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Old 06-07-2008
Rob Robinson's Avatar
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Default 8V92 Article

I saved the following article several years ago and every once in a while I go back and read it over again.

The 92-series Detroits are two-cycle engines.

All current production diesels are 4-cycle.

Detroit stopped production on the 2-strokers due to EPA requirements - and for no other reason. They simply would not meed EPA emissions requirements on or off-road, no matter what they tried - and try mightily they did, with their DDEC and then DDEC-II (electronic control) systems.

Ultimately, they were forced into 4-stroke production.

It is true that modern electronic engines get better fuel efficiency. However, there is a LOT to be said for a basic engine design that goes back to WWII!

I have 6V92s on my boat (two of 'em.) Detroit's basic design was simplicity itself, and ingenious. The supercharger on these engines is necessary; they will not run without them. There is no intake valve system at all. The valves are all for exhaust; as the piston moves down on a power stroke, the exhaust valves open and at the same time the piston uncovers a port, much like a 2-stroke outboard motor, that leads to an airbox that is pressurized by the blower. The clean air forces out the exhaust. When the piston moves back upward the valves close and the ports are covered; compression occurs, and fuel is injected at the appropriate time. Injection is performed by a cam-driven unit injector. The design is extremely simple - ingenious, really. The emissions problem comes from being unable to perfectly scavenge the exhaust. However, these engines tend to run very low EGTs compared to 4-stroke turbodiesels due to the overabundance of air that flows through them on a given power cycle.

The nice thing about Detroits is that there is no high-pressure injection pump or electronics. They will run, once started, so long as they have fuel and compression. You can also replace the entire fuel system (the injectors) for about $100 a hole and the low pressure fuel lift pump for a couple hundred bucks - these are unit injector engines. With under $200 worth of special tools you can keep a Detroit running in tip-top shape for a loooong time, and properly maintained they are great motors. They have a reputation (somewhat earned) as oil leakers, which is due to the fact that Detroit made the blocks so they could be "doubled" - thus, you have 6V92s, 8V92s, 12V92s (two 6V92s end-to-end) and 16V92s (two 8V92s end to end!) This, however, means there are oil ports and such on the ends of the blocks that have plugs in them and thus they tend to leak oil....

The other thing to be aware of is that Detroits are quite inexpensive to get parts for. A cylinder kit, for example, is about $600 - that's the liner, piston, con-rod, rings, etc - the whole shot. One new hole, coming up. So for about $5k in parts you can do a complete kit replacement, and it can be done "in-frame" - without pulling the motor.

Detroits have no glow plugs and "off the shelf" no starting assist. They are ENTIRELY dependant on engine compression to start. They also require (not recommend, REQUIRE) straight weight 40 grade Cx-II oil. Multigrade oils are strictly forbidden due to the high shear strength required by the injector followers - you WILL destroy cams if you run a 15W40 in them, for example, and you'll also get incessant low oil pressure warnings and probably a spun main to go with it. Unlike "modern" diesels its not uncommon (nor a problem) to have oil pressure readings as low as 10psi at idle when fully warmed up! Normal oil pressure at power (1800 rpmish) is in the 45-50psi range though, just like modern engines. What this means is that in cold weather you need STOUT batteries or you will not be able to roll them over at a high enough RPM to get 'em to light. Block heaters are strongly recommended for the winter months. Ether is very dangerous to use on these engines; I know people who have and do, but my recommendation is "never" on a Detroit.

The nemesis on the 92 Series Detroits is overheating. This is a wet liner design with elastomer (O-ring) seals at the top and bottom of the cylinder liner. If you overheat these engines, even just a bit, the liner seals will be compromised. The result will be oil to cooling system leaks, and if not caught very quickly, damage to the mains or even worse, a spun main and damaged crank. Cooling system maintenance is THE big deal on these motors. Keep them running cool and all is well. Let them get hot and you will be rebuilding them.

Also, later versions of these engines in "turbo" trim used aftercoolers, which are under the blower. That needs to be kept clean; getting to it requires removing the blower, which requires disturbing the governor and fuel rack. Its not a tough job, but it is a pain in the butt. Thus, its important to avoid exhaust leaks and use a good air cleaner so that becomes an infrequent problem rather than a frequent one.

