Detroit are notoriously easy to turn over, specially in there older age. Leaky injectors slowly drip onto the piston and begin to roll the engine over. Mechanical injection, no key needed for the engine to run If the kill cable isn’t left fully engaged there is nothing to stop the engine from lighting up as soon as it starts to roll over. Definitely easier on a engine that is still warm from running all day long. Sounds outlandish but I saw it a lot, this is largely able to happen since when the engine is shut down the injectors are in the wide open position (full fuel) to enhance a easier start. Warm engine, warm diesel, both move easily few leaky injectors and autostart happens. Replace injectors and it quits doing it, or leave the kill cable locked
That reminds me I should make an emergency kill flap for my yanmar clone. To shut it down you have to set the accelerator all the way down, but I like some redundancy. Compression release they say it isn’t good to use all the time to shut down for these engines.
Thanks to all comments and information about the DD 3-71.
I have a couple of more questions.
Let me explain first that this motor belongs to a FWD 10 ton crane, GVWR 15 tons, that could be used for long hours on a farm at low RPM and/or idle.
I read that a DD 2 stroke engine doesn’t like to idle. (fact or myth) ?
I’m open to changing the above equipment for a 80 HP 4 stroke diesel 6 ton crawler tractor, if you all think that my first choice could be an issue.
In regard to the DD runaway I found some literature that quotes another way it could happen in detriment to my dual fuel use project.
Why does a Detroit Diesel runaway?
Diesel engine runaway occurs when a diesel engine ingests a hydrocarbon vapor, or flammable vapor , through the air intake system and uses it as an external fuel source. … If not stopped immediately, it can cause the engine to overspeed, the valves to bounce, and flames can pass through the manifold.
Let me know your thoughts.
Again, thanks for your help.
Basically that’s the nice way of saying to dont use to much ether, the flame speed is to fast and if the engine revs out and fire is still in the cylinder it can come back up into the intake and catch fire to oil/grease/carbon deposits which ignites and then feeds back into the intake as flammable vapor fuel which is fanned to hotter flame by the blower/turbo and the cycle continues untill the motor burns down. Usually doesn’t happen with ether though, if you spray to much it will lock up. Usually. Many people think ether will kill them, which is a myth. I have been around many many MANY old diesels that had ether injection ports, or took the ether pills that crack open and release into the air stream. This is also why many Detroit’s had both a kill cable that pulled the rack back and killed the injectors, and or a flapper valve right on the intake manifold with a cable that totally shut down air. Both were very handy, whenever I’m starting a Detroit that has sat I have a chunk of plywood handy to slap over the air intake Incase of a runaway. Luckily never had to use it
I have never known a Detroit to not like to idle? Granted they do love to rev, but they still run a lot of them in the very very cold north where they will idle for DAYS on end, because if it shuts off and gets cold ( I’m talking -30 to -50°f) they pretty much will not start. They will continuously run for sometimes 3 months, only time they are ever shut down is in a heated shop for service then fired right back up. Got a friend in the Alberta oil patch that runs a 6v71 Kenworth that does this, his truck won’t start after -40°f
I saw in youtube that there is a supersede rack that comes with springs that doesn’t let runaway the engine.
This video is of a 371N powered DD Cletrac.
It was April 2008. The snow was just off, and they were offering $350 per car, or $200 a ton for sheet metal. Everything was being hauled in. The only machine I had that would haul the cars through the mud was this Cletrac.
To operate this machine’s engine, one had to just open the rack far enough that it started to run away, then close the rack enough to control it. The crankcase oil it’s burning is filtered hydrogenated vegetable oil…just about the most unburnable fuel you can try.
To start this engine you have spray nearly a whole can of ether.
I traded a 63 Rambler and some copper bar stock for it. I paid $400 to have it moved. Up until April of 2008 I thought I had gotten ripped off, but we must have hauled 30 cars out that month so I got every bit of my money out of it.
Later at the new bush, I was widening the road with the T-9 crawler loader, pushing a beaver dam off the shoulder, and suddenly became a sub commander. The T-9 valiantly went to the bottom running. I had now choice but to ether the crap out of the DD and take it down to the road and pull the T-9 out. I put one of those snaky funnels in the engine oil fill and big hose in a five gallon bucket of veg oil and kept pouring it in as the 371 ran away. The DD has 4 HI so I shagged it down to the T-9 really fast and moderated the runaway by slipping the hand clutch.
My girl friend used a flashlight to guide me down to the T-9, and hooked up the chain while I frantically worked the rack trying to keep it running but not running away. As soon as I was chained on, I let it runaway and dumped the clutch in 1LO…I shredded the road with both tracks but hauled the T-9 out of the beaver pond.
