OMC Cobra SX

[spartanpele]

Greetings,<br /><br />I'm looking at buying a 1994 Four Winns, 17ft (Freedom), and it has a 135hp OMC Cobra SX.<br /><br />Can anyone give me some insight into if this engine setup is reliable?<br /><br />What kinds of things should I be looking at besides the normal: hear it run, check plugs, look for leaks, wear & tear. I know car engines pretty well...can I look at this engine like I'm looking at a car engine? What about engaging the drive (can I call it a transmission?). I'm planning on bringing muffs and a tub for testing. <br /><br />I've been an outboard person all my life and this is my first venture into the I/O's. Any help you guys can provide is greatly appreciated!<br /><br />Thanks!!

 

[rodbolt]

Re: OMC Cobra SX

DO NOT TUB TEST IT<br /> the muffs are ok<br /> check the color and condition of the drive oil. be aware of the seal failure problem on the prop shaft. in fact if it has not been done have the updated seal installed with the new tool. all the old style seals failed some failed many times. check the records for gimbal bellows and bearing replacements. the bellows needs to be replaced at 3 year intravals. the SX was a solid unit barring the seal failure problem. also replace the seawater pump if not done recently. my experience shows that after about 3 impellers the pump seals are normally shot and leaking. the best advice I can give is to forget anything you ever knew about a car. while its all similar its a completly different animal operating under completly different conditions. pull the drive and check the coupler alighnment. a coupler is close to 300 dollars sitting on the counter. while the drive is off check for any roughness in the gimbal bearing and replace the bellows. I also reccomend a water test<br /> it should idle almost smooth. all the 3.0 motors are some rough. should accelerate fairly smooth and turn to about 4400 RPM with no major problems. but forget the tub thing<br /> all you will manage to do with the tub is melt the impeller<br /> also check the circulating pump weep hole. they tend to leak.

 

[spartanpele]

Re: OMC Cobra SX

rod...thanks for the info!<br /><br />I know that taking it out on the lake would be the best situation, but if thats not possible, then I can bring my muffs and skip the tub.<br /><br />In looking over your comments, (forgive my naivity as I'm thinking outboard-2 strokes), when you're talking about the drive oil, are you talking about the lower unit oil? On my old outboard I have a drain plug at the bottom of the skeg...on the I/O, is it the same? I know with the outboard l/us, if the seals are bad the water gets in and the oil turns milky and discolored...same situation with I/Os?<br /><br />You mentioned pulling the drive off (check the coupler, gimbal bearing, bellows)... is that something I can do right there in their driveway, or is this a suggestion for after its bought?<br /><br />The circulating pump weep hole...where and what is that?<br /><br />The seawater pump... same question...isn't that the water pump (with the impeller inside) and something that can only be checked if the drive/lu is pulled? Or are suggesting it for maintenance after its bought? <br /><br />When using muffs...the water will flow through with pressure anyways, regardless of whether the impeller/water pump is working... correct? I know with the tub the pee hole will have water coming out as proof of the water pump working correctly...but with muffs, thats not possible..or do I just assume that if water is coming out the pee hole that everything is fine?<br /><br />With using muffs on an outboard its not recommended to rev the rpms too high... is it the same thought on I/O's?

 

[texsun]

Re: OMC Cobra SX

Before I'd pay any $$ I'd want to check the crankcase oil for color and smell, lower the drive in the driveway and remove the dipstick(should be at the top of the drive-9/16 nut maybe) look at the fluid level on the stick & rub the fluid between your fingers checking for metal and making sure it's not milky. Look at the prop and skeg(that big blade beneath & in front of the prop) for nicks/dings.<br />Put the muffs on and turn on the water about half force- make sure the muffs are in proper position before you attempt to start. Start the engine and run it at about a fast idle 1500rpms 'til it comes up to operating temp 170 Degrees. If temp passes 170 & approaches 185 I'd be suspect. Now go to idle. Should idle @ about between 750-1000rpms. <br />Now, if it passes those test - go to the lake. Now you're ready to check shifting and drive. At operating temp 170 you should be able to move into both gears and come back to neutral smoothly. You should be able to throttle up in forward and also reverse. Take it easy in reverse. Now your ready to check out acceleration & wide open throttle performance. Put it in gear and accelerate to about 4000 for about 3 minutes, keeping constant look at the temp gauge. Temp should be able to maintain 170 or so. Bring it back to idle and it should idle. You may be able to tell the temp is important indicator for the overall condition of the engine itself.<br />Ask the owner if he's done any service on it. <br />The people on this forum have helped me tremendously and I hope this helps you.<br /><br />Good Luck!<br />Mark

