Hot Tube Engine Starting

[Jim Gorter]

Hi to all, I have been collecting information on hot tube oilfield engines and I have a question about starting these engines.
The hot tube length determines the timing. Compression determines the length the fuel mixture is pushed up the tube. My thinking would indicate that you could not retard the timing any more than TDC. After TDC the cylinder pressure would decrease so the fuel mixture is going away from the hot spot. So my question is how to start these engines without kickback. I know they have been starting these engines for a long time, I would like to have the mechanics of the process explained so my simple mind can understand. Any tricks the oldtimers used would be appreciated also. Thanks, Jim

[Bob Johnson]

Hi,

I am far from being an expert on this but to simplify what I do to start my 15 HP Reid is to back fire it so when it does backfire it is going in the right direction and away it goes in the right direction. Hope this helps some. Adjusting the heat on the hot tube does make it run better, seems like I have to cool it down to get it to run slow, About 65 to 80 rpm.

Bob Johnson Out west on the high desert

[Forrest A]

The hot tube must be at operating temp. Rolling it backwards is the best way but be careful. The point at which compresion is high enough to get enough fuel/air mixture through the small passage to the heated part of the hot tube varies and so will the point at which it will fire. These engines also used a match head stiker to initiate starting. A match was placed in a collet, threaded into the cylinder head and then a plunger would be pushed to srike the head of the match and thus would ignite the fuel air mixture. Some Lanz diesel tractors used this method for starting.

[Andrew Mackey]

Rolling the hot tube engine over backwards is the way to go. Your best bet is to have an experianced engine person start it with you several times, until you get the motion timing down. Starting these old engines is almost a science! A lot of hot bulb engines can also be started in this manner. For that matter, it also works on almost any large size engine.
I reverse start my hercules 5 HP igniter engine this way: Pull engine thru 2 intake strokes - full choke. Open choke 1/4 way, retard timing lever, and pull engine up against compression, sharply, in the reverse direction. The engine will fire - well advanced, and will start in the proper direction, nearly every time. When the engine is hot - no choke!
Andrew

[Zach Williams]

I agree it takes experience on the starting part.

I'm still pretty young (20) and know plenty of people hurt by incorrect starting procedures even at shows! A person can get easily hurt or killed if they dont know what they are doing.

We even back start our 12hp 4 cycle pattin, although a lot of 4 cycle hot tube engines had a form of compression release as i understand.

[RHudson]

like others have said, i think also that the "dwell" or length of time the charge is in contact with the hot tube surface would cause some retard. in other words by cooling the tube just a little the gas/air will take a few thousands of a second to heat up enough to fire, allowing the crank to be at or just past center. a hotter tube will cause early firing. thats my guess anyway.

i have found that i can crank my oilcity best with the help of my son. compression release open, he opens the intake valve by hand while i pull the wheel through intake (in the "wrong" direction). he knows to release the intake valve at the end of the intake cycle. by this time i have the wheel up to as fast a speed as i can. i then run forward and close the compression release and the engine comes up on compression and sometimes ignites. repeat until someone gives up. either the engine or the cranker.

[Patrick McNallen]

I have several 2-cycle oilfield engines with hot tubes. They are easy to start in any weather. You shouldn't need to mess with the intake valve to start one. There is a possibility of fire blowing out the intake, too, so it's best to stay clear of it. If you have to hold the valve open, the spring may be too tight or it may be sticky with oil. You should be able to hear the valve "rattle" when you rock the engine back and forth. Be aware when rocking the engine that it can fire in either direction with plenty of force to break bones. Many of these engines have an extra gas inlet on the mixer. You can hook a valve to this to vent gas when starting the engine. This will prevent flooding. There are safety issues involved here, since letting unburned gas escape around the lit hot tube furnace can cause a fireball. I don't use the compression release at all when starting my engines. They are useful for clearing a flooded engine. Be aware that opening the compression release valve and cranking or rocking a flooded engine with a lit hot tube (or a magneto ignition) can result in a jet of blue flame shooting out of the compression release valve under high pressure. This jet of fire can deliver a really horrible burn in a split second!