Finally, there is the matter of airbox drains. The airbox on a Detroit is where the blower "accumulates" the charge for scavenging and the new combustion cycle. The blower seals, as the blower ages, and turbo seals will eventually leak small amounts of oil, and the compression and then cooling of the air charge causes water to condense. The airbox drains allow this accumulated crud out of the airbox instead of having it sucked into the cylinders where it will cause abnormal wear. On turbo motors there are check valves located at each drain; these must work properly. If they stick open or closed its bad news; many people neglect these service items. They should be pulled and cleaned at every oil change, and if you have motors where Detroit routed them back to the oil pan (they did on some motors, as the EPA had a kitten about the original design which just allowed the slop to go onto the road) you will do your engine a huge favor by removing that and routing them to a "**** can" that you then empty once in a while (at oil change intervals is a good choice.)

I'm very much "up" on the 92-series engines, since I own two and maintain them myself. Set up for reasonable power levels (500HP from an 8V92TA is reasonable) and proper maintenance they provide extraordinarily good service. The 8V89TA CAN be "hot-rodded" to as far as 750HP quite cheaply just by changing injectors and a few other things - don't be tempted, as the service life in that configuration can be as short as 1500 hours or less between overhauls!

The DDEC and DDEC-II versions of these engines replace the mechanical fuel rack with electronic control of the injectors and a bunch of sensors in an attempt to get cleaner and more fuel-efficient operation from them. Its mostly successful, but now you're into the computer-controlled realm and simple mechanical maintenance procedures go out the window.

If I was going to own a Detroit-powered coach, I'd want one with mechanical injection - if I'm gonna buy an electronic engine, I want one of the new design ones, as if I'm gonna get the warts I want the benefits too. With a handful of parts and a few tools on board I can fix these things by the side of the road if necessary so long as I haven't spun a main or something equally catastrophic - something you simply won't be doing with "today's technology." Author Jim Scoggins (RIP)
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Last edited by Rob Robinson; 05-13-2010 at 09:25 AM.
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  #2  
Old 06-07-2008
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Howdy, Rob.

Thank you very much for posting the article. It is a keeper.


Best regards,
Jack and Liz Pearce
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  #3  
Old 06-07-2008
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Hi Rob,

Thanks’ your post is good information for owners of 6v92 and 8v92 2 cycle engines.

Over the years I have talked to several owners of Birds with two cycle engines who were surprised when I mentioned that they were supposed to use only SAE 40 - 2 cycle (CF-2) engine oil in their engines. The Detroit Diesel documentation that came with my Bird shows pictures of excessive cylinder liner wear in as little as 100 engine hours when using 4-Cycle type multi-weight oil in a 2 Cycle Detroit Diesel engine.

Another thing that a few owners don’t seem to be aware of is that it is important to use supplemental coolant additives (SCAs) to properly maintain the coolant in Detroit Diesel 2 cycle engines. Among other things SCAs add Nitrites which provide Cavitation protection for the steel cylinder liners. Without the Nitrite protection the steel liners can get pitted and eventually get holes in them allowing coolant into the cylinders.

For anyone who hasn’t checked their coolant for proper additives I’ll mention that Detroit Diesel sells 3-way coolant test strips to help evaluate the coolant. When you dip a test strip into the coolant it shows the Glycol percentage, checks for Non Approved Additives and shows the Nitrite level of the coolant.

I suspect that at least some of the failures of Detroit Diesel 2 cycle engines with low mileage on them are caused by not using the recommended oil or by not maintaining the coolant additives.

I know things can still go wrong but using the right oil and maintaining the coolant should at least improve our odds of getting more miles from these engines.
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  #4  
Old 08-16-2009
parris001 parris001 is offline
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Quote:
Originally Posted by Rob Robinson View Post
I saved the following article several years ago and every once in a while I go back and read it over again.

The 92-series Detroits are two-cycle engines.

All current production diesels are 4-cycle.

Detroit stopped production on the 2-strokers due to EPA requirements - and for no other reason. They simply would not meed EPA emissions requirements on or off-road, no matter what they tried - and try mightily they did, with their DDEC and then DDEC-II (electronic control) systems.

