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Monday, August 5, 2013

British AMCO 3.5 cc PB Rebuild Story

 Allbon Spitfire and Amco 3.5 cc PB Rebuild Stories

AMCO 3.5 cc PB
ManufacturerAnchor Motors Co., Newgate, Chester, UK
DistributedAnchor Motors Co., Newgate, Chester, UK
Series / Serial No.s / n
Year of manufacture1948
Displacement0,2.14  cu. in. (3.5 cc)

Power classDiesel
Type of carburetorFixed without speed control
AdmissionFront rotary valve (crankshaft)
Inner bearingNot
Outdoor BearingNot
Crankshaft to crankcaseIf
Crankshaft on bronzeNot
FuelEther / Petroleum / Oil
Comments This is a classic diesel steel jacketed radial transfer four channels, casting piston and crankshaft mounted directly on the cast aluminum crankcase. 

Rebuild Story:
These engines were made in Chester England until April 1952 when the company was sold to an aeronautical electronic engineering company

Reproductions from CS in China, Arne Hende have been available in the past
This is typical of the damage that occurred on those early Amco engines when the crankshaft failed.

Two new extra light piston with a drilled out wrist-pin made from chrome vanadium steel were the first items I made for this project

To improve gas flow I smoothed out the lead in to the transfer flutes at the bottom of the cylinder and removed the sharp corners inside the crankcase.

I purchased a vintage Ambird Sportsman C/L plane and this Amco is one of the engines considered to power it. The Amco has an exhaust stack option.....so I decided to take that idea one step further......   

This is an over square design where the bore is lager than the stroke (17.46 to 14.29 mm respectively). The power output is just under 0.3 horsepower with a constant torque from 9,000 to 13,000 R.P.M.
The older used engines have heads burned brown by the heat, where as the new engines were made with black anodised heads.

The AMCO PB was a sensation when released because of its light weight and high power giving it an unbeatable power to weight ratio. In the beginning there were problems: the crankshafts were too thin and had a bad habit of failing without warning. Engines after serial number 5000 were much better with redesigned thicker wall cranks.

I have one complete engine and one that is missing the piston and connecting rod and I intend to make these missing parts.The original engine had an extremely heavy piston and an unbalanced crankshaft; I will correct these problems in my engine by machining out the useless internal material from the piston and hope the resulting power output will be in excess of 0.35 horsepower.  

Original parts shown on left and my improved designed parts with the counterbalance crank; drilled out wrist-pin made of chrome vanadium steel and slotted connecting rod big end on the right. 
One of my new light weight pistons and connecting rods with its slotted big end, for improved lubricating of the crank pin.
These are the engines I was considering powering the antique plane with.

The optional Amco exhaust collector stack makes a handy mount for the custom twin mufflers.

The stock engine on the right and the modified engine fitted with its twin mufflers on the left.
OK! Let's take it outside for a test run, but I must not forget my chicken stick; I need all my fingers for these rebuild projects.

The engine will still need a lot more runs with increased oil content in the fuel to properly be run-in, then the power will increase noticeably. Propeller size for these first runs is a 9X4.  

Published on 21 Jul 2013 After a quite period on my channel a new episode of another British well known diesel. The notorious 3,5 AMCO "finger-biter". The Amco company made only 4 engines.The 0,87 diesel in 2 versions,and the 3,5 in plain and ball bearing.The Amco had a good reputation established by their first 0.87 diesel engines.Thats why it survived after the early 3,5 failures. The crankshafts were too thin,and combined with a soft alloy conrod; most  never survived long enough to get old. The mistakes were corrected by AMCO, and the engine was very popular in control line flying and as a free-flight engine; mostly in the UK. My two engines are ser. numbers 8450 and 8483!! So they were produced at approximately the same time. Engines from numbers 5000 and up are known as the better ones. The intake passage in the shaft is smaller and that gives a thicker diameter to the rod, which is also made from better materiel. It has a lower rpm output, but it will hold together ...and run for many hours. I have 2 examples, one is a poor runner, since the wrist-pin and rod are worn out. The other is almost new, but is missing the piston, rod and wrist-pin. I made those parts new, but made the wrist-pin a little bit thicker.(3,6 mm to 4,0mm). The heavy piston is reduced in weight together with a drilled out pin. Further I added the crank-web counterweights, which makes the engine run very smoothly now. A radical short stroke engine with a heavy piston is not a good idea. Amco should make at least some efforts, to change this condition in their design. But I guess money is like always the reason behind this shortcoming. I would like to use the Ambird sportsman C/L plane. The excellent power to weight ratio and long shaft make it an ideal powerplant for that project. I changed the wing design (thicker airfoil and build up wing instead the 2 piece prefabricated wing); added flaps and build the bird far lighter than it was intended by the kit designer. The nice exhaust will make it for sure a nice vintage racer. After maiden flight is done, there will be a clip of this nice and rare racer! Thanks for drop in and more diesels and rebuilds on my channel;. And many more engines still to come. Keep your fingers out of danger and happy flying!
YouTube Channel Valic000


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