WW2 Iron

[mitch504]

Willie, all Detroit 2-strokes, (which is all DDs before the late '80s) used blowers. They won't run without them.

 

[RZucker]

Willie, all Detroit 2-strokes, (which is all DDs before the late '80s) used blowers. They won't run without them.

I think he mentioned larger blowers on the puller engines. ?

 

[mitch504]

yeah, he said they put blowers on them, and if they had factory blowers they put larger ones on. I was just pointing out they all had factory ones. (just continuing the DD education of Willie B...)

 

[DMiller]

I'm a thinking the black one was the lower, been wrong before but that brain cell DID fire this morning! Black being a wear-in surface and shiny was chromed for friction relief, it followed the black sacrificial Razor down the bore on less oil.

 

[John C.]

The blower issue could just be semantics. Detroit called the engines without a turbo charger a normally aspirated engine. I have heard the engines with turbos called turbo super charged.

 

[old-iron-habit]

The blower issue could just be semantics. Detroit called the engines without a turbo charger a normally aspirated engine. I have heard the engines with turbos called turbo super charged.

The Detroit blowers were not superchargers. They boosted the volume of air and helped scavenge the cylinders while introducing more air but they operated at very little pressure. There is a thread on here somewhere that has the actual numbers. Detroit blowers became a super charger only when they were geared way up in rotational speed as when transplanted on top of a gas engine.

 

[John C.]

The turbo chargers were at times referred to as turbo super chargers. It's just a name.

 

[RZucker]

The Detroit blowers were not superchargers. They boosted the volume of air and helped scavenge the cylinders while introducing more air but they operated at very little pressure. There is a thread on here somewhere that has the actual numbers. Detroit blowers became a super charger only when they were geared way up in rotational speed as when transplanted on top of a gas engine.

This is correct. A 2 stroke Detroit without a blower would choke on it's own exhaust and quit running. Most of my experience has been with 71 V engines and they did have 3 different blower drive ratios, The highest speed did have a small supercharge effect that cut down on the black smoke when using larger injectors with standard cam timing.
IIRC, airbox pressures vary from 1.5 to 5 psi depending on the number of cylinders and drive ratio of the blower.
Now we can add the turbos to the mix.

 

[hillbillywrench]

If you look at a small, single cylinder, gas 2-stroke, when the piston travels up (toward the head, after passing the intake port) it's creating a larger air-space in the crankcase. This pulls a vacuum and sucks air (and fuel/oil mix) from the carburetor thru the reed valves into the crankcase. As the piston travels back down (power portion of the stroke) it's decreasing the crankcase volume, closing the reed valve, and pressurizing the air/fuel mix. When the piston clears the intake ports the pressurized mix flows into the cylinder above the piston. With a multi-cylinder engine, either you isolate each piston/cylinder (some outboard boat engines did) or you pressurize the entire crankcase (detroit used a roots blower). I guess detroit could have added reed valves and eliminated the blower on the 1-71 if they had wanted to?? But only on that engine.
The roots blower (positive displacement pump) will create enough pressure at starting rpm to get the engine to fire, but pumps air volume at a set ratio to engine rpm (determined by blower gearing). It doesn't "build" boost like a turbo.
Didn't detroit build a few models (92 series?) that bypassed the blower after the turbo started building enough boost to maintain pressure in the air box? More power/better fuel economy without the blower drag?
I think that's how it works? I'm often wrong, and please correct me if I am! I forgot what an ego was years ago, lol.

 

[hillbillywrench]

I realized this morning that I didn't explain that the detroit used an air box between the blower and cylinder ports. This isolated the crankcase from the intake charge so a standard oil-lube system could be used instead of oil-mix like a gas 2-stroke.
I believe this box was the source of most of the "green leaker" oil drip comments. As the piston rings passed the intake ports it allowed a small amount of oil to enter the airbox. This oil had to be drained off through a small weep hole or it could build up and become a fuel source. Oil (fuel) + air going into the cylinder would run the engine without any throttle control creating a runaway! My dad found a nail somebody had jammed in the weep hole on his 3-71 powered dozer to "stop that oil drip". That engine behaved much better after the air box drain was cleared!

