Ohrndorf 5 Cylinder Radial

[minh-thanh]

HI @petertha !
A Great thread , Great pictures . Thanks for sharing !
@anday1
Maybe I'm wrong to say this, it's better if you create your own thread and post your pictures .

 

[josodl1953]

I may be wrong but post #219 and # 220 are about a 4-cyl. boxer engine where this thread is about the 5-cyl. Ohrndorf radial.
Maybe an error?

Jos

 

[anday1]

Glory shot of valves and a few spares. All the soldiers ready for action.

hi Peter
could you advise on the springs you will be making or purchasing for the valves

many thanks
andrew

 

[petertha]

Andrew I used the ones prescribed by Ohrndorf, link below. I suspect you might be asking because of your boxer engine? FWIW, Gutekunst has a vast assortment of high quality metric compression springs at very reasonable prices, no problem there. But they were brutal to deal with because they required wire transfer of funds, no credit card, e-transfer, Paypal, money order or any form of modern payment. At least originating from a N-Am customer. So I was looking at $45 wire transfer fees to buy $10 of springs & even that turned into a nightmare. Maybe they have subsequently changed their ways, its been a few years, but just a heads up.

So I spent time looking at potential substitutes without straying too far from the design. I found imperial springs pretty close to the force/displacement of the Gutekunst but would have had to modify the head holes or valve cage stems to accommodate. Turns out that wasn't so easy. I found some OS or Saito springs of the right wire diameter & ID/OD but wrong length, so different resulting valve force. In the end I found a German middleman that bought the Gutekunst springs & mailed them to me. PITA!

Valve springs on our little engines might seem stiff, or at least they did to me. But I think Ohrndorf chose correctly. Ether by some calculation or mimicking what is on RC engines which I have corroborated with commercial RC 4S engines. There are a few design considerations. I think Terry.M may have delved into this subject on one of his builds. But the one factor I paid attention to from personal experience is exhaust valve float (if that's the right term). Valves are still open across TDC (overlap). So if the spring is not maintaining the lifter to the cam profile, there can be an unhappy intersection. This usually happens at higher RPM but higher is a relative thing. Rocker gap setting, head shim, liner height or incorrect timing gear tooth position can enter the picture. The valves on my radial enter the head at a relatively steep angle so valve ends up quite close to piston contact at TDC. I've seen incorrect or lazy springs on RC engines with valve dents in the piston (or worse). Many flat top piston commercial engines have the partial relief profiles for this reason. It makes room without affecting CR too much as a compromise. Your engine is probably a different valve layout but something to be cognizant of because methanol CR's are typically 7-9 :1 just as a guess so the squish height will typically be close & I suspect he stuck with his similar valve timing.

I'm contemplating another engine right now & facing similar issue, specific (metric) springs although I have more modification latitude. I found what I was looking for on AliExpress although I'm always suspicious of their specs.


https://www.federnshop.com/en/products/compression_springs/d-129.html

 

[anday1]

Thanks peter
martin has come back to me regarding the spring rating and i am talking to an English maker of springs i will let you know how it goes. Martin has said this only: "with a force of about 900 grams to 1000 grams of preload after installation" if that is any help to you but no spring wire dia or length. I will keep you posted if there is any further info. Loving the build pics and the approach is helping me make 4 of everything, is a new procedure for me, the fixture route is definitely the way to go. Did your plan to call for brass guide valves as my plans show using the aluminum head cut for the guides etc?

I will try to keep my questions as close to your build as i do respect the forum rules of engagement.

keep posting

regards
andrew

 

[petertha]

Martin has said this only: "with a force of about 900 grams to 1000 grams of preload after installation" if that is any help to you but no spring wire dia or length.