Ultimately, they were forced into 4-stroke production.

It is true that modern electronic engines get better fuel efficiency. However, there is a LOT to be said for a basic engine design that goes back to WWII!

I have 6V92s on my boat (two of 'em.) Detroit's basic design was simplicity itself, and ingenious. The supercharger on these engines is necessary; they will not run without them. There is no intake valve system at all. The valves are all for exhaust; as the piston moves down on a power stroke, the exhaust valves open and at the same time the piston uncovers a port, much like a 2-stroke outboard motor, that leads to an airbox that is pressurized by the blower. The clean air forces out the exhaust. When the piston moves back upward the valves close and the ports are covered; compression occurs, and fuel is injected at the appropriate time. Injection is performed by a cam-driven unit injector. The design is extremely simple - ingenious, really. The emissions problem comes from being unable to perfectly scavenge the exhaust. However, these engines tend to run very low EGTs compared to 4-stroke turbodiesels due to the overabundance of air that flows through them on a given power cycle.

The nice thing about Detroits is that there is no high-pressure injection pump or electronics. They will run, once started, so long as they have fuel and compression. You can also replace the entire fuel system (the injectors) for about $100 a hole and the low pressure fuel lift pump for a couple hundred bucks - these are unit injector engines. With under $200 worth of special tools you can keep a Detroit running in tip-top shape for a loooong time, and properly maintained they are great motors. They have a reputation (somewhat earned) as oil leakers, which is due to the fact that Detroit made the blocks so they could be "doubled" - thus, you have 6V92s, 8V92s, 12V92s (two 6V92s end-to-end) and 16V92s (two 8V92s end to end!) This, however, means there are oil ports and such on the ends of the blocks that have plugs in them and thus they tend to leak oil....

The other thing to be aware of is that Detroits are quite inexpensive to get parts for. A cylinder kit, for example, is about $600 - that's the liner, piston, con-rod, rings, etc - the whole shot. One new hole, coming up. So for about $5k in parts you can do a complete kit replacement, and it can be done "in-frame" - without pulling the motor.

Detroits have no glow plugs and "off the shelf" no starting assist. They are ENTIRELY dependant on engine compression to start. They also require (not recommend, REQUIRE) straight weight 40 grade Cx-II oil. Multigrade oils are strictly forbidden due to the high shear strength required by the injector followers - you WILL destroy cams if you run a 15W40 in them, for example, and you'll also get incessant low oil pressure warnings and probably a spun main to go with it. Unlike "modern" diesels its not uncommon (nor a problem) to have oil pressure readings as low as 10psi at idle when fully warmed up! Normal oil pressure at power (1800 rpmish) is in the 45-50psi range though, just like modern engines. What this means is that in cold weather you need STOUT batteries or you will not be able to roll them over at a high enough RPM to get 'em to light. Block heaters are strongly recommended for the winter months. Ether is very dangerous to use on these engines; I know people who have and do, but my recommendation is "never" on a Detroit.

The nemesis on the 92 Series Detroits is overheating. This is a wet liner design with elastomer (O-ring) seals at the top and bottom of the cylinder liner. If you overheat these engines, even just a bit, the liner seals will be compromised. The result will be oil to cooling system leaks, and if not caught very quickly, damage to the mains or even worse, a spun main and damaged crank. Cooling system maintenance is THE big deal on these motors. Keep them running cool and all is well. Let them get hot and you will be rebuilding them.

Also, later versions of these engines in "turbo" trim used aftercoolers, which are under the blower. That needs to be kept clean; getting to it requires removing the blower, which requires disturbing the governor and fuel rack. Its not a tough job, but it is a pain in the butt. Thus, its important to avoid exhaust leaks and use a good air cleaner so that becomes an infrequent problem rather than a frequent one.

Finally, there is the matter of airbox drains. The airbox on a Detroit is where the blower "accumulates" the charge for scavenging and the new combustion cycle. The blower seals, as the blower ages, and turbo seals will eventually leak small amounts of oil, and the compression and then cooling of the air charge causes water to condense. The airbox drains allow this accumulated crud out of the airbox instead of having it sucked into the cylinders where it will cause abnormal wear. On turbo motors there are check valves located at each drain; these must work properly. If they stick open or closed its bad news; many people neglect these service items. They should be pulled and cleaned at every oil change, and if you have motors where Detroit routed them back to the oil pan (they did on some motors, as the EPA had a kitten about the original design which just allowed the slop to go onto the road) you will do your engine a huge favor by removing that and routing them to a "**** can" that you then empty once in a while (at oil change intervals is a good choice.)

