It's an ex-Coast Guard 27' utility boat. Hull is in excellent condition, deck was spongy, but deck and house have been professionally replaced and look nice. It's in running condition, but needs to have the cabin fitted out and equipment (which is present) reinstalled. Haven't seen the underwater profile yet, but am assuming with that power it will run at semi-displacement speeds, which is fine for me.
Bob
Thanks for the info, Bob.
I had a forty footer, steel-hulled trawler with a 3-53 in it and loved it. In a trawler, the 3-53 is a great engine.
All two-stroke Detroits have a blower. It's necessary to the operation of the engine, does the job that crankcase pressure does in a little two-stroke. On the inline motors it mounts on the side of the block.
John
If a "blower" is defined by you as a turbo (i.e. .., device to increase air flow into the cylinders), then you are in error. I know several people with
2 stroke DD 6-71's. Some are naturally aspirated, some have turbos (blowers).Eisboch
A "blower" generally refers to a direct driven super charger, not an exhaust driven turbo charger.
The Detroit Diesel is a two stroke, diesel. The piston goes down on the power stroke and comes up on the compression stroke. Without the mechanical driven "blower" which simply blows air in through the cylinder ports and through the exhaust ports at the beginning of the compression stroke there would be no way to get a charge of air into the engine.
If you wanted to increase the pressure and volume of this air flow you could add a exhaust driven compressor before the "blower", But you must have the "blower" for the engine to run.
Bruce in Bangkok (brucepaigeATgmailDOTcom)
Gotcha. I was confusing "blower" with turbocharger as Pete C. pointed out.
Eisboch
Neither being a two-stroke nor using diesel oil (nor indeed the combination) requires a blower/turbo for such an engine to operate. It is true that engines can be designed so that, were the blower/turbo with which they are normally equipped to be removed they would not run, that would be due to other design decisions, not to the choice of fuel, method of ignition, and/or two/four-stroke operation.
On large stationary diesel generators using Detroit diesels, there a often both shaft driven " blowers" and turbochargers. The blowers are used to start the engine and get it up to speed. Afterwards, the blowers are cut off by damper valves and the turbochargers take over the air supply job. This is done because the overall engine efficiency is better using the turbochargers.
Randy
Running a Detroit 4-53 without a blower (and maybe all Detroit 2 strokes -shrug- I dunno) would indeed take a complete and major league re-design. Not just a few bolt on changes for sure.
Rick
Absolutely right. The Detroit 2 stroke design requires a blower to move new air into the piston and purge the ehaust gases. It will not run without it, and little or no increase in volumetric efficiency is achieved. A turbo charger on the other hand is designed to increase the air charge to the piston above atmospheric pressure, and therefore horsepower is increased as the effective cylinder volume is increased.
The confusion arises from the fact that a Detroit blower can also be used on a gasoline engine as a supercharger. Same basic device but a different purpose and result.
Find a cutaway picture of a Detroit Diesel, you'll see what the blower does and you can figure out how. Don't pay no 'tention to turbos, a turbo isn't a blower. A naturally aspirated Detroit two-stroke has a blower.
John
Being a two-stroke, and a Detroit, it requires a blower to operate. Come to think of it, I've never heard of any engines that are two stroke and do not use forced induction of one form or another. Even little chain saws use the crankcase volume as a blower. Seems as if those two eliminated strokes--intake and exhaust--are taken up by the blower. How would you build an 2-stroke engine without forced induction?
My 3-53 had an emergency shut-down, which was a spring-loaded damper door that when tripped, it shut off the air from the 'blower'.
O.K. Assuming that your statement is correct And starting from the power stroke of a two stroke diesel engine.
(1) Diesel fuel is injected into the combustion chamber where air has been compressed until it exceeds the ignition temperature of the duel. (2) The rapidly expanding gases created by the burning fuel act to push the only movable part of the combustion chamber, the piston downward. At the bottom of the power stroke the gasses inside the combustion chamber still are far hotter then ambient temperature and thus exceed ambient pressure.
(3) the piston having reached the bottom of its power stroke begins to be driven upward by the crankshaft and connecting rod. When it piston reaches roughly the top of its compression stroke another injection event occurs.
Now, as temperature of the gasses within the combustion chamber and thus the pressure, is higher then ambient temperature and pressure at the bottom of the power stroke the flow should be from the high pressure area to a lower pressure area. In which case the engine would not receive any air for the next stroke.
So, where does the two stroke diesel engine get the air necessary to support combustion of the next injection of diesel fuel if not through the use of a mechanical air pump, usually referred to as a "Blower" in D.D. parlance
Bruce in Bangkok (brucepaigeATgmailDOTcom)
Presumably it would get them by using the crankcase as a compressor like a gas 2stroke does.
Whether it is possible to get the necessary compression for ignition, especially while at cranking speed, while dealing with transfer ports etc is left as an exercise for the student.
del
2 stroke diesels will run without a blower. I have a model airplane engine diesel that jsut uses the crankcase like a gas rig. And there were a lot of those 1 lunger diesels in Montereys, etc, that did not have a blower.
Bruce:
"Del Cecchi" wrote:
Problem with that assumption is, a DD crankcase is designed like a 4 stroke, with an oil bath and filter. A DD crankcase is not connected in any way to the intake port (not to mention, a DD cylinder has no exhaust port. it has an exhaust valve, and rocker arms, and pushrods, and cam, like a 4 stroke). A DD 2 storke design is nothing like the 2 stroke design we're all familiar with for outboards etc. Its air intake comes directly from outside, not through the crankcase. And without a blower to push the air in, it won't run.
Rick
Sure you do and it worked just like a glow plug engine. You mixed oil for lubrication and some nitro-benzine, or something like that, and it ran. Exactly as do sea scooters, 2-stroke motor cycles and chain saws.
And the reason is that you use the bottom of the piston coming down on the power stroke to compress the fuel/oil mixture in the crank case to force it into the combustion chamber.
But we were talking specifically about a Detroit Diesel 2-stroke and the fact that it does need the mechanical driven "blower" to run.
Bruce in Bangkok (brucepaigeATgmailDOTcom)
All 2 strokes are not designed alike. The term "2stroke" refers to how often the piston goes up/down per power stroke. Not how air or fuel is fed to the cylinder. The crankcase of you little diesel 2 stroke is designed like an outboard. A DD crankcase is designed like your automobile engine's (assuming it's a 4 stroke). A DD 2 stroke can't run without a blower.
Rick
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