Ohrndorf 5 Cylinder Radial

[petertha]

I also did some tests silver soldering 2 similar sized dummy steel blanks together, more out of morbid curiosity since I have no prior experience with this. I could get what appeared as an acceptable looking joint that seemed to be penetrating the annular gap which needs to be quite small for gear concentricity. But I was getting enough of a fillet that I thought was going to interfere with the teeth meshing & filing it out did not seem like fun. The tester blanks came to a decent red glow by the time the flux turned glassy & silver solder melted. I don’t think the heat would adversely affect the commercial gear alloy as they were unhardened. But it also took some effort to clean the blanks after soldering, so I am going to have to figure out pickling & all that. In summary it was an interesting exercise I would like to return to one day, but I chickened out for this application.

 

[petertha]

Then I tried drilling some ‘pin’ keys centered on the joint line, again using dummy blanks. This actually worked quite well. So, I figured if Loctite was good & pinning was good, maybe I would just go overboard & combine them.

 

[petertha]

Once the cam timing was established relative to TDC, I tacked the gears using CA glue to preserve the position & marked the gear teeth with little ID dots for reference. I set the gear cluster into my prior boring fixture & replicated the pin key drilling operation. I re-checked timing one more time, all appeared good. Now just a matter of assembling the cluster together with Loctite outside the engine. Including a picture of the 5mm OD axle for idler gears sitting in the front gear plate with its bronze spacer washer & retention screw.

 

[petertha]

Just to revisit the timing on this engine which I reverse engineered using the cam profiles. Inlet opens & exhaust closes equally either side of TDC, which makes it relatively easy to set the cams (I suspect by intent). With piston at TDC, you just rotate the cam plates until the tappet travels are equal to one another during the transition point.

 

[Vietti]

Peterha,

Outstanding! Just for reference in some of my engines I have used knitting needles for push rods. The aluminum ones have cool colors. The stainless one from China are hollow, light and strong and cheap. Adjuster screw can go up inside the tube.

 

[petertha]

Thanks Vietti, that's good to know. I have had other applications for tubing like that, never considered the end use product.

 

[ajoeiam]

Just to revisit the timing on this engine which I reverse engineered using the cam profiles. Inlet opens & exhaust closes equally either side of TDC, which makes it relatively easy to set the cams (I suspect by intent). With piston at TDC, you just rotate the cam plates until the tappet travels are equal to one another during the transition point.

Very interesting (very very nicely done too by the way) - - - what are you using to create the wonderful drawing fro jpg 1 and 3 (#2 is a spreadsheet of some kind)?

 

[petertha]

Thank you @ajoeiam . 1.jpg is a screen grab from CAD program (Solidworks) imported into Excel & then annotated a bit for visual reference. 2&3 are from an Excel spreadsheet I made to evaluate cam timing in terms of more conventional valve open/close BTDC, ABDC etc. since it wasn't documented on the plans & I was curious how it compared to other engines. If you are interested, I extended this to a comparison tabulation of other model 4-stroke engines. Quite a surprising range but I suppose there are reasons for this.

https://www.homemodelenginemachinist.com/threads/cam-timing-methanol-glow-engines.33280/

 

[Vietti]

Your cam timing diagram is the best representation I've seen. Easier to understand than the usual circular ones. Thanks.

 

[petertha]

This is maybe a good spot to insert some miscellaneous items.

GASKET MAKING
My instinct was that gaskets on specific mating surfaces they would be beneficial. Or at least that’s what I usually see present on commercial engines to seal air/gas, fluids or even help with fastener retention under vibration or heat cycles. The plans were a bit vague on this other than the nose case oil bath area.

I did some experimenting with typical squeeze tube type sealant/gasket products with mixed success. There are so many products out there & admittedly I don’t really understand the variations of metal-to-metal vs in conjunction with gaskets. Actually, of the goopy products I liked, the problem was usually they worked too well. Disassembling the engine parts was quite difficult because of their delicate size & cleaning off stuck residue was a chore. I expect to be in & out of the engine often so I wanted something that lent itself to that. I can produce CAD based export formats for a computerized cutter, I don’t have a machine & it seemed excessive to outsource it for the low parts count plus spares. I see there are some interesting cutting machines used by crafters for cutting stickers & such, but I suspect the software/import capability might be another rabbit hole & again hard for me to justify.

