Another Edwards 5 Radial

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Yes it will have wasted spark and the one I have ordered uses a dual hall sensor in one unit. One part of the sensor is triggered by the positive side of the magnet and the other side is triggered by the negative side of the magnets.
A 5 cylinder engine will have 5 south facing magnets and one north facing magnet.
I will attach a file that explains how it works. I have never seen this setup before but it is manufactured by Rcexl a well known company.
It will be about 10 days for delivery and not cheap so I hope it works. This could solve many problems for many different model engines.



  • CDI-Set-up.pdf
    1.5 MB · Views: 31
Looking forward to your CH/RCEXL system ignition integration. I've decided to go with a CH for my next project (opposed 2-cyl boxer) primarily to get up to speed on sparky stuff. No prior experience.

Will you run gasoline or methanol based fuel?
Your attached file makes it easy to understand. The sensor sees the reversed magnet and then fires number one and continues firing the cylinders in order until it see the reversed magnet again and starts over.
I would sure like to talk to anyone that has used this or a similar module.
One major question is how close together can the magnets be mounted without causing interference with the next magnet and with this in mind should I use ceramic magnets?

I have been mainly working on the cast iron liners for the cylinders. It takes a lot longer doing 5 than just one. I do have them all cut out and Loctite in to the cylinders. I let them set for 24 hours with a weight on them before I deck the cylinders so they won't move when they cure.

I did get the new mounting board done and installed.

Thanks for looking
Just curious about your cylinders. Maybe optical illusion on the pics, they look close to flush on the top side? When you say 'deck' them do you mean to equalize the CR as per plans? I believe the Edwards has equal angle link rod spacing layout on the master rod, resulting in unequal CR. So trimming was his was his way of equalizing, as opposed to 'compensated' master rods where the LR pin layout angle is varied.


Hi Ray,
I notice that you use a 4 hole pattern for the head bolts. The original head has 5 bolts . Doesn't that give problems when fitting the rocker arm supports?


Good questions as I was kind of waiting for someone to ask why are you doing it that way.
First my pistons will not be domed but flat and the cylinder head will be flat also. The piston will stop 0.150 short of the end of the cylinder which will give a CR of 6.65 to one not 8.5 to 1 as per the plans. I plan on adjusting the piston pin location if needed to compensate for the master rod issue but I am not sure just how much difference in CR it actually is. I will find out when I get to that point.
The cylinder head will be flat not domed and the valves and the spark plug all stand straight up not angled. This is a configuration that I have used on several other engines I have built with good results. I have not designed the rocker arm supports yet but I do have a couple of ideas rolling around.
While my build is similar to the Edwards design almost every part of it is different in some way and that's what it is all about for me.

Thanks for looking
I honed the cylinders and am just about ready to mount them but one more step.
When I replaced the backing plate with a larger diameter one I found that the plate would interfere with the cylinders. Over to the mill and remove 0.200 off one side of each. I installed two head bolts in order to clock the cylinders correctly in the vice.

And here they are all done.

Pistons and rods next.

Thanks for looking
I plan on adjusting the piston pin location if needed to compensate for the master rod issue but I am not sure just how much difference in CR it actually is
Well I found out just how much difference the master rod makes and it is not acceptable. I made my piston and rod combinations all the same length and they were measured within 0.008 of each other. I measured my cylinders and they were within 0.010 of each other so the master rod issue is real. I don't want to change either the rod combinations or the cylinders so when I make the heads each head will be for a specific cylinder. Two of the heads will be fine but the other three will need a combustion chamber cut into the head to lower the CR. One head will have a 0.02 deep chamber, one head will have a 0.050 deep chamber and one with a 0.065 deep chamber. This will bring the CR to about 6.36 to 1 and that works for me.

Picture of the piston and rod combinations.

All cylinders installed and working smoothly.

And another view.

Thanks for looking
I suppose the alternative is a spacer at the head gasket or beneath the barrel? - I assume you cannot skim excess height off pistons, as the top land (top of top ring to crown) will already be minimised?
Not enough room left to skim the pistons and I thought about a shim but they would have to be three different thicknesses. And they may distract from the appearance and draw your eye directly to them not that I am making a masterpiece but I am trying to make it look nice.

