I acquired recently on Ebay for a project that I had in mind: a replacement engine for my Red Zephyr sea plane. 
From the point of view of competition success, the  Webra's outstanding engine to date. Twice winner of the world R/C aerobatics championship. this German engine became almost standard wear for American R/C contest models during 1970-1973 and swept the board in the U.S. National aerobatics events of 1971 and 1972. Improvements put into effect in the mid 1970's include a rebalanced crankshaft  with wider valve port that opens very early and extends the induction timing by a further 10 degrees. Another improvement is the switch from a solid gudgeon-pin to one which is tubular with brass pads held in place by circlips. And the big end which formally was plane is now bronze bushed.
The Webra two needle valve carburettor, whose automatic mixture control principal was copied my most manufactures over the years, is unchanged over the earlier Blackheads except for the adoption of a larger 8 mm inside diameter choke that increases the effective choke area to approximately 34 square millimeters. 
Bench test Results:
Using 5 percent nitro fuel and the Webra glow plug produced a maximum power of 1.2 b.h.p.
propeller                             with muffler                  without muffler
12 x 6 Topflight Maple             10,700                         11,400
11 x 6         "                            12.200                         13,100
10 x 6         "                            13,600                         14,800

Webra.61 R/C Blackheadglow0.607424mm22mm15.8MANSep-69Chinn

Watch and hear how she performs in the air when we "go flyen".

Sunday, October 27, 2013

Russian MAP 2.5 cc Diesel

Russian MAP 2.5 cc Diesel

ModelMARZ Mk. II
Series / Serial No.s / n
Year of manufacture2003
Displacement2.45 cc (0.150 cu. In.)
Bore15.5 mm. (0.610 in.)
Stroke13 mm. (0.512 in.)
Power classDiesel
Type of carburetorFixed (no speed control)
InductionRear Valve
Inner bearingIf
Outdoor BearingIf
Crankshaft to crankcaseIf
Crankshaft on bronzeNA
FuelEther / Petroleum / Oil
ConditionNew in Box
CommentsSecond series of this engine we can consider best seller and now manufactured from Russia. Practically equals the original model, but have improved casting processes such as crankcase and diesel cylinder sleve is classic: a steel jacketed type with radial transfer slots, piston of cast iron, crankshaft on two ball bearings and intake valve at the rear driven by a false rotary crankshaft.

This is not considered to be a high quality diesel engine by most experts. During the running of this new example I discovered that it is strongly advised that the engine be examined for loose head screws. After only what was a very short first run my engine began running rough and eventually stopped. When I checked for the cause of this I soon discovered that the three head screws holding the head down to the cylinder had backed out by almost a quarter of an inch; allowing the head and contra piston move upward by that amount. Its a wonder that the engine would even fire under these circumstances.
It was difficult to tighten the head down with a tiny slotted screw driver, but I managed to get them tight enough for more runs. Before I run this engine again I will locate some socket head screws of the appropriate size and length, which will eliminate this particular problem for once and for all.
I will also remove the back plate and have a look inside to check for foreign material which may have been left behind after the manufacturing operations have been complete. It is not unusual; particularly for engines manufactured in Russia during the last regime.     

Uploaders' Comments (David Crocker)

  • Cathead Biscuit 
    Hey David, another great vid of what seems ro be another great little diesel. What would be a good first diesel for someone wanting to get into diesel engines? I can tune nitro engines pretty well and I'm looking to get my first diesel. Thanks.
  • David Crocker 
    Thanks! From my perspective I would have to say the English PAW with throttle control engines are easy to live with inexpensive and practical for RC flying, but messy like all diesels, You should also keep checking the head hold-down screws for tightness because, they can fail from metal fatigue in flight and destroy the engine. That actually happened to me when I started in diesels. Check out my vid (Starting and Running the PAW 2.5 cc Diesel).
     ·  in reply to Cathead Biscuit
  • valic000 
    Hey David! Is that the new engine I send some months ago together with the ohers? .The engine run wel on a 9X4 prop.My new Marz also hat problems with a too tight contrapiston.It shoud free up,when use moore runs,If it goes too tight at a hot run,I just uscrew a bit,so it jumps out of it stocked possition,and than turn in til the right compression is archived .Otherwise unscrew cilinder,use a wooden dowel,and force the contrapiston out,and with 1200 wet paper grind it of a tiny bit.
  • David Crocker 
    Yes Peter! It is the engine that I got from you last fall. It runs great for the first run and with a little use it will run even better. Did you notice where the head screws backed off and had to be retightened? Did you see the list of new engines that I just picked up at the EngineTradingPost?
     ·  in reply to valic000
  • David Crocker 
    Perhaps I will have to perform that procedure if it does not loosen up naturally. The pliers will work to a point; until I bend or break the "tommy-bar" as the English call it.
     ·  in reply to valic000

All Comments (7)

David Crocker