Reproduced from the RCM&E August 1978, with the kind permission of the Editor, Nexus Specialist Publications.
Now available direct from the manufacturer, the superbly made production version of the Fisher Redshift 60.
Production Redshift 60
Sixteen months ago, in this column, we expressed considerable enthsiasum for an entirely new British engine, the Redshift 60, a prototype of which we had been invited to examine by the designer and constructor, Dick Fisher of Sheffield. As was then stated, this motor was (and still is) one of the most technically interesting 10c.c. R/C engines to come our way for a very long time and, while it has taken a little longer than was anticipated to get the Redshift into production, the end result
has, we believe, been well worth waiting for.
The current production model, as illustrated here, is beautifully made and is a credit to the British model industry. The engine's performance is something that we shall be reporting on in due course but, so far as overall standards of finish are concerned, the Redshift must rank with the two makes that one has come to regard as being at the very top of the tree. It was a delight to dismantle this motor and contemplate the finish of its component parts and the care that has been put into its construction.
Compared with the prototype, a number of changes have, of course, been made. First and foremost, the sand castings used for the crankcase, front housing, etc., of the prototypes, have been superseded by heat treated investment castings. These are extremely good examples of aluminium investment casting, crisply finished and with machined joint faces. The piston is a gravity casting in high silicon content aluminium alloy and a separate prop stud is now used, screwed into the hardened
nickel-chrome steel crankshaft. .
What makes the Redshift so interesting from the design angle are its cylinder bore coating and, especially, its unconventional crankshaft main bearing set up. the cylinder liner is of brass and is used in conjunction with a ringless piston, as in an ABC type engine but, instead of being hard chrome plated, the cylinder bore has a Drayloy coating having a harder surface and, allegedly, a lower coefficient of friction.
The crankshaft and front end assembly, as explained in detail in our earlier article, has the advantage of permitting a large valve port with an oversize induction passage, while avoiding excessive primary compression chamber volume or the need for non-standard ball baring sizes. The diameter of the shaft at the valve port IS 17mm (instead of the standard 15mm o.d. shared by most current 10 c.c. shaft valve motors) and this is increased to a 20mm journal diameter at the rear , enabling it to be carried in a standard 20x32mm ball baring. In the prototype, a 13mni
i.d. gas passage was used but Dick Fisher later found that an equally good performance could be obtained with a slightly smaller bore and this is now reduced to 11.9mm, while the induction period is extended by having the rotary valve close later. The prototype's unique method of reducing effective crankcase volume, by having the counterbalanced crankweb running within a sleeve extension of the front housing, is continued in the production model but is further refined: the bore of this sleeve is now machined 0.06mm eccentric to allow for the downward loading on the crankshaft.
This close attention to detail is also evident in the fitting of the cylinder head to the latest production examples of the Redshift. Finned cylinder heads are inevitably stiffer parallel to the direction of the finning than across it, and the slight distortion that this can cause, when the head is pulled down, can result in a degree of ovality in the cylinder liner which, though extremely small, may nevertheless be undesirable in a ringless A\BC type engine. To overcome this problem, the latest production Redshlfts are fitted with a brass ring encircling the head screws between the head and main casting. The ring is machined to a thickness precisely matched to the thickness of the head flange and shim and to maintain a good gas tight joint between the head and cylinder flange these latest engines have this joint sealed with a liquid gasket compound.
At the time when the prototype Redshift was described in this column, various carburettors had been tried and a decision had then to be made as to which type would be supplied as standard equipment. The type eventually chosen was, appropriately enough for a British engine, the British made E.D. 'Multi Carb', but with a slightly enlarged choke. This now checks out at 0.297in. or 7.54mm bore and since, with the E.D. carb, a surface jet is used, the effective choke area works out at a generous .069 sq. in. or 44.7 sq. mm.
Complete with E.D. carb and a suitable glowplug, the production Redshift examined scaled 529 grams or just under 18.7oz. No silencer is supplied with the engine at the present time but a number of existing 60 size silencers will (or can be easl)y adapted to) fit the engine, Including Enya, HP, 0.S. and Webra. Drilling and tapping the ends of the exhaust duct for a bolt-on attachment is to be preferred, but if the strap-fitting HP or Webra is used, care should be taken not to risk distorting the cylinder by excessive tightening.
Because of the cost of manufacturing a motor of the Redshift's high quality, the engine is available only direct from the manufacturer at the present time, price £72.50, plus £2 post and packing. Orders should be sent to Fisher Engineering (Sales and Service), 9 Portland Avenue, Aston, Sheffield S31 0FN.
Above: Redshift's exclusive Drayloy coated brass liner, excellent
piston and rod assembly and cylinder head with special 'anti-distortion' ring.
Below: Redshift's excellent investment castings. Note how front housing encloses crankdisc to reduce crankcase dead volume.
Below right: Redshift 60's unique front end assembly features a 17mm diameter shaft with 20 mm rear journal.