# Running in a steam engine



## smfr (Jul 5, 2012)

I've come to the point in my first "real" from-castings steam engine build that I can turn over the crankshaft/conrod/crosshead assembly, but all the parts are still fairly tight. I can turn it over by hand with the flywheel attached, but not just with fingers on the crankshaft. You can see a video at the bottom of this post: http://www.homemodelenginemachinist.com/index.php?topic=17746.msg199110#msg199110.

So I'm wondering how folks go about running in a newly built engine. More specifically, I'm wondering:

* Whether I should consider running it in before it's fully assembled, or whether it's OK to run in the parts I have so far.
* What kind of lubrication to use. Should I consider any kind of grinding compound on stiff parts?
* How long to expect to have to run it in before things turn over easily by hand

Thanks!
Simon


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## lordedmond (Jul 5, 2012)

If you are running on steam then you must use steam oil for the cylinder/s , use any single weight oil for the rest not to thick

on air use the same single weight oil for the cylinder/s

Stuart


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## Florian (Jul 5, 2012)

smfr  said:
			
		

> * Whether I should consider running it in before it's fully assembled, or whether it's OK to run in the parts I have so far.



Hey Simon
If you are going to finish-machine the piston on the piston rod, this should work so far.




			
				smfr  said:
			
		

> * What kind of lubrication to use. Should I consider any kind of grinding compound on stiff parts?



I would use some petroleum because it is very thin and lubricates not so good (that finally means breaking takes less time) 

When the machine is running, you should frequently (every 15 minutes or so) put some new oil on it to be shure there is always enough lubricant. 



			
				smfr  said:
			
		

> * How long to expect to have to run it in before things turn over easily by hand



Well, this can depend very much on how it has been built and what you are using as a running in lubricant. 
But it can take several hours ! 

I would check every half hour (just loosen the connection from the chuck to the crankshaft and turn it by hand)
and repeat until it is running as easy as you want it to. 


Finally, I would not use any grinding compoud as it is difficult to get it off once applied! (The grains will stick to the softer material and not come off easily! ) 


By the way; For the connection of the conrod with the lathe chuck, I would use a piece of garden hose as it will compensate any offset between chuck and crankshaft.

Regards
Florian


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## steamer (Jul 5, 2012)

I agee with Florian.

It'll break in on its own accord with a lubricant...no compound!

You can "motor" it as is without fear ....just keep it lubricated

A straight 20 or 30 weight bearing oil is fine

If you have a spindle oil for use on your lathe, that will do fine for motoring on the lathe.

I can recommend "Blue Velvet" brand "PB" for bearings while under steam....though it hardly justifies buying a gallon...


Dave


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## Blogwitch (Jul 5, 2012)

Simon,

Be very careful if you are going to run it in by turning the crank. That is the total opposite to how an engine runs and can be disastrous if done too much.

I have a V4 oscillator steam engine knocking about somewhere that someone built and tried to run in by turning the shaft with an electric drill. After only ten minutes, the whole engine was ready for the bin, basically none of the moving parts were any good any more. All bearing and pivot points were worn oval.

The best way is to put a bit off air into it and just let it run in under it's own steam.


John


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## steamboatmodel (Jul 5, 2012)

John has it right, also if running it on air use air tool lubricant on it.
Regards,
Gerald.


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## Florian (Jul 5, 2012)

Hey Bogs

Dont' you think the problem with the electric dill was not the direction of the load but rather the high rpm compared to what a team engine does when under steam...? 

And if the bearigns and pivots get damaged by running it by the crankshaft, then the material used is not very suitable for that application! Or that guy used some grinding compound which makes the bearings and pivots to wear very quickly! 

Well, for me it does just not make any sense that the bearings should wear that fast if the the moving parts are under no load except their own weight and friction; assuming that they are being broken in with aproppriate rpm. 
I mean, the bearing loads will just be into another direction and also the loads are more even because of the constant rpm of the crankshaft. (driven with the cylinder, the loads will vary as the cylinder produces a force up or down....) 



But the point with running it with compressed air is of course right; I also do it that way as soon as the parts rotate free enough. 


Cheers Florian


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## Ogaryd (Jul 5, 2012)

Hi Simon,

    I've been watching your progress on this engine and it looks very nice to me. I would recheck all friction surfaces
      and find the stiff parts. When I do final assembly I carefully spin crankshaft after each new part is installed. That
      way I can usually find the problem area. Personlly I wouldn't use the lathe or drill motor. I'm with Bog's, run it on air.

