Removing Oil Injection on '94 Sport Jet 90HP

[hckrphil]

I have a 94 Mercury sport jet 90hp engine that I'm going to rebuild myself (after the run in with the awful backyard mechanic that messed up the block).

Anyways, initially it needed a rebuild because it lost pressure in the middle cylinder.

The ring on the piston was broken. The engine has oil injection.

The reason the 2nd cylinder failed (I believe) is because the oil line shooting into that cylinder was plugged! I don't think it was properly being lubricated.

Now, if I wanted to remove oil injection from this engine, can I just pre-mix my gas, and remove all of the little rubber lines running around the engine? Or do those lines have another purpose?

I've unplugged it now, do you think I should KEEP the oil injection......... or just remove it and premix.

Once I get this engine all back together, I'd hate to have it fail again....

Thank you!
~Phil

 

[j_martin]

Re: Removing Oil Injection on '94 Sport Jet 90HP

I have a 94 Mercury sport jet 90hp engine that I'm going to rebuild myself (after the run in with the awful backyard mechanic that messed up the block).

Anyways, initially it needed a rebuild because it lost pressure in the middle cylinder.

The ring on the piston was broken. The engine has oil injection.

The reason the 2nd cylinder failed (I believe) is because the oil line shooting into that cylinder was plugged! I don't think it was properly being lubricated.

Now, if I wanted to remove oil injection from this engine, can I just pre-mix my gas, and remove all of the little rubber lines running around the engine? Or do those lines have another purpose?

I've unplugged it now, do you think I should KEEP the oil injection......... or just remove it and premix.

Once I get this engine all back together, I'd hate to have it fail again....

Thank you!
~Phil

The oil is injected into the fuel, just as if it was pre-mixed. The difference is that it turns down the amount of oil at low speeds and limits the smoke and carbon build up.

The little lines are called bleed lines. They take excess fuel puddled up at the reed blocks and let it go into the opposite cylinder. If it's plugged, it can cause a little flooding at the associated reed block, usually messing up idle, but has little other effect. The bleed lines are not oil injection lines. They need to be on the engine.

You have other problems, such as a missing ring gap locater pin. I suggest you get a copy of the factory service manual, and read it until you understand it before you tackle this engine.

hope it helps
John

 

[hckrphil]

Re: Removing Oil Injection on '94 Sport Jet 90HP

Yuppers. I got the manual........ Also bought a manual. The manual I downloaded free (in PDF format) is amazing....... the one I bought leaves a lot of steps out.......

I have the oil injection plug and cap to get rid of the oil injection....... but do you recommend just leaving the oil injection in place?

I'm trying to find a place that will bore my block out and not rip me a new one.

So far I found a place in NC that will bore my block and exchange my pistons for me for $300. Does that seem ok?

 

[j_martin]

Re: Removing Oil Injection on '94 Sport Jet 90HP

Yuppers. I got the manual........ Also bought a manual. The manual I downloaded free (in PDF format) is amazing....... the one I bought leaves a lot of steps out.......

I have the oil injection plug and cap to get rid of the oil injection....... but do you recommend just leaving the oil injection in place?

I'm trying to find a place that will bore my block out and not rip me a new one.

So far I found a place in NC that will bore my block and exchange my pistons for me for $300. Does that seem ok?

The oil injection, I believe, is driven by a plastic gear on the crank. As long as the engine runs 6500 rpm or lower, and is not grossly overheated, they last a long time. If they go, you have to tear down the engine to fix it. I run mine on an XR4, but I cover my butt a little by mixing about 1 ounce of oil per gallon of gas in the tank. That'll get me back to the landing with a total failure of the injection at 25 knots or so. It also gives me about a 40:1 mix at WOT, which I can use because it's running pretty hard at that point.

Oil injection is pretty idiot proof. I've seen old timers that know better have a brain fart and forget to oil their gas, and wreck the motor. One time is all it takes. It's a long, continuous running debate as to premix or inject.

300 bucks for 3 holes is pretty cheap. Just be sure the shop is a marine engine shop, not an automotive shop that thinks they can do it. There's more to it than punching out an automotive 4 cycle engine.

hope it helps
John

 

[rndn]

Re: Removing Oil Injection on '94 Sport Jet 90HP

300 seems cheap. Is the work guaranteed? Leave the oil injection in place.

 

[Dale002]

Re: Removing Oil Injection on '94 Sport Jet 90HP

I rebuilt a 90HP a couple of years ago for the same reason as yours. the #2 piston had broken rings. i only went over size on two of the cylinders and standard on the other. No problems yet. I also deactivated the oil pump.
I just disconnected the control rod from the throttle linkage and mixed the oil when I added fuel again no problems. I had the machine shop at NAPA do my cylinders but he had done marine 2 strokes before. I was charged 40 bucks per each cylinder that was bored and 20 for the one that got honed,got it back ready to install pistons. If you haven't installed the egine check the impeller and housing in case it may need some work. it's better to fix it now than when the engine is installed as the engine would have to come back out. Also make sure the temp. sensor is installed in the head as it's almost impossible to installed with the engine in the boat. What type of manual did you download for free? do you have a site where I can take a look at it. I can use a new one. If you have any question with your boat email me @ dizdale@yahoo.com I be more than happy to help with any info you may need.
By the way,this boats are alot of fun!!!

 

[boattech]

Re: Removing Oil Injection on '94 Sport Jet 90HP

$300 isnt horrible for borring. I usually pay $50 per hole though. but you said somehting about changing out your pistons?
As for the oil injection. the final decision has to be yours. Ive been rebuilding engines for 15 years and most of them are do to a oil injection failure. I recomend to every customer that comes in my door to remover the oil injection once the motor is 10 years old. despite what some people say about the safty of oil injection it is far from safe. most things that go wrong with the oil injection systems out there dont have warning horns. your warning horn is when the motor seizes and your wake splashes you in the back of the head! HEHE! No question especially with your 3 cyl. deoil it! also the three and four cylinder mercury big bores like yours have a bad reputation for being succesfully rebuilt. they tend to blow with no obvious reason sometimes. I would recomend you look very closely at everything to determine what happened.