So, I went old school & just hand-made ‘acceptable accuracy’ templates from scrap MDF to act as a cutting guide. I laminated my paper shop drawings onto the MDF & cut them out on the scroll saw. The gasket material I found (actually copied from another builder on the forum) was Teflon sheet, I believe also known as PTFE. The nice thing is it comes in very thin sheet thicknesses, starting at 0.001” depending on the supplier. Its impervious to oil & fuel & even used as head gaskets that see significant heat. I sprayed a light mist coat of adhesive onto the material which tacks it into position on the template. Then cut the outline along the template with a sharp Xacto or scalpel on a cutting mat.

I first tried drilling the gasket clearance holes for, in my case, M3 fasteners to pass through but a drill seems to make a raggedy non-circular profile even with backing board behind. So, I made a simple tool from O1 so that I could harden it & preserve the cutting edge. I used a 4mm ball end mill which made a natural edge to the ~3mm shank. It cut the sheet with a slight twisting motion or using cordless drill. I think the slight give of the cutting mat helps & also preserves the cutting edge. A punch style template might make better holes but would involve another mated template. I also think a thinner, harder cutting template like 1mm aluminum or plastic might allow better access for the blade on internal holes, but the MDF will last for what I need it for. To release the finished gasket from the template, it just needs a spritz of acetone or thinner. The spray adhesive dissolves clean & the PTFE is impervious.

 

[petertha]

Manifold gasket

 

[petertha]

I found a stick of Teflon/PTFE online & used it to make the washer seals for intake & exhaust ports. It mates between the head counterbore & the trumpet profile on the metal tubing, squeezed by the port nut. The material machines quite nice as long as the tools are sharp.

 

[ajoeiam]

Thank you @ajoeiam . 1.jpg is a screen grab from CAD program (Solidworks) imported into Excel & then annotated a bit for visual reference. 2&3 are from an Excel spreadsheet I made to evaluate cam timing in terms of more conventional valve open/close BTDC, ABDC etc. since it wasn't documented on the plans & I was curious how it compared to other engines. If you are interested, I extended this to a comparison tabulation of other model 4-stroke engines. Quite a surprising range but I suppose there are reasons for this.

https://www.homemodelenginemachinist.com/threads/cam-timing-methanol-glow-engines.33280/

OT

(Blubbering in my water - - - - if only I had the $10 to 15k usd for a copy of solid works (with the options that I think I want) - - - - but then I'd have to run M$ Win and then my mood has to improve.) Fortunate man to have such.

Thanks for sharing - - - - hopefully I'm not too grumpy!!! (LOL)

 

[petertha]

With the sub-assemblies now coming together, I revisited my original master rod components & made a few re-do’s. I decided I wanted a slightly better fit between the bronze crankpin bushing bore on the crank pin OD. So rather than ream the bushing which I think was the reason for slightly loose fit, I used a boring tool. The wall thickness is quite thin, maybe that influenced reaming. I also tweaked the front facing flange thickness while I was at it to accurately center the MR to the bores, even though it isn’t really critical. I used Loctite to retain the bushing into MR body & with that done, drilled 3 oil passage holes at slightly offset positions down the crankpin length.

 

[petertha]

The spacing had a domino effect on pin plate thickness & I this time I made a bronze washer which will see some occasional rubbing from the retention clip

 

[petertha]

Around the same time, I came to notice how close the face of master rod occurred relative to the crankcase recess groove. I thought surely, I must have machined something incorrectly but everything checked out to plans. The MR is centered & nothing should really allow it to drift fore/aft too much, although the MR does have a bit of necessary clearance float between the crankpin bushing & retainer clip. It just made me a bit uncomfortable should a tiny fragment decided to lodge in there, or if I didn’t seat the bearings quite right or… Not that we can predict disasters but I didn’t think crankcase strength would be compromised by opening up the groove a bit. So, I made a holding fixture, dialed in the ID & took off some material either side of the groove, preserving the same depth. Made me feel better.