[Jim Gorter]

Thanks Guys for all the information. The more I find out about these engines the more dangerous they sound. some common sense and starting procedures would make the starting a lot safer. Thanks again, Jim

[RHudson]

Thank you Patrick. i've been asking questions about oilfields for about a year and a half so far. with not much informtion returned...Thanks for the information.. but let me ask you..how do you get the engine through an intake stroke with a closed compression release valve. last time we tried to crank the oil city with closed valve neightor two 240 lb people or a belted jd tractor could get it through an intake. Again Thanks for any information you can give me...there are no oilfields in southcentral virginia.

[Zach Williams]

on all of our engines we have a compression release valve, its impossible to roll them over safely without one to clear out the cylinder.

you shouldnt have the problem of a jet engine flame if you have the valve plumbed correctly, just make the valve as close to the head or whatever it is attached to and then just have some plumbing away from the hot tube.

you need the valve to be as close as possible so you wont lose compression too much.

[RHudson]

Everything i have done so far on the three oilfields i have, has been trial and error. seems there would have to be a manual out there somewhere. or at least someone that has a manual. anyway.

i take the point about holding the intake valve open manually could be dangerous, on the other hand my valve is as clean as can be and with no spring pressure at all will barely open (if at all) when rolled over by hand (with release opened). i wonder if my fuel pressure is too low (11 inches).

i start cranking engine with release fully open. so on the intake stroke (which is also a compression stroke on the oilcity) air is expelled out the compression release. during the start of what would be a power stroke (if there had been a charge and if there had been ignation) i run up and close the release. which i "think" (sometimes i worry about my thinking) will cause a slight vacuum to occur as the piston opens the rod side ports to allow a charge into the combustion chamber the release is closed. although sometimes i leave the release slightly open so i can hear the engine "SWOOSH" to let me know that things are progressing well. I can also see a danger in this. i might replumb my engine to exhause the release up through the canopy inseat of the 45 degrees down that i have now.

again i first started the engine belted up to my IH H tractor and without an opened release, the engine will stall the tractor.. at the engines first show we belted it up to a JD A that happen to be sitting infront of the engine (Thank you Ned Stebbins) and it would not turn the engine over with valve closed. so i don't think i have a choice on that.

i have cranked the engine by myself by just turning the wheels as far and as fast as i can and letting it bounce off the compression, then turning in the opposite direction. but its a 50/50 chance on which direction the engine will fire on and run. i know that can't be the correct way to start an engine. Again any and all help and information is usefull.. and by the way it seem that all the engine heads we have here, we could get a printed set of directions and manuals for just about every engine out there. doesn't it?

[Zach Williams]

do you have an accumulator tank for your propane? an accumulator tank can help quite a bit from keeping the engine starving for gas

also its wise to keep the gas pressure very low, like only a few ounces, you want the engine to suck the gas in not be blown in

also how hot is your hot tube a lot of people have the bad habit of getting it too red and that seems to cause some problems for starting as well.

[Patrick McNallen]

Zach is right about the fuel pressure. 11 oz. plenty, and less may work better. Too much pressure will force gas past the intake valve and flood the engine. A leaking gas throttle valve can also cause flooding problems. I never use the compression release on any of my 2 cycle engines unless I think I have flooded it. I never crank them over compression, either, because I can't. I always stand on the ground on the cylinder side of the flywheel and pull the engine backward against compression, pushing down on a flywheel spoke with one foot, then allow it to "bounce" back. Many of these engines have a worn spot on the flywheel spoke where the pumper always put his foot when starting. "rocking" the engine this way causes the engine to open the intake valve and suck in some air and gas. Usually, you can hear the valve operating. It usually takes about 3 pulls to get the mixture into the cylinder. At this point, if the mixture is about right and the tube hot enough, the engine will fire as it is rocked backward. To avoid having the engine start backwards, don't pull the flywheels much past "bottom center" in the direction the engine runs when you are rocking it. I get good results by having the hot tube red hot, but not extremely hot. These engines are easy to start when you get the hang of it. I wouldn't run one of these things faster than about 120 RPM, either. They seem to like to run about 70 to 80 RPM with no load, and you can usually get one to run about 60 RPM or a little less without too much trouble. To run slow, you'll need to run the hot tube cooler than at higher speeds. If your engine backfires when it is running, especially at higher speeds, you probably need to get the tube hotter. It is also important that the packing on the piston rod not be leaking air, but it must not be tight enough to cause drag. If it is leaky, it can make it harder to start the engine and it can make it backfire or run erratically. I usually start the cylinder oiler dripping about 10 or 15 drops a minute first thing when starting, then I light the hot tube and oil everything else, including the piston rod. This takes a few minutes, and by then the tube is usually about hot enough to start and I know there is oil on the piston and rings. Once the engine is running 8 to 10 drops of oil per minute is usually plenty on the cylinder, and the bearings can do with about half that. Oil is much cheaper than engine parts, so I always use plenty of it. Using plenty of oil helps flush dirt out of bearings, too. When the hot tube is at the correct temperature with the engine warmed up and running at medium speed with no load, it will only fire every 2 or 3 revolutions. If it fires every round and seems to labor, your hot tube is either too cold (late timing) or too hot (timing advanced too far) it may take a minute or so for the engine to respond to a change in the hot tube flame adjustment. Backfiring usually indicates a cold tube.

