I am a member of a model train Club in S E Queensland, Australia, we give kids rides on our model railways, Steam engines are popular but beyond some of us. I have built a Fairmont 6 man Gangers trolley powered by a mower engine. It does real work pulling up to 16 people on our 7 & 1/4 inch track.
Opposed twin Onan engine in half scale
- Thread starter teeleevs
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More work on the crankshaft since last post, 1/ & 2/ second crank pin on track, went over to my big 4 jaw chuck, 3/ this is a large chuck, have only used it once this century, 4/ pieces coming together.
Thanks for watching
Thanks for watching
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More on the Onan opposed twin, picture 1/ nearly ready to press together, so far I have reduced a 20 pound piece of 3 inch round bar to just 4.2 pound i e about 2 kg, 2/ a good piece of Queensland Rail steel becoming connecting rods, 3/ boring the bigends and litttlends.
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Todays progress, photo 1/ setup between centres on Gils Harrison Lathe 2/ the shape beginning to appear 3/ conrods finished one Honda piston fitted, roller bearings fitted 4/ crankshaft ready for assembly. Thanks for watching, Ted from down under
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I'm watching your build with interest. I have a Onan that used to power my skid steer loader, a Hydra-Mac from 1972. The engine is a 25HP NC model. It suffered from the common failure of exhaust valve seat coming loose. And when Cummings purchased them a few years back, they stopped all support of the existing engines.
I was able to bore my cylinders on my vertical milling machine back 25 years ago, to 0.030 oversize.
There was a design flaw by the Hydra-Mac skid steer design, they used a triple V-belt pulley to drive the hydrostatic pump/motors (Sunstrand Model U), this put too much radial forces on the power take off shaft, which only had a babbitt bearing, not intended for these forces, which produced early wear out.
Looks like your using ball bearings in your crank interface.
I'm interested in how you build the cylinders. The original engine I have has cast iron sleeves that were cast into the aluminum block.
I was able to bore my cylinders on my vertical milling machine back 25 years ago, to 0.030 oversize.
There was a design flaw by the Hydra-Mac skid steer design, they used a triple V-belt pulley to drive the hydrostatic pump/motors (Sunstrand Model U), this put too much radial forces on the power take off shaft, which only had a babbitt bearing, not intended for these forces, which produced early wear out.
Looks like your using ball bearings in your crank interface.
I'm interested in how you build the cylinders. The original engine I have has cast iron sleeves that were cast into the aluminum block.
Thanks ignator, I have some 2inch cast iron to make the sleeves, the Honda pistons are 39mm, the alloy cylinders will be built up from cast pieces, the valve guide and seat will be one piece glued in with J B Weld, picture 1/ polystyrene pattern, 2/ a casting, the fins will be cut in the mill once I know where the bolts go. Some of my pictures are under another guys thread Building a Flat Twin, and some are under Castings. My only experience with the full size engine was back in 1963 direct coupled to a Lincoln welder and 1974 I owned one myself, the unit bolted down in the back of my Land Cruiser was so handy with its 240 volt power outlets.
Ted from down under
Ted from down under
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I used J B Weld to repair the valve seat. I made a new one using O2 tool steel. I never could find what sort of steel the hardened seat inserts were made of. So I used what I had in my shop. It worked, but I got the press fit size a bit small, as it came loose again after 20 hours of running. So I used the epoxy to put it back. It held until I replaced the engine with a Honda back in 2011. All was well, but doing some earth moving for a new shop I wanted to build this summer, I broke some spur gear in the drive train. I have not disassembled to see what is damaged. Parts can be had for much money. It was very close to one of the original skid steers ever produced in the USA. Previous owner abused it. I could see where repairs were only made when it would not move. Pig farm operation, cleaning out manure.
So your casting, do you leave the foam in place which is melted and vaporized during the pour?
Yes that is the way it is done, a bit like lost wax casting, the job turns out a little rough but I need finer sand. I have used wood patterns with good results but sometimes it very difficult to make a shape that will come out of the mold without making complicated cores. All good fun.
Thanks
Ted
Thanks
Ted
Thanks ignator, valve seats should be no problem as any auto repair/ rebuild shop have them in all different sizes. Photos today 1/ trueing up the crank 2/ almost finished the final cutting, only have to split it up and mount the conrods then Locktite final assembly trueing it up as I go.
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I recall seeing your CAD drawing having fasteners to hold the crank shaft conn rod throws in place. Appear to be flat head screws. I would have thought in this size engine the inertia impulses from throwing the pistons would shake this apart.
Well for valve seats, I have lathe, and local engine shop was not wanting to help me unless I let them do the machine work. So I was more interested in what hardness the seats were. This was back in 2007, and I could not find any links on the internet that had tool steel material type and Rockwell hardness level. I have a Black and Decker valve seat grinder and valve grinder dating from the 1960s.
The Onan did not lap the valve seat, at least on my NHC model. The made the valve 44 degree and the seat 45 degrees, call this an interference angle. The attachments are from the shop manual below: Probably nothing new here for you, but someone else reading this may gander some useful information.
I hope you are wrong but the crank pin is only 12mm so putting it in tension under an 8mm countersunk bolt will stiffen it up, I have built another engine that only has an 8mm bolt through a ballrace bearing with a locknut and it runs fine. I worked for a service station back in 1968 and used the Black and Decker Valve Facer quite often. But when the valve is only 14mm diameter it is hard to achieve a good seal when the seat is produced with a drill at 30 degrees, still one manages. photo 1 the model and 2 the real 1898 machine used on the Normanton line in Far North Queensland, Australia.
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It was more of a question as to if this is sturdy enough. You have experience with this sort of crankshaft build. Every engine I've seen that is production has a forged crank, even the very small engines used in weed wackers, and leaf blowers. I can see this working without issue in a miniture model, but I'm curious about larger engines. My experience with a crank build a few years back stopped me as I could not make it run true. I'm going to have to get back to that. It was for a Stirling engine. So I'm trying to see how it's done here, as there is much success.
As you say, it is very difficult to make it run true, I am yet to find out if I am successful. I found on the drawing board that there was insufficient clearance between big-ends and the cams so opted for roller bearings without bolts through, I might yet regret that decision. On your full sized model, the 15 HP up to 20 HP had ordinary car like big-ends but when they lengthened the stroke they ran into the same problem.
Last couple of days work on the Onan opposed twin, 1 the rear bearing housing, drilled one hole in the wrong place? 2/3 decided to lighten the rods, poor little pistons are the lightest parts in the whole project. 4/5 cutting an oil groove. 6 looking good
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Some may question the rotary table? I was given a 97 tooth gear about 30 years ago. What can you do with a 97 tooth gear? It is mild steel, I counted the teeth on a Holden ringgear 135, cut 15 out and carefully pulled it in and welded it, giving me 120 teeth which can be divided by numerous numbers. Turned part of the 97 teeth away, fitted the ringgear, had a worm wheel that fitted, onto that I can fit any combination of lathe change wheels or drive it with a motor. Drilled holes and threaded 3/8 W
Those connecting rods look super duty! Interesting 4 jaw setup to carve them.
Another day on the Onan opposed twin half scale. Photo 1 I have set up the crankcase on a spigot to turn true bolted the timing case on and bored through for the crankshaft, faced back the case ready to fit the Lifan Chinese ignition coils and flywheel, photo 2 turning the seal seat inside the timing case.
Ted from down under
Ted from down under
