F100 four stroke

[Chrisgrand]

Dear friends.
I got a problem with these motors Yamaha F100 four stroke.
The cylinder head is cracked in 3 of these motor after 3000 hour.
Between the spurkplug and the 2 valves .
I don't know why ,because these motor never overheated and use thermostat.
Definitely this is a factory failure or what the f***. I'm disappointed about this.
Yamaha in Peru know nothing it means there is no gurantee buying this motor.
Any reply is welcome.
Thanks.
Christian Granda

[ausnoelm]

3,000 hours and you're disappointed? what exactly are you expecting?

[99yam40]

What are the model #s
how old are they?
are they run is salt water and flushed with fresh after runs every time?

A lot of info is missing to say what could have caused this

[boscoe99]

If a head was cracked from the factory how could you have gotten 3000 hours time from it?

Yes, it is cracked now but there is no way of knowing what caused the crack. What octane gasoline do you use? Poor gasoline can create all sorts of mischief. Usually it will damage pistons but it can tear up rods, bearings and the head itself. Where on the cylinder head is the damage? Is it in the vicinity of the number two and three cylinders?

I agree with the man from the land of Oz. Having gotten 3000 hours from that model motor I would think that you have gotten your moneys worth.

Install a new head and who knows maybe you can get another 3000 hours.

[rodbolt17]

typically cracking between valves is due to excessive combustion chamber temps.
typically caused by poor fuel quality or over propping for that days load.

[Chrisgrand]

F100BTX regular maintenance given.

* Every 90 hours change oil, motor and lower case.
* Every 180 hours spurkplug change.
* 1000 hours. Piston ring set st. belt. thermostat .
* 2000 hours.
Plane bearing crankshaft 1
Plane bearing connecting rod
Piston rod assy 0.25mm
Bolt connecting rod
Piston ring set 0.25mm
* Oil seals/ valves
*Belt/ gasquet
*Block Rectified and more
after all thsee maintenance with brand new parts and mecanics from Yamaha I expexted more .

Thanks every one.

[boscoe99]

It would be interesting to know how the motor is used, how it is propped and what grade of gasoline is used.

Propped right, good quality fuel and not run continuously at more than 4500 RPM all of the time these motors can last a long time. Otherwise, they may fail in much less time than you got on yours.

[99yam40]

My thoughts also, this motor must be run commercially and abused if it had to get a ring job at 1000 and all the other stuff at 2000

[Chrisgrand]

F100BTX
These engines run on salt water in a 30 feet speedboat with 25 seats in a touristic place
Also use gasoline 90 Oct, almost 2 hour a day. Prop is 13/ 1/4x 17 .The max. RPM used is 4800 rpm according to the passangers weight.
At 2000 hour I spent US$ 4000 in each engine for a overhauling. A new engine F100 in Peru cost US$ 12000 and a 200 hp 2 stroke cost US$ 14000
I have more than 8 years working also with 2 stroke and so far not problem at all except for the gasoline comsuption.
What is better?
thanks everyone for reply.

[rodbolt17]

that motor will accept 90 octane ok.
it WILL NOT accept overpropping with THAT DAYS LOAD.
it MUST be able to turn over 5500 RPM with THAT DAYS LOAD.

cracked valve seats and holes in pistons occur if its over propped for THAT DAYS LOAD.

[boscoe99]

Select a propeller that will allow the WOT RPM to be at or near 6000 with the boat loaded. If at such time the boat is lighter than normally loaded then back out of the throttle so as to not over speed the motor.

Those motor(s) are pushing a heck of a load. Might be hard to find an appropriate propeller. Is that one F100 on the boat or three motors on the boat?

I don't believe the F100 has a knock sensor for detonation protection. Here in the US the new version of the F115 has one. People were damaging cylinders two and three, in high numbers, on the earlier F115's as a result of detonation. So, Yam added a countermeasure in the form of a knock sensor.

If a motor is over propped (two much diameter or pitch) for the application, in which case it won't get to the upper end of the RPM range at WOT with the boat loaded, then the engine is being what we refer to as "lugged". Simply stated it is too much manifold pressure for the RPM. Bad, bad sh1t can happen as a result.

Hopefully, you will get your motors propped correctly, use clean fresh fuel of sufficient octane, and your problems will be behind you.

You say you have 90 octane in Peru. What octane rating system is used in Peru? Seems to me I recall hearing that different countries use different ratings. Such that what we call 87 octane here is not the same as 87 octane in another country.

[Chrisgrand]

F100BTX
Dear friend

I have two engines on this boat with full Load they reach 5400 RPM each maximum.
and it planes perfectly but we run only at 4800 rpm, very smooth using the same prop
Recommended by Yamaha dealers for around 6 years. About gasoline is gotten from PRIMAX or SHELL named before. 84/90/95 and 97 oct.
In this bay there are more than 40 boats using Yamaha 2 stroke doing the same service 4 of them use F100. 5 use F200 four stroke for 40 passanger. One of this F200 the head also cracked with just 500 hours ,he complaint at Yamaha company and he get a new one for half price. One more with the same problem. I think that 2 stroke is only for recreational use and four stroke for hard work.

[boscoe99]

Try another propeller that will allow the motor to reach at or near 6000 with the boat loaded.

Try a better grade (higher octane) of fuel.

I forgot to bring up the matter of the fuel tank. Is it clear or a whitish translucent colour? And maybe on deck where the sun can get to it? A number of F115's and F150's here in the states have been damaged by the use of the tanks being out in the sunlight. The sunlight degrades the fuel and reduces its octane rating. Fuel needs to be out of the sunlight. In complete darkness if at all possible.

The F200 is another high compression Yam model that does not have a knock (anti detonation) sensor. That motor also can be killed by being over propped or by the use of substandard fuel.

You got to do something different. We have a saying here in the states that says "the definition of mental illness is someone who keeps doing the same thing, getting the same bad results, while expecting the outcome to be different each time." Or something to this effect. All I can think of is to reduce the load on the motor by the use of a lesser pitched propeller, the use of clean fresh gasoline with a higher octane rating, and keeping the gasoline out of sunlight.

Good luck.

[2002y100hp]

crankshaft

Just wondering if you fixed that motor cause I need a good crankshaft for my 2002 F100. rebuilding it. thank