Oiling big-end bearings on Stuart Score

[jamespetts]

As I have mentioned before, I am in the process of setting up a Stuart Score to power a small dynamo and generate some electricity, which should hopefully be enough (if my calculations are correct) to run a small computer at 35-40W.

However, to produce that power output for any sustained time would mean the engine running at high speed under high torque for a sustained period, which would require serious lubrication. Most of the places on the Score have oiler cups, but the big end bearings of the connecting rods and the eccentrics do not seem to have anything. Here are some pictures:





The eccentrics might, actually, have some oiling system, since they have a little hole in the front and a small nipple inside, just underneath the hole: is one supposed to put grease in that hole? If so, where would one find the right sort of grease?

The big end connecting rod bearings, however, have no oiling/greasing provision at all. I have seen some smaller Stuart engines rigged up with oiler cups on the big end bearings (presumably with suitable holes drilled and tapped), but, if I am going to run this engine at high speeds, I should imagine that a lidded oiler cup would be necessary to avoid the cup being emptied from the wrong end as soon as the engine starts moving at any speed. Is it possible to obtain such lidded oiler cups, or can anyone think of a better solution for oiling the big end bearings of my engine?

Edit: Here is an example of what I have seen on other engines:



I have also seen photographs of more elaborate arrangements, including wick oilers and all sorts of things, but I cannot remember where now.

[steam4ian]

G'day James

Tough question. I'll jump in You could drill an oil hole in the top of the bearing with a small open cup. if the cup was cut away on the leading side it could be made to wipe a wick from an oiler suspended over it; the big engines used this method side.

You could make up a trough to go under the big ends end put a scoop on the big end to scoop oil up to the bearing.

Over to the others.

Regards,
Ian

[Tel]

It's easy enough to fit an oil cup to the big end bearings by drilling & tapping for them and 'waisting' a short section of the top bolt where it coincides with the oil passage. 'At high speed' with the Score, or similar engines is a relative thing & I don't think it would attain such great speeds that the open cups would be a problem. I guess little lidded oil cups would be available somewhere if they were needed however.

Eccentrics generally have some provision for drilling an oil cup & passage.

[jamespetts]

Thank you both for your replies :-) Tel, I am told by the nice people from Stuart that the Score is capable of 1/10hp (~74W) at 2,000RPM - is 2,000 RPM too fast for an open oiler cup? The only lidded ones that I have seen are 1/4" or larger, which is too large for my application.

[Tel]

Hmmm - I see your problem, and, rather to my surprise, none of my suppliers seem to list oil cups of any sort. I've always just made the open type, but then again, I don't run my engines at anything like 2000 rpm.

Given that the engine is intended for serious work for, presumably, extended periods, have you given any thought to a central oil tank with flexible lines to the dynamic parts, you could even lightly pressurise it for greater reliability.

Now, I don't mean to cast any nasturtians at Stuart, but 2000 rpm, again, for extended periods, seems a bit of an ask for the Score. I should have thought that the Sirius, regretfully much more silvery, would be a far better option.

[circlip]

No consolation at this point in time James, but this is probably why the Sirius was used on the WW2 steam generating plant for the Resistance Agent radios for recharging the batteries. What about running the engine at lower revs and gearing up? Pulleys and belts? Ian.

[jamespetts]

Thank you both for your replies :-) As to the engine choice, the Sirius is a 1" bore and 1" stroke, whereas the Score is 3/4" x 3/4": I doubt that a 504 boiler could cope with a Sirius running at high speed and load. Stuart used to make an engine called the Sun, which was like the Sirius but smaller, at 3/4" x 3/4", which would have been more suitable. In any event, however, such engines are not easy to source - even the Sirius is available only in unmachined castings (I do not have access to a workshop with machine tools) and does not regularly appear on eBay. In any event, the open crank engines are far more pleasing to watch.