 

[Robar]

Re: OMC Cobra SX

Why not tub test? I saw your mention of not tub testing, and wonder why. I am replacing seals/impeller etc. on a Cobra, and was going to run it in a large tub to check water flow from the impeller to the engine. Any problem with this procedure?

 

[rodbolt]

Re: OMC Cobra SX

problem with the tub test is not all the holes in the pump drains are covered and at engine start most the tub water dissapears somehow . if you use muffs turn the hose wide open. you need all the water you can get. the circ pump has weep holes just like a car does. only with water dribbling it will cause major headaches elsewhere such as rusting holes in the timing cover. no need to take it easy in any gear. in fact easy shifting tears up as many drives as stumps and rocks. shift firmly and quickly. dont try to ease it in. the SX is a cone clutch and if the oil level is correct will slip into gear with a barly audible thump. if over full it may cause a delayed engaagement. the SX has no pump in the drive. its either a belt driven pump on the engine or a crankshaft mounted pump. all the 3.0 motors that I know of use a belt driven pump in the i/o application. at 1500 rpm if you have a good set of muffs there is a good chance that it will suck the hose flat if the seawater pump is in good shape. it should idle about 700-750 rpm and no higher. keep it about 1000-1100 for warm up a bit then let it idle<br /> without a seatrail your buying blind. dont do it.<br /> or at least pay a professional mechanical surveyor to test it.<br /> Robar<br /> DO NOT TUB TEST YOUR COBRA<br /> tub testing a cobra usually melts the impeller as it will suck air instead of water from the pump vent/drains. use the muffs or back it overboard.

 

[Lou C]

Re: OMC Cobra SX

You'd be amazed how fast one of those inboards sucks up water with a good impeller, I use the better muffs with the dual inlets with a 3/4 diameter water hose and it will run nice and cool at idle on the muffs as long as you want. Best test would be to back it in the water to submerge the lower unit that way you know for sure it is pulling up enough water.

 

[Robar]

Re: OMC Cobra SX

When I refer to "tub test", I have a water trough that totally submerges the drive, and has 75-100 gallons of water in it - its probably 5 feet long, 2 ft. high, and 18" wide. Bought it at a farm supply place, and it fits under the drive just right. <br /><br />I don't see how testing in a tank this size can be bad. I would keep the hose running to add water, and possibly fill the block before starting. I think just starting it and shutting it back down to refill the initial draw should work fine.

 

[Lou C]

Re: OMC Cobra SX

I guess the issue is can your hose deliver water to the tub as fast (preferably faster!) than the engine sucks it up, so the level does not drop below the top of the water intakes. With the muffs as long as they fit right and you have good pressure you will not have a problem running it at idle speed.

 

[Robar]

Re: OMC Cobra SX

Its probably got to suck up 50 gallons of water before it drops to the intakes - its a big tank. I would also stop after a few seconds to top it off after it fills the system. <br /><br />I have a set of muffs, and they seem to fit like crap - lots of back pressure = spraying water all around the perimiter of the muffs. <br /><br />I'll try the tank and let everyone know how it works out.

 

[Lou C]

Re: OMC Cobra SX

Get the dual inlet Tempo ones, they are expensive but worth it (~$30 or so) will save your impeller!<br />And pretty much all muffs will spray out until the motor starts then it will suck it in and you shouldn't see spraying.