I'm very much "up" on the 92-series engines, since I own two and maintain them myself. Set up for reasonable power levels (500HP from an 8V92TA is reasonable) and proper maintenance they provide extraordinarily good service. The 8V89TA CAN be "hot-rodded" to as far as 750HP quite cheaply just by changing injectors and a few other things - don't be tempted, as the service life in that configuration can be as short as 1500 hours or less between overhauls!

The DDEC and DDEC-II versions of these engines replace the mechanical fuel rack with electronic control of the injectors and a bunch of sensors in an attempt to get cleaner and more fuel-efficient operation from them. Its mostly successful, but now you're into the computer-controlled realm and simple mechanical maintenance procedures go out the window.

If I was going to own a Detroit-powered coach, I'd want one with mechanical injection - if I'm gonna buy an electronic engine, I want one of the new design ones, as if I'm gonna get the warts I want the benefits too. With a handful of parts and a few tools on board I can fix these things by the side of the road if necessary so long as I haven't spun a main or something equally catastrophic - something you simply won't be doing with "today's technology". Author Jim Scoggins (RIP)
Quote:
Originally Posted by Dieselbird01 View Post
Hi Rob,


Another thing that a few owners don’t seem to be aware of is that it is important to use supplemental coolant additives (SCAs) to properly maintain the coolant in Detroit Diesel 2 cycle engines. Among other things SCAs add Nitrites which provide Cavitation protection for the steel cylinder liners. Without the Nitrite protection the steel liners can get pitted and eventually get holes in them allowing coolant into the cylinders.
Kudos to Rob for what is a very good description on the ol' 92 Series engine. A lot of my colleagues hate this old engines because it's really only good for about 250,000 miles and not of a super robust design. But working off of a design that dates back to WW2, I get pretty nostalgic about it. The 92 Series engine was a spin-off of the 71 Series engine which was actually a dry liner design. And the research and development of that old 71 series V engine (the inline 71 was already in existence) was actually done by the Cadillac division of GM. One of the weakest points in the 92 series engine is the fact that it has to make do with the same main and rod bearings of the 71 series, along with essentially the same connecting rod.

As far as SCAs being a factor, never has really been an issue with the 2 strokes. It was only after the 4 stroke Series 60 engine came about that we ever heard that term. The higher cylinder pressures of the 4 stroke engines produce the frequency that leads to cavitation if not kept in check. The old 2 strokes are pretty low compression mills that while may benefit from a coolant with SCAs, don't really require them.
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Last edited by Rob Robinson; 05-13-2010 at 09:27 AM.
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  #5  
Old 08-20-2009
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Dieselbird01 Dieselbird01 is offline
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Quote:
Originally Posted by parris001 View Post
Kudos to Rob for what is a very good description on the ol' 92 Series engine. A lot of my colleagues hate this old engines because it's really only good for about 250,000 miles and not of a super robust design. But working off of a design that dates back to WW2, I get pretty nostalgic about it. The 92 Series engine was a spin-off of the 71 Series engine which was actually a dry liner design. And the research and development of that old 71 series V engine (the inline 71 was already in existence) was actually done by the Cadillac division of GM. One of the weakest points in the 92 series engine is the fact that it has to make do with the same main and rod bearings of the 71 series, along with essentially the same connecting rod.

As far as SCAs being a factor, never has really been an issue with the 2 strokes. It was only after the 4 stroke Series 60 engine came about that we ever heard that term. The higher cylinder pressures of the 4 stroke engines produce the frequency that leads to cavitation if not kept in check. The old 2 strokes are pretty low compression mills that while may benefit from a coolant with SCAs, don't really require them.

