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| Bog's Paddleduck Engine |
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| bogstandard:
Sorry Kirk, You are perfectly correct, but not a lot. About 0.050", it is there mainly for final tweaks to adjust for for piston and rod length mismatches. John |
| kvom:
Very soon I will be needing to get all the sliding fits working, and there are a lot of them (valves, pistons, bearings, conrods, piston rods, crossheads). I don't have over/under reamers, so all the holes for these parts have been reamed to same size as the part that slides through them. On my previous engine I had only one valve and one piston/piston rod. My "technique" was to use emery cloth on the sliding part until it could enter (albeit tight), and then use toothpaste to lap it to fit. So far I have done that somewhat with the bearings using some short pieces of drill rod. Is there a better approach? Also I am wondering if reaming out the crosshead bores to the next drill size would be OK, as opposed to lapping? |
| bogstandard:
Kirk, Remember, this engine was designed for beginners, and as such, if the fits aren't very good, it will still run perfectly satisfactory. Just get it fitting to the best of your ability. Reaming to size for the matching rod will be perfectly acceptable. In fact it is only on engines like flame lickers and sterlings that very fine tolerances have to be adhered to, purely because they have so little power, waste one tiny bit thru leakage, and they just won't run. If you can get nice sliding fits on all parts, that will do. By the time the engine has a few hours on it, all those superfine fits will be lost anyway. If you can get the bits to fit together and turning without rattling or wobbling, you are onto a winner. For the bores, if the piston will enter from both ends, and with a bit of oil in there, seal over one end of the bore, and pull the piston out of the hole. If it comes out with a pop, it will be just fine. The only critical parts are the piston valves, they need to be lapped with a bit of brasso or toothpaste, but I have also seen engines running perfectly well with steam coming out of the top and bottom of the piston valves from new. The Wilesco range is a very good example, like they were made by cavemen with stone tools, but they still run OK. A tight fit on those engines would be about 0.002" clearance between the parts. John |
| kvom:
I finished the other two temporary columns this afternoon, and started on getting the sliding pieces to fit. First up were the bearings. Here's my alignment/lapping setup: I ran it about a half hour with the toothpaste, cleaned it up and oiled it. The drill rod turns pretty smoothly now. I then did a bit of catchup by drilling and tapping the holes for the setscrews on the eccentrics. Next I lapped the bores of the crossheads in the same manner as the bearings. I discovered that one of my crosshead guide bars was slightly bent, so that's a job for another day. |
| kvom:
John's shipment of solder arrived today. Thanks very much. Now I need to get on the ball and get the other necessary items. |
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