ox66 or not?

[dannyD]

Hi, I am trying to figure out if I have an ox66. I have a 2000 Yamaha sx200txrx saltwater series 2 and it looks exactly like the ox66 when the cover is off, but I'd like to know for sure. Where do I look for this info? On the ID plate it says: 666 x 001546 u. Does that help any?

The other question is, does this engine shut down cylinders when under a certain rpm? I'm chasing a rough idle and a rough engine until I'm at higher rpms, then it runs great.

And lastly, when I did a compression check, all cylinders were at or close to 95. I really thought about a rebuild but before spending the money thought I'd ask the pros.

Thanks

 

[seasick]

Yes its an OX66, one of the most reliable motors made.

That motor does shut down 2 cylinders at low revs. I don't remember which 2 though but one is definitely not cylinder #1 which feeds the oxygen sensor.

That motor may idle a bit rough when cold but in general shouldn't be super rough. It will run rougher if out of the water on muffs.

The rough idle can be a lot of things, some easy to check and others not so easy. If this motor is new to you, replace the plugs before anything else. They are not expensive. Take a look at the plug boots. There is a test method to check their resistance. It's in the service manual which you should have if you plan on doing some maintenance yourself.
I am surprised by your compression test though. Did you do it yourself? The reason I ask is that the compression ratio is different for two cylinders and therefore the compression on those cylinders should be a bit lower than the other four.

I would run it till it dies or becomes unreliable. It doesn't make sense to 'rebuild' a 20 year old motor. There are too many things that wear our over time that you will still have to repair/replace from normal usage and many of those are pretty expensive.

 

[dannyD]

Thank you. I am new to outboards. Seems like here in Florida thats the way to go. In Virginia I've always had stern drives. So I have been doing everything I can to maintain this engine. So Far I changed the fuel water separator, the fuel filter, the low pressure fuel pumps (2), gear oil twice (because it was milky the first time due to a missing washer on the top vent plug) and changed the plugs. The plugs were oily and even after I checked the new plugs, I assumed because it's a 2 stroke.

I bought a cheap amazon prime gauge and tested the cylinder pressure with that. My plan was to try and find a reputable yamaha mechanic in Daytona area or within reasonable distance to check everything out, but there are so many fly-by-night backyard mechanics here and they all say "certified"..lol I want to make sure I am not stranded.

Thanks

 

[seasick]

If you don't know the maintenance history, there are things that may need changing like the water pump and thermostats.
Regarding the oily plugs, first of all make sure it's oil and not gas. If oil, you may want to check the oil pump linkage adjustment. If out of whack or if the retainer pops, maximum oil will pump at all time. Normally the oil amount is regulated by throttle position.

After a few hours of use, maybe 10 or so, I would check the lower unit oil again for water. You don't have to drain a lot of oil, just a sample but it should be done after running the motor and gears a bit so that any water will get churned up and turn the oil milky. I understand what you said about the missing gasket, but I am not so sure that was the issue. Down the road, a pressure/vacuum test may be in order to check lower unit seals. Also, next time the boat is on land, pull the prop and check the main shaft for leaks ( you need to remove the prop to do the pressure test correctly. Home Depot usually carries the stainless steel cotter pins that fit that main shaft. Although 5/32 by 1 1/4 is ideal, HD carries 5/32 by 1 1/2 I think. They work fine and are low priced for a pack of three.
Two recommendations I can offer are that the Yamaha motor doesn't like in general to reuse gaskets. There are some places where you can get away with reusing a relatively new gasket but not many. Secondly, since you are new to the motor, don't try to disassemble the O2 sensor or the VST tank. Those parts can be damaged easily and are really expensive. Later you may need to get into them but not now.
As I mentioned earlier, a service manual is mandatory. The original factory manual is quite good but hard to find and can be expensive.
If you post your email address or send it to me in a private message on this forum, I can try to send you an electronic version of a service manual. It is a large file and your email may not like that. You can print out the sections you need.

 

[Parthery]

I thought only the 76 degree V6s (225 and 250 OX66) dropped a cylinder at idle but I could be wrong.

I'd replace the plugs (not expensive)...replace the low pressure fuel pumps (also not terribly expensive) and see if that smoothes it out. The fact that it runs well at higher RPMs leads me to believe that you don't have an issue with the injectors.

Use Pennzoil XLF for oil....$18/gallon at Walmart or Academy. Use Ring Free and either Sta-Bil or PRI-G in your fuel, and go enjoy it. They are great engines.

 

[Family Tradition Fishing]

Not sure how far you want to travel but Mike Manier in Jacksonville is an excellent Yamaha mechanic. He's been doing all my work aince I've owned my Marlin. Morning Star Marina Mayport Fl. 9048383743

 

[SkunkBoat]

I have a few recent posts about my ox66s. Do a Tag Search for "ox66"

 

[Paul_A]

I've owned several Yamaha 2 strokes and do my own work up to rebuilding. If it's running well with decent fuel economy that 95 a cylinder is no problem. 110 would be better, more normal but the gauge and the method can affect the reading so no worries.