I do plan to gear up in any event: the motor that I plan to use as a dynamo requires 4,100RPM to produce 12v: with the right sprockets, I can gear to ~3:1 (25:8), meaning that the engine would have to run at 1,366RPM. If I could find a way of packing the centre hole (10mm) on the larger sprockets to fit snugly onto the end of the crankshaft of the Score (7mm) (would leather and a grubscrew do the job?), I could get a ratio of 38:8, or 1:4.75, which would require only 863RPM.

As to the centralised tank with flexible lines, that is not a bad idea: presumably, one would use copper pipe from the tank, and copper pipe threaded into the hole drilled in the connecting rod big ends, connected to each other by a short length of neoprene pipe? I imagine that gravity feed would be the easiest system - I cannot think of any easy way to pressurise a tank at present! This does seem like a potential way forward, however.

[circlip]

Beware model size chain drives at that speed James, You're going to have to make guards for them so the centralized lube system may be the best bet. Chain drives are a bit noisey though.

[jamespetts]

Circlip,

what sort of guards ought one make for chain drives - the sort to prevent fingers getting injured, or another sort of guard?

[circlip]

Primarily to prevent finger crushing but also in this case to keep from oil flinging.

[ausdan]

- just some thoughts-

wanting to run electricity would require a constant force for a period of time, I would have a guess that the cups on the eccentrics etc would empty fairly quickly, and you would have to stop to re-oil , which then would shut down the gen set. (would the computer then shut down and have to rebooted every few minutes)

The central oiler would be the best bet, pressure to the oiler could be from a oil tight compartment with a little steam piped into it

or an compartment (like a syringe) with a lid on top loaded with a little amount of weight pushing on the oil

also a grease nipple, with teh ball removed, makes a good connection for the tube to mount to (like a mini barb) a sml twist of wire should hold it from flinging off

[jamespetts]

Ausdan - interesting thoughts, although some of those seem quite complicated to accomplish. I had thought of just suspending a miniature bucket above each big end bearing, drilling a very small hole in each bucket, and filling them with oil, which would drip out over the big end bearing as the engine is running, and work its way inside. Can you see any particular problems with that approach?

(Of course, it is not a problem that the cups run dry, as long as the bearings have oil on them. I have noticed that the cups run low very quickly, but the bearings retain oil for some time - at least, with the oil that I have been using, a fairly thin synthetic bicycle oil).

[steam4ian]

G'day James

I refer you back to my previous post. The idea, used on real engines ;D is like yours only there is a wick which delivers oil to the engine. The moving parts have a cup which stays virtually empty but the cup has a wiper which strokes the wick on each pass. In this manner a small amount of oil is picked up each time. In one pattern the oil container is a cylinder, sometimes glass, with a wick tube up the middle; the wick dips in the oil and then leads down the tube the wiping point. To start/stop the oil you lift the wick in/out of the oil. the other pattern has a dripper which drips the oil onto the wick; the drippers have a screw for adjustment and an on/off level on top of the lubricator.

Your bearing could have a similar drip feed or wick leading to pipes the bearings.

Be warned, at 2000 RPM oil is going to go everywhere; what the wall paper.

Best idea, take yourself on a trip to museums to see what the big boys used. I am sure most operators would delight in explaining it to you.

Regarding you CI cylinders, I would put a capped T into the exhaust pipe for injecting some oil at the end of the run. More soldering!

Regards,
Ian

[jamespetts]

Ian,

thank you for your reply :-) The wick suggestion seems interesting, but I am doubtful that I have the engineering ability to pull it off. I do think, however, that my engineering ability could probably stretch to drilling a very small hole in a miniature bucket or two ;-) Or am I imagining what you are suggesting as much more complicated than it really is? Perhaps diagrams would help?

I am hoping to gear the engine up far enough to be able to run it at closer to 800 RPM, which might help a little.

[Paul Boscott]

Ian

As you are planning to use your engine for a real purpose rather than a scale model an option could be to over bore the con-rod and fit a nylon type bearing no lubrication required. I have used bearings from www.igus.co.uk successfully (note i am just a customer)