Hi Jeff,

I’m not a diesel mechanic but according to the information I have from both Wanderlodge and Detroit Diesel the Series 92 Detroits do require SCA’s. My 1984 ½ Bird was powered by a 6V92 and the 1991 Bird that I currently own is powered by an 8V92. Both of them came with documentation from both Wanderlodge and Detroit Diesel that state that SCA’s are required. The Series 92 “Engine Operator’s Guide” that came with my 8V92 says “It is imperative that DDC-selected product supplemental inhibitor be added to all Series 92 engines”

The Series 92 “Engine Operator’s Guide” also says:

“DDC-selected product supplemental coolant inhibitors protect the metallic surfaces of the cooling system against corrosive attack - pH control chemicals are used to maintain an acid free solution - water softening chemicals deter formation of mineral deposits - Cavitation suppression chemicals minimize the formation of vapor pockets, preventing erosion of cooling system surfaces

The Series 92 “Engine Operator’s Guide” also says that the coolant nitrite concentration in a Series 92 Engine must be tested at each oil change (150 hours or 15,000 miles) and that the nitrite level must be maintained at between 800 ppm and 2400 ppm.

As to “the old 2 strokes are pretty low compression mills” don’t the Series 92 and the Series 60’s both have 17:1 compression ratios?
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1991 40' WB ...From 2008 - Present
1984 ½ PT-36 .From 2000 - 2008
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  #6  
Old 08-20-2009
parris001 parris001 is offline
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Quote:
Originally Posted by Dieselbird01 View Post

The Series 92 “Engine Operator’s Guide” also says that the coolant nitrite concentration in a Series 92 Engine must be tested at each oil change (150 hours or 15,000 miles) and that the nitrite level must be maintained at between 800 ppm and 2400 ppm.

As to “the old 2 strokes are pretty low compression mills” don’t the Series 92 and the Series 60’s both have 17:1 compression ratios?
Heck, maybe the liners never stayed in these things ling enough to cavitate. All I know is that I NEVER, NEVER saw a two stroke where the inside of the block was cavitated. And back then all that we used was essentially Shellzone antifreeze that lacked any SCA package at all.

It wasn't until we started pulling Series 60 engines apart that we ever saw our first incidence of cavitation. We had to have a Cummins guy even tell us what it was and what was going on!!!

Any engine can benefit from SCAs. The danger is when you experience silicate drop-out which is where the additive level gets too high and the silicate drops out of suspension and turns into a gel that coats the inside of the engine and inhibits heat transfer. The coolant sender can even get coated in the goo and not even let you know it's happening.


2 strokes did have a decent compression RATIO, but they have considerable lower compression PRESSURES. That's the point I meant to make..............
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  #7  
Old 08-20-2009
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I agree with Jeff.
I have never seen or heard of a cavitation in a 92 series engine.
But,thats not to say that SCAs are not important as far as keeping the radiator clean and the block from getting rusty and nasty inside.

I have seen and heard of cavitation in all other 4 stroke diesels,and I have seen a C15 cat that had perfect SCAs for its life,have bad liners from cavitation.
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Old 08-20-2009
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Quote:
Originally Posted by Randy Dupree View Post
I agree with Jeff.
I have never seen or heard of a cavitation in a 92 series engine.
But,thats not to say that SCAs are not important as far as keeping the radiator clean and the block from getting rusty and nasty inside.

I have seen and heard of cavitation in all other 4 stroke diesels,and I have seen a C15 cat that had perfect SCAs for its life,have bad liners from cavitation.
That's because SCAs are a band-aid approach to the real issue: a lack of nickel in the block castings. Cavitation is caused by a frequency that the internals of the engine vibrate at from the extreme cylinder pressures. Most of the time you'll find that cavitation attacks the very top portion of the liner or the counterbore of the block because it is here that the pressures are the highest. If the blocks were more robust from nickel content this would be less of an issue. But being that nickel is also very heavy, that's probably another reason manufacturers shy away from it.
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Old 08-21-2009
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When you're sitting at 50,000 gross, what's a couple of extra pounds???? I agree, there certainly should be a way to build a block that doesn't need SCA's. I would certainly hope the engineers are smart enough to recognize a couple of extra pounds in the block wouldn't hurt anything, if it protects the engine and lowers maintenance. Of course, you just never know.
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Old 08-21-2009
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cost

nickel has been leaving our engine casting for quite some time~~~~
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