Make sure it's propped so it can hit max rpm and be sure to let it eat at least a few minutes every trip. Great motor.

 

[dannyD]

Not sure how far you want to travel but Mike Manier in Jacksonville is an excellent Yamaha mechanic. He's been doing all my work aince I've owned my Marlin. Morning Star Marina Mayport Fl. 9048383743

Thanks
Family Tradition Fishing, I'm only an hour and couple minutes from them, I'll look into it. I'd like to do this before the ocean calms down so I can experience what everyone talks about as far as fishing.

 

[dannyD]

Thanks everyone for all the information. I feel more at ease and I will get that manual and start learning this motor. Ever since my navy days walking around with PMS cards, I've always been on top of maintenance, and the thought of waiting for USTowBoat to pick me up 20 miles out scares me.. So I'm going to get it checked out.

Thanks

 

[gw204]

95 psi is low for that engine. If I remember correctly, a 225/250 ox66 should be more like 115/120. Check your compression again or have your mechanic do that first before you start throwing money at it.

 

[SkunkBoat]

95 psi is low for that engine. If I remember correctly, a 225/250 ox66 should be more like 115/120. Check your compression again or have your mechanic do that first before you start throwing money at it.

I'm no gear head but I did stay at a Holiday Inn Express...
so...
My 225s (both of them) read 90 give or take one or two ( the bottom 2 cylinders lowest, as expected)
Engines had been fired a few times but were not hot. You will get a different range of readings depending on temperature and throttle position....and gauge calibration.
90's is fine.
Readings all the same is the main point. They can't all go bad exactly the same...

 

[Lite Tackle]

I just performed a compression test on the 225 OX66 I am selling. Ran motor 10 minutes and then checked compression on each cylinder with throttle closed. Got 125 -130 across the board. I was surprised and buyer was pleased. The winky blinky cable is invaluable if you plan to maintain and repair motor yourself.

 

[Bdsp1234]

Hi, I am trying to figure out if I have an ox66. I have a 2000 Yamaha sx200txrx saltwater series 2 and it looks exactly like the ox66 when the cover is off, but I'd like to know for sure. Where do I look for this info? On the ID plate it says: 666 x 001546 u. Does that help any?

The other question is, does this engine shut down cylinders when under a certain rpm? I'm chasing a rough idle and a rough engine until I'm at higher rpms, then it runs great.

And lastly, when I did a compression check, all cylinders were at or close to 95. I really thought about a rebuild but before spending the money thought I'd ask the pros.

Thanks

The rough idle you are referring to takes place at about 1800 to 2200 rpm. Yamaha designed this to run only four cylinders as a fuel saver while trolling. Between 1800 and 2200 is when it transition up to all 6 cylinders. A Yamaha tech will tell you that the TPS switch is back or out of tune. Don’t bother paying for repair. It will go out on you very shortly after repair. I had a 250 ox66 for ten years. Very thirsty on fuel and oil, but still the best motor I’ve ever run.

Btw. If you throttle up hard you won’t even notice it. It’s at slow throttle up you feel the hesitation.

 

[Harpoon]

great motors. I ran one for years.

Plugs
Low Pressure Fuel Pumps
Thermostats
Clean O2 sensor
Fuel Filters
Water Pump
Gear Oil
Grease

Beyond that if you have any fuel problems check/clean the screen in the VST tank
Another common item was overheating because poppit valve gets dirty/stuck.

Best 2 stoke ever built.

 

[glacierbaze]

Lite Tackle, why check compression with the throttle closed? I always heard fully open, for max air flow.

My old 200(Not OX66) usede to foul plugs, and run rough at idle. Switching from Yamalube to the Pennzoil semi-synthetic seem to have cured that.

 

[Lite Tackle]

Lite Tackle, why check compression with the throttle closed? I always heard fully open, for max air flow..

I thought it was open but my buddy turning motor over was playing with the controls and I didn’t realize it until we were done. I was real happy with the results and didn’t feel the need to recheck.

 

[glacierbaze]

Remember not to have him assist in diagnosing any problems with the motor running, and the prop on!

 

[Lite Tackle]

Remember not to have him assist in diagnosing any problems with the motor running, and the prop on!

Lol

 

[seasick]

I thought it was open but my buddy turning motor over was playing with the controls and I didn’t realize it until we were done. I was real happy with the results and didn’t feel the need to recheck.

I don't think that for older 2 strokes, the throttle open vs closed makes that much difference.
95 psi compression is not really low either. The compression ration for that motor is only 6.4. The cylinders with a bit lower compression (6.1) are the bottom ones; 6 and 3.