Yamaha 9.9 4T oil consumption

[pakostane]

I am not first owner of motor. Motor is from 2004. I bought them with may boat 5 months ago. I know that motor worked only in summer season during 3 month in year. Motor has a perfect cold and hot start. Motor works fine except oil consumption. How looks process of decarbonating engine? Need motor deassembly or it is cemical process with aditive?

[TownsendsFJR1300]

not the first set i have successfully decarbonized.

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

Wouldn't the DEALER ONLY available de-carbonizer be worth a try (W/O breaking the engine down)?

[pakostane]

Probably at first I will change only valve seals. One service told me that it is not necessary to disassemble the head. Do you know clearances of intake and exaust valve?

[TownsendsFJR1300]

The cylinder has to be pressurized to swap out seals while assembled.

The spec's should be in your shop manual. If you don't have one someone may post the spec's here..

It wouldn't be a bad idea to invest in a shop manual...

[cleddau1]

This is an old engine and not worth throwing money at. I would just keep topping up the oil, consumption may settle down if the engine gets some more hours done anyway. Half a litre for ten hours motoring is an inexpensive way forward.

[pakostane]

This is spark plugs:

[TownsendsFJR1300]

Very nasty, old and definitely needs replacement.

[rodbolt17]

how many ways can we get oil in a cyl?????
past a leaking intake valve seal,both being bad at the same time, what are the odds.

past the piston rings,both being stuck with carbon,odds are way better.

past the carb via the air box? that is going to make a mess in the cowl.

two pages of posting and still no leakdown test.

[pakostane]

I removed head and there is for my opinion too much carbon. I visited valve seals and it looks fine. Definitly I will change seals with new it si not so much money.
I am not sure is it worth to change piston rings? Is it possible to check rings without deassmbly cylinder? It is so much work.

[cpostis]

I removed head and there is for my opinion too much carbon. I visited valve seals and it looks fine. Definitly I will change seals with new it si not so much money.
I am not sure is it worth to change piston rings? Is it possible to check rings without deassmbly cylinder? It is so much work.

Wish you would have done the "leak down" test. Anyway, if you rotate the engine, can you see any scratch marks on the cylinder walls? Can you hear any scratching noises from a possible broken ring? If you fill you head cavities with, say mineral spirits, do you have any leakage through the intake valves?

[pakostane]

Wish you would have done the "leak down" test. Anyway, if you rotate the engine, can you see any scratch marks on the cylinder walls? Can you hear any scratching noises from a possible broken ring? If you fill you head cavities with, say mineral spirits, do you have any leakage through the intake valves?

No scratching noises. No scratch marks on the cylinder walls. It is in pretty good condition. I did not tested yet leakage intake valve. Can I put petrol in head cavities and testing intake valve leakage. Valve clearence was ok.

[TownsendsFJR1300]

I did not tested yet leakage intake valve. Can I put petrol in head cavities and testing intake valve leakage. Valve clearence was ok.

As long as the valves are NOT lifted by the camshafts, putting fluid in there is fine(keep the spark plug in). Nothing should leak out...

How many hours on this engine?

The one cylinder is much wetter with oil than the other.

Also, look at the valve stems, especially INSIDE THE HEAD, where the exhaust would flow. Do you see a bunch of carbon build up on that stem? A leaking exhaust valve seal would allow past it, and with the hot valve, it would stick and build up on it...

[pakostane]

I went to check thermostat and when I open housing there is no thermostat. All past time engine worked cold. I desided not to change piston rings. I will buy new thermostat and change only valve seals, head gasket and impeler. I have one question about impeler. Have I to buy something else except impeler, some seals or ring?

[pstephens46]

Buy the water pump KIT. Should have everything you need.

[TownsendsFJR1300]

Plus 1 on the entire kit.

Hope your going to clean all the carbon from the head and piston tops...

You may want to try soaking the cylinder/bore(with the oiled up head), with some sort of de-carbonizer. let it soak past the rings and MAYBE, loosen, dissolve any carbon in the rings. It can't hurt..