Model of a Bessemer Hot Tube Oil Field Engine

[Brian Rupnow]

Glad to hear you are well. I have had a rough fall myself, but seem to be on the mend now.----Brian

 

[larry1]

Chuck, Glad to hear that you are well, again. larry

 

[cfellows]

After what seems like a lifetime, I'm finally able to get back into the shop and get to work on this engine. I'm trying to catch up and figure out what the next step is going to be.

I've decided that I need to get the cylinder and piston machined. I would like to make the piston out of aluminum for weight considerations, but it's more complicated than that. First, because of the intake and exhaust ports in the cylinder, I don't want to use piston rings if I can get away from it. That means that the piston is going to have to be a really close fit if I have any hope of getting the required compression. So, I'm concerned that an aluminum piston would have a different heat expansion rate than the steel cylinder meaning I might need too much clearance when the engine is cold. This leads me to think I probably need a cast iron piston which would have close to the same expansion rate as the steel cylinder.

Anybody got any thoughts on this?
Chuck

 

[modelman1838]

Hi Chuck
If I were you I would definately stick with cast iron piston material in a mild steel or cast iron cylinder as I am sure the differential expansion coeficients will creat a problem, but after saying that if I remeber correctly all those little model aero engines used to run a light alloy piston in a precision lapped steel liner and these were all compression ignition so needed good compression, but they did have a contra piston which may have helped.
Hugh.

 

[idahoan]

Hi Chuck

My vote would be to use a cast iron ring or rings and pin them to keep them out of the ports.
Its good to see you back in the shop by the way.

Dave

 

[cfellows]

So I'm going to go with the cast iron piston. And, I'll attempt to get it to work without piston rings first.

Unfortunately, I don't have a lot of experience lapping. Does anyone have a link to a website where I can brush up? Don't want to invest a lot in tools if I don't have to. I do have some clover valve lapping compound, both course and fine. And I've got a bunch of different grades of diamond lapping compound.

The cylinder is a piece of DOM tubing with a very smooth bore. I'm assuming it's probably also pretty uniform in diameter but I'll need a way to check that.

Lapping the piston to fit the cylinder seems like the trickiest part. I would be happy to see some info on that if anyone has some to offer.

Chuck

 

[Goldflash]

Hi Chuck
When I built my Hot air Engine for the Power cylinder I bought a Brake Cylinder Hone from the local automotive accessory shop ( You can adjust the pressure on these ) and it cost about about NZD$19,00 which would be about USD$15.00 and it worked really well and gave me a true bore with a nice cross hatch finish ( I used CI Piston in a Stainless Steel cylinder ) The piston I just turned to Size and polished the OD with 800 Grit wet and dry paper wrapped round a bit of flat plate to give a parallel finish to the piston. It worked and I got a good finish with a nice parallel piston that had about 0.001" clearance. ( I am planning to Teflon Coat the piston so I can run it dry without any lubricant )
With regards to Piston Rings as I want to build a similar type of Engine I would talk to people who do repairs to Weed Eaters and see what they have available as some of the smaller weed eater pistons are in that 1.25-1.5 inch range etc. If your ports are not that big then I dont think you really have to worry about pegging the rings as the old two stroke bikes I played around with as a kid had fully floating piston rings

Regards Ralph

 

[Brian Rupnow]

Chuck--I am far from being expert---but---here's what I have learned. Firstly, the piston should be about .001 undersize from the bore inner diameter. I have had my best results using 600 grit abrasive in an oil base. You have to have some kind of handle on the piston---the connecting rod works just fine. Coat the i.d. of the cylinder with lapping compound and wiggle the piston a bit untill you get it started into the cylinder. It won't want to go in, as the .001 clearance is damn tight when you get the lapping compound on there. I put the cylinder in a vice so it can't run away on me, and work the piston back and forth (full stroke) in the bore. this requires a certain deftness of hand, as you don't want to push the piston all the way out the far end, nor pull it out from the near end. After you work it back and forth about a dozen times by hand, it will get much easier. You should now be able to rotate the piston in the cylinder, by hand. Now comes the terrifying part!!! Set your lathe on its slowest speed and grip the cylinder in the chuck, with the con rod hanging out the opposite end where you can grip it. Hold the con rod firmly in your right hand, say a short prayer, and turn the lathe on, while holding your breath and with your left hand poised over the stop button. If you have lived a good clean life, as I have, the cylinder will start to rotate, and the piston will not rip your arm out of the socket. As the cylinder rotates (I stress SLOWLY), work the piston through its full stroke in teh bore, being carefull not to push it all the way through nor pull it all the way out. Let the lathe run for about two minutes while working the piston through its full stroke. Shut the lathe off. Say another short prayer (Thank You, this time.) You're done!!! The piston and the bore should both now have a uniform dull color. Please note---This is what I DO. If anyone else tries this and ends up like that guy who was always being chased on The Fugitive, don't come looking for me.---Brian.

