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Wednesday, November 14, 2012

Irvine 20 Diesel Rebuild Story


Design History:-
Designed and manufactured as a diesel-i zed version of a nitro glow engine in England in the mid 1980's



Design Features:-
Front through the shaft induction; ABC piston/cylinder technology; advanced design carburetor and bolt on muffler without pressurization tap.


Table of Contents:
ItemDescriptionPage Number
TABLE2
Background History, Specifications, Experiences3
Rebuild section Start of Rebuild5
Parts selectionChoosing used parts for the new runner6
Liner reworkFinishing and tapering liner with special tools 9
New piston Processes and material selection 17
CastingInspecting crankcase and deburring flaws22
Running inMounting, propeller selection and fuel mixture27
Final observationslessons learned and future plans for improvements to the rework process28



The Irvine 20 ABC Diesel Engine

Design History:-
Designed and manufactured as a diesel-i zed version of a nitro glow engine in England in the mid 1980's


Design Features:-
Front through the shaft induction; ABC piston/cylinder technology; advanced design carburetor and bolt on muffler without pressurization tap.

Specifications:-
Displacement 2.5 cc

Observations:-

"This is the latest and, perhaps, the most significant example of the diesel-ization of an existing glow plug engine, in that it was initiated  and developed by the engine's manufacturer. Ever since they began  producing their own motors in 1977, Irvine Engines have specialized in glow engines (the sole departure being their production of the Mills 75 replica) and the fact that Ron Irvine decided to press ahead with the production of this diesel version of the well-liked and very successful Irvine 20 series, obviously indicates considerable faith in its capabilities.

The Irvine 20 has not been extensively redesigned for diesel operation. It has a new crankshaft; otherwise, dieselization is confined to the cylinder head assembly, plus small modifications to the carburetor and silencer".

After describing the reduced-choke carburetor, the author continues....

"The reason for having this much reduced choke area is to enable the engine to be operated without the assistance of an exhaust pressurized fuel system, which is the reason why the diesel version of the silencer has the usual pressure nipple replaced by a screw-in plug.
Why no exhaust pressure feed ? Simple! Exhaust gases condense to form a certain amount of H2O when they come into contact with the cool fuel in the tank. A little water in the fuel does not matter in a glow engine; it is miscible with methanol-based fuel and a small amount can be tolerated...Diesel fuel, on the other hand, is petroleum based (usually kerosene, occasionally DERV). Ergo, the water remains separated and, having a higher specific gravity than that of the fuel, settles in the bottom of the tank, where it may be sucked up by the clunk weight. Not even diesels like running on water. Result: malfunction of one kind or another...".

The author was Peter G.F. Chinn: the author of numerous articles on model airplane engines of his day .


Although it is generally regarded as a fine engine it is not my favorite by far. Looking for a practical RC Diesel to power a Kitty-Wake sport float plane, I settled upon the Irvine 20 ABC diesel to do the job. After a short ground run I made a very bad decision and decided to opt for a first flight. As I recall the flight did not last very long, nor did the poor Kitty Wake. The Irvine suddenly quit and I was faced with the worst of all situations for an RC flyer; a down wind dead-stick landing on a new model. Needless to say the landing didn't go well, ripping away the floats on impact.

That Irvine itself never ran again. All attempts to start it proved unsuccessful and the reason was obvious. There was almost no compression, the once tight engine had gone from lots of compression to none in the matter of a few short minutes (unbelievable!). The engine was thrown into a corner and forgotten for a number of years, until one day I got around to disassembling it for a close examination. What I found was the engine had eaten itself. The piston and sleeve were severely scored, with deep vertical grooves running full length in each. All attempts to find replacement parts (matching piston and sleeve) proved to be impossible so, I thought if I could find a used Irvine 20 engine for parts that would be the answer (not!). The other used Irvine 20's that I managed to find were ringed engines, with marginal compression and I knew from the beginning that they would never start as a diesel.


The Irvine 20 Rebuild Story Starts Here:

The runner was created from parts harvested from three clapped out engines, an ABC diesel and two glow engines. The rebuild subject has a reworked glow cylinder and a new Dispal alloy piston.


The Irvine 20 Rebuild Story Starts Here:
The runner was created from parts harvested from three clapped out engines, an ABC diesel and two glow engines. The rebuild subject has a reworked glow cylinder and a new Dispal piston.




Read how the rebuild was performed


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Watch our rebuilt Irvine on the test stand