Oil injection system failures in modern 2-strokes

[dandreye]

What hp engines were those plastic gears used ?

In fact my 2001 90hp (90ELPTO) appears to be one of those - it's the master gear that sits on the crank right next to the bearing (only the driven one is metal):
https://s26.postimg.org/i65h38hix/43...ction_Gear.jpg

Is anyone aware of any particular reasons other than weight/cost saving why Mercury decided to make it plastic and not metal? If not are there any risks from replacing it with a bespoke metal version (unless Mercury makes metal ones these days)? Just feeling unsafe about any plastic part inside cylinder block, especially when it comes to such critical components. I'm obviously nowhere near Mercury's knowledge and experience at it all and really hope the plastic one is there for a reason.

 

[Faztbullet]

The oil system is bottom gear driven and rarely fails. That why there is no rotational sensor to monitor it like the V-6 motors(center driven). On these motors the only problems are float in oil tank coming lose and oil /temp modules failures(beep all time)

 

[dandreye]

Yeah I understand from all the responses above that it's quite reliable even as is.

The powerhead was last taken apart almost 10 years ago (very low hours since then though) and nothing bad was reported about that gear back then, hope it's still allright...

 

[QBhoy]

Like many have said...some of the oil delivery failures can be put down to lack of maintenance and inspection.
That said...certain engines are known to be weaker than others.
Yours is known to be one of the stronger more reliable systems. So is that of the Merc 3 cylinder engines.

One to watch out for are the big 90's Merc v6 variants. These are known to fail. I can testify to this, I'm afraid.

 

[dandreye]

Like many have said...some of the oil delivery failures can be put down to lack of maintenance and inspection.

Is there a way to check that plastic gear on the crank w/o taking the powerhead apart? (I guess the answer depends on whether the driven gear (the long metal one) can be pulled out of the powerhead after removing the oil pump) Everything else I've been visually checking every spring already.

 

[jimmbo]

You seem so worried about the system weakness you keep looking for problems. Well, you can do a few things. 1) Disable the injection system, mix the oil in to the gas. Then you can worry about if you mixed it correctly, and that the mix is consistent through the entire tank. 2) Get rid of the motor and your worries are over.

 

[Silvertip]

Forget about the temp gauges as those with the thermo-couple under the spark plug are unreliable. Instead of overthinking this put a good water-pressure gauge in and go boating. Unless you are constantly watching the gauges how will you know it overheats before it's to late. If the motor runs out of oil it or runs lean on oil that gauge will tell you nothing. And If your motor runs out of oil or runs lean you are screwed before that gauge will tell you anything. Normal temp at the plug will be higher because the plug is not cooled by the water jacket.

​A water pressure gauge is no guarantee an engine is not overheating. It merely tells you the pump is working. Gauges are quite reliable and along with the horn should provide as much warning as one needs. Ignore them and what they are warning you about then becomes expensive. Temp gauge AND water pressure were are always used on my boats.

 

[dandreye]

jimmbo:

I already did my best explaining the reason why my attention to any potential points of failure is well above average. The OB is fine as is, at least I like it much more than this contemporary 4-stroke stuff with connecting rods breaking through the crankcase now and then and the makers blaming the owners for things like stopping abruptly and triggering a hydrolock via exhaust, just as one of a few examples of great engineering work being beta tested by customers around the world (often at their own expense).

Anyway... I suppose there's no way to check that plastic gear on the crank w/o taking the powerhead apart, right?


Silvertip:

I'll likely end up adding Faria 13821 water pressure gauge then (assuming the standard high temp buzz in remote control counts as a temp gauge). The reason I was initially thinking about thermo-couples under spark plugs was to notice temperature rise early and regardless of the root cause, be it a shortage of water or a shortage of oil (I hear it can run w/o oil several minutes before locking up) - but what's the point if they're unreliable.

 

[flyingscott]

​A water pressure gauge is no guarantee an engine is not overheating. It merely tells you the pump is working. Gauges are quite reliable and along with the horn should provide as much warning as one needs. Ignore them and what they are warning you about then becomes expensive. Temp gauge AND water pressure were are always used on my boats.

Actually if you look at what I said was the gauges with the sensor under the spark plug are unreliable. The ones with the externally mounted sensor are fine but water pressure gauge as far as I am concerned are better. Cars come with temp gauges look how many of those overheat every year. Unless you are watching it regularly it won't matter if it overheats. If you are pulling a skier or tubing it's impossible to watch a temp gauge enough.

 

[dandreye]

The ones with the externally mounted sensor are fine

Do you mean those mounted under a bolt somewhere nearby or something entirely different? Just trying to imagine what they're like.

A water pressure gauge with a low pressure buzzer (or even a buzzer alone instead of the gauge) would be ideal I suppose.

 

[flyingscott]

Yes the sensor that gets held down by a bolt, the ones under the spark plug fail quite a bit. They also cause problems because they can cause the spark plug not seat correctly.

 

[dandreye]

Yes the sensor that gets held down by a bolt, the ones under the spark plug fail quite a bit. They also cause problems because they can cause the spark plug not seat correctly.

Looks like such senders are part of the Faria CHT kits, e.g.:
- FAR13829 Cyl Head Temp 20?-100?C & SENDER
- FAR13806 Cyl Head Temp 60?-220?F & SENDER

 

[racerone]

Remove the oil pump.----Remove the metal " driven " gear.---Look at the plastic gear through the hole.----Rotate crank to inspect entire gear.

 

[dandreye]

Remove the oil pump.----Remove the metal " driven " gear.---Look at the plastic gear through the hole.----Rotate crank to inspect entire gear.

Spot on - thank you: just noticed it sits in adaptor 17335A3 and so likely comes out along with it.


Key takeways from the thread:

- Depending on the OB model the oil injection drive gear sitting on the crank may be plastic rather than metal, in which case it can melt in case of overheating, adversely affecting oil injection system operation and possibly triggering a lock up. As a result it pays to have it checked occasionally, at least following any suspected overheating. It can be visually checked by means of removing the oil pump / adapter / driven gear altogether, exposing the drive gear through the hole.

- a CHT gauge with a sender mounted under a bolt near the spark plugs + a water pressure gauge (besides standard buzzer in remote control) can help prevent overheating in cases like cooling water intake clogging or impeller failure or restricted oil supply.

Many thanks to everyone for your valuable input.