                                                                             Garys


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## Captain Jerry (Jul 5, 2012)

Simon,

If you had just rebuilt your 16 cylinder Ferrari and it would not spin freely with the heads off, would you get an 8ft cheater bar and try to get it to move? I don't think so Tim.

Same thing. If it is tight, you have to find out why.

Jerry


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## steamer (Jul 5, 2012)

steamer  said:
			
		

> I agee with Florian.
> 
> It'll break in on its own accord with a lubricant...no compound!
> 
> ...



My comments come from Mr Smiths book "How to build the 10V".

Dave


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## steamer (Jul 5, 2012)

Oh and yes...it is assumed that it's turning on it's own accord without *undue  * friction...some judgement is required.

If it's bound up don't just chuck it up and start the lathe!

Dave


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## Runner (Jul 5, 2012)

Well how lucky am I not to get egg on my face? I was considering placing here my experience in freeing up a twin cylinder vertical steam engine that I am constructing. Well forgetting the " ........ angels fear to tread" here goes.

It is at the stage Simon is at except that it includes Stephenson's reverse gear so the 4 eccentrics and straps are in place. The size of the engine is comparable. I am able to easily turn the crankshaft by hand and with the flywheel fitted can spin with a flip of the finger 1 revolution. I did this by stages crankshaft in the bearings only using plenty of light machine oil run with an electric drill. One bearing was warm so I applied fine grinding compound.(my view is if there's tightness some small amount of metal needs to be removed, fine grinding compound gets you there quicker). Next was pushing the conrod and crosshead to and fro into the tube by hand, it should drop under its own weight. This I found was a big area for creating friction so the fine grinding compound again did the trick. And so on. Bigend bearing shouldn't be a problem.

I don't think my engine so far is ready for the bin, but registering the comments that grinding compound is difficult to remove maybe it will eventually.

Brian


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## Blogwitch (Jul 6, 2012)

I knew I had a couple of piccies of the engine I was on about, a Peter Arnot V4.

It looks a real mess, but this was taken after sitting in a junk box for a few years. It's still there as far as I know.








And this was how things ended up all over it, worn out in about ten minutes.
BTW, it was by using a battery electric drill, not a mains one, so not as fast as first thought by some people.






The reason for all this damage?

One of the feed pipes from the control valve was almost blocked by silver solder, causing a back pressure whenever it was turned over, beating and wearing things into a new shape. If it was fed by air, it would have become apparent that there was a problem.

Hundreds of man hours down the drain.

John


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## Maryak (Jul 6, 2012)

If your steam engine is going to run using saturated steam, cylinder lubrication is optional and depends to a large degree where the exhaust is going. Believe it or not water is a very effective lubricant with cast iron or bronze cylinders and pistons/rings.

If your steam engine is going to run using another source such as air or superheated steam then cylinder lubrication is necessary. Some so called steam oils and all airline oils are emulsify-able and some are straight heavy mineral oil; again the choice is mostly around where the exhaust ends up, i.e. you don't want emulsify-able oils anywhere near a steam engine where the condensate is returned to the boiler. They also don't work all that well with displacement lubricators.

Probably IMHO, as my old mentor was want to say, you can probably pee in it and it will run for years. We are talking 12" : 1ft here so a model is hardly likely to wear out or fail when one thinks how few hours most of them actually run.

For all the external parts SAE 30 straight oil will do the trick.

Bedding in is a matter of personal preference the so called running in compounds are aluminium oxide suspended in a carrier oil. If you choose to use a grinding compound from toothpaste on upwards in severity then thorough cleaning of the mating parts is essential after you are satisfied with the result, or they will keep on keeping on grinding.

Just my 1 Bob's worth and worth around what you paid for it.

Best Regards
Bob


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## Florian (Jul 6, 2012)

Hey John

Oh well, that with the blocked pipe is of course not good and for shure the reason for that extraordinary wear of those parts. 

Furthermore, I must admit that I hadn't written anything about checking all the parts. 
Of course I dont' start turning any engine (or moving parts) before I am not absolutely sure that all the friction is just because of a tight fit and still in a "normal" range. 
And I would also check the function of any soldered steam ports (and pipes) after silver soldering them. This usually happens when I wash the parts after pickling. Then I always check with water to see if all the ports and tubes are free... 