Appreciate the aesthetics - even if I can't spell the word! I thought shims 0.5m,1mm etc could be almost invisible be beat the cylinders, and leave major machined parts as interchangeable.
I ended up shortening two cylinders to bring the compression up and milling pockets in the other three to bring the compression down. All now will be at 6.43 to 1.

Five cylinder head slugs cut to size and thickness.

Because of the equal distance Master Rod issue I had to cut some pockets in three of the heads to keep the compression ratio equal.

Rod guide, spark plug, pockets and head bolt locations done on CNC.

Head bolts and valve guides drilled out.

Valve guides next

Thanks for looking
"shortening two cylinders to bring the compression up and milling pockets in the other three to bring the compression down. All now will be at 6.43 to 1."

An excellent solution. But having adjusted the height of the top of the cylinder, why do you still need pockets etc in a couple of heads? Surely all the adjustment for the true location of the Big-end of each rod has been completed so the heads can be common? - Or maybe I misunderstand the problem? (Highly likely!).
My rational goes something like this... (probably completely crazy?) Calling Master rod "1" and going clockwise around the cylinders, for 2,3,4,5...
Cylinder 1 is OK as designed.
Cylinders 2 & 5 have a 1/sin72 degree factor added to the motion/stroke,
Cylinders 3 & 4 have a 1/sin 144 degree factor added to the motion/stroke.
But you talk of changing 2 cylinders and 3 heads?
Surely cylinder 1 is "as designed?" and the other 4 need "shortening" to avoid the higher compression you are trying to avoid?

I haven't plotted this geometrically to get my head in line so maybe I am off at some irrelevant tangent, so just tell me if that's the case and I'll figure it out with a drawing (I guess you have already done so).
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Well I will try to explain what happened in my situation. After first assembly of the measured cylinders and piston rod combinations I found all were in error. I wanted 0.150 clearance between the piston top and the cylinder deck. Master rod #1 was only 0.144 not so bad but everything else was way off. This is when I started looking for some common ground that would fit all the cylinders. I decided I wanted to make them come out to 0.157.
This sheet shows the original measurements and what I did to make them all the same CR.

Cylinder Number​
Measured Depth​
Compression Ratio​
Pocket Depth​
Final Ratio​
Desired Deck Measurement = 0.157
0.020 Head Gasket on All Cylinders

On 2 and 3 I removed material from the base of the cylinder to increase the CR.
On 1, 4, and 5 I cut a pocket into the head to reduce the CR.

I don't know if this piston height change is common or if my built is off somewhere and I messed up but they are all the same now.

Thanks Ray, I understand where you are coming from now. First impressions are that you are now in charge and have a real plan to adjust the build to make them the same CR.
I am just a nosey amateur, and query things I don't understand, just to learn, not criticise.
In my head, the system seems straightforward....
The big-end of the Master rod is centred on the crank pin so describes a circle.
The remaining rods have big-ends running on eyes on the master rod . The motion of these eyes is not circular, but the combination of the crank centre and a rocking motion from the master rod swaying from side to side. Therefore the distance between eye centre and small end is not fiixed, but the combination of two elements times their sines of angles as they deviate from the straight line. ... or something? I think the ends of the stroke give a piston stroke equal to the Master piston stroke. But the motion of pistons is not exactly sinusodal. - I think? Must study some more!
I suspect perhaps you and have both assumed that at TDC and BDC of the secondary pistons, that the centre of crank to Small end distance equals the radius of eye centre plus length of rod. But this is not a straight line due to the master rod "swing". Thus the discrepancy of measurements you obtained is a real geometrical quirk, not a machining error.
An interesting problem, but I think you have a workable solution.
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Thanks K2 I am sure there are some machining errors also.

I decided that I should cut the cooling fins in the heads before I work on the valves.

This is the setup I used with my rotary table.

I used a 0.060 slitting saw at a depth of 0.150 and cranked slowly with a lot of WD 40.

Fresh off the mill.

Back to the mill to remove the fins for the intake and exhaust connections.

Still need to clean them up and de burr but here they are.

Thanks for looking

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