Tohatsu Seized 9.8 HP 4 stroke

[ubxf]

Re: Tohatsu Seized 9.8 HP 4 stroke

i've been running the engine for a few hours in neutral in a big tub of water
monitoring the oil level and the temperature, still ok so far. can i count this as part of the break in procedure or does it need to be done in gear under load.

 

[pvanv]

Re: Tohatsu Seized 9.8 HP 4 stroke

The factory-recommended break-in no longer applies to the powerhead, since it was seized. An extra oil change is a good idea, since there may be some metal that was shed into the oil during the seizure, or shortly after getting it unstuck.

As for the rest of the motor (LU gears, etc.), yes, operating under load is needed to mate the bearing surfaces. After the 10-hour break-in, the rods and gears will be as mated as they ever will.

Check the service manual; You will want to check the valve lash after 10 hours as well.

The clearance is set when the motor is cold. Intake spec is 0.13 - 0.17 mm; exhaust spec is 0.18 - 0.22 mm. There's a special tool, also used on a lot of motorcycles and foreign cars -- not absolutely required, but nice -- for the factory-recommended method to adjust the clearances.

In many cases, the valve lash does not need to be adjusted at the 10-hour mark, because it is still within specs, but in your case -- after a no-oil seizure -- I'd at least check it. If you don't have the appropriate feeler gauges, or are unsure about the procedure, a dealer can do it. You DON'T want to set the clearance too tight, or you risk burning valves. If it's a little loose, the only side effect is a slight, maybe imperceptible, reduction in horsepower.

 

[ubxf]

Re: Tohatsu Seized 9.8 HP 4 stroke

Thanks Paul, i'll bring it to the dealer to check the valve lash.

 

[ubxf]

Re: Tohatsu Seized 9.8 HP 4 stroke

I did'nt get a chance to check the valves yet and may be that would be the answer to my question but i'm going to ask anyway. When i run the engine
it seems like i get to full power at about 1/3 of the throttle after that if i keep opening up it sounds like the engine is making more sound there is more exhaust but not more power or speed. it sounds like it's hitting a rev limiter ?
btw i changed the oil and like you predicted it was necessary (pretty dark)

 

[pvanv]

Re: Tohatsu Seized 9.8 HP 4 stroke

I doubt you are bumping into the rev limiter. The rev limiter for the 9.8 is set to engage at 6250 RPM. The 9.8 also has a low oil pressure limiter. If it engages, the red light comes on, and the speed will then be limited to about half (roughly 3000 RPM), until the motor is shut down and restarted. That's a "limp-in" failsafe mode, that allows you to return to the dock if the oil warning has engaged. You would definitely need to shut the motor off to clear the limiter.

If your motor is pumping more exhaust (more bubbles) as you open the throttle, it is in fact displacing more air/fuel mixture, and hence making (some) more power. The intake roar is not much of an indication of power; rather just that you hear a different note when the throttle plate is opened more.

Are you testing on the water? You really need to do that. A tank test will not be conclusive. A good tachometer will remove all doubt. If correctly propped, the motor should achieve 5000-6000 RPM at WOT. You may be able to borrow a shop tach, or you can purchase a cheap TinyTach for testing purposes.

If the valve lash is set too loose, that can limit power, because less air/fuel goes through the motor. This is typically a minor loss of power, which many owners don't even notice. This would probably not be happening at only 1/3 throttle, but I suppose it is possible. Do not adjust the valves unless you have the correct feeler gauges and understand the procedure. Setting the lash too tight will burn valves.

 

[ubxf]

Re: Tohatsu Seized 9.8 HP 4 stroke

yes i was testing on the water. i noticed it in the tank first and the same thing is happening on the water. i will get a tach meter and check rpm's. the red light works it turns on for 8 or 10 sec at start up but it doesn't turn on when
i reach the half throttle and the power seems to level of.

 

[pvanv]

Re: Tohatsu Seized 9.8 HP 4 stroke

Sounds like oil indicator is working right. Check RPM's. If you have a bad rubber hub in the prop, the RPM's will go up without giving you any additional thrust.

 

[ubxf]

Re: Tohatsu Seized 9.8 HP 4 stroke

i couldn't get a Tiny Tach but i got a multimeter with an inductive pickup
that reads RPM. Is it ok to run the engine at wot on the water without the cover or do i need to pass the cable probes through and put the cover back on?
i'm just wondering if splashing could harm the engine and if close could the heat melt the probe ?

 

[pvanv]

Re: Tohatsu Seized 9.8 HP 4 stroke

You're OK with the cowl off for testing. Try not to allow the air silencer to ingest any water, or you may encounter serious liquid lock, and possible mechanical damage, such as bent rods.

 

[ubxf]

Re: Tohatsu Seized 9.8 HP 4 stroke

before mesuring the rpm on the water i decided to do it in the test tank in neutral. i attached the inductive pickup to the spark plug cable and it looks like
i'm reading twice the real amount ie 1500 rpm idle should be 750. is there
another place to take measurement from or do i need another meter with more advanced features(i'm using an ATD 5540 automotive multimeter).if i order a Tiny Tach which model would be right

 

[pvanv]

Re: Tohatsu Seized 9.8 HP 4 stroke

Hey, no big deal. It's for testing only. If the meter will read to 12,000, that translates to a crankshaft speed of 6,000, the max designed WOT RPM.

Some inductive pickups can read stray signals from the adjoining plug wires, giving you extra tach pulses per revolution. The TinyTach is also known for that if not perfectly installed. Also... many OB's fire twice (an extra, "wasted" spark on exhaust, due to economy of engineering design), and the 9.8 4-stroke may do this. I haven't checked to verify whether it does or not, because I use the low-volt factory tach setup when a tach is needed. A more flexible meter may give you a direct 1-to-1 reading, but again, for testing only, not a problem as is.

Remember that a 4-stroke cylinder has... 4 strokes (2 up and 2 down) -- the piston comes up twice per cam revolution. The crank turns twice for every cam revolution. So if the 9.8 fires an extra pulse on exhaust, that is why you are reading double. Again, not a big deal, as long as you can read over 10,000 on the meter (5,000 RPM), since the motor's WOT range is designed to be 5,000-6,000.

DO NOT run to WOT RPM in neutral. You need a load on the bearings at speed. Especially on your previously-seized motor. You must test on the boat, in the water, to get reliable results.

If you want to buy a cheap TinyTach, they make several models, and their website should help you, or you can call them for advice on which exact model to buy. Keep in mind that they are cheap, low-end instruments, not shop tachometers.