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40hp Bessemer hot tube question

Dave Myers

Registered
Age
67
Last Subscription Date
12/07/2018
We have a 40hp Bessemer 2 stroke that runs real well. On the buzz coil it will run merrily all day long, easy to control, great engine. Have been trying to get to perform on the hot tube without much success. Discarded the supplied torch (homemade), replumbed the gas line (torch was fed off the accumulator, barely lit the flame) and did some repairs to a junked out torch. Now have a good flame, tube getting nice and orange, and it will fire up easily enough and run along for a bit (varies) and afterfire and then usually slow to a stop, in the video it did actually catch back up but another 30 seconds it coughed and rolled to a stop again. If I catch it right and feed more gas it generally will keep going. Any ideas on what we need to look at. I have found out that hot tube is much touchier
with the fuel than spark plug!
Thank you, David

https://youtu.be/ILaLvYVH-pU
 

Andrew Mackey

Moderator
Last Subscription Date
05/14/2017
Sounds like yoour fuel supply is leaning out. Spark ignition is more tolerant of lean mixtures, hot tube is not. The fact that the engine will continue to run if choked, definately points to a lean mix. Are you running off an accumulator or straight off a regulater? Size of your fuel source?
 

Dave Myers

Registered
Age
67
Last Subscription Date
12/07/2018
Andrew. About 5 gal size accumulator after 2 regulators. Don’t know how many inches of propane in accumulator. Fed by 100# tank. We throttle the gas with the handwheel on the governor. It definitely acts like it’s starving for fuel after the afterfire like has used up all the reserve fuel (?), don’t have a better description for you. We have tried various combinations of choke plate setting and gas settings with not much change in this condition but the gas setting is always very touchy with the hot tube vs quite broad with the plug. We have never brought it up to a speed where the governor actually acted. Not even sure if the flyweights fly. Color us chicken😳
David
 

David A.

Subscriber
Last Subscription Date
04/10/2019
not an expert but I have a few hot tube engines, I suspect you are running the mag at tdc or retarded just a bit, hot tube ignition will allways be advanced, that being said it takes less fuel to run at a set speed with hot tube verses mag, that's where you get into the lean situation and it cross fires, fires when intake gases hit unburned fuel when intake and exh ports both open, I have found by restricting air supply, large gate valve is what I use, or just use reducers to get to a 3/4 pipe opening in intake works good, then adjust fuel for a little faster than you want then give it more fuel, should start running rich and slow down, they all are a bit different but this works for me, when all is set it should hit every revolution
 

Dave Myers

Registered
Age
67
Last Subscription Date
12/07/2018
David, good information, Thanks. have tried using choke plate this fall instead of totally replumbing cooling system to install a valve but will try that next. We winterized the engine yesterday after a lot of trial & mostly error and with the museum water supply shut down we are actually done for the winter. Late April I will be back on it when we fire up the water supply again.
Again I appreciate the information from all, especially the timing, didn't know that.
We will conquer this! David
 

Dave Myers

Registered
Age
67
Last Subscription Date
12/07/2018
Do they make a guage in 'inches'? I am assuming it's operating at about 11 inches based on the style regulators. What would be an optimal range?
Thanks, David
 

Kirk Taylor

Registered
We have a 40hp Bessemer 2 stroke that runs real well. On the buzz coil it will run merrily all day long, easy to control, great engine. Have been trying to get to perform on the hot tube without much success. Discarded the supplied torch (homemade), replumbed the gas line (torch was fed off the accumulator, barely lit the flame) and did some repairs to a junked out torch. Now have a good flame, tube getting nice and orange, and it will fire up easily enough and run along for a bit (varies) and afterfire and then usually slow to a stop, in the video it did actually catch back up but another 30 seconds it coughed and rolled to a stop again. If I catch it right and feed more gas it generally will keep going. Any ideas on what we need to look at. I have found out that hot tube is much touchier
with the fuel than spark plug!
Thank you, David

https://youtu.be/ILaLvYVH-pU
"Cross-firing" into the rear of the cylinder consumes all of the fuel on the back side of the piston and fills that space with exhaust gases. It then takes several revolutions to purge and re-charge the rear of the cylinder to restore a normal operating mixture. Cross-firing is often an issue with our beloved oilfield engines. As others have said, adjusting the air can make a difference. Changing the amount of cylinder oil can make a difference. Try a little more; just enough to give a wisp of blue in the exhaust. If you have blue smoke now, try a little less. Another thing that can make a significant difference is the heating of tube. You say that the tube is a "nice orange". Try turning down the heat a bit to a dull red.
David A. made a profound statement when he said that they are all a little different. You just need to start tweaking this and that. Even things that you wouldn't think would make a difference, might. These things were designed to run at rated speed under a load. We often create the issues that we have by leaning out the mixtures and slowing them down.

Kirk
 

Andrew Mackey

Moderator
Last Subscription Date
05/14/2017
One other thing to consider - is the hot tube original? If so, it may have a build up of carbon internally, that needs to be cleanned out. carbon inside the tube wil change the timing, as it will insulate the hot metal, and when itself gets hot will cause pre-igniyion. A hot tube will always fire advanced always, down to TDC only, never later than TDC, depending on length of tube and the point of flame and heat. A dull red will fire later than an orange heat, and a cooler tube wil last longer than one heated to a near yellow-orange heat. On our OCSP, the tube is heated to a bright orange for starting (flame about 1/4 way up the tube), and then the hot tube flame is turned down to a dull red heat, once the engine warms up. When shutting down, we just turn off the hot tube gas supply, and let the engine run until the tube cools enough to stop firinng the charge. it had been noted that the tube has cooled below even a dull red heat and the propane stil keeps lighting! As a safety note - NEVER observe a hot tube by directy looking at it. use a mirror to view the tube in operation. This is done for 2 reasons. 1) looking at the red to orange heated hot tube exposes your eyes to infra-red radiation - it can burn your retinas!. 2) if the tube should fail during the compression/firing event, the tube will be expelled like a bullet, or it may explode completely. Many years ago, I saw a tube blow a chimney clean off a Reid engine - not a pretty sight! Dont be discouraged by your engines performance on the tube. it takes practice and experiance to get things down pat. When my engine club got their OCSP running, it took us over a month of daily running to get its running idiosynchrities down to where we can run it reliably and steadily for a show. it takes time to get all the bugs out, I can tell you! i hope you get it sorted out next year, when you get it running again!
 

Dave Myers

Registered
Age
67
Last Subscription Date
12/07/2018
Oh the wealth of knowledge on this board! Never thought such a simple system could be so complex. You guys have given us a great deal of ideas to try (and how to try them). I knew this was the right way to go. Thanks very much, David
P.S. If anyone else wants to add their 2 cents (or any denomination) of things to look for I welcome all to do so. :)
 
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