Resources/Information for Crank Lubrication?

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TriangleTom
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Resources/Information for Crank Lubrication?

Post by TriangleTom » Thu Mar 15, 2018 1:31 am

I'm currently working on my own engine design, and it seems like the biggest source of headaches is the crankshaft design and lubrication. I haven't been able to find anything regarding the crank bearings or lubrication.

I'm currently planning on doing something along the lines of a built-up, bolted together crank turning in forced lubrication Babbitt bearings, but I'd really like to hear from y'all regarding this.

Thanks!

Thom
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Lopez Mike
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Re: Resources/Information for Crank Lubrication?

Post by Lopez Mike » Thu Mar 15, 2018 4:34 am

If you don't mind going in a non-traditional way, think about ball bearings for your mains. My Strath Steam Warrego built in Australia has ordinary sealed single row ball bearings and they have required zero attention in years of hard running. There are two on each side of the crank webs. Helps keep the crank aligned. And they will take any amount of thrust. The crank is a simple pressed together design.

The other two areas of concern and difficulties can be the ends of the connecting rod(s). For the small end, Rod Mueller, the designer and builder, chose a relatively large diameter and hollow pin which has holes in the two end caps. You add oil about once a day to one of the holes until it comes out the other. The the oil seeps through and additional drilling to the brass wrist pin bearing.

The big end is more unusual. There is a round aluminum disk on the side of one of the crank disks. It has an undercut rim and a small copper line from a drip lubricator ends such that the oil drops collect in the undercut. There is a drilling at an angle from the undercut all the way to the crank pin. This lubricates the ordinary plain brass big end bearing by centripetal force. It consumes very little oil. This the engine, a single, only has two drip lubricators, one for the rod bearing and one for the crosshead, the wrist pin, filled very occasionally, and various lubrication points on the valve gear.

The other thing that makes for low maintenance is that the Stevenson valve gear eccentrics are relatively large and contain large diameter sealed ball bearings.

This all is relatively unobtrusive but probably would not look right on a very traditional engine. I'm more of a runner than a fiddler and, although I love to look at wonderful engines like those built by steamboat jack, I am happy with my power plant.
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Re: Resources/Information for Crank Lubrication?

Post by Lionel Connell » Thu Mar 15, 2018 5:02 am

What type of engine are you planing to build? i.e. Single, twin, compound?

If you have suitable machinery, it can be less work and less problematic to machine a crank from sold rather than to fabricate it.

As far as bearings and lubrication are concerned I am with Mike. Modern sealed ball or roller bearings have replaced plain bearings for good reason. I personally like to stick with tradition, it gets down to what you personally prefer in terms of styling. If you like to run around the engine with an oil can and be very hands on, then go with that. If you want the engine to look after itself then that takes a different approach.

Is the engine going into a boat or is it for some other purpose?

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Re: Resources/Information for Crank Lubrication?

Post by Lopez Mike » Thu Mar 15, 2018 5:22 am

Lionell,

I dunno about machining a crank from stock. It seems like you would be removing 90% of the steel to end up with the final shape. A lot of work.

I have built a few cranks by making up the mains and crank pins from off the shelf drill rod. Very nicely finished, easily hardened and closer to the specified diameter than I can hope to achieve with a lathe. It also allows me to make the crank webs in the right shape for balancing if that is desired.

I press the parts all together with about .001" interference per inch of diameter. One part per thousand. Any tighter fit may exceed the yield point of the steel and if so will enlarge the holes permanently so it won't achieve much. Once pressed together as close to being lined up as I can make it, I get things dead on with the ugliest lead hammer you ever saw. I don't let the customer watch that part. I've never had one shift in use.

Either way will produce the right shape but I'm lazy at heart. And ending up with a nicely hardened crank pin is an attractive thing.
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Re: Resources/Information for Crank Lubrication?

Post by Lionel Connell » Thu Mar 15, 2018 5:52 am

Mike

The crankshaft for my 6A.

Machined from solid P20 tool steel, very close relation to 4140. 40 hours total work including cylindrical grinding and machining the counterweights.

Image

The photos of all of the machining steps are on my Facebook page https://www.facebook.com/pg/steam.launc ... 7133109506
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Re: Resources/Information for Crank Lubrication?

Post by Lopez Mike » Thu Mar 15, 2018 5:57 am

Beautiful. Just beautiful. Machinery porn.

But I still wouldn't do it that way. Most of us peons are lucky to have a lathe and a mill or access to one.

Thanks for the pix.
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Re: Resources/Information for Crank Lubrication?

Post by Lionel Connell » Thu Mar 15, 2018 6:07 am

Mike,

Thanks.

That is why I started with "If you have suitable machinery".

The best way to do something is the way that works best for you. Me, I just love making chips.

Cheers

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Re: Resources/Information for Crank Lubrication?

Post by TriangleTom » Thu Mar 15, 2018 6:14 am

That crank is beautiful Lionel, and it's really making me reconsider bolting mine together. I'm not really familiar with the 6A, so where does the eccentric for the cylinder away from the camera go?

The engine I'm planning this for is going to be a pyramidal 5-cylinder quadruple expansion with a reheating receiver between the IP cylinders. It'll be going in a boat similar to Ron's (fun fact, he was the one who piqued my interest in steamboating).

Mike, what do you mean when you say get it dead on with a lead hammer? Do you just beat it into staying in place? Also, thanks for the suggestion about the lubrication system for the bigend and the ball bearings. Bigend lubrication was actually what was causing me to look at the Babbitt in the first place.

I'm planning on building this as an enclosed engine, so for the little end I'm just going to shower it with a high pressure oil spray. Should do the job nicely and lubricate the crosshead as well.
Last edited by TriangleTom on Thu Mar 15, 2018 6:18 am, edited 1 time in total.
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Re: Resources/Information for Crank Lubrication?

Post by Lopez Mike » Thu Mar 15, 2018 6:17 am

How big is this engine to be? Bores and stroke?
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Re: Resources/Information for Crank Lubrication?

Post by TriangleTom » Thu Mar 15, 2018 6:22 am

Lopez Mike wrote:How big is this engine to be? Bores and stroke?
1 7/8"+3 7/8"+8 1/8"+ (2) 10" X 7 inch stroke. I'm still doing the math on the heat transfer in and out of the cylinders and resuperheater as well as condensation in the valves and receivers, so those bore numbers are subject to a little further refinement.
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