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Author Topic:   Yamaha OX-66: The Ultimate Two-Stroke

jimh posted 10-09-2007 01:12 AM ET (US)
If you categorize the direct-injection two-stoke motors (like the Evinrude E-TEC and Mercury OptiMax) separately from the rest of the two-stroke motors, I have to observe that the Yamaha OX-66 V6 motors are probably the ultimate evolution of the classic two-stroke outboard. They feature electronic fuel injection with a closed loop system employing an oxygen sensor. I do not recall any other two-stroke motor that had this refinement. They also had a very reliable and relatively trouble-free oil mixing system which used electrical pumps to lift the oil to the motor and a gear-driven (all-steel gears) mixing pump. The rest of the motor was the typical well-designed and high-quality outboard that gave Yamaha market leadership in saltwater V6 markets like Florida and the Carolinas. Their water pump impellers and propeller shaft seals would last for a decade. Their instrumentation was top-notch, and provided visual anunciators for various alarms to help distinguish the intended meaning, as well as an aural alarm. The started easily and ran smoothly. And their size was in proportion to the other outboard motors of the day.
Those OX-66 motors were very fine outboards!
Peter posted 10-09-2007 08:45 AM ET (US)
Yes indeed. Interestingly, however, I found that the O2 sensor in my 225 Ox-66 was a bit of weak link in the design. If one didn't use Yamaha's RingFree carbon reducing additive or equivalent, the O2 sensor would get fouled up and when that happened, the sparkplugs would foul because the motor would run richer than necessary (defaulted to a rich setting).
The 225 and 250 Ox-66 also had a cylinder/displacement management system like we are now starting to see once again in automobiles (remember the Cadillac V8-6-4?). From idle to approximately 850 RPM, the motor would run on 5 cylinders, from 850 to about 2200 RPM using 4 cylinders and 6 cylinders above about 2200 RPM. The transition from 4 to 6 cylinders was noticible but coincided perfectly with the transition to being on-plane on the Revenge 22. The cylinder management did take some getting used to.
The motor was reasonably quiet at low engine speeds.
jimh posted 10-09-2007 08:53 AM ET (US)
Another reviewer finds the Yamaha OX-66 to be a top performer:
http://www.docksidereports.com/YamahaOutboards.htm
Peter posted 10-09-2007 09:43 AM ET (US)
I found this passage in Pascoe's article rather interesting and possibly misguided.

quote:
...After all, outboards have a well-deserved reputation for being gas guzzlers, which is one drawback they can't overcome by virtue of the fact that outboards burn a combination of gasoline and oil. That means that the fuel they burn is not as powerful as any engine that has a crankcase of oil for lubrication. That translates to having to burn more fuel to attain similar power outputs over a conventional gas engine.
Makes me wonder whether Pascoe really knows how a conventional 2-stroke actually works. The high fuel consumption of a conventional 2-stroke versus "any engine that has a crankcase of oil for lubrication" has virtually nothing to do with the fact that the fuel contains oil. Rather, it has almost everything to do with "leakage" caused by the fact that the inlet and exhaust ports are open at the same time and so necessarily some of the fresh fuel charge coming in to the combustion chamber from the inlet passes through the combustion chamber and out the exhaust port, never to be burned and turned into useful work. When the DFI outboards came onto the scene to seal up the "leakage", the fuel consumption of the 2-strokes rivaled and in some cases bested the "engine that has a crankcase of oil for lubrication."
I suspect that this article was written before DFI 2-strokes were established.
I also found this interesting:
Add to this the fact that outboard propellers are not as efficient as inboard props and you have two good reasons why outboards burn more fuel.
I have seen articles that show a conventional (not DFI) 2-stroke outboard powered boat with the engines hanging off the back with their propellers sitting relatively high to the water to be more fuel efficient than the same boat with the in-boards having all the running gear hanging under the boat deep in the water.
BQUICK posted 10-09-2007 10:46 AM ET (US)
The HPDI (High Pressure Direct Injection)Yamaha is a further refinement of the OX-66.
LogeyPogey posted 10-10-2007 08:26 PM ET (US)
I have twin 99 250's on the back of my Grady. They have been great so far only have 650 hrs on them. Plenty of life left in them .
http://i185.photobucket.com/albums/x276/logeypogey/020cRussBoat.jpg
cc13 posted 10-11-2007 03:26 PM ET (US)
I agree that they are fine engines. Apparently, so does the thief that stole mine right off of the transom.
fabricator posted 10-11-2007 04:30 PM ET (US)
"I agree that they are fine engines. Apparently, so does the thief that stole mine right off of the transom."