My girlfriend walked me up the road with the flash light as the exhaust caught fire. I wish I pictures…it looked like a big tire fire. I kinda had to watch the ditch.because she kept pointing the flashlight into my eyes…
We made it back and the T-9 had been in gear the whole time. It must have spit out all the water, because it started right up!
Also the car in the video is a diesel powered Oldsmobile. 4.3l V-6
Bruce; Are you making a living “growing” old cars back in the woods? TomC
Hi Tom,
We have one car, a Caviler. Now we grow trucks and bulldozers. We’ll prolly selectively cash out again during the next scrap bull run.
Sorry but it is a fact with the Detroit piston ported 2 strokes that they are not as fuel efficient as a typical 4 stroke engine of the same power output. The ports in the cylinders are exposed before the air/fuel charge has imparted all of it’s optimal energy upon the piston. In order to prevent the pressurized combustion gasses from filling the airbox - the exhaust valves must open BEFORE the intake ports are exposed to relieve the combustion pressure. This increases the amount of fuel energy lost to the exhaust rather than powering the engine.
This valve to port timing is why I was able to run a 53 series without the supercharger operating. The exhaust opening before the intake scavenged gasses - leaving a void/vacuum that allowed the piston to draw in sufficient air to burn some of the injected fuel. The vacuum was so significant that it would make the supercharger spin to allow air to continue to enter the engine.
The super charger consumes power. On some models as much as 60hp. This a a significant portion of the added fuel consumption.
When I replaced the 1966 Diamond T truck with the 180net hp 6v53 engine with a newer 1973 IHC that had a Caterpillar 1160 of 210net hp - I ended up with a truck that got 15- 20% better fuel economy even though it grossed 16,000lbs more weight than it’s predecessor. (48,000lbs vs 64,000lbs).
Fitting the Detroit 2 stroke engine with a turbocharger helps recover some of the wasted exhaust energy as the pressurized air from the turbocharger will push it’s way through the supercharger turning the supercharger into an air motor and driving the engine through the supercharger gear drive. The shaft seals in the supercharger have to be changed so that pressurized air does not leak past the rotor shafts and blow the oil off the rotor shaft ball bearings and out of the rotor timing gear oil well. Initially they only fitted 1 turbo to the engines and changed the engine designation to have a suffix of “T” such as 6v71T. Then GM fitted 2 turbo chargers. This engine would have 2 "T"s as a suffix. Such as 6v71TT.
I actually worked with GM engineers in the last years of the 2 stroke division to glean data for an aviation engine design that did not utilize a supercharger to save weight. At the same time I got to know Mike Early - an engineer from Garrett turbo - a division of Honeywell - through a DYI-gas turbine yahoo group. Mike helped provide information on turbo charger testing that he was involved with at Garrett when GM was experimenting with the 2 stroke engine as an alternative to gas turbine engines for business jets. They added water injection and much larger turbo chargers. The water turned to steam during combustion with the added exhaust volume increasing the turbocharger output - and pressure to the supercharger.
Having child and a business failure at the same time side tracked my project. Health issues arising from when I was electrically burned 40 years ago became more of an issue. Then a $1M fire 3 years ago destroyed most of my manufacturing capability, prototypes, components and all documents were lost.
Excellent, RonO. Just Excellent.
You brain and remembrances still works well enough.
Detroit 2-stroke are just like Mazda Wankel’s. A lot of engineering thrown at them to make them workable.
Use 'em up, wear them out now because the circumstances that spawned them are long gone. And they will never be coming back into production.
Best Regards
Steve Unruh
True, an engine that consumes it’s additive laden oil has metal oxides in the exhaust that destroy the catalytic converters required to meet modern emission requirements.
One place they found much favor was mining equipment where their small power to weight was advantageous. However - developments in workplace noise restriction have also made it very difficult to meet equipment operator noise exposure limits with an inherently noisy supercharged 2 stroke. Part of my 70% hearing loss is specific to the supercharger whine sound frequency of the 6v53 powered truck I drove for over a decade. Employees working at my plant could hear the whine of the truck returning to the plant after a delivery when the driver - typically me - would decelerate on a down hill grade to a stop sign 1.8 miles distant. My mom could often hear the truck’s whine when it crested a hill 2.7 miles from the plant.
In Western Canada they really liked them in the small ( under 45’ ) tugs because they had a fast response time (acceleration) especially forward to reverse. Could get you out of a tight spot. Plus were lots of parts ( now getting much harder to source ) and lots of people knew how to work on them. Pretty reliable too, if they had air and fuel they usually ran. Fuel cost and emissions are killing them though.