Regards 
Florian


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## NickG (Jul 6, 2012)

Hi all,

I am not trying to be confrontational here but in all honesty I've never run an engine in yet, just taken care to build it with appropriate clearances, or in some cases larger than appropriate! :big:. Seriously though, I bet many people would be surprised how forgiving steam engines are. This is why I find it strange that people go to the nth degree trying to lap bores and pistons and running in tight big ends and main bearings when it's really not necessary unless you're competing in specific power output competition or something. However, most engines are either run on air a few times and put on a shelf or run at exhibitions a couple of times a year. An engine with a bit of clearance in its joints will run more smoothly and slowly and consume less air than a tight one.

I think sometimes the drawings and articles are partially to blame. Model Engineering drawings tend to give nominal sizes rather than anything toleranced which is ok as these things aren't intended for mass production and they assume the builder will machine parts in a logical order and machine them for fit rather than an actual size. Sometimes the build instructions just assume this though, they'll just tell you the method of manufacture and neglect to mention anything about fit or clearances on certain parts. 

An example would be your crank webs between the bearings and the big end between the crank webs. You need a certain amount of end float in these as if your bore isn't perfectly square to the cylinder end face, piston rod perfectly square to piston, cross-head guide perfectly square to cylinder etc. it will cause a tight spot. If however, a small amount of clearance is built in, it can allow for the build up of the other geometric tolerances. 

Attached is an extract from the an old British Standard BS4500 which gives a number of different types of fit and specifies the dimensions you would require to create that fit for your particular sizes. Well worth a look if you haven't before.

In my view, if an engine doesn't turn over freely by hand (and that doesn't mean there's excessive play anywhere) it's really too tight and has the wrong fit somewhere. That's not to say that running in with grinding paste and the like doesn't work, it may do if the right precautions are taken but it would just giving it the clearances that should have been there in the first place. 

Looking at a car engine for example, if the correct clearances weren't there in the first place, the chances are it would quickly overheat and probably seize or destroy itself quickly. The only thing gets 'run in' is the piston rings, everywhere else there has to be room for a film of oil between the two parts otherwise it wouldn't do it's job. 

It's a similar story when loctiting something ... it's no use trying to loctite something with a tight press fit and 2 smooth surfaces, there has to be somewhere for the loctite between the two surfaces otherwise how can it do anything? Another reason that a perfect mirror finish is not desirable on cylinder bores and pistons, better to have surfaces that can retain oil.

Just my 2p worth anyway.

Nick


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## steamer (Jul 6, 2012)

Nick,

There's a difference between discussion and healthy debate and personal attacks.  _No one _ is doing the latter

Discuss!.....Debate....Show respect for each other....all is good!

Dave


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## Tin Falcon (Jul 6, 2012)

> I've never run an engine in yet, just taken care to build it with appropriate clearances.


You are very fortunate IIRC my first couple of engines ran ok without running in by an external motor my third did . 

Thanks for the clearance chart I sure it will be helpful. Not enough clearance and the engine will not run too much and it will leak air or steam. 
I must also add that some of the build books i have read ,recommend running in engines with some form of electric motor. 
so if yo can build an engine that need no running in fantastic. if you build an engine and there are some minor rubs that need working out I see no shame in running it in and with a motor if needed. 
And yes make sure there are no real issues before trying to run in an engine. 
Tin


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## Mosey (Jul 6, 2012)

There's an old story about the BMW boxer twin race bike being prepared for Daytona back in the late 60's early 70's. The engine was built by a gentleman named Udo Gietl, who tells how he ran in the new engine absolutely dry of oil for a very short time to seat all of the surfaces. I believe that that bike was a big winner in it's time. Nice story anyway.


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## Tin Falcon (Jul 6, 2012)

I seem to remember the original VW beetle was run in on a light oil for the first couple hundred miles then the oil was changed out for the normal weight stuff. 
Tin


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## Brian Rupnow (Jul 6, 2012)

I find that the more engines I build, the less they need to be run in. No doubt this is a testament to the fact that my machining abilities are improving with experience. One of my favourite engines, my twin horizontal which was built early on in my machining life was so stiff that I broke a silver soldered joint in the crankshaft while attempting to "run it in" with an electric drill. I don't personally see anything wrong with "running in" an engine with an electric drill, so long as the engine is free enough that it can be turned over by a hand on the flywheel, and everything is kept liberally coated with oil during the "running in". Speeds should be kept low, and the running in shouldn't take more than half an hour. ----Brian


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## lensman57 (Jul 7, 2012)

Tin Falcon  said:
			
		

> I seem to remember the original VW beetle was run in on a light oil for the first couple hundred miles then the oil was changed out for the normal weight stuff.
> Tin



Hi Tin,

I remember many decades ago while I was livung in Iran, the normal running in practice for a new engine was exactly as you mentioned. light oil for the first 600 KM, rpm between 1200 and 2000 and no undue load on the engine, then the car was taken to the garage and the oil drained and valevs adjusted and so on. That is how my mum ran in her first car engine, my dad wouldn't drive, an iranian built Hilman Hunter and it lasted for 8 years.

