Another Edwards 5 Radial

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Hi Ray, Don't discount the geometry of this engine.... Double check the CAD/drawings and if possible plot motion of master cylinder versus an adjacent cylinder to see what it really does. (I may do that soon?).
Have you got a simple section through the assembled engine so I can have a play with the numbers? I am just curious as to why you have such measurements, when I'm sure it is geometry, not just a slip of the settings when machining?
In this old post #59 you can see my graphical representation of the uncompensated Edwards master rod effect on CR. This was based on a spreadsheet calculation by another individual written some years ago on another forum. These days I solve it by CAD. It boils down to choosing one parameter locks you into another. Its a give & take thing.

A compensated link rod/master rod layout yields equal CR and identical components but timing is slightly different if related to equal spark ignition events for example (but less of an issue on a glow plug engine). Doing an equal 360/5=72 deg angle results in unequal CR unless you then secondarily compensate head position by shimming/cutting. There are other possible tweaks involving link rods or piston placement, so it kind of depends on what you want to control or deal with in the end.
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Thanks Petertha. I don't need to reinvent the wheel in this case. You have explained it clearly (for me). I now understand why Ray has to change lots of parts to reset the compression ratios the same all around.
Thanks petertha and k2 for your replies. I read through that old thread of yours but I quickly got lost and I even downloaded a Excel file from someone else and that was way over my head.

I made up the valve guides with seats today but I forgot to take any pictures of the operation.
This is the result.

Thanks for looking
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A huge step forward in the project as I have the cylinder heads completed. All the holes are drilled and tapped even the spark plug hole. The valve guides are installed and the counter hole has been drilled through the guides.

Drilling the intake and exhaust ports with a 0.100 offset.

After some cleaning up.

4 of the 5 heads have a different depth pocket so the ports are at a different height also.
This is head #1 with a 0.013 deep pocket.

All lined up.

Large deep pocket for the spark plug.

Just remembered the rocker arm supports will need at least one hole in each head but that will be later.

Thanks for looking
Those 1/4-32 miniature spark plugs look right at home on an engine this scale. Do you have the boot/harness to see how it fits the clearance hole & depth etc?
Making valves today.
You can't do a production run on the valves as the stem and seat must be made at the same time without removing the stock from the collet. They must be concentric and that takes a lot of fiddling around with the cross slide and angles.

Here are a couple of shots showing the setup.
Making the stem.

Making the seat.

The finished product.

Family shot.

The valves still need to be lapped and checked for sealing before the heads are installed but my ignition module came in today petertha.
They fit the spark plugs perfectly and the 90 degree end will make for a nice compact installation.

I will have to stop with the valves for now and mill a place in the nose housing for the hall sensor to mount in. I want to have that done before I install any of the heads.

Thanks for looking
I didn't think the hall sensor would be as big as it is so I had to remove a lot of the nose housing to make it fit.
I put the prop back on so I could see what it looks like

A view from the bottom

The magnets are in the aluminum ring directly behind the prop.

It did change the looks but not as much as I had expected.

What do you think?

Thanks for looking
I didn't think the hall sensor would be as big as it is so I had to remove a lot of the nose housing to make it fit.
I put the prop back on so I could see what it looks like
View attachment 147243

A view from the bottom
View attachment 147244

The magnets are in the aluminum ring directly behind the prop.

It did change the looks but not as much as I had expected.

What do you think?

Thanks for looking
That hall sensor doesnt look to bad. You could make a small housing to cover it
I changed the design for the hall sensor as I mounted it on an adjustable spacer and further out.

I also made a new magnet ring and placed the magnets around the outside of the ring. Even though they said the sensor would work fine with the magnets passing across the front of the sensor it didn't work for me. My friend Chris brought over some 5mm magnets that I glued in appropriate holes.

View from below

I think it looks better now.