 

[Birken Vogt]

Didn't detroit build a few models (92 series?) that bypassed the blower after the turbo started building enough boost to maintain pressure in the air box? More power/better fuel economy without the blower drag?

Yes they did, almost forgot about that. I believe some 92s had it, others didn't, all DDEC 92s did I was told.

In the larger railroad sized units they had/have centrifugal blowers driven by the engine at low speeds from an overrunning clutch but there is also an exhaust driven turbine so when it loads up the exhaust drives it faster than the engine. Probably possible because it is larger with lower RPM than trucks.

 

[DMiller]

That would be a EMD as they use in Tows and Railroad engines, wild drive mechanism on those blowers. Want to see someone run REAL fast, don't test the wrist pin seals on a 6L71 and have one leak. Saw a nitwit do that, always 'Trusted' his installs and failed to seat them to a vacuum test, one failed miserably. That engine ran for almost 6 hours before gobbled enough engine oil to fail dramatically. Four bad rods, full liner/piston sets, reground 10/10 crank and new cam. Gear train SEEMED to be alright so they did reuse that. For an out of frame it cost the company 2 1/2 times what they could charge for it.

 

[old-iron-habit]

That would be a EMD as they use in Tows and Railroad engines, wild drive mechanism on those blowers. Want to see someone run REAL fast, don't test the wrist pin seals on a 6L71 and have one leak. Saw a nitwit do that, always 'Trusted' his installs and failed to seat them to a vacuum test, one failed miserably. That engine ran for almost 6 hours before gobbled enough engine oil to fail dramatically. Four bad rods, full liner/piston sets, reground 10/10 crank and new cam. Gear train SEEMED to be alright so they did reuse that. For an out of frame it cost the company 2 1/2 times what they could charge for it.

I would love to see video of that mess happening

 

[RZucker]

That would be a EMD as they use in Tows and Railroad engines, wild drive mechanism on those blowers. Want to see someone run REAL fast, don't test the wrist pin seals on a 6L71 and have one leak. Saw a nitwit do that, always 'Trusted' his installs and failed to seat them to a vacuum test, one failed miserably. That engine ran for almost 6 hours before gobbled enough engine oil to fail dramatically. Four bad rods, full liner/piston sets, reground 10/10 crank and new cam. Gear train SEEMED to be alright so they did reuse that. For an out of frame it cost the company 2 1/2 times what they could charge for it.

I have always used the suction cup test. I did see the remains of a 4-71 that had the same issue. The block ended up with a couple of holes in it that really didn't belong there. The new paint was pretty.

 

[RZucker]

I realized this morning that I didn't explain that the detroit used an air box between the blower and cylinder ports. This isolated the crankcase from the intake charge so a standard oil-lube system could be used instead of oil-mix like a gas 2-stroke.
I believe this box was the source of most of the "green leaker" oil drip comments. As the piston rings passed the intake ports it allowed a small amount of oil to enter the airbox. This oil had to be drained off through a small weep hole or it could build up and become a fuel source. Oil (fuel) + air going into the cylinder would run the engine without any throttle control creating a runaway! My dad found a nail somebody had jammed in the weep hole on his 3-71 powered dozer to "stop that oil drip". That engine behaved much better after the air box drain was cleared!

Air box drains... I had a GMC 9500 with an 8V-71 that had a 3-4 gallon catch tank for the drains, I usually drained it twice a week, It made for good relations with the grain elevators that did not like to see oil on their concrete.
One thing a guy want's to do is check for airflow from those tubes at every oil change, I've seen quite a few plug internally where the little weatherhead fitting screws into the block. Usually a chunk of top piston ring. It's funny how much fire ring they can lose and still run strong.

 

[John C.]

The blower box drains on a good engine put out very little oil. The ones I did see were the leaks on the end plates and at the oil pan corners. We staked the plates to hold the gaskets in place, glued them on one side or the other and finally went to a thin bead of silicone which seemed to hold them longer. Probably the worst offenders were the engines that sat idling all the time. They start the drips and forever marked their territory after that.

 

[DMiller]

If draining from those tubes in any volume is BAAADD JuJu!!