 

[Goldflash]

Chuck further More to cylinder bores after honing or lapping.
Boil them for half an hour in hot soapy water to get the minute abrasive particles out that have embedded themselves in the surface of the Bore or piston.
The Heat opens up the pores of the metal and allows the embedded particles to fall out
You will be surprised how much black dirt will come out when wiping through with some white tissue paper/ rags etc.
Then remember to oil the parts afterwards to stop rust.
used to build multi-stage compressors up to 11 inch bores and we always boiled the cylinders after honing. Better to wear in than wear out.



Regards Ralph

 

[Jasonb]

Have a read of Ramon's thread on his pair of tigres and also my one on the Firefly, both have CI pistons lapped to the bore.

http://www.homemodelenginemachinist.com/f31/super-tigre-g32-1cc-diesel-5cc-version-17674/

http://www.model-engineer.co.uk/forums/postings.asp?th=70308

 

[cfellows]

I've got the cylinder pretty well finished I think. I found a piece of aluminum tubing that was just a tad bigger than the ID of the cylinder. I cut across the tube about 2/3 of the way through, than slit the tube from the end to the cross cut. The length of the slit is about 1/2" longer than the cylinder.

I then mounted the tube in my lathe and used CLover fine lapping compound and made numerous passes through the cylinder from both ends with the lathe running pretty slowly. I wiped down the lap, applied just oil, then made more passes with the cylinder. I repeated this process 5 or 6 times. I've got a nice finish with no sign of circular tool marks. Also, no measurable taper.

I doubt if you'll find this method in any of the books of best practices, but it seems to have worked well for me. After I've turned the piston down I plan to lap it into the cylinder. Never done that, so I will use the info Jason provided plus whatever else I can find on the net.
Chuck

 

[cfellows]

I've finished the piston and got a really nice fit in the cylinder. I first turned the piston oversize by about .010", then mounted it onto the piston rod shouldered down to 1/4" x 20 threads. After the rod was tightened as much as I could get I finished turning and polishing the piston to size.

I also mounted the two crosshead guide bottoms. They are made from left over pieces of the engine frame, are 4" long and 3/8" thick. I purposely left them oversized and rough on top. I'll mill them flat and to size in the assembled position to assure I get them parallel with the cylinder.

The guides are attached to the frame with socket head cap screws from the inside so they look like an integral part of the frame.

Chuck

 

[cfellows]

After a bit of a sabbatical I got back to work on this engine today. I made significant progress on the crosshead piece.

I was a bit skeptical about my ability to get everything lined up so the piston and rod would slide easily, but, through luck and/or patience, I seem to have gotten it right.
Chuck

 

[Brian Rupnow]

Great Stuff, Chuck. I was beginning to wonder what had happened to you. Nice project.---Brian

 

[idahoan]

Hi Chuck

Great work on the Bessemer!

Thanks for the update,
Dave

 

[rleete]

but, through luck and/or patience, I seem to have gotten it right.

Highly advanced skill. Never admit to anything else.

 

[cfellows]

So I'm getting serious about starting work on the transfer port which will move the fuel mixtue from behind the piston to the combustion chamber. It will be about 2" long and I'm wanting to make it 5/32" inside diameter. Keeping in mind this will be a low RPM engine, does anybody think the transfer port needs to be bigger?

Chuck

 

[cfellows]

Well, the holidays are over, the much loved kids and grandkids have moved into their own house and I seem to be pretty well recovered from my second case of the creeping crud in as many months. Oh, and the detour for the Lister engine is now behind me. So, time to get back to work on the Bessemer.

After much deliberation, I've decided to use the pressure controlled fuel transfer port used by Jan Ridders on his vertical 2 stroke. I like the idea of having the inlet port in the head rather than middle of the cylinder and in letting the pressure control the fuel inlet instead of the port. Jan seems to get pretty good results with his setup and I'm hoping for the same.
You can see in the picture I've drilled a hole in the bottom of the cylinder and tapped it for 1/4" model pipe taper. I threaded in an elbow and will hook up the rest of the plumbing as I get it built. If 1/4" turns out to be too small, I can always step it up to a 1/16" npt.

By the way, I figured out how to use Dropbox to host photos. Much faster and simpler than Photobucket.

Chuck

 

[cfellows]

This is what the transfer port assembly should look like...

Pretend there is an opening from the rightmost elbow into the back of the cylinder. Forgot to draw it!

Pipe and fittings are all 1/4" model taper.

Chuck

 

[skyline1]

Hi Chuck
Been looking at this
have I got the timing right it's a sort of two stroke but uses the lower half of the cylinder as a compression chamber rather than the whole crankcase ?