Oil Injection Caution !!

[Dennis]

HI,
This is probably the wrong place to post this but Louis talking about RFI and DI terninology reminded me of something. Often in the forum advice is given on how to correctly do away with the oil injection and go to premix. We must keep in mind when giving out this advice that you CANNOT do away with the oil injection system on the 787 RFI or the 951 DI engines because the oil systems are different on these engines and doing so will ruin the engine.

Thanks, Dennis

 

[seadoosnipe]

O.K......

Thanks for the input Dennis. I have never really given advice to remove the injection system but have relayed information from people who have done this to people who want to do this. If you read the queries on this topic, the people looking to remove their injection system are from Doo's of the early 1990's. Normally the naturally aspirated 787, 717, 657 and the 587cc engines. Myself, I still use the injection system and support it be maintained mostly because the boats value is better retained if you keep everything in it's original configuration.
You have brought up a good point that I really haven't researched but with the comment, plan to.
For those who have read my posts on this issue and may have the fuel injected engines, please refrain from choosing to block off your injection system to start premix until further notice. I will research this and re-post at my earliest convenience.
Thanks again for your input!....it's a very good point that deserves a second look. :cheers:

 

[seadoosnipe]

Research complete!

O.K. Dennis, I gave this topic a second look and for the moment, I will concure with you about the idea of premix in the RFI and DI engines. Not because I don't think it can be done but because there is the possibility of an incorrect sensor reading and changes that could be made by the ECU/ECM. In the newer engines, the Engine Control Management system uses a host of sensors to determine how the engine is performing and will make changes as needed. For instance, when you first start your motor, or during the colder parts of the season, the ECM will send signals to increase the fuel/air ratio to compensate for the denser air temperatures for optimum combustion. If you change to premix, the oil in the fuel could cause a fault in the sensor input, thus creating the possibility of engine damage.
Therefore, I will agree with your comments about the idea of users with RFI or DI engines, to not use the premix in their ski's.
Most, if not all, the requests so far from members who are looking to change over to premix are the 1998 and earlier year models with the 787 engine and smaller. I've not seen anyone with the 787 RFI or 947 engine ask this question.
Thanks again for bringing that point up!....I think it was a very important observation that I for one, didn't think of. Thanks again "Dawg"......:cheers:

 

[Dennis]

Oil Injection

Hi SEADOOSNIPE
Your advice on this subject has always been correct and my post was never meant to suggest otherwise. My reason for not premixing the 951 DI is because the air compressor for the fuel injection system has an oil line going to it from the oil injection pump. To do away with the oil injection pump would leave the air compressor without lubrication and it would surely fail and probably cause crankcase damage.
My reason for the 787 RFI (unlike carbureted models) if you remove the oil injection pump there will be no lubrication for the rotary valve that's spinning under the intake cover that the oil injection lines went to. The only things that would be lubricated by the premix would be the crank and pistons because of how the premix enters the engine.
Now that you thought of it, I'd bet money your right about premix having a bad effect on the MPEM sensors, air/fuel ratio, etc.
DAWG

 

[seadoosnipe]

Kudo's

The input for the RFI and DI engines is well warranted. You are one of only a few who have a compressor system for the DI engine that actually works!.......
There have been a few post of people with bad experiences with the compressor system. Although I have done research on this system, I didn’t go deep enough into the lubrication aspects.
As for the RFI, or any Rotax that uses the Rotary valve and chamber, I have posted several replies about doing away with the oil injection system but always adamant the tank remain, due to the lubrication of the rotary shaft. The shaft is between the two pistons and is filled with oil. There is an oil seal on each side that prevents this oil from bleeding into the compression side. The rotary valve itself is lubricated by the oil injection behind the carbs. The valve will get sufficient lubrication from the premix. If you have the newer model RFI engine (2000 and above), I would be concerned more so about the inputs from the sensors to the ECU as stated in my earlier post.
I appreciate your vote of support in my advice but I always give credit where credit is due. I honestly never gave much thought to the change in sensor input, which would obviously be created with the change in the fuels specific gravity and the difference to thermal changes the mixed oil would create.:cheers:

 

[seadoosnipe]

Oil injection or premix has been a big topic in the forum for quite some time. Whether it's better or not better, depends on who's doing it on what and why you want to......in other words, it's preference.
Dennis and I have been going back and forth with each other in PM and forum post about the pro's and con's on doing away with the injector pump and going to premix. He has made an observation on a specific type of Seadoo engine that I have just been made aware of and I think it warrants users to be aware of this issue. DO NOT ATTEMPT TO DO PREMIX IN THE RFI 787! Without any further research at the moment, I'd also recommend that if your engine runs a fuel injection system, either direct or rotax, this should apply. Rather than explain this, I've copied a PM from Dennis, who is one of our Premium members (and a mechanically smart one at that), who has explained his reason why we shouldn't and I totally agree with his theory. The below is his message to me. Thanks for the valuable insight Dennis!

I'm going to try to explain the problem that occurs if you try to premix a 787RFI. Keep in mind that I totally understand that the rotary gear and shaft still have to have oil and that is why the oil tank (with oil in it)is left in place, so that the rotary shaft and gear, that are inside the cases, still have lubrication. The problem I'm refering to occurs outside the cases at the rotary valve itself. Also keep in mind that a carbureted 787 will NOT experience this problem. Only the RFI 787 will because ,when on premix, the rotary valve (on the outside of the cases) that is being spun by the rotary shaft and gear (inside the cases) will no longer have lubrication because of where the premix enters the engine. With a carb 787 the rotary valve, rotary valve cover, intake manifold and carbs are on the right hand side of the engine. Air and premix(gas and oil) leave the carbs, go thru the intake manifold and rotary valve cover (where the oil injection lines used to be connected) then by the rotary valve (which is spinning in order to time when the air and premix enter the engine) and finally into the engine. The spinning rotary valve is being lubricated by the premix and therefore is not a problem. The problem you run into on the 787RFI is that the premix is not entering on the right side of the engine(where the spinning rotary valve is). The premix is entering on the left hand side of the engine because that is where the fuel injectors are located. This leaves the rotary valve with no lubrication because the only thing going by it as it spins is air from the throttle body(no premix and the oil injection lines have been disconnected). Needless to say the non-lubricated, spinning rotary valve eventually grinds it's way into the cases and ruins the engine.

If I could Dennis, I would have taken credit for this but that's not my nature. I think this was a very good observation and you should get all the credit for writing it. Very informative and I hope those looking to go premix read this post. I fully understand now what we were talking about in PM's. I'm not much into the fuel injection engines but I'm glad we have members in the forum who are!............Good job "Dawg"!........:cheers:
Louis

 

[kustomkarl]

It's a group effort here!

I agree Dennis, Good job on the observation. That's why this is a public forum and not just a one man show. It would be impossible for one person to have every bit of information to cover every seadoo year and model.This place is about a group effort to help solve problems and have answers to issues that arise. Thanks Dennis and seadoosnipe for your reasearch and inputs on this important subject! I'm sure it will help me and other members as well in the future...:hurray: :cheers:
Karl

 

[Dennis]

Kudos

Thanks for the kind words you guys but as my dad used to say "even a blind squirl can find a nut sometimes! LOL

DAWG