Hopefully I'm recollecting metric math correctly. I believe you can use the published spring rate factor times compression distance. Example my D-129 springs with a preload distance of 3 mm: Force = 3.034 N/mm * 3mm * 101.9 gf/N = 927 grams. You would have to work out or measure your preload distance from engine plans showing rockers / keepers in valve close position. And of course spring force will be proportionately more at valve open position as the spring compresses more as a function of cam displacement. Be mindful of published max spring deflection & any engine specific OD & ID constraints. My spring OD had to fit within a counter bore hole in the head & also the spring ID over the valve cage stem diameter, both with appropriate clearance. Hope this helps.

I've been working on my intake manifold spiel, hopefully post sometime soon.

 

[peterl95124]

I got tired of using the spring force formula, and found this to be helpful,
I can specify my desired ID or OD, installed length, and installed force,
and play around with wire thickness and number of turns until I like it.

I usually wind wire around a metal rod only slightly smaller than final ID,
and make it close wound with many more turns than I'll need,
then cut sections with the right number of turns and stretch them
past the installed length so they have the right tension when installed

https://www.thespringstore.com/spring-calculator.html

 

[petertha]

Next up is the intake manifold assembly. Hopefully this topic won’t put many of you to sleep. After making the components according to plans, some issues came to light and & I ended up adapting things a bit differently. Maybe some of the modifications & reasons behind them will also be of interest to those contemplating a similar build.

The manifold part is bolted to the rear of the crankcase using 10x M3 screws. The forward-facing section is basically a lip machined to fit snugly inside the crankcase housing ID. It also incorporates an O-ring for seal which I noticed was not featured on the O9 radial. The middle flange section has 5x M4 threaded holes for motor mount standoffs to connect the engine to the firewall. The rear section is the manifold where the intake tubes tie into & carb is mounted into.

On each intake stroke, fuel mist is drawn through the carb, into the manifold’s center hole, into the crankcase chamber (red dots). Because oil is premixed with the methanol fuel, the intake mist lubricates the components within the crankcase before carrying on to the heads. This is typical RC engine style lubrication. Fuel mist exits rearward from the crankcase, out through one of the 5 manifold holes (orange dots) through its respective intake tube into the head’s intake port.

If you recall earlier in the build description, the plans call for the nose case chamber to be partially filled with an oil bath to splash lubricate the front-end components, the cam plates, cam bearings, lifters & planetary gear train. In other words, a separate lubrication system to the rear crankcase mist flow. After much indecision & hand wringing on this issue, I decided not go this route for now. Rather, I opened up the front gear plate with an array of apertures (holes) working around the existing idler gear & bearing layout. So, I’m depending on the same incoming mist to carry on further forward into the nose case & also lubricate the nose case jewelry.

From what I can tell, this mode is similar to other methanol glow radials such as Jung designs, commercial engines like OS & Saito, possibly others. I do feel there is a bit of risk here because the crankshaft counterweight & master/link rod assembly blank out a healthy percentage of open flow area apertures & the O5 seems a bit more crowded compared to these engines. If my decision turns out to be a lubrication fail, hopefully damage will be something short of catastrophic & I will have to revert to a nose case oil bath.

 

[petertha]

The O5 plans called for the same flow nozzles prescribed on O9 radial. They are basically profiled rings, inserted into the 5 front facing port holes & retained with Loctite. Maybe I'm wrong but aside from a bit of standoff distance from the center carb port & a slightly curved leading-edge profile, I didn’t really much advantage given the turbulent gas flow & long tortuous route each intake charge takes toward the head.

 

[petertha]

For parallel interest I attached a picture of the OS-FR5-300 radial manifold showing spiral flow path grooves milled in the manifold. It seems by the article description that the incoming fuel charge is sealed off from entering the crankcase. It flows directly from carb into each spiral groove into intake tube. So, no mist lubrication to rod components? The Edwards radial is a similar, even simpler gas distribution box flowing from carb to tube, but it has an independent oil pump system. The OS-FR7-420, possibly a later engine, shows what appears as vane pump somehow driven off the crank. I’m not sure the pressure boost could be high but it must be there for a reason. But again, sealed off from crankcase. If anyone has more insight to these OS engines I’d like to hear. I’ve seen similar vane pumps on other radials like this Whirlwind.