Ouch.
I had an old Yammi on a Aquasport, it was the most relaible engine I ever had........
macfam posted 10-11-2007 10:17 PM ET (US)
This summer I sold my 25' Revenge WT with the OX66 250hp.
That IS a great motor.
Never had a repair, never had a hiccup.
And what power!!!
Used YamaLube and RingFree religiously.
The only difference with the design of the 250 hp is that at idle, it ran on 5 cylinders, and over 900 rpm it ran on 4 cylinders and over 1300 is really smoothed out with all 6 cylinders.
So until it got to 1300 rpm there was a slight roughness, but nothing annoying.
gss036 posted 10-12-2007 01:50 PM ET (US)
I would agree that they are a great engine. Yamaha took the notch up a couple of steps in the 2 stroke technologly, but at the same time, took the maintance requirments to the point that it is difficult for the layman to do all the testing required on the components.
We have the SeaSport and Osprey manfactured here in town and BoonDocks handle the sales (same company), but on all the new boats, all they install are the new 4 stroke engines, usually twin 150 hp to twin 250 hp /single 250's on the 22/24 ft boats. I cannlt remember when the last time I saw one thier boats w/a 2 stroke engine.
macdougall70 posted 10-20-2007 06:10 AM ET (US)
MY 98' TWIN 250's run my 27 like a champ but 1.2 mpg at cruise is hard to swallow
GSH posted 10-24-2007 11:31 AM ET (US)
Perhaps most of you know this already, but I just read in finnish boating mag 'Kippari' that Yamaha will soon stop making the HPDI 2-strokes. Sad, if you ask me.
-Seb
onlyawhaler posted 10-24-2007 01:44 PM ET (US)
I got back from the weekend down at Lake Powell for a last season ending outing.
I have only recently aquired a late 90s Outrage with a 225 OX66 and I have had it out 10-12 times and I can't say enough about how much I like this engine
My past experience has been with the 80-to early 90 era OMC Johnsons carb engines which have been great, but this is a big step up.
The instant starting, less smoke, great gauges with real information that is helpful and that Yamaha binnicle mount is the smoothest feeling throttle I have ever had.
I look under the hood and it looks quality, the hood itself is heavy and insulated well and fittings and castings look first rate.
It is powerful and gets on to plane quickly. It seems like the best of the two stroke world back when things were simplier and less regulated. Raw two stroke power and light weight with the advantage of basic fuel injection over carburation. Clean, not really, quiet, a bit more than my older OMCs and great great performance.
It has been such a postive engine and experiece(and the engine goes along way towards making the boat) makes me wonder if I should grab for that last new 225 OX66 225 at Eds for sale at 8k and just store it away for the eventual repower years ahead.
It does sound like Yamaha is getting out of the two stroke market altogether. Too bad, they have done a good job.
Onlyawhaler
ThomasT posted 09-19-2013 09:23 AM ET (US)
[Revived this six-year-old discussion to change the topic.]
jpgbu1 posted 09-26-2013 05:54 PM ET (US)
I purchased a 1988 22 outrage with a OX66 250 on the transom from an estate sale in the spring of 2012. The boat was spotless and all it needed was a t-top and a trailer. (got both for 2.3K) the boat was 13K. I took a chance not being able to speak to the owners, as they had passed, but did speak to the marina maintaining the boat. They showed me records of maintenance from every year since the purchase of it new in 1999. The test run was flawless, and the outboard turned perfectly at 5600RPM. I got the boat home and while tinkering with the digital tach, found the hour gauge. It had 29 hours on it! I just pulled the boat to change the poppet valve and at 101 hours I still have 145PSI across the bank at WOT. not to shabby for a 14 year old motor. I think it still have 10-15 years left in her at the rate I am using it!!! It is by far the best running/performing outboard I have owned. And I have owned over 20 since I was a kid.
montauk madness posted 09-26-2013 07:37 PM ET (US)
I sure like my 200HP OX66 on my Outrage.
jimh posted 09-26-2013 09:02 PM ET (US)
As far as I can tell, the Yamaha Ox66 was the high point of classic two-stroke-cycle engine development, mainly due to the use of a modern, multi-sensor, closed-loop fuel injection system, something not seen in other two-stroke-cycle engines.

