Galling on a steam engine

[kennycrawford]

I bought a Mamod steam engnine from a swap meet for 20 bucks last year. It was missing some componetry. But having a mill and a couple of metal lathes I should be able to fix it. It was missing a connecting rod, cylinder and piston. It did have a "block" that the cylinder soldered in to that looked to never have had a cylinder attached. It was missing all of the fittings and the blow off valve for the boiler too. Being from england from the mid sixties meant it was not metric or SAE threading either. Well long story short I made the cylinder, piston and connecting rod then fitted it together (dimensions were hard to come by so I got close and rounded to the nearest practical size). Everything worked great on air for testing but when steam was used it will run for about 10 or 15 seconds then slow down rapidly and stop. If you re-oil the cylinder it do it all over again. I have done this for about 15 minutes on a full tank of water to see if the piston would seat in. It hasn't. I have tried very tight( about .0005 inch gap) to very loose (.005 inch gap) but nothing seemed to help. I have made 3 pistons out of brass and 1 out of drill rod, installed o rings on a couple, tried greases, vaseline and bought regular steam oil, nothing seems to fix the problem. On either side of top or bottom dead center the piston seems to bind not allowing the cylinder to move. During the exhaust or power stokes it seems to move very freely. Could my choice of cylnder material be "sticky" or am I missing a very obvious but critical bit of information? Any help to guide me down the correct path on this would greatly be appreciated.

Sincerely,
Kenny

 

[Woodster]

Could be bent crankpin, poor alignment or possibly hydraulic lock if the piston is covering the exhaust port at TDC. But i think the bent crankpin is most likley from what you describe.

 

[kvom]

Usually when an engine runs well on air but binds on steam it's because the heat causes metal to expand, and somewhere it becomes too tight. Given your varials trials I look elsewhere than the piston/cylinder fit.

 

[kennycrawford]

I will check the crankpin to see if it is bent in any way. Would an aluminum piston slide any better on the brass bore? It is one thing I have not tried yet.

Thank you,

Kenny

 

[kennycrawford]

I did find a slight bend in the crank pin so with the help of a 123 block and a small milling vise I was able to straighten it out. This did not solve the problem though. I turned another piston and fussed with it trying to get things working but was unable to keep the little engine running. In my final attempt I decided to turn one out of Delrin. It took 3 attempts and I had to ream the bore out with a letter Q reamer plus I had to fit the piston about 3 thousanths of an inch under sized to keep it from sticking in the bore when it got hot. I am assuming this stuff expands a bit when heated. Finally I was able to see the steam roller under it's own power. I ran 3 tanks of water through it and tore it down to inspect it. Everything looked just as when it was assembled. It made plenty of power and ran without incident using plumbers grease as a lubricant. So for now I am calling this one done.
Two lingering questions remain that maybe someone can answer:

Could using the same brass for both the piston and the cylinder cause the binding. If so what type of material should I order in the future. Should they be made out of dissimiliar material?
Why don't I see delrin used more as a material for steam engines, particularly the small ones. My experience with it was amazing. I intend to order some of this stuff just to have on hand.

Thank you,

Kenny

 

[Mechanicboy]

Use steam engine oil. If you has not steam engine oil available: Mix 25% rapeseed oil into motoroil SAE 20W-50.

 

[Hopper]

I doubt that piston material is the cause. I have run brass pistons in brass bores on small oscillating steam engines for years without problems.

What air pressure did you test it on, compared with what steam pressure are you using? It may be the lower pressure rather than the heat of the steam that is showing up some kind of binding problem.

I would look carefully at two things: alignment of the mainshaft, crankpin, con rod and cylinder bore. They all need to be dead on to let things turn freely. The other thing I would look at is alignment and matching of the steam ports in the cylinder, faceplate and main body. A little burr in that area, or around the pivot pin etc could cause a hang up around T or BDC like you describe.

If all else fails, do what we do with reluctant Stirling engines and hook the engine flywheel up to an electric motor and leave it run for an hour or two to "break it in" and wear off the high spots.

 

[Mechanicboy]

The Mamod steam engines has 2 small V-groove on piston to improve lubricate the cylinder/piston. Are your piston plain or has V-groove on piston?