Regards,

A.G


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## Tin Falcon (Jul 7, 2012)

My Mum got one of the first vw bugs in the area in IIRC about 1963 . I was still a toddler at that time . so The memory of the run in procedure is a little vague. 
Tin


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## rkepler (Jul 7, 2012)

The only running in that I've done on engines was in the bearings - they don't always come out perfectly in line and can tighten up a bit when the caps are tightened. In those cases I mix a little Timesavers lapping compound with light oil and put it in the bearing and run the engine with the caps loose, replenishing the oil/compound mix as I tighten up the caps. It usually doesn't take too long to get everything turning smoothly.

The nice thing about this method is that the Timesavers compound starts to break down as soon as it's mixed with oil, so it can be easily flushed without a complete strip and clean.

After the main bearings are run in (most of the time no lapping is needed) I run the engine on air with a light spindle oil, usually letting it run in the shop while I'm working. A couple of hours running usually makes things nice-n-smooth, an engine that wants 10psi at the start can end up running the same speed with 5psi after a couple of hours.

One source of "tightness" I've seen is when someone cranks down on an o-ring seal. They don't need much if any pressure to seal, loosen them up until they leak a little bit and see if things run. If so, let it run in a bit before tightening them back up, it'll loosen things nicely.


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## Sshire (Jul 7, 2012)

I wasn't aware of Timesavers but it looks like it could be useful. 
There is a "sample" kit which looks to be enough for a lot of the small engine lapping.

Tech info here

http://www.newmantools.com/lapping/time.htm

Best
Stan


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## Sshire (Jul 7, 2012)

Wow! I just checked the prices. Rof}

http://www.newmantools.com/price.htm#TIME

Best
Stan


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## Mosey (Jul 7, 2012)

Me too, now what else is there?


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## Sshire (Jul 7, 2012)

I love the idea of the lapping compound getting finer and finally not cutting and easily removable.
Is there anything else like this?
Best
Stan


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## steamer (Jul 7, 2012)

My 2 pence....if the abrasive is not "friable" like timesavers....I wouldn't do it!

You would be better off scraping in the bearing with a toolmakers reamer or a scraper, than risking it.....

....My 2 pence


Dave


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## rkepler (Jul 7, 2012)

If you look here: http://www.ws2coating.com/index.html Here you can find the yellow and green kits separately for $30, so figure about $70-$75 for both and shipping. Someone sent me a link in the last few months for a full kit at the $70 price but I can't find it (gotta thank the KDE folks for screwing up a nice mail system).

(Poked around a little more - if you're getting both sets the McMaster price of $73 might be better).


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## Sshire (Jul 7, 2012)

Thanks for the info. Since I'd mostly use it for aluminum and brass, the 1/2 yellow kit should be a good starting point. A lot better than the first prices.

Thanks again
Stan


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## Florian (Jul 7, 2012)

Stan, you can get a set of diamond lapping paste for about 40$ (25.65 £).
I did order some of this compound from rdg tools; works quite well (I use it for honing)

You can also get them seperate if you only want some grit sizes. 


Cheers Florian


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## steamer (Jul 7, 2012)

Again, be careful with the abrasives that are not friable ( that don't break down)....I piece of grit left in there and it will tear it self up.....

Dave


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## rkepler (Jul 7, 2012)

Florian  said:
			
		

> Stan, you can get a set of diamond lapping paste for about 40$ (25.65 £).
> I did order some of this compound from rdg tools; works quite well (I use it for honing)
> 
> You can also get them seperate if you only want some grit sizes.



I only use diamond in an embedded lap and don't know another way. In the past I've embedded diamond in a Flex-o-lap when I had several holes to be lapped to the same dimension, using several of the brass ends to go from heavy action to light lapping action. The problem is that you can't change from a coarse lapping compound to a fine unless you turn off the surface and clean meticulously, I expect that even then you're likely to get some of the coarser grit into the fine lap and scratch the new surface. That's the nice thing with the Timesaver lapping compound, you can clean off the coarse and go to the next finer grit with no real concerns. That way you can use one lap for all the grades. The downside is that the lap gets eaten up some and won't do as many holes as it wears past adjustment.


