Another Edwards 5 Radial

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I've wondered about this aspect myself. All the rocker arms I have come across on commercial 4S engines are steel, which I assumed was maybe more about wear than strength? The valve springs around this size equate to probably 2-3 pounds max depending on pre-load. The rockers on the O.S. 4S engines I've seen almost look forged, not machined. Maybe that's a function of their minimal mass with the inverted 'T' section profile. I unscientifically ran a file across the material on valve end (not the pad itself) and it seemed quite hard.


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Forged parts are cheap.. Heat red hot, then 1 or 2 big hits in the press with hard steel dies and the parts are accurately made, ready for machining. The grain structure is much better than cast, and the controlled cooling gives a ductile core and hardened outer layer. Car wishbones and stub axles are forged for material strength, good grain structure and fatigue resistance. Parts you never want to fail in service. The blacksmith's art was always about material processing to make things as strong as possible. E.g. plow-shares and swords, horse shoes, chains, etc.
You are all correct in your thoughts of the rocker arms and as it was pointed out I rarely build my engines from the designated materials but from materials I have on hand. This is my ninth engine build over three years and all are still running happily to this day and all have brass rocker arms. I usually start and run at least one of them every week to keep them in good shape. I like to have slow running engines with an idle of less than 700 rpms not an engine screaming at thousands of rpms.
I would be curious to know what the rpms of WW2 radial airplane engines were. I owned a 1964 Cessna Sky Hawk for some time and I think the max rpm was around 2500.

Maybe my thinking is wrong but it has worked for me in the past.
Thanks for the comments.

Thanks K2

Made up the push rods and timed the valves. I was off one tooth on the timing gear.

I exercised the motor some more with the electric motor and it is running smoother now that the cam ring has some work to do. There was a very little catch in the timing gears every so often before but now it's gone. I do have compression and the intakes are sucking air so all is good for now.

I will try to bend some exhaust pipes next.

Thanks for looking

I like the phrase "exercised the engine" - very apt!
I did this on a small single diesel, but the main bearing was not suited to the belt tension side thrust and wore badly very quickly. (Probably : Short of lubrication as there was no oil-in-fuel passing through the crankcase? A squirt of oil in the intake wasn't good enough?). I had to change the steel-shaft-in aluminium to a tiny ball race adjacent to the crankcase, and a brass bush at the outer end...
Take care you don't do the same? A propeller doesn't apply side thrust to the shaft. Arrange an end feed of the exercising drive motor if possible? - Like the conical starter arrangement?
Hope this helps! - Learn from my mistakes?
That's good to know K2 and very true but this engine has sealed ball bearings except for the rod that has a roller bearing.

As I said before I was going to try to bend some exhaust pipes. After two days of failures I built a special bender just for this tubing size. Having the right size dies helped a lot and annealing the pipe helped too but packing the tubing with damp fine sand made the biggest improvement. I mean really pack the sand in using a steel rod and a hammer.
The quality of my brass tubing was very poor and when annealing the tube it showed defects in the material so I decided to paint the pipes to cover up the defects and the engine needed a little more color anyway.

I made up 5 of these that screw into the cylinder heads.

The tubes go over the outside with a close fit. I made some brass collars 1/4 in thick with a set screw in them and they fit over the pipes next to the head. Tightening the set screw locks the pipe in place but still allows the repositioning of the tube if needed. (sorry I forgot the pictures)

A few Pictures with the prop installed.


Number 3 cylinder pipe has an additional bend to direct the exhaust to the side.

I bought 6 feet of brass tubing and ended up with 5 pipes 6" long the rest was scraped.
I have learned one think from this I am not a tubing bender person so I will have to find a different way to make the intake runners.

Thanks for looking
Hi, I had thesame problem, I fixed it by filling the annealed tubes with trade product called cerrobend, another name for it is "Woods metal", I think its an alloy of lead and bismuth. It does however have a very low melting point 154 deg C. As yourself I also needed to make a right size 9/32 set of dies and bender. Essential for the intake tubes. With heating post bend the alloy does empty completely from the tubes


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A friend bent 1 1/2" dia. pipes for motorcycles using a re-usable resin (hard wax?).
I have used plumber's lead (Tin-man's) solder, candle wax, electrical solder, bending springs, etc. for bending annealed copper tubes, typically ~6mm OD.
The bending springs were hardest to remove!!
I will be giving cerrobend a try at a later date to see how it works.
I tried the springs but I didn't have the right size so it was a disaster.

I have decided on a possible way to make the intake runners but I had to order materials for the job so I started on the ignition.
The ignition module and battery holders are mounted along with some of the plug wire straps.

That's all for today

Thanks for looking
There are several options that I may try later K2.

I finished strapping the spark plug wires to the frame and made a shelf. The shelf has an off/on switch and an indicator that flashes when a cylinder fires. The shelf will also hold the gas tank and the throttle control as well as cover up some of the wiring.



I set the ignition timing to just before top dead center for starters.

Thanks for looking

I made the plate that the carburetor mounts to and the intake manifold I guess you call it.

The manifold will have 5 threaded holes in it for the intake runners.
I am using a Traxxas 4033 carb with a 6mm bore. I have used this carb on several of my other models.

Thanks for looking
I'm not familiar with the Traxxas specifically but here is some correlation work I did (post #319). I chose a similar orifice for my O5 radial (OS carb) to start, but cant comment on results until prop flip, hopefully soon now. I have a slightly larger & smaller Perry to try but I do like the looks of Traxsas, particularly needle valve orientation.

Since I have never built a five cylinder engine before I really don't know but I do have two twin engines that I built and used this carb on them. Hopefully it won't be too long before I will know for sure.

Thanks for the comments.

Gas tank day.
Started with an aluminum tube and cleaned up the outside and the inside on the lathe. I cut a recess 0.200 deep in each end for the plexiglass to fit in.
I covered a piece of plexiglass on both sides with masking tape and marked around the outside of the tube. Rough cut on the scroll saw outside the line.

I pressed the plexiglass between a shaft in the chuck and a short shaft in the live tool post.

This shows the parts of the gas tank before assembly.

And all assembled.

Next will be some mounting brackets for the tank.

Thanks for looking
Loos very good. What did youi use to seal the ends to the tube?

Vietti I don't know my plastics well enough to give you an answer. Maybe someone else will be along soon with an answer.

Ron I used two part clear epoxy for sealing the ends.
That has worked well on several other tanks still in use.

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