Oil Injection Removal -Yamaha 50hp - 2 Stroke - 3 Cylinder

[Johnny Reb]

I have been recently questioning the reliability and performance of the oil injection system on my 50hp. I have had the motor 12 years and am the original owner. It seems like it isn't using as much oil as it used to. As a result I have been adding some oil to my gas just in case. After reading Willyworm's Xpress project thread and seeing the pictures of his fabbed plate to cover the worm gear...it got me thinking about taking my oil injection system off.

Pro Tip Needed: Looking for one of you Shade Tree Yamaha Marine pros to walk me thru the removal process.

Is it as simple as Removing the tank, pump, and lines? Assuming you have to plug the ports on the carbs where the lines used to connect?

Also what are the Pros/Cons on leaving the gear in place and not putting a plate over it?

I searched for old threads covering this topic and could find anything with specific details.

Thanks for your help.

[turbo]

It is as simple as you stated. However, you MUST remove the drive gear and buy or build a plate to cover the opening.

There should be plenty of info via google should you still have any questions.

[Johnny Reb]

Did some googling on the interweb and goodlordhavemercy there are some differing opinions about the removal of the oil injection...

You guys that have done it...why did you do so as apposed to repairing/maintaining?

[turbo]

My 90 was built without it.

My 70 was not. I did not remove it. It failed.

It's easy to pull it off.

The only downside is disproportionate crankcase pressure on the bottom cylinder due to the increased volume caused by the removal of the drive mechanism.

Unless you're using the motor like Dale Jr. uses his car, it matters naught to you.

[mdb2]

Interesting subject. I have 1997 40 that is low hours, but I am worried to death about the oil injection

[turbo]

They don't all fail.

The ones that do, do so in spectacular fashion.

In my opinion, it's just too easy to mix your gas and not worry about it. It will, literally, take you less than an hour to remove the system.

[Waldo]

I always remove mine. Who do you trust more? Yourself knowing you added the correct amount of oil into the gas can or the little Jap kids that built and installed the pump 5, 10, or 20 years ago?

[scmoose]

Ive got an 05 50HP. To me its nice not having to worry about mixing, but yall got me wondering. Isnt there an alarm if the system fails?

[Mobetter]

Isnt there an alarm if the system fails?

The alarm sounds like an engine seizing up. And maybe some beeping.

[scmoose]

The alarm sounds like an engine seizing up. And maybe some beeping.

Point taken.

[turbo]

The alarm sounds like an engine seizing up. And maybe some beeping.

[huntinghagen#12]

I blew a 120 hp Evinrude about 8 years ago because of that issue. Every motor I've owned since has been hand mixed with the pump taken off.

[wdhigh]

Johnrudes are the exception, they should be taken off.

Yamaha and mercs are pretty damn good.

[Gone South]

One benefit to premix as opposed to oil injection is I feel that pre mixed gas doesn't go bad near as fast as plain gas sitting in the carbs.

[TKB]

All of mine I just scuff up the hole and fill it up with marine epoxy, very easy and dries quick.

[Gone South]

Johnrudes are the exception, they should be taken off the boat, scrapped, and replaced with a Yamaha.

Fixed it.

[wdhigh]

Haha. I was trying to be nice.

[willyworm]

Just removed mine and posted pics. It's easy.

[Turpentine]

My 90 was built without it.

My 70 was not. I did not remove it. It failed.

It's easy to pull it off.

The only downside is disproportionate crankcase pressure on the bottom cylinder due to the increased volume caused by the removal of the drive mechanism.

Unless you're using the motor like Dale Jr. uses his car, it matters naught to you.

I know this thread is old as dirt but I have a question. About how much compression do you lose on the bottom cylinder when you delete oil injection and oil drive parts. Both motors I've rebuilt seem to have anywhere from 7 to 9 psi loss. One is a 1986 50 that needs rebuilding again. It's tired. The other is a 2006 that I rebuilt and went with Wiseco 20 over pistons. Jeff Dunn did the machine work. Had to put a sleeve in the middle cylinder. Other two holes were egg shaped so he bored them 20 over. It's a strong motor. Runs very well. Compression is 133 top, 133 middle, 126 bottom

[Gone South]

Without making any other changes to the engine, ie: rebuilds, skimmed head, have you checked compression with and without the gear, back to back? Theoretically the motor only makes compression from the time the exhaust port closes till TDC, the worm gear is on the crankcase side therefore compression should not be directly affected. I’ve never been worried enough to split hairs on dynamic compression differences from individual crankcase volumes and the effect on the intake signal charge when removing the gear. Can reed plate design and flow per cylinder vary as well? Are all 3 boost and transfer ports equally matched from crankcase all the way to the sleeve?

If you want to dive deep, cranking compression is different than running and the pressure waves of a 2 stroke expansion chamber will act on each cylinder differently. Checking compression on a 4stroke you have to open the throttle or else you will notice a difference due to induction vacuum. A 2 stroke exhaust is always first to open and last to close, proving it draws air/gasses from the exhaust and will have a cylinder charging effect on pressure.

There can be other reasons for compression variance, egt’s from cyl 1 and 2 passing by 3 and absorbing more heat, coolant flow path hot spots, combustion temp vs ring seal, if it’s a machined head are all 3 chamber volumes equal? Yada yada yada

Short version: pretty much every cylinder on any engine will be slightly different, and engine to engine you will see a converging similarity. For example, watch individual egt’s on a v8 engine they will all be different, and compare to 3 identical engines and they will respectively mirror each other