 

[petertha]

The carb is integrated directly into the rear section of the manifold boss, counterbored to match the throat OD & length, so that’s how I machined it. I suspect the intent is for a compactness, keeping the carb assembly within the motor mount standoffs, forward of the firewall.

Around this same time, I realized I probably made an error with my carb choice. It was for a 2-stroke 0.40 CI glow engine but the venturi hole appeared rather big. This led me to a more detailed review of carb sizing for 4-stroke glow engines which I have posted elsewhere on the forum. This confirmed I was probably wanting a smaller orifice, especially where idling & transition was preferred over top end. I started looking at options from RC suppliers. Getting them was easy enough but it turns out that their throat bodies come in a multitude of dimensions. Sleeving the existing manifold bore and/or the orifice was do-able but not a great option. I ordered some candidate carbs & moved onto the next issue.

Carb sizing link post#6
Looking for inexpensive carb for trial running of Seal Major 30cc

 

[petertha]

Manifold & Tube Union. The plans show the intake tubes tying into the manifold boss via aluminum ring fittings which are grooved to hold a captive O-ring for gas seal. The fittings are permanently Loctite glued into counterbored holes of the manifold & these holes connect to the axial flow passages. Here I ran into some assembly problems. The specified tubing was (metric) 8mm OD aluminum. I found some sticks from an RC supplier but bending the pipe was not pretty. This is a subject unto itself, usually involving filling the tubes with a filler alloy or material. But I acquired some aluminum 5/16” OD Versatube from Aircraft Spruce which is dimensionally very close. There was no problem bending this with my hand tool. The bigger issue was straightening out the coil as it was shipped, but I have since found some shop made solutions which I will add to the to-do list. The initial tester parts were coming out semi-promising but more refinement still required.

On the ring fittings I tried a few different O-ring sizes, durometers, materials & O-ring cut depths which gave varying degrees of seal against the tube (or not). I’m trying to mitigate any chance of air leak across the O-ring because it would adversely affect fuel mixture & cause running problems. The ring fittings were proving to be quite fussy & it wasn’t going well. I didn’t want to resort to silicone adhesives because I expect the engine would be knocked down & assembled many times.

Another issue was with the assembly itself. The tube end first has spud into the O-ring fitting but is limited by a shallow depth. The tube has to have sufficient wiggle room to then position the flanged tube end into the head & secure with nut. If the pipe bend profile or cut length was off just slightly, one or both ends did not fit well in my opinion. I was paranoid of stripping the fussy threads in the head which enter the head at an angle & partially cut across cooling fins. So, I abandoned the O-ring fitting idea & made some short extended ‘stack’ fittings to go into the counterbores. The idea was to couple the stacks to the tubes using a short segment of flexible tubing. Not as pretty, but seemed more functional & hey, big engines do it too!

 

[petertha]

Tube Bend Profile. I’ll detail the intake tube making separately, but at this point I was getting the hang of making somewhat plausible tubes from a straight>curve>straight layout pattern. I could bend the radius, form the trumpet end to the head & mostly land somewhere near the manifold stack segment. What I wasn’t thrilled about was the overall look & fit of the pipes. It was quite evident that the tubing axis was kinked where it met the manifold mini stacks. Another indication was the tube ends needed to be mitered to line up. This geometry issue was probably the root of my original problems using the O-ring fittings. The segment of flexible coupler disguised some of the sins, but it just wasn’t pretty. I could have called them functional & moved on, but…

 

[petertha]

I spent some time in CAD with the assembly & it slowly became evident what was going on. Not to bore you with details but because my 5/16” tubing bender tool was constrained to a single, defined radius, there was no geometric solution that would satisfy the tube axis coming off the head port angle, around a radius & ultimately intersect the existing manifold port holes in their existing location/orientation using any combination of straight + curve segment lengths in a 2D plane. I could make it work by either a more complicated 3D bend sequence or a specific bend radius that was smaller than my bender tool.

