Shade Tree Mech Help On Yamaha F9.9 Outboard.

[roosterlips]

First of all I am a shade tree mechanic...I had started up my Yamaha F9.9 outboard while connected to a garden hose. I placed it in forward gear and began revving it up not knowing that It would overheat without being submerged in water. Anyway the repair shop says it no longer has compression and that it would cost more for them to repair than it is worth ($1'000.00). Whats the chances of me repairing it myself. Does anyone know where I could find a rebuild manual etc. for this motor?
(1986 Yamaha F9.9SJ 4 stroke outboard)

[99yam40]

Not that you would call it a rebuild manual, but they are Yamaha service manuals
YAMAHA MANUAL STORE

There are also aftermarket ones that some think are OK, but they normally cover too many years and HP models for my liking.

How long and hard did you run that motor on the hose attachment to destroy it?
And was it a flush hook up on power head or the one on the suction intake of the water pump?

[mphelle8vld]

You didn't tell us the symptoms that caused you to take it to a shop. Did it just stop running and not restart or temporarily sieze? It might just be a simple blown head gasket, you could pull the head and check if it is still straight and look at the cylinder walls while it's off. Sounds like a good project for this time of year.

[roosterlips]

I had hooked up the garden hose to the water check plug input located on the lower casing just above the anti-cavitation plate. I was able to get the motor started and allowed it to idle for 10 minutes or so. At that point I placed it in forward gear and began to rev the motor up...6 or 7 times (high short revs) during one of the revs I heard a clank and the motor stopped. I was able to pull the manual start cord however the motor never again would fire.
I was able to find a service manual at the site you suggested...$80.00. I think I'll pull the cowling and see what I can find prior to dropping the $80.00 bucks...recently retired and on a budget.

Thanks you guys for your help!

[99yam40]

I am Not sure it actually overheated,opening it up to see what the damage is will tell more.
But reving a motor without a load on it is not good for it no matter what kind of motor it is.
Post back what you find and maybe we can help determine what actually happened to your motor

[roosterlips]

I'll do it!

Thanks Again

[mphelle8vld]

+1 to 99yam40's post. Hearing a "clank" is never a good thing.

[roosterlips]

Update...1986 Yamaha F9.9SJ with no compression.

Guy's,
I have removed the head and both pistons move when I manually move the crank shaft. Again the shop I had taken it to said that the motor did not have any compression. Am I correct in assuming that with both pistons moving that the problem is most likely a blown gasket. Is there something else I should look at....I am not a mechanic but I would not think that bad piston rings could be the problem because the failure occurred abruptly.

[mphelle8vld]

Was the camshaft drive belt intact and functioning properly before you removed the head? On some models, if the belt snaps the piston can come into contact with an open valve, bending and interfering with seating. Check for a fresh scar on one of the piston domes, that clank came from something.

How did the head gasket look? How did the cylinder walls look? Did you notice any water in either cylinder?

[roosterlips]

Update

The camshaft drive belt was intact and is fine.
The cylinder walls look fine and I did not notice any water.
The head gasket looks ok...it's burggered up from me removing the head but I did not notice a spot that appeared to have been venting hot gas.
I noticed a slight quarter moon scar on both piston domes.
In looking at the valve head it appears that the piston dome scars may have been made by the smaller of each pistons two corresponding valves (exhaust & intake valves).
Stupid question follows...Are the exhaust valves smaller than the intake valves?
Each of the smaller valves have a slight discoloration at the same spot that matches up with the cylinder head scars.
Here is another stupid question...when I turn the valve head drive gear the two larger valves for each cylinder open and close fully...The smaller valves always stay in their open position. I can slightly tap on them and they will go to their closed position, however when they travel to their full open position they remain open...are these valves driven closed by cylinder pressure or should they also close when I manually move the valve head drive gear?

[mphelle8vld]

Nice descriptive post, I've spent plenty of time under a shade tree myself.

Yes, the exhaust valves are smaller than the intakes.

The valves should close on their own under valve spring pressure (check for broken springs), I can't tell you from here why they don't, they either contacted the piston because the belt slipped time, or the valves floated because of revving the motor without a load, or there's some other reason the shafts are sticking in the guides.

I would think the next step would be removing the exhaust valves and evaluating why they are sticking. Let us know

[roosterlips]

I will investigate tomorrow.

Thanks for your help bud!

[bumperfood]

You may have bent the valves, now they can get stuck in the guides. They are likely bent just where they enter the valve guides, so to prevent further damage, I would stop trying to move them back into the head remove the valves, and roll them on a flat surface, if they are bent you will notice it when rolling them. You should also inspect the valve guides for cracks or other damage. If this is the case it may be prudent, to check the pistons for damage, unnoticed cracks.

[roosterlips]

Ok and Thanks

[roosterlips]

Exhaust valves condition update

I removed the exhaust valves and both are bent.
Valve springs and guides appear to be ok.
Pistons appear to be ok as well.

I have ordered new exhaust valves also ordered lifter valves which set on top of the exhaust valve spring retainers. They appear to be damaged.

I went ahead and dropped the $80.00 bucks for the service manual for this outboard because I have never set the timing nor adjusted lifters on motors before. Hopefully the manual will guide me through those setups.

Thank You Gentelmen!