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Author	Topic: Yamaha OX-66: The Ultimate Two-Stroke
jimh	posted 10-09-2007 01:12 AM ET (US) If you categorize the direct-injection two-stoke motors (like the Evinrude E-TEC and Mercury OptiMax) separately from the rest of the two-stroke motors, I have to observe that the Yamaha OX-66 V6 motors are probably the ultimate evolution of the classic two-stroke outboard. They feature electronic fuel injection with a closed loop system employing an oxygen sensor. I do not recall any other two-stroke motor that had this refinement. They also had a very reliable and relatively trouble-free oil mixing system which used electrical pumps to lift the oil to the motor and a gear-driven (all-steel gears) mixing pump. The rest of the motor was the typical well-designed and high-quality outboard that gave Yamaha market leadership in saltwater V6 markets like Florida and the Carolinas. Their water pump impellers and propeller shaft seals would last for a decade. Their instrumentation was top-notch, and provided visual anunciators for various alarms to help distinguish the intended meaning, as well as an aural alarm. The started easily and ran smoothly. And their size was in proportion to the other outboard motors of the day. Those OX-66 motors were very fine outboards!
Peter	posted 10-09-2007 08:45 AM ET (US) Yes indeed. Interestingly, however, I found that the O2 sensor in my 225 Ox-66 was a bit of weak link in the design. If one didn't use Yamaha's RingFree carbon reducing additive or equivalent, the O2 sensor would get fouled up and when that happened, the sparkplugs would foul because the motor would run richer than necessary (defaulted to a rich setting). The 225 and 250 Ox-66 also had a cylinder/displacement management system like we are now starting to see once again in automobiles (remember the Cadillac V8-6-4?). From idle to approximately 850 RPM, the motor would run on 5 cylinders, from 850 to about 2200 RPM using 4 cylinders and 6 cylinders above about 2200 RPM. The transition from 4 to 6 cylinders was noticible but coincided perfectly with the transition to being on-plane on the Revenge 22. The cylinder management did take some getting used to. The motor was reasonably quiet at low engine speeds.
jimh	posted 10-09-2007 08:53 AM ET (US) Another reviewer finds the Yamaha OX-66 to be a top performer: http://www.docksidereports.com/YamahaOutboards.htm
Peter	posted 10-09-2007 09:43 AM ET (US) I found this passage in Pascoe's article rather interesting and possibly misguided. quote: ...After all, outboards have a well-deserved reputation for being gas guzzlers, which is one drawback they can't overcome by virtue of the fact that outboards burn a combination of gasoline and oil. That means that the fuel they burn is not as powerful as any engine that has a crankcase of oil for lubrication. That translates to having to burn more fuel to attain similar power outputs over a conventional gas engine. Makes me wonder whether Pascoe really knows how a conventional 2-stroke actually works. The high fuel consumption of a conventional 2-stroke versus "any engine that has a crankcase of oil for lubrication" has virtually nothing to do with the fact that the fuel contains oil. Rather, it has almost everything to do with "leakage" caused by the fact that the inlet and exhaust ports are open at the same time and so necessarily some of the fresh fuel charge coming in to the combustion chamber from the inlet passes through the combustion chamber and out the exhaust port, never to be burned and turned into useful work. When the DFI outboards came onto the scene to seal up the "leakage", the fuel consumption of the 2-strokes rivaled and in some cases bested the "engine that has a crankcase of oil for lubrication." I suspect that this article was written before DFI 2-strokes were established. I also found this interesting: Add to this the fact that outboard propellers are not as efficient as inboard props and you have two good reasons why outboards burn more fuel. I have seen articles that show a conventional (not DFI) 2-stroke outboard powered boat with the engines hanging off the back with their propellers sitting relatively high to the water to be more fuel efficient than the same boat with the in-boards having all the running gear hanging under the boat deep in the water.
BQUICK	posted 10-09-2007 10:46 AM ET (US) The HPDI (High Pressure Direct Injection)Yamaha is a further refinement of the OX-66.