[Chuck Martin]

I start a 20 hp Bessimer by turning it "backward" against compression.
I have a compression relief valve on hte head. I open the relief valve with the gas off, and turn it over a couple of times to clear the cylinder. Then close the relief valve and turn it over one full rev. intake to the compression stroke (backwards) 1 time with the gas on, this primes the cylinder. The next step is to climb on the flywheel and pull it hard into the compression stroke, getting off before any compression is reached, letting the momentem of the flywheel roll it into the compression zone, and it will fire sending it in the correct direction.
Getting the gas pressure and springs in the valve set up correctly is the tough part.
On the Bessemer, 2 stroke, it is hard to tell if it is too lean or too rich.
When I encounter starting problems, I will open the turn off the gas, open the compression relief valve, turn the engine over a couple of times to clear it and try again.
If that does not do the trick, something is wrong. After checking gas, seals, and other obvious items, You need to determine if its lean or flooded.

A method I use and must be done with care...........

After a miss start, turn off the gas and open the compression relief valve, using a propane torch hold the flame near the relief valve outlet and SLOWLY turn the flywheel through the compression stroke only.
If the mixture is good, the flame should be blue and simalar that of the propane torch. If it is yellow and rolls out like gassoline being poured out, it is flooded and too rich, Sputter and popping with little flame is too lean.

Extreme care must be taken if you try this. It assumes that you have plumbed things correctly, have no gas leaks, and have enough sense not to burn the pants off the guy holding your beer!

[Graham]

I have long experience running a hot tube engine on maximim load (about 30hp). I certainly confirm that the temperature of the tube is vitally important to get power from the engine. If too hot it suffers detonation, and possibly pre-ignition. My late grandfather, father (now aged 90) and I have had wonderful service from this big slow-running engine (200rpm).
Apart from tube length and temperature, a vital adjustment on the enging is the opening movement and spring tension on the atmospheric air inlet valve. This movement regulates the charge of air taken into the cylinder. If the valve is allowed to open too far, then too much air is taken in, and - think about it - the compression will be raised to a point where ignition occurs too far in advance of TDC. This causes pinking, serious stress on the engine, and loss of power.
By the way, the engine drives a meal mill used for producing oatmeal and barleymeal.
Starting: 1 Pre-heat the ignition tube to dull red tip, no hotter. 2 Move the exhaust valve cam follower to half-compression. 3 Insert a wedge to the rocker to hold the ehaust valve open. 4 Fill the primer cup with kerosene. 5 Open the fuel control valve one turn. 6 Spin the engine forwards up to minimum 1 turn per 2 secs (guess). 7 Release the exhaust rocker to allow compression. 8 The engine fires, and if all well goes over compression!
To spin the engine (twin 6 ft flywheels, 11 inch bore, 22 inch stroke) takes two fit men on the starting handle, or a good battery on the truck starter I have offered to a truck flywheel and starter ring I have machined and keyed onto the 3.825 inch diameter main shaft.
The engine runs well on kerosene (home heating oil or av-gas), better mixed about 3:1 with diesel fuel.
The engine is located in Scotland, the land of its manufacture. It was fitted to its present location in 1908, but I am not sure if it was new then.
Graham.