Yamaha 9.9hp 4 stroke parts interchange?

[looserivet]

Over the weekend I picked up a super clean, and likely low hours 1990 Yamaha 9.9hp 4 stroke motor.
Someone threw is away in the trash, a neighbor who trash pics gave it to me.
The thing looks great but its got two broken off spark plugs, both broke off flush in the head, and both holes have some sort of extractors broke off flush in the holes.
While I suppose there's a chance I can pull the head and get the broken bits out, chances are also good that who ever did this likely applied so much torque to the extractors that it probably expanded the remains the spark plugs locking them even harder into the head. The good part is that he also got the fuel tank, hose, two life vests, and a box of new spark pugs to fit it.
This is my first run in with a Yamaha four stroke.
What years were these motors the same? I'm thinking that maybe the easiest way to fix it is to grab a parts motor or a good used head.
What surprised me is that the motor has absolutely zero paint loss, not even on the prop. The oil looks new, and there is no sun fade to the decals. It was either very rarely used or it sat in dark storage for a long time. I'm not sure why the plugs broke off, nothing looks corroded, and the broken bits of the plugs, which were hanging in the plug wires, are clean and shiny, almost new looking. I'm sort of thinking they broke off new plugs putting them back in, so maybe its a matter of some crossed threads and a big wrench?

Also, I was told by someone that some Yamaha 9.9hp four stroke motors are detuned 15hp motors, and a carb swap is an easy upgrade? Is this year one of those motors?

 

[tpenfield]

Sounds like a challenge. Check the parts diagram to see what you would need to a head swap.

As for the 9.9 vs. the 15 HP. Check the parts diagram and listing of your engine vs. the 15 hp of same year/vintage. I had check the Yammy 9.9 vs. the 15 hp in the 2-cycle days and it looked to be only a throttle setting difference. Just about every part to have to do with the power were identical (same P/N) between the 2 engines.

I have seen this in other types of engines (yard maintenance equipment mostly) where engine having 2 different HP ratings were identical, except for the maximum throttle setting.

 

[looserivet]

One dealer I called said he thought 85-93 were the same but couldn't be sure about the head. Without a model number to look up, there's no way to figure it out.
The closest manual I could find was for a 1998, it looks similar but I doubt if its a perfect match. The same dealer was the one that told me that one version of the 9.9 was just a detuned 15hp, the whole carb was different, with the 15hp having larger jets, a larger venturi opening, and they added an accelerator pump. But I'm not sure if mine is in those years, or even how many versions they built that were 9.9hp over the years.

 

[Mohawkmtrs]

...got a model/serial number?

 

[looserivet]

The model is FT9.9ELD I'll have to get the serial number later, I didn't write that down.

Can the head be removed without pulling the whole power head?
I gave the plug hole situation a good look and I don't see much chance in getting at the broken bits from the outside.
The top threaded bit of the plug moves a bit but it only wants to thread in further, it won't back out. There's only about three or four threads left in the top, the bottom looks like its got the whole threaded portion of the plug stuck in the head and its got a pretty big chunk of easy-out or a tap stuck in the hole on a bit of an angle. The top plug hole had a silver colored easy-out in it but I was able to tap a bolt to it with the welder and it backed out of the hole.
By the look of how the lower hole is jammed up with the easy-out on such an angle, I'n as optimistic it'll come out totally unscathed, maybe needing some sort of thread insert or welding and re-tapping.

 

[looserivet]

I got the serial number off the motor, so the model is FT9.9ELD, the serial number is 466465, the last two are vague, something rubbed the numbers a bit but it looks like a 6 and a 5 on the end.

I got the upper plug threads to back out after basically wedging a screw driver in the hole and with lots of oil, worked it back out. The bottom isn't budging, The broken tool won't budge and there's nothing to grab.The best bet is going to be to tap out the broken tool from the inside and then work on the broken end of the plug from the combustion chamber side.

 

[looserivet]

I got the lower unit off, I removed the flywheel, timing belt, and unbolted the manifold.
The intake will not clear the oil pump, and the oil pump won't come off due to interference with the pan.

It appears the power head or pan has to come off, since the pan appears to bolt down from the top, the power head has to come up. I removed 6 bolts holding the power head but there seems to be more?
The head will not come off until the manifold is off,, and even if I got the head loose, it likely won't clear the pan.
I have two manuals, one for a 1998, which doesn't match this power head, and one that covers many years and it doesn't list all the bolts or their locations.
How do you drain the motor oil? Will separating the power head from the mid dump oil?
I called a couple of dealers, which were of no help, nor are they interested in doing the job. I was told "Its too old", "Toss it and buy a new one". Sorry but $3,400 or so for a new motor isn't in the budget. Its why I'm dealing with a trash picked one. Its just nuts and bolts. Someone out there has to have had one of these apart in the past? From what I can tell, these were basically the same from 1988 to 1992 or so. Its a High Torque model but I don't think that affects the power head.

 

[raczekp1]

what for arey you unbolting the powerhead.
just remove the head to extrackt broken spark plugs.
i did few head removeal, so you can do it also

 

[looserivet]

The intake manifold has long studs, the head won't move until the intake is free, the oil pump on the side is blocking the intake from sliding off the studs, and the lower cover pan prevents the oil pump bolts from being backed all the way out. The lower oil pump bolt is only 1/4" from the lower pan.
I tried to remove the studs that hold the manifold but they won't turn. They just wind up and feel like they're going to snap.
I have the head cover unbolted but it won't come free at the bottom? It feels like its hooked on something and won't slide back or up. There's only about 1/8" between the head cover and the lower pan/latch area.

 

[looserivet]

For some reason in the past week the steering has locked up on this thing, it won't turn even the slightest bit. I removed the lower mount, but see nothing there, it don't look like a saltwater motor and I see no signs of it being dunked. The oil is clean but not new, the lower unit oil as full and clean, and there was no signs of corrosion in the one cylinder I did get a plug back in. The motor turns over fine and feels like its got good compression on both cylinders.

The oil pump won't back out, no room, the intake had four studs, I was able to remove two, the other two won't budge. I suppose I could remove the cab and take the head back with the intake and pump attached?

I unbolted the head cover, it won't come free, as if something is getting caught down low inside? It won't come back far enough to come off. (I just noticed that the rear latch unbolts, so maybe that'll help get the cover off.

The lower unit had to come off either way to get a new water pump.

I'm not sure what's going on with the steering pin? It was totally free when I hung the motor on the stand, it was flopping around fighting me the whole time I was trying to balance the motor and get it centered on the stand so I could tighten down the clamps.