 

[petertha]

I don’t think I showed pictures of the piston with the OS-56 rings. Here they are. I basically mimicked the groove dimensions to the stock OS piston including the same crown undercut to ease ring installation. As far as I could determine they were a good fit in the liner bores but will be proven later. For interest sake, the section dimensions are quite close to Trimble calculations. Next engine project I will have a go at making my own.

 

[petertha]

When my propeller arrived, it was a different nominal thickness than what the plans presumed which had a knock-on effect to the drive washer & therefore the split cone its mated to. So those parts had to be re-made. I made a slightly bit thicker bolt plate while I was at it & matching drill jig.

 

[anday1]

stunning work peter

 

[petertha]

The mechanical parts were basically complete at this point. I decided to make a leak down tester rig to sanity check the cylinders under pressure prior to running. The basic principle is you have two identical pressure gauges with a small diameter orifice restriction between them. Regulated pressure is applied to the input upstream gauge. The downstream gauge output is connected to the cylinder head by a fitting screwed into the glow/spark plug hole. With the piston at TDC & both valves closed mimicking combustion, the gauge pressures should read the same. If the downstream gauge pressure is lower and/or diminishes over time, it indicates a leak in the system. But it can’t distinguish leak between ring seal, ring gap or valves... because it’s a collective system. This is why the tiny orifice restriction between gauges is important, we want to see any pressure change without the supply replenishing just as fast so to speak. I don’t have a feel for how much pressure over how much time is acceptable. More of a Houston, we have a problem thing. My valve/seats were vacuum tested to the extent of negative pressure previously, so I was hoping this would show more ring fit results at elevated positive pressure.

The parts were relatively inexpensive Amazon components including the hose & quick connect fittings. I machined an extended length spark plug adapter fitting to match the thread & incorporated an O-ring to seal. Apparently on full size engine testers the orifice is of defined size. But because our model engine volumes are smaller, the orifice must be reduced. The smaller the hole, the more sensitive are the readings. I’m not sure if it should be reduced proportional to displacement, but I had a few data points from other model testers I came across. My friend used a #80 drill (0.0135"). I asked him how he came up with that & he said it was the smallest drill he had at the time & it works, ha-ha. Also, Don Grimm on HMEM published his tester plans which I subsequently stumbled on & I believe he used 0.026”. I found a tiny restrictor we used on RC pneumatic retract gear systems, but the hose barb diameter is very small ~1/16” so would have required extra machining to integrate. So, I made a restrictor by plugging a standard pneumatic brass coupler fitting with a #80 pre-drilled orifice segment, glued with Loctite. It seemed to work. Then I realized what I thought was a regular on/off pneumatic valve I purchased was actually a pretty fine adjustable needle valve. It already has threaded fittings so I installed it in between gauges to compare. If I just crack the valve, it flows quite slow to the extent the downstream gage takes a while to equalize the upstream gage with the tubing blocked off. So for simplicity & some flow variability, I would recommend going that route if you build your own.

I went ahead & tested the 5 cylinders thinking it should at least be indicative of apples-to-apples comparison among all cylinders. I used about 45 psi initially & then 60 psi when nothing bad happened. The pistons had a light coating of oil normal for assembly. The good news is, no problematic leak off was seen. The gauges equal one another & will sit that way for several minutes at least. I left the crankcase open so I could see the underside of the pistons. Over time a tiny bubble could be seen which I attribute to ring gap & brand-new rings/liners. If I push on a valve, it blows down, re-seats & gauges re-equalize again. I put the same test rig on a known used RC engine & replicated the result.

It is advisable to somehow mechanically lock the crankshaft at TDC before applying pressure. Otherwise, the engine will faithfully reproduce a combustion stroke with an unexpected & jump on the workbench. Ask me how I know.