Yamaha 9.9 4T oil consumption

[pakostane]

Hi,

I bought may used boat 5 months ago. I got yamaha 9,9 4T 2004g with them. I notice abnormal oil consuption. In cca 10h it spent 0.5L of oil. I think that it is not normal oil consuption. In smoke I can smell a little bit of burnt oil. Is it problem of piston ringd or oil seal on valves? Other things is perfect on engine except that oil consuption.

[rodbolt17]

have you done a leak down test?

[pakostane]

No, I do not have gauge for that test. Engine have a perfect cold and warm start.

[pakostane]

I open yellow plug for oil on cylinder head. I can feel some presuure on hole. I know that is normal on one cylinder 4 stroke engine. On cars four cylinder engine that is not normal. How is it on two cylinder 4 stroke engine?

[boscoe99]

I open yellow plug for oil on cylinder head. I can feel some presuure on hole. I know that is normal on one cylinder 4 stroke engine. On cars four cylinder engine that is not normal. How is it on two cylinder 4 stroke engine?

Almost any pressure that can be felt coming out of the oil fill port indicates to me that there might be excessive "blow by". This means perhaps that the piston rings are not sealing as effectively as they should.

There should be a hose that runs from valve cover to the intake manifold. Some T9.9's may have an air/oil separator installed between sections of the hose. Remove the hose and check for the presence of excess oil or other contamination. That is also an indicator or excessive "blow by".

If air can get across the piston rings then so too can oil cross the piston rings and get into the combustion chamber, resulting in excessive oil consumption. A leak down test can quickly confirm if the piston rings are leaking excessively or not. If you don't have a leak down tester maybe find another way to provide air pressure to a cylinder via the spark plug hole. Put the piston at top dead center on the compression stroke. Add about 50 psi or so of air. Keep the motor from turning. Remove the oil fill cap and put your ear near the hole. If you hear a lot of hissing that indicates the piston rings are leaking.

In the meantime, you can try to decarbon the engine. Also, possibly shifting to a heavier weight oil can mitigate (but won't solve) the problem. If this is the problem.

[pakostane]

There should be a hose that runs from valve cover to the intake manifold. Some T9.9's may have an air/oil separator installed between sections of the hose. Remove the hose and check for the presence of excess oil or other contamination. That is also an indicator or excessive "blow by".

My F9,9 CMHL doen not have oil separaor. I already checked that hose but in intake manifold I can not find some oil. On that hose no smoke and no pressure in working. My engine has CMHL label. I can not find that label on purchase yamaha parts page.

[boscoe99]

My F9,9 CMHL doen not have oil separaor. I already checked that hose but in intake manifold I can not find some oil. On that hose no smoke and no pressure in working. My engine has CMHL label. I can not find that label on purchase yamaha parts page.

What is the PID for your model. It begins with the number 6. Will be found on a data plate on the left hand side of the motor. On the clamp bracket.

Looks something like this.

https://www.google.com/search?q=yama...idahSBOJ-8M%3A

[pakostane]

56N My engine is from EU

[boscoe99]

You have a model that was not distributed here in the USA. That is why you can't find the parts catalog for it at this, or any other, Yamaha US dealer website.

Your model looks to be the equivalent of a US F9.9MSH2. Or maybe an MSH2K model. No air/oil separator I see, as you say.

2006 and Later F9.9MSH2 Yamaha Outboard INTAKE Diagram and Parts

[pakostane]

For piston rings set for equivalent model I found this i cataloq. How I can know which of this fit on my model?ć


PISTON RING SET (0.25MM O/S)
PISTON RING SET (0.50MM O/S)
PISTON RING SET (STD)

[boscoe99]

For piston rings set for equivalent model I found this i cataloq. How I can know which of this fit on my model?ć

PISTON RING SET (0.25MM O/S)
PISTON RING SET (0.50MM O/S)
PISTON RING SET (STD)

A motor is dismantled and if necessary the cylinder is honed to clean up any damage there may be. Or, the cylinder may have to be bored and then honed.

The cylinder is then measured to determine the size of the piston and piston rings that are needed. Or, if the block is reusable.

I think that you may be a long long way from needing new rings and pistons. Hope so anyway.

[pakostane]

Is it good idea change only piston rings not to bore ande honed cylinder and valve seals? Which of this three rings set is for original cylinder.

Why do you think I am a long long way from needing new rings? What is reason for oil consumtion if not rings and valve seals?

[boscoe99]

If a cylinder has never been bored or honed over size, and does not need to be bored or honed oversize, and if following honing for new rings it is still within original tolerances, then the standard rings (STD) are used.

Over size rings (O/S) are used if and when the cylinder has to be opened up and a new O/S piston installed.

When I say that you are a long way from needing new rings it is really my wishful thinking. I would like to think that your engine might only need a good decarboning job to get the rings to seal as they are supposed to. If it were my motor I would carefully inspect it before I started to be thinking that new rings are needed. That is a good bit of work and money. But it is your money. Yamaha would like to have some of it.

[99yam40]

How many hours are on motor?

did it ever go under water or sit for long periods of time?
Did it ever overheat ?
might have rusted cylinder walls, broke wrings, stuck rings, or other problems.
is one cylinder's plug show more signs of oil burning than other?
testing is the proper way to go, not throwing parts at it to hope that will fix it.


I do not know about Yamaha small 4 strokes, but a lot 2 cylinder 4 stroke motors will push air and oil out the dipstick/oil fill hole if run with it pulled/open

[rodbolt17]

leave the dip stick out of any 4 stroke Yamaha and it will blow the oil out.
it is normal.
as the pistons go up and down it creates positive and negative pressures.
on BOTH sides of the piston.

not the first set of rings I ever saw stuck with carbon.
not the first set i have successfully decarbonized.

it is a lot of work and a lot of money to access the rings.