Magnum Open rocker 4 stroke engines

[Barry Dedeurwaerder 1]

Hello everyone,

I have a few questions regarding the UK made Magnum 4 stroke engines.

I searched the internet, and found out that they also manufactured a 120 size single cylinder engine. A model engine collector told me that they also fabricated a 240 V twin, besides the 182 v twin engine.

I assume I have a 240 v twin magnum, the place where normally 182 v is mentioned on the engine housing, is machined blank..

My engine has black cylinders, and red anodized cylinder heads.

Also a 'US' type prop hub ( much bigger then the normal version)

Could anyone enlighten me with some info please?

[Denis Watkins]

Your photos Barry

[Barry Dedeurwaerder 1]

Many thanks, the right cylinder has some sort of alu disk, preventing the piston to hit the cylinder head! imagine that I guess manufacturing standards on these where not so high?

[Former Member]

[This posting has been removed]

[Jon H]

if you take a head off you can measure the bore/stroke and work out the capacity. Lovely looking engine, if you want to run it but are having trouble or need help let me know, its always fun to play with engines

[Barry Dedeurwaerder 1]

I measured the bore ,and that says 31 mm, and as the 91 cylinder bore was only 27mm, it really is a 240

[Jon H]

Some quick maths says you should have a stroke of about 26.5mm for it to be 20cc per pot and thus 40cc (or a 240) overall.

As i cant find a manual for the old magnums i am not able to check

[Mike T]

It may be my fevered imagination, but didn't these guys (or somebody) use those pots in a 5-cylinder radial?

[Tim Flyer]

Lovely looker! Hmm we might have to persuade Laser to have an anodised option? 😉

[Barry Dedeurwaerder 1]

I might trade or sell the Magnum , we will see  

Edited By Barry Dedeurwaerder 1 on 20/01/2017 12:56:21

[Barry Dedeurwaerder 1]

There was a 3 cylinder radial magnum.. but those where 3 91 cylinders

[Former Member]

[This posting has been removed]

[Jon H]

I am working on the issue. We have done a handful of black anodised engines in the past and people love them. The silver black and red also looks really good but trying to convince my boss is another story as to him its just another cost.

I suppose the question is if a coloured version of the engine was available, would customers be prepared to pay a small premium for it like saito do with their golden knight?

As for Rays Radial, it was glow and about 150cc. A bit of a non starter from a commercial point of view these days, and in those days fewer people had models large enough to take one.

[Solly]

When these engines first appeared three of us from my flying group bought one, - they were not a success. Every one was eventually returned to the factory and I settled for a refund. One of the problems was the cams were too aggressive and the valve springs were not up to the job. After a short time the engine would suffer from valve bounce and since it was an interference engine the valves would come into contact with the piston, causing damage. There was also a problem with bottom end lubrication and all three engines developed damaged big ends. Also the carb was prone to icing up! You could see a layer of frost forming on the intake tube while the engine was running. I met the designer Peter Rolfe at Old Warden and he was a very nice chap. I suppose there was nothing wrong with the engines that couldn't be rectified but they disappeared after a time.

[Jon H]

what rpm were you running them at? From the bore/stroke ratio I would have run them quite slowly

[Solly]

Hi Jon. I can't remember, this was many years ago. But I'm sure that we would have been using the recommended props and fuel, something I have always done.

[Luke Lane]

A little bit of history behind Magnum Engines.

Magnum engines where made as a side line, by Custom Enclosures, Concorde Street, Luton, Beds, during the 80's to early 90's. The company was dissolved about 20 years ago. There was a 3 cylinder radial with a starter, and from my memory was spark ignition, running on petrol, that they where trying out.

At that time, I was putting lot of precision engineering work their way, and as a thank you, they gave me the Magnum 91S that was shown at the Nuremburg Toy Fair 1988. A heavy engine and not as powerful as any of the competition, these engines where mostly seen on large vintage models. By swapping the valve push-rods, it could then run backwards ( clockwise ). When I came out of the hobby in 2003, I sold it along with all my other gear at the Watford swap meet. I hasten to add, that I'm well and truly back into the hobby.

[Mike T]

Percy,

In my minds eye, I was sure I'd seen an ad. by Magnum for a 5-cyl. version using the .91 pots - definitely not a Laser derivative.

I'd heard of the Robinson (skew-gear driven rotary valve?) and a friend had a Vega .91 (sleeve valve?) but before I knew him. Apparently, rice puddings feared not for their skins...

[John Davies 4]

I have one of these Magnum 91`s kicking around somewhere and was going to put it in a GY20 Minicab , which I did start Years ago , and got about three quarters built , but never finished it , this was the engine i`m sure Dave Womersly used in his own model. My part built airframe is still kicking about gathering dust and a little bit of hangar rash over the years . Must finish that one, it`s a pretty little aeroplane. I must ask on here if anyone else has built a Minicab from the model world plan. Getting back to the Magnum, I may even sell it as they seem to fetch quite good money on fleecebay , unless someone convinces me to finish the Minicab and put it in that.

[Martin Harris - Moderator]

I don't think it went into production but I have actually held a 5 cylinder Magnum prototype, brought into work by a friend of one of the partners in the business. This may well have been what was featured in the advert. I have the plans of the Stearman that it was planned to put it in in my loft!

[Martin Harris - Moderator]

I've checked with my source and there was a 7 cylinder radial under development when the company stopped producing engines - all the parts were made but it was never assembled.

[Robert Putley 1]

I have one of the early 90's Magnum's which I purchased new in the mid eighties. Fitted this in a vintage Goliath (it's fifty years old now). Which was flown as recently as last year.

It doesn't compare with the Laser 75 which I had purchased previously. Would guess the power is similar to the Laser.

It flies the Goliath with great authority. I use a 17x6 wooden prop, it is easy to start, and has never given me any problems, apart from the fact that the supplied plastic bodied carb would seize up during the winter. Solved that by swopping it for a carb from an Enya 60. Idle also doesn't compare to the Laser. Last year fitted an on board glow, I think from South Herts Models.

Haven't said all that, I have a soft spot for this motor and always enjoy operating it.

[Jon H]

Posted by Martin Harris on 23/01/2017 13:52:17:

I've checked with my source and there was a 7 cylinder radial under development when the company stopped producing engines - all the parts were made but it was never assembled.

gimme gimme gimme, i will assemble it :D

[Martin Harris - Moderator]

Ha - I've already probed that subject and the whereabouts are (currently) unknown. On top of which, you haven't got time to be messing about enjoying yourself!

[Don Fry]

I have acquired, as a stoke of genius, or madness, a truely lovely Fiedler Storch, built from a Svenson kit circa 1980 to 83. I have sorted the fitted Multiplex gear fitted, thanks to Percy Verence, and is now on a fusion of Multiplex and Spectrum. It has a British built Magnum 91, open rocker 4 stroke fitted. On the basis, not broke don't fix, I will at least try the engine.

I have no knowledge of engine history

Three questions.

I assume it runs on a standard modern fuel, 5 % nitromethane, correct?

I think a six in pitch prop is good for this airframe, what diameter?

If replaced, what is a modern equivalent for power. I am told, in its day it flew on this motor, but was not over powered.