Ohrndorf 5 Cylinder Radial

[petertha]

The master rod bushing is made from bearing bronze. Straightforward turning other than the features are quite thin. It has the proper sliding fit on the crankpin OD and also has a face flange feature between the master rod body & the crankshaft pin area. This was v1, I ended up making another v2 during final assembly with some tweaked dimensions to manage the clearances.

 

[petertha]

Some shots of the master rod & link rod assembly at this stage.

 

[ajoeiam]

Some shots of the master rod & link rod assembly at this stage.

Very very nice - - - - thank you for taking us along on your journey!!!!

 

[petertha]

The pistons were made from 7075 aluminum. I mentioned earlier in the build post that I decided from the onset to use commercial piston rings for the O5 as opposed to making my own. I wasn’t sure I would be up to the task of rings on a first engine build. Maybe not so much machining the rings & fixtures, but doing the proper treating for the gap because I don’t have an oven & wasn’t quite sure about using a torch. I wanted to provide the engine the best chance to run, so this seemed logical at the time given all the other variables of engine building. As mentioned during liner making, buying the rings might be kind of false logic, or at least on a multi-cylinder engine, because it thereby requires you to make each cylinder bore identical to one another, to a correct dimension within tenths and to a correct finish, 5 times plus spare(s). Collectively, I think is more work & more challenging.

The O5 bore is essentially the same as an OS 56 4-stroke (0.56 CI). So along with the rings I also I purchased a single piston to replicate the ring grove dimensions and slight diameter reduction around the crown. Picture shows the commercial die cast? piston alongside my tester blank. Also of interest, the OS piston ring dimensions & open gap with is pretty much bang on what Trimble method works out to. The pistons are 0.0025" undersized to liner so just requires careful finishing & measuring using the same micrometer.

 

[petertha]

The ring groove was cut using an undersized Nikcole grooving tool. I set up a tenth’s indicator on the carriage to better monitor carriage displacement. The width was verified with a feeler gauge stack matched to the O.S. piston. The inner diameter (depth of ring groove) was measured with blade micrometer.

 

[petertha]

The piston blank was parted off oversize, flipped & trimmed to length. I used tape to protect the finish from the collet.

 

[petertha]

The 5mm wristpin holes were drilled & reamed while the blank was still solid. On my initial tester, I drilled the hole after internal material was removed, but I didn’t like the feel of the drilling through the wall, breaking out in the middle & continuing the hole through to the other side. I couldn't actually measure out-of-square but just preferred this solid method, basically pecking 0.050", clear chips & repeat.

 

[petertha]

Re-chuck the pistons back in the lathe to drill a 0.375” pilot hole to remove material & counterbore the skirt ID.

 

[petertha]

I made a mill clamp fixture to hold the piston orientated to a dummy wrist pin dowel. Then the rod clearance slot was milled away.

 

[petertha]

The non critical edges were lightly deburred with rubber abrasive, part cleaned & dimensions confirmed. I installed a ring to do a test fit in a lightly oiled liner. Insertion & movement felt about right and the ring gap seemed the same as the commercial assembly.

 

[anday1]

hi Peter
good progress i was thinking of locking the pin in the cylinder with grub screws and lock tight them to avoid making the small Delrin caps he recommends, what do you think?.
nice fixture for cylinders ( i will copy that) . BTW i'm making good progress with the split bearings (silver soldered together and worked a treat) i will post pics soon.

Kind Regards
Andrew

 

[petertha]

I've seen that set screw method employed Andrew so its definitely an option. It would eliminate making & gluing & profiling the pads which are a bit fiddly, but otherwise straightforward. Maybe a matching surface on the wristpin like a flat or dimple would be preferred so that would have to be orientated? It might assist with wrist pin fits which still mystifies me a bit. It seems to me on commercial engines the running fit on rod is just a teeny bit looser than relative to piston. The way I solved it was reaming the holes the same targeting the piston/pin fit & then lapped the rod a bit with super fine compound which gave the running fit. The rods always seemed to require a bit touch up after drilling the oil bleed holes (internal burr?).

On the cons side, if the set screw came loose it would be a bad thing rattling around. The right Loctite should address that but the piston also see's heating/cooling cycles. So glue needs to withstand elevated temp that, but still give up upon disassembly. I've had to use a soldering tip on some stubborn assemblies to cook the glue if accessibility is there. If the setscrew hex ever gets corrosion or oil mung buildup inside it, or worse gets inadvertently rounded out on the wrench, then disassembly becomes more challenging. But these are worst case scenarios.

 

[anday1]

my method of making the 4 conrods

 

[petertha]

The wrist pins were made from O1 drill rod, brought to diameter using the sandpaper lapping block method previously described. I reamed the piston and rod holes the same diameter so the piston fit was a snug sliding fit. And I lapped the rod hole using super fine compound just slightly to what I thought felt like a close running fit. The rods always seemed to require a bit touch up after drilling the oil bleed holes (internal burr?). The wristpins are solid but each end is drilled slightly to accept aluminum pads on either end intended to wear vs scratch the liner bore should the wristpin drift. I have seen Teflon pads used in commercial engines but I didn’t have the right material & was less confident of how to retain them.

 

[petertha]

I hardened the wristpins using torch method. I’m not sure hardening is required because they run inside aluminum.

 

[petertha]

The aluminum end pads had a little bleed hole drilled through which I learned the hard way is required, otherwise they can ‘hydraulic’ when the Loctite is applied & can set up in an incorrect position. I left the diameters slightly oversize so that once bonded, they get blended to the pin diameter, chamfered & finish length in one lathe operation.

 

[petertha]

Final assembly pics

 

[anday1]

it can never hurt to harden

 

[anday1]

bit of rotary work and filing and the conrods are done...2 weeks and lots of learning

 

[anday1]

conrods done now the real challenge starts with the heads