Designing a new engine for a big(ger) boat...

[fredrosse]

Alignment of bearing surfaces on the walking beam engine I built was also a PITA. If I had it to do over I would use spherical rod end bearings for several pivots, and a spherical race roller bearing for the big end of the connecting rod. The A-frame walking beam engine has more motions that need to be aligned, but you might consider the self aligning features of these type bearings for any mechanism that is made from a weldment.

[Albert]

Hi Bart, take a look at this picture of the "aseptically" engine:



Albert

[Lopez Mike]

I love that 'crosshead' design. I wonder how much the pillars wear with time? If I could change to a sealed ball or roller for my rod big end something like this for my crosshead, I would be mostly free of oil flying around.

Mike

[barts]

I love that 'crosshead' design. I wonder how much the pillars wear with time? If I could change to a sealed ball or roller for my rod big end something like this for my crosshead, I would be mostly free of oil flying around.

Mike

From the previous shot earlier in this thread, it appears the contact surfaces are Delrin bushings turned to the profile of the rods, so wear might be minimal. Cross head load depends on the maximum angle of the connecting rod; the longer the rod the lower the load. On my big engine w/ say a 12" length connecting rod, connecting rod angle is less than 12 degrees - so cross head load is 600 lbs max when running at full cut-off. How to figure out the acceptable load in this application is tricky, though, given the curved line of contact.

- Bart

[Lopez Mike]

I probably won't get to it this Winter what with going to Baja to kayak, ride my motorcycle and generally hang out, but one of these times I am going to tear in to my engine and see about either this roller design or a Watts linkage. I love a silent engine.

My crank is a pressed and pinned assembly so I am going to see if there is enough clearance for a sealed ball bearing in the big end. I'd have to make myself a new connecting rod so perhaps I can see about the wrist pin as well. No clicking!

Mike

[Albert]

Bart, Mike

Here some more pictures of this interesting engine:











The crosshead guide (no slides, but rollers) as well as the pistons consist of PEEK material (which includes among other components graphit, glassfiber and PTFE). The engine needs no lubrication at all. Note the interesting drive for the poppet valves. The vertical boxes house the corresponding heat exchangers for preheater and condenser. Note that the main steam pipe comes from under the floor... Yes, the steam generator is located down there, the stack is located in front of the cabin.

Albert

[fredrosse]

Albert, I am sure many of us would like to have a full description of your boat "Min Deern" and engine, such fine work, and a new design with many good features.

I would recommend you post it in the forum thread "Member's Steamboats - A Simple List for All", as much data and pictures as are available please!

If there are problems with English-German, go to Google and call up "Translation", you can write something in one language, and the translation comes up immediately. Works well, some times a steamboat word is not translated correctly, but mostly OK, although your English appears very good anyway.

[Oilking]

Bart,
Uniflows, unlike counter flows, have longer cylinders and exhaust through ports in the middle. This leaves the mid part of the cylinder much cooler than the ends where addmission ocurres. On the Skinners the cylinders are made so that the cold diameter is larger in the middle than at the ends. When hot, the ends will expand more than the cooler middle making the sides straight, and avoiding a piston stuck half stroke.

I'm not sure how much of an issue this could be in smaller bore engines. The expansion rate of the piston and cylinder would need to be taken into account, and then would some work with a hone midstroke do the job? Or, would the tolerences be small enough to get away with ust leaving the piston a bit sloppy.

Any thoughts?

Dave

[barts]

Bart,
Uniflows, unlike counter flows, have longer cylinders and exhaust through ports in the middle. This leaves the mid part of the cylinder much cooler than the ends where addmission ocurres. On the Skinners the cylinders are made so that the cold diameter is larger in the middle than at the ends. When hot, the ends will expand more than the cooler middle making the sides straight, and avoiding a piston stuck half stroke.

I'm not sure how much of an issue this could be in smaller bore engines. The expansion rate of the piston and cylinder would need to be taken into account, and then would some work with a hone midstroke do the job? Or, would the tolerences be small enough to get away with ust leaving the piston a bit sloppy.

Any thoughts?

Dave

Well, at worst the top of the cylinder will be at saturated steam temp at 250 psig, or 406 F. Assume exhaust temp of 150 F - we have a 250 F temperature difference between middle and top. With a temp coeff. of gray cast iron of about 6 microinches/inch per degree F and a 4.25" bore, that means 4.25 * 250 * .000006 = .006" difference in diameter - assuming the top of the cylinder reaches the full inlet steam temp, which is quite unlikely. The piston is going to expand some average in between, so as long as we start with a reasonable clearance when cold, I really don't expect any problems. Piston skirt clearance on 71 diesels was 6 - 9 thou - I'll likely use that figure. Note that the 71 had the same issues - the botton of the cylinder (intake on original application) is cool. the top of the cylinder is hot.

- Bart

[Lopez Mike]

I believe that I used some of that PEEK or something close to it on what is called a 'ruling machine' for making diffraction gratings. Sort of a flat version of a prism to sort out light into its various wavelengths. The PEEK, of whatever it was had at least PTFE and graphite in it. It's virtue in that application was that the static friction was extremely low. No vibration from stickiness at the start of motion.

Please tell us what PEEK stands for so that I can look into it.

Mike