 

[petertha]

So, my options appeared to be 1) make a general-purpose tube bending tool assembly to facilitate different diameter forming dies in order to bend the required radius 2) use my existing bend tool & make a new manifold that would accept this fixed bend radius. I did some reading on shop make bending tools. Eventually I want to make one, but for now, moving forward with a new manifold seemed worth a shot. This would also allow me to tweak the other issues - generic adapter plate for different carbs, eliminate the crankcase O-ring & just replace with a sheet gasket & skip the flow nozzles & just chamfer each hole.

The net effect was a mixed blessing. To solve the geometry issue using a straight-curve-straight recipe and bend radius all in a 2D plane, the tubes needed to enter the manifold at a steeper, oddball angle as opposed to the original design which was a simpler radial spoke pattern. The manifold boss itself also needed to be a bit longer, but that was of no consequence. It also required shifting the M4 mounting studs to some degree. And one set of M3 screws were a little less accessible which I didn’t even consider until the part was machined. So, in hindsight maybe a new tube bender may have been a smarter choice but it is what it is for now. Next radial I will be wiser on these issues.

 

[petertha]

Some machining pictures of the new manifold

 

[petertha]

Some machining pictures of the new carb adapter part.

 

[petertha]

The tool I purchased to make the curve segment for both the intake tubes & exhaust stacks was a Ridgid Instrument Bender model #36092 for 5/16” tubing. It has a bend radius of 15/16” (~0.934” or ~24mm) which is a fixed dimension as a function of the die head. It worked quite well for this particular job. The only downside for general model engineering is each tubing diameter requires a corresponding tool which in turn has its own minimum radius. They are not exactly cheap & also limited to 180-deg curve if that’s an issue. So, a future project for me will be a shop made bender tool where I can vary the die diameter and if possible, somehow do 3D profiles

The intake tubes were made from a product called 3003 Versatube purchased from Aircraft Spruce, 5/16” OD x 0.035” wall thickness. This size reasonably matched the metric 8mm diameter called for in the plans. The big incentive for this material was that bending was not really difficult, no internal support filler like Cerrobend was required & they kept a pretty uniform circular section with no kinks. About the only thing I would do different is invest in making a tube straightener device from roller bearings because the tubing comes shipped in ~12” coil, so straightening it out beforehand to lay out my straight > bend > straight profile. I basically cut a longer working section, carefully un-bent I by hand & then rolled it on a hard flat surface. There are some YouTube videos that do a better job describing the roller devices. The exhaust stacks were made the same way except from copper alloy auto brake tubing which I thought would be better for exhaust heat. They were just simple 90-deg bends only.

https://www.ridgid.com/us/en/400-series-instrument-benders
3003-O Versatube | Aircraft Spruce Canada

 

[petertha]

Using a pattern drawing, I marked out roughly where the bend section would occur first, leaving excess straight material on both the head end & manifold end to be trimmed later. The operation was set the lock & bend the tube X degrees to a mark. There is minor spring so just a bit of trial & error.

 

[petertha]

For the head end, I referenced a line on the straight segment & attached my steel shop made flaring tool. It’s basically a split die that lightly grips the tubing so the trumpet can be formed by screwing in a chamfered shaped profile die. I ended up threading the die hole & then bored most of the threads off so the remaining serrations it would provide enough grip to the tube, hopefully without too much resulting bite marring. Without these ‘teeth’ I found the tube could slip during the trumpet forming. Maybe this could have been mitigated with Cerrobend or some kind of plug material. I cut the tubing slightly longer than the face of the flare tool & used a ~1/32” thick aircraft plywood template as a guide to flush file the end. This was to allow the right amount of material to be flared, determined by trial & error. The flare profile is necessary for the head port nut to tighten against.