LogeyPogey	posted 10-10-2007 08:26 PM ET (US) I have twin 99 250's on the back of my Grady. They have been great so far only have 650 hrs on them. Plenty of life left in them . http://i185.photobucket.com/albums/x276/logeypogey/020cRussBoat.jpg
cc13	posted 10-11-2007 03:26 PM ET (US) I agree that they are fine engines. Apparently, so does the thief that stole mine right off of the transom.
fabricator	posted 10-11-2007 04:30 PM ET (US) "I agree that they are fine engines. Apparently, so does the thief that stole mine right off of the transom." Ouch. I had an old Yammi on a Aquasport, it was the most relaible engine I ever had........
macfam	posted 10-11-2007 10:17 PM ET (US) This summer I sold my 25' Revenge WT with the OX66 250hp. That IS a great motor. Never had a repair, never had a hiccup. And what power!!! Used YamaLube and RingFree religiously. The only difference with the design of the 250 hp is that at idle, it ran on 5 cylinders, and over 900 rpm it ran on 4 cylinders and over 1300 is really smoothed out with all 6 cylinders. So until it got to 1300 rpm there was a slight roughness, but nothing annoying.
gss036	posted 10-12-2007 01:50 PM ET (US) I would agree that they are a great engine. Yamaha took the notch up a couple of steps in the 2 stroke technologly, but at the same time, took the maintance requirments to the point that it is difficult for the layman to do all the testing required on the components. We have the SeaSport and Osprey manfactured here in town and BoonDocks handle the sales (same company), but on all the new boats, all they install are the new 4 stroke engines, usually twin 150 hp to twin 250 hp /single 250's on the 22/24 ft boats. I cannlt remember when the last time I saw one thier boats w/a 2 stroke engine.
macdougall70	posted 10-20-2007 06:10 AM ET (US) MY 98' TWIN 250's run my 27 like a champ but 1.2 mpg at cruise is hard to swallow
GSH	posted 10-24-2007 11:31 AM ET (US) Perhaps most of you know this already, but I just read in finnish boating mag 'Kippari' that Yamaha will soon stop making the HPDI 2-strokes. Sad, if you ask me. -Seb
onlyawhaler	posted 10-24-2007 01:44 PM ET (US) I got back from the weekend down at Lake Powell for a last season ending outing. I have only recently aquired a late 90s Outrage with a 225 OX66 and I have had it out 10-12 times and I can't say enough about how much I like this engine My past experience has been with the 80-to early 90 era OMC Johnsons carb engines which have been great, but this is a big step up. The instant starting, less smoke, great gauges with real information that is helpful and that Yamaha binnicle mount is the smoothest feeling throttle I have ever had. I look under the hood and it looks quality, the hood itself is heavy and insulated well and fittings and castings look first rate. It is powerful and gets on to plane quickly. It seems like the best of the two stroke world back when things were simplier and less regulated. Raw two stroke power and light weight with the advantage of basic fuel injection over carburation. Clean, not really, quiet, a bit more than my older OMCs and great great performance. It has been such a postive engine and experiece(and the engine goes along way towards making the boat) makes me wonder if I should grab for that last new 225 OX66 225 at Eds for sale at 8k and just store it away for the eventual repower years ahead. It does sound like Yamaha is getting out of the two stroke market altogether. Too bad, they have done a good job. Onlyawhaler
ThomasT	posted 09-19-2013 09:23 AM ET (US) [Revived this six-year-old discussion to change the topic.]
jpgbu1	posted 09-26-2013 05:54 PM ET (US) I purchased a 1988 22 outrage with a OX66 250 on the transom from an estate sale in the spring of 2012. The boat was spotless and all it needed was a t-top and a trailer. (got both for 2.3K) the boat was 13K. I took a chance not being able to speak to the owners, as they had passed, but did speak to the marina maintaining the boat. They showed me records of maintenance from every year since the purchase of it new in 1999. The test run was flawless, and the outboard turned perfectly at 5600RPM. I got the boat home and while tinkering with the digital tach, found the hour gauge. It had 29 hours on it! I just pulled the boat to change the poppet valve and at 101 hours I still have 145PSI across the bank at WOT. not to shabby for a 14 year old motor. I think it still have 10-15 years left in her at the rate I am using it!!! It is by far the best running/performing outboard I have owned. And I have owned over 20 since I was a kid.
montauk madness	posted 09-26-2013 07:37 PM ET (US) I sure like my 200HP OX66 on my Outrage.
jimh	posted 09-26-2013 09:02 PM ET (US) As far as I can tell, the Yamaha Ox66 was the high point of classic two-stroke-cycle engine development, mainly due to the use of a modern, multi-sensor, closed-loop fuel injection system, something not seen in other two-stroke-cycle engines.