Running in a steam engine

[steamer]

Point taken Ryker, I think perhaps the valve grinding compound is probably Aluminum Oxide and it breaks down with time....Admittedly today I lapped the PD of the oil pump gears for my Wallaby with fine automotive rubbing compound while mounted revolving against each other in the lathe....which I think is a pumice based product, but no matter, I know it will break down, and I also know I can remove the compound...worked a treat and left nicely polished flanks on the gear teeth.....and a ever so slightly smaller Pitch Diameter.

I don't think I'd try the same thing with a diamond compound as it will not break down with age....it just keeps cutting.. and will bed into the base metal..so how do you KNOW its clean?.......

I lapped the bores of my launch engine with a Clover compound which is ALOX based with an aluminum lap and also got great results.....and that was about 15 years ago.

Of course, the question with me is academic, as I don't have any diamond base compound in my shop :big:

Dave

 

[Ryker Carruthers]

left nicely polished flanks on the gear teeth.

That is exactly what it did to our gears, i'm shure all of the grinding compound is gone because if it wasnt there would be scratch marks on the surface, correct? We use a hotsy to steam clean it once a year I would think that would clean it out for how much crap gets blown out that we didnt even know was there. Ill find out what exacty dad used and let you know
Ryker Carruthers

 

[steamer]

My Launch engine was tight at first....then I put it on the dynomometer.....and beat the piss out of it for about an hour....wasn't tight anymore!
:big: ( nice bark!)

 

[steamer]

Most traction engines I see have exposed gears...I gotta think the act of using the greased up tractor in a dusty field has more adverse affects to the moving parts than just about anything we can do to them!
:big:
Dave

 

[Don1966]

Gee! Dave you should of videoed the whole thing. I for one would like to see that. Love the launch engine.

Don

 

[steamer]

Didn't have a video camera then...about 14-15 years ago....and I was kinda busy anyway! :big:

Dave

 

[NickG]

I'll stick by my original opinion on this one. If the parts are made with correct clearances in the first place and lubricated properly, there wouldn't be any appreciable wear as there wouldn't be a great deal of metal to metal contact or friction. It's the manor in which plain bearings are supposed to work, a thin film of oil between the shaft and the bearing, if it's stiff, there's metal to metal binding and no room for the oil. If you made a car engine in such a way it wouldn't work, I know a car has a pressurised lubrication system but it's the same principle.

In my view it's just worth stopping and thinking about what limits, fits and surface finish is necessary for the function of each component before smearing stuff with valve grinding paste and connecting to an electric drill.

 

[Runner]

Nick your first post made sense to me. I accept that grinding compound and electric drill method is to be avoided. However your table did not help me at all because it was just words. I need quantitative data, to engineer clearances say between a crankshaft and bearing how much is enough and how much is too much? My method is self correcting accepting that there's a danger that it can go on too long. I did register your comment that steam engines are very forgiving in keeping going with seemingly a bit of wear.

Brian

 

[ProdEng]

Brian,

A Normal Running Fit on a shaft size 1/2" - 3/4" would be .0006" to .0024" clearance between bearing and shaft. The low end is likely to be a bit tight and I would aim for the middle to top to avoid a stiff engine. A little more probably won't hurt unless you intend running a lot or with heavy loads. The information on limits and fits can be found in Machinery's Handbook; highly recommended.

Jan

 

[Ryker Carruthers]

Most traction engines I see have exposed gears...I gotta think the act of using the greased up tractor in a dusty field has more adverse affects to the moving parts than just about anything we can do to them!
:big:
Dave

:big:
Thats why most of the big engines you see have quiet gears. It does get annoying having loud grinding gears. Our quarter scale case has almost no sound in the gearing after almost fifty years of a hard running... Grandpa didnt make it to just be looked at :big: I have to make a new wrist pin every year for it and dad did the same since before i was born, I wanted to know why they needed to be replaced so often so I take the con rod off and the set a square against the crank pin and the face of the disk and right away I noticed IT WAS BENT! I still cant belive that little engine could have bent a 1/2" hardend steel pin. Do you think I will be able to press it back out being bent? It isnt extreamly bent but with a press fit It might not want to come out. I asked dad about the grinding compound and he couldnt remember what exactly it was he just remembers very fine valve grinding compound.
Ryker Carruthers

 

[Ryker Carruthers]

I'll stick by my original opinion on this one. If the parts are made with correct clearances in the first place and lubricated properly, there wouldn't be any appreciable wear as there wouldn't be a great deal of metal to metal contact or friction. It's the manor in which plain bearings are supposed to work, a thin film of oil between the shaft and the bearing, if it's stiff, there's metal to metal binding and no room for the oil. If you made a car engine in such a way it wouldn't work, I know a car has a pressurised lubrication system but it's the same principle.

How much clearance would you think an oil film needs? I recall hearing that some of the original steam traction engineers would wrap the shaft with paper before pouring the babbit but I would think the paper would burn and that be too much of a clearance but hey what do I know. When they pour babbit in the bearings they usually put shims in for adjust ment and when you take a shim or to out the hole becomes oval and the shaft gets tighter and has to wear in again. After you do that is a good Idea to let it idle for a while before working it or the bearing will get hot

 

[Runner]

Jan thanks for the data.

A Normal Running Fit on a shaft size 1/2" - 3/4" would be .0006" to .0024" clearance between bearing and shaft.

To achieve that for me produces practical problems. To begin with I can only measure to +/- 0.001". Say I chose to use 1/2" dia steel rod to fabricate the crankshaft and the bearings were drilled and reamed 1/2", depending on the accuracy of the stock steel rod and the reamer used I could easily have a 0.002" too loose or too tight a fit. Three bearings on a twin throw crankshaft has some alignment inaccuracy, all these tolerances go towards creating a tight engine. Correction we are only considering the crankshaft running in it's bearing mounted on the bed. At my skill level and measurement capability I could not begin to determine quantitatively where the crankshaft was tight. I need to improve my skill level and increase my measurement capability to produce running fits without resorting to palliative measures.

Brian

 

[steamer]

The old rule of thumb for plain bearings under boundry layer lubrication is .001" / inch of journal diameter.

Dave

 

[Mosey]

How about measuring the stationary torque of a good running engine with a motor torque wrench and comparing that to the reading of a new engine not yet run in. You might measure the new engine a section at a time...with crank only, add pistons, add cam, etc.
Anyone ever try this?

 

[NickG]

Nick your first post made sense to me. I accept that grinding compound and electric drill method is to be avoided. However your table did not help me at all because it was just words. I need quantitative data, to engineer clearances say between a crankshaft and bearing how much is enough and how much is too much? My method is self correcting accepting that there's a danger that it can go on too long. I did register your comment that steam engines are very forgiving in keeping going with seemingly a bit of wear.

Brian

Yeah you're right Brian, I was going to put the tables that linked the quantitative data in but it was taking ages to extract it from the PDF document I have! It is all there in the standard though. There may be copyright issues so I'll have to see if it's in the public domain.

Good point about our abilities to machine to this level of accuracy but still useful just if to give people an idea, clearances become more critical when building things like hot air and flame gulper engines where low friction is essential.


Nick