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## steamer (Jul 7, 2012)

rkepler  said:
			
		

> I only use diamond in an embedded lap and don't know another way. In the past I've embedded diamond in a Flex-o-lap when I had several holes to be lapped to the same dimension, using several of the brass ends to go from heavy action to light lapping action. The problem is that you can't change from a coarse lapping compound to a fine unless you turn off the surface and clean meticulously, I expect that even then you're likely to get some of the coarser grit into the fine lap and scratch the new surface. That's the nice thing with the Timesaver lapping compound, you can clean off the coarse and go to the next finer grit with no real concerns. That way you can use one lap for all the grades. The downside is that the lap gets eaten up some and won't do as many holes as it wears past adjustment.



Agreed, the diamond is imbeded in the lap.  Perfect!  If you put it in the bearing with the shaft, the bearing becomes the lap ( the diamond embeds into it) and the shaft takes a beating.......which is why I suggested scraping instead of abrasive....

Dave


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## Florian (Jul 8, 2012)

As I said, I only use diamond compound for honing...!

But you're right with the fact that diamond grits will stick in the softer material. 
When I finished honing with one grit, I always clean the mandrel and then make some turns without any compound, just oil until the oil does not turn black immediately. That tells you when the abrasion is almost zero and therefore there are no diamonds anymore in the mandrel. 

And it seems to work as I usually use 3 grades and I have never found any scratches from the coarser grits... 

Whatever; the point is that diamond compound will stick to the softer material and therefore *is NOT suitable * for running in bearings! 

Regards Florian


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## steamer (Jul 8, 2012)

Oh and to be very clear....as the written word doesn't show facial expression or inflection, I'm not upset or emotional about my statement.....just sayin. ;D

MYO....I don't like abrasives in engines....I just think you can never ever really get it all out.



Dave


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## Blogwitch (Jul 8, 2012)

I am a little like yourself Dave, but I have used my own diamond mixture on very hard steel cylinders that normal grit won't touch very well.

Normally, I only use oxide grit as the first cutting agent as it breaks down into smaller and smaller pieces as it gets used, eventually becoming almost inert in it's operation, and very easily cleaned out.

I usually finish off afterwards with jewelers rouge if I want a truly polished bore.

BTW, I have just treated myself to a set of castings to make a pair external hones. I don't know how they will work out, but I should be able to show the results in the not too distant future.


John


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## steamer (Jul 8, 2012)

Agreed Bogs...but 1 differrence...I suspect you finished the cylinder with a dedicated lap, and you didn't use the piston as the lap......That's the bit that goes against my grain.....just sayin.

Dave


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## Ryker Carruthers (Jul 8, 2012)

If you are building an engine like a 1/2 scale or 1/4 scale traction engine you should be worried if it isnt tight the first 6 or so runs, it may be real easy to turn over by hand but that just means when all the bearings get seated and wore in a little it will pound and knock like no other. when our 1/2 scale was finished 30 years ago dad said the gears would grind really bad so he started to mix valve grinding compound with the grease for the gears. 29 years later I see no scratches on the surfaces and the gears honestly look brand new. If the cylinder you use is cast iron and you cant get the finish super smoothe just run in with cast iron rings and you would be suprised how smoothe the bore is then and your rings will be conforemed exactly to the bore 
2 cent
Ryker Carruthers


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## steamer (Jul 8, 2012)

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


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## Ryker Carruthers (Jul 8, 2012)

steamer  said:
			
		

> 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


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## steamer (Jul 8, 2012)

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!)


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## steamer (Jul 8, 2012)

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


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## Don1966 (Jul 8, 2012)

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

Don


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## steamer (Jul 8, 2012)

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

Dave


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## NickG (Jul 9, 2012)

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.


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## Runner (Jul 9, 2012)

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


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## ProdEng (Jul 9, 2012)

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


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## Ryker Carruthers (Jul 9, 2012)

steamer  said:
			
		

> 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


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## Ryker Carruthers (Jul 9, 2012)

NickG  said:
			
		

> 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


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## Runner (Jul 10, 2012)

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


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## steamer (Jul 10, 2012)

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

Dave


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## Mosey (Jul 10, 2012)

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?


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## NickG (Jul 10, 2012)

Runner  said:
			
		

> 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


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