 

[kennycrawford]

Thanks for all of the help. I did check the aignment on the crank, the mounting area where the cylinder clock attaches and the crank pin. Everyting works very smoothly when first assembled, but it is definately sticky when heated. An observation, my cylinder is a 2 piece thing with a lower assemby cconnected to the "cylinder" with silver solder. Now I had to make the cylinder and solder then re-drill the port hole. I am now wondering if the cylinder became out of round when it was soldered to the lower assembly. It did start working after I reamed the bore with the Q sized reamer. The Delrin piston just happened to be what I made the final piston out of. I am confident the port is in theright spot as this was already drilled when I bought the unit. Like I said this was a project in a bag unit.
As far as pressures go my gauge is not real readable under 20 psi and the air pressure I tested it on was definately less than that, I can guess somewhere around 10 psi would have been max with the set up I had. I did purchase a pop off valve safety valve on line but had to remake it a bit as the threads were different than on my engine. When running real well it just barely bubbles around the top of the safety valve. I ordered some brass today. Using my old one I may try and make a whole new unit for it. Any measurements someone else may have would be very appreciated.

Thank you,
Kenny

 

[RichD]

Since most of the mechanical alignment/fits have been checked/discussed, I didn't see any mention of condensate as a possible cause. Do you have any bleeders on the cylinder?
Just a thought.

Another thing I've run into over years of running steam operated equipment is when starting, less is more when you initially open the steam valve. Start with bleeders open with very little steam opened into the machine.

Rich

 

[RichD]

Try this link for oiling choices
It's a good read.
Rich

 

[kennycrawford]

The link to steam oils was very interesting reading. Thank you Rich. I did use someting called "steam oil" that was purchased from a local hobby shop. After reading about the different oils and how they behave with water and in the presence of heat it seems that possiby what I used was not in fact sufficient for what the little engine needed. Since there is no mechanical oiler in the system you must oil everything and then fire it up. Also no way to throttle it either. I imagine the oil would go away pretty quickly leaving some metal on metal contact. I know these little engines work and work well when new (or even well used). I still believe it was something I have done through ignorance. Like I mentioned earlier the delrin piston solved my problems and some brass is currently on the way for me to try and build the entire unit over again. Thank you to all who contributed to my education in this area. It is clear I have a lot to learn, my goal is to be able to attack an internal combustion engine!! Maybe some day.

Kenny

 

[RichD]

The equipment I used to operate had some pretty simple oilers. They had reservoirs to hold about a half gallon of Stevoil and were provided with plunger-type buttons you could push down with your finger for prelube, and a simple rachet type of drive to keep the oil injected about once per stroke once the equipment was running. Some of the larger equipment was about as big as a car, but most were about as big as a wheelbarrow.

The oiler brand names were "Trabon" and "Manzell". Most common were the "Trabon" brand.

I'll see if I can find a link to the "Trabon" site.

Usually a top off on the oil would last beyond a 12hr shift or so.

Rich

 

[RichD]

http://www.trabonlubrication.com/?gclid=COaQitf2jcQCFc6TfgodEp8A6Q

 

[RichD]

http://www.fredcgilbert.com/FCGCAT/Lubriquip.htm

another link to follow...

 

[Hopper]

I've never found a need for bleeders on a little oscilating engine like that. Just keep flipping the flywheel over to keep the cylinder clear. Or push on the spring loaded pivot pin to lift the face plate enough to allow water to dribble out.

Yes, just cracking the steam valve on the boiler is the way to go. It "wire draws" the steam through the small opening and dries it out. Technically, you are then running superheated steam into your line to the engine, which is now at slightly lower pressure than the main boiler.

 

[kennycrawford]

Thanks again, the learning never seems to stop! My brass should be here next week. I have pretty much narrowed it down to bad craftsmanship due to incorrect procedure:

I soldered the unit after reaming the bore. I am sure this made it out of round.

I redrilled the hole after soldering and reaming meaning I probably distorted the bore by the port in some way.

I am thinking that the alignment of the bore is probably not squae to the port side of the oscillating block. Probably because the 2 piece process that was used to make it.

After reaming the bore AFTER the unit had been soldered together and then making the piston out of delrin the engine ran great. But I don't know if it was piston material or the fact that things became more lined up after the secons reaming of the hole. Probably a combination of both, the delrin material is slipprier allowing for a tighter bore and is more flexible allowing the rod to bend around the minor misalignment. The re-reamed bore is undoubtedly more likely to be "round" and probably smoother making the cylinder move easier.

Kenny