Ohrndorf 5 Cylinder Radial

[Vixen]

Hello Peter,

I was sure you had developed your o-ring seal arrangement sufficiently to run with.

The adhesive lined heat shrink tubing idea was only offered as an alternative, a quick fix. ATEM is only one brand, there are many others available, it's prime role is in waterproofing cable joints. Just search for "adhesive lined heat shrink tubing" on e-bay or even Amazon and you will find a wide choice of manufactures. As you said, a useful material with many potential uses.

Mike

[Admiral_dk]

On the Digi-Key site, you put a mark in the "In Stock Box" and then scroll to the right to fin the "Feature Window" and select the over all type - Adhesive, Chemical etc.

I loved both your O-ring and Rubber-boot solution and I'm confident that you will find a satisfatory solution Peter 

Per   

[petertha]

The pushrods were pretty simple to make so only one picture to share. I used 2mm diameter O1 tool steel only because it was easy to obtain in metric & I wasn’t quite sure if either end would be hardened. The cam followers are hardened but not the rocker adjuster screws, so we will see. The diameter did matter because the pushrods make a 3D motion inside the tubes & according to my CAD drawings, come close to the edge of the tube wall at certain maximum deflection positions. I could go a little it bigger diameter but not much. The intake & exhaust pushrods are different lengths owing to fore/aft cam plate positions.

To turn the ball end profile, I initially played around with a HSS profiled tool but it had limitations. Even short material stick-out from the collet was enough to see deflection even by feeding the tool axially vs across the stock. The profile wasn’t exactly spherical & harder to control length. So, opted to first part them finish length plus a couple thou, blued the ends with a felt pen & just shaped the ball end profile using a fine file & magnification. I then inserted them into my Dremel collet as far as it would go in & did finishing with paper. Pics showing various stages of completion. You can get a mirror finish but I doubt it will stay that way for long anyways.

In hindsight, because the Dremel can spin up at much higher RPM than the lathe, it might lend itself to grinding the ball end profile on something a stronger/harder alloy like piano wire or similar shafting stock, which I suspect is stronger than annealed state O1. 

[petertha]

Next up is timing the planetary cam gears & retaining them into final position. A 15T (module 1) crankshaft gear drives a 15T idler gear which is attached face to face with a 10T gear, these two are the idler cluster that run on an intermediary shaft. The 10T then drives the 40T internal (ring) gear which is connected to the cam plates. The CS to ring gear is 4:1 but the cam plates have 2 sets of intake/exhaust lobes 180-deg apart, which yields the 2:1 crank to cam ratio. The cam plates rotate in opposite direction of the CS.

The plans call for using Loctite to retain basically all of the gear surfaces. I was a bit apprehensive about how to make these joints while getting them into timing position & allowing them to cure because access & visual alignment is a bit hidden. I also had this nagging feeling about glue failure one day. For better or worse I decided on a modified path. Loctite the ring gear into the aluminum cam cup because it has a lot of surface contact area around the perimeter. I decided to drill the CS gear with a cross pin running through the CS so the gear could be removed & replaced one day if required (although matching the pin hole would be an adventure for another day). If I did my math right, the pin should be able to take a decent load but I don’t have a good feel of what loads are involved with driving the cam plates. With these CS gears & ring gear now locked into position, that leaves the relative clock positioning of the 15T & 10T idler gears to be rotated between each other to achieve final cam timing relative to TDC & then locked into that position.

CRANKSHAFT GEAR RETENTION
Before drilling the CS gear, I tried to set myself up for future replacement if the unfortunate requirement ever arose in the future. I positioned the CS between Vee blocks in the mill vise & indicated off both sides of the counterweight flats so it was horizontal, the crankpin pointing up. Then I rotated the 15T gear until I could center align between 2 teeth just using a cone shaped tool extended down from the quill pointing into the gear valley. Then I offset a specific distance along the CS axis from the counterweight surface datum, positioning the pin hole on the reduced diameter segment of the gear. With the gear tacked in this position, the hole was spotted & drilled completely through, slowly pecking & clearing, hopefully to keep it straight. The pin itself is made from a HSS drill. Once the pin is inserted through the gear, a brass sleeve was made to cover the hub so the pin can’t fall out. This shows the assembly in progress. There are also some other spacer shims rings in the driveline to make up various clearance distances between components.

[petertha]

more pics

[petertha]

Idler Gear Retention. How to properly retain the idler gears together face to face caused me some head scratching, mostly due to small dimensional constraints. The smaller 10T gear which has a PD of 10mm & root diameter of ~8mm & runs on a 5mm idler shaft, so there isn’t a lot annular hub material left for mechanical retention. I followed the plans & turned down about half of the 10T gear to 7.5mm OD which basically inserts into the 15T gear reamed out to that same diameter. This becomes the mating surface to which the Loctite would normally be applied.

[petertha]

My calculations suggest Loctite should be as strong or stronger than the small diameter axial ‘pin’ key I could accommodate assuming all went well. I did Loctite tests on blanks of 1018 steel mimicking the gears. Face to face bonding was a fail rather as expected. The joint definitely required the step down reduced hub to resist radial shear? It seemed pretty strong just hand wrenching.

[petertha]

I also did some silver soldering tests on two 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.

[Admiral_dk]

Nice looking parts 

Thank you very much for taking us along your thoughts, experiments and final solutions 
Repetability is indeed very important in production and service 

Per     

[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]

Similarly, manifold gaskets.

[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.