Yes, you find a lot of them in marine applications. The military used them in the Vietnam era river boats with jet drives.
At the end of the Vietnam war there were some swamp buggies ordered from each of the major auto manufacturers. They were amphibious. The GM units had 6v53’s in them with wet clutches. I have one of those that I put in my 1966 Diamond T. It was that engine that had me call GM for the first time as the cam shaft numbers and timing gear markings were confusing. It was set up for opposite direction rotation and I needed to change the cam timing to reverse the engines rotation. Come to find out it was assembled by the experimental division. It has 2 valve pistons and injectors but 4 valve heads.
I had a stack of new in box 3 chamber 2 valve 53 series heads at the shop. They lay on what was the garage floor now - the shop burned down around them but they actually still had the cardboard boxes on them after the fire. I just haven’t brought myself to scrap them yet.
I have a couple 6-92 not 6v92 engine cores that oddly came out of a pair of Freightliner semi tractors. They were more common in boats with twin engines as the in-line configuration was not as wide as the V.
GM made some quite large 2 strokes engines also. I didn’t even know of those until a few years ago.
A lot of the little boomboats had the inline 4-71s and 6-71s. I ran a LeTourneau log stacker that had a 8v91 8v92 8v93? I think 8v92. It was diesel over electric. Start at idle then spool up to run continuous at operating speed. Lot s of power but unforgiving of mistakes.
I own 2 - 1954 GM Buses, one is Parlor Diesel that has been upgraded to a 6V92TA with a 730 Allison Auto, the other has the original 671 with a manual 4 speed and manual steering. These thing are monsters!
I’ve been toying around with a combination wood gas / Hydrogen setup. I am new here, anyone tried combining Hydrogen and wood gas yet?
Woodgas already contains some hydrogen in the mix. Or do you mean an even more concentrated amount of hydrogen gas?
If you intend to feed woodgas to the the Detroit engine you will need to be very careful of tar so that you do not glue the supercharger rotors to the housing and each other. Of course - tar could collect in the airbox and glue the pistons in place.
You would want to ensure that you run the engine for a bit after feeding it woodgas to help clear any tar.
The 6v92’s are nice. The turbo helps recover some efficiency. I was told some of the busses got 12mpg. How does yours do?
I’m not sure yet. I am just getting started. I played with making hydrogen and feeding it directly into the carb of a car years ago. It was an interesting experiment that included a half gallon glass jar, some pieces of stainless and a little power. I noticed the more power I added the more gas I got. I didn’t try and store the gas, (thank god, lol) just fed it directly into the carb throat with a hose. Since I had no way to control the flow of gasoline it didn’t change much. The only safety device I had was the key switch, when I turned off the power to the car it also turned off the power to the jar. I never took it to the next logical step.
Amazingly enough mine gets about 10 mpg. If you want to see it, just search GAB for it. GM TDM 4801. Amazingly the bus only weighs about 18k even though its 38.5 feet long and 102" wide. Since I have plans for the entire inside of the bus, I thought I might design a trailer I could hook to the back of it that would be the woodgas generator. Originally the 671 had 2 valve heads. The plan is to upgrade to 4 valve heads for better flow characteristics. I am considering a turbo but not sure how I can successfully apply that for the woodgas. I have a question. My pea brain seems to remember that the tar created by wood burning was actually water soluble. If so, it might be possible to engineer a hot water injection system that could be used to flush those tars from time to time while the engine is running. … Just a thought. Until I ran across this information (which I have seen before and forgot about) I was thinking about ways to create dimethyl ether to run the bus on.
Hi,
I camped next to a guy a few years ago who had one of the stainless steel GMC busses like used by Greyhound in the 1960’s His was professionally converted to a motorhome and had been repowered with a 6 or 8v92T. I was stunned when he said he was getting 12 mpg on trips from Florida to Michigan and back.
My sister would love that fuel economy with her RV. They bought a new 44ft Newmar Dutch Star last year. They are averaging 7mpg to an occasional 7.5mpg.
Water filters have been used for decades and yes - they can trap a lot of tar. The down side is limitations caused by freezing in winter weather.
Water injection could be used to some extent but understand - quite a bit can end up in the crank case. The air box drains could end up dumping a lot of nasty tar/water on the ground. I’ve not seen it done. I previously mentioned Mike Early. Now deceased most of a decade. When they injected water into the Detroit 2 stroke they found that they could inject ever increasing amounts of water with correlating increases in output - to the point where the water was cooling the engine resulting in water condensate simply running out of the crankcase vent and fouling the motor oil.
With the days of 6-71 and 6-53 engine overhaul kits costing $700 now long gone - I would hesitate trying such aggressive tactics today,