The ignition works just fine now but I learned something I didn't know. I needed to place 5 south pole magnets and 1 north pole magnet around the spacer for the ignition module. In order to determine which pole of the magnet was sticking out I used a compass and brought the magnet close to the compass and watched which way the needle was pointing. Like poles repel each other and unlike poles attract each other. The needle on the compass is magnetized and will point to the north pole of the earth. I then assumed that that end of the needle had a polarity of south so it would be attracted to the earths north pole. I installed all the magnets using this theory but only one cylinder would fire. I checked and rechecked everything many times and finally went on line to get my answer.
The earths north pole has a polarity of south that is why the compass needle that has a north polarity is attracted to it. I removed all the magnets and reinstalled them the correct way around and everything works fine.

From Wikipedia, the free encyclopedia
"Because opposite poles attract, this means that as a physical magnet, the magnetic north pole of the earth is actually on the southern hemisphere."

Thanks for looking
Thanks Minh Thanh and Scotty

I made a test plate to mount the heads on to check the valves for sealing.

I also cut some head gaskets using my drag knife and a vacuum table mounted on the CNC mill.

I made the valve spring keepers and a few extra as I usually lose some along the way.

Thanks for looking
I have been working on sealing the valves, lapping them. This job didn't seem to be so tiresome on the last engine I made but it was a single cylinder. On this five cylinder I have worked on them for two days. I am afraid my quality control may have gotten a little lax after many hours of lapping. I usually take between 45 minutes and an hour to get where I am satisfied on one cylinder but some of these took well over an hour each.

Well they are on the engine now and we will see how many I will need to do over later on.


I plan on notching out the area of the wood board under cylinders 3 and 4 so I can gain better access. It will sure eliminate a lot of cussing in the future.

Thanks for looking
I made two half round cutouts in the base board to gain better access to cylinders three and four.
Much easier now.

This shows some of the rocker arms and one standoff I cut from a brass plate.

Test installed arms and standoffs to check for length and any binding but all is well.

Now they have to come off to drill for the valve adjusters but not today.

Thanks for looking
Hi Ray, I am surprised you chose brass for rockers? I should have chosen steel of a good grade? I am sure you are aware (but others may not be so?) that the rockers take extreme repeated bending and as a crystaline material are more prone to fatigue cracking than wrought materials - (I think? - Any metalurgists to help here?). So I should have used a fatigue resistant steel. I know many cars, trucks, etc. appear to have cast rockers, but they undergo lots of fatigue testing to prove the design. I am sure your engine will not need to last as long (many 1000s of hours!), so will probably be OK, but I simply believe the best material should be used where practical on models. - Mostly they outlast us!
Also, will you be lightening the "arms" of the rockers to H-sections? - removing "redundant" mass? The mass that is oscillating in the valve train causes power losses and wear of cams and followers, so minimum mass should be attained where possible. More mass means heavier springs are needed to permit higher revs, etc. before "bounce" occurs, so should be carefully minimised.
When proving tests were done at the factory where I worked, we built rigs for 1000hour idling tests, as that was the test mode to develop maximum cam and follower wear. (due to lubrication and loading of the cam to follower interface). But fatigue tests were at maximum revs for a couple of thousand hours and cycling from idle to max, holding for long periods at certain "resonant" speeds! Rockers were wrought steel from a SOH Camshaft. (post 1990 engines had DOHC with bucket and shim cam followers. - MUCH more durable than rockers.).
If anyone can correct my thinking on "materials", I should like to learn more from your expertise.
I agree with Steamchick that brass is not the material of choice for rocker arms on this engine. The Edwards design specifies 7075 aluminium but Forest Edwards designed his engine to be a workhorse on an RC plane. It seems to me that longevity is not important with this engine ( bearing in mind the aluminium camring, for example)

Fair comment Jos. I was told by a local model maker that he doesn't expect his engines to last more than 1 hours running, as compression drops off as clearances appear. I finished a small diesel single but after 5 mins running lost compression.

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