Gear Play Back

[Barema Bullet]

Just damage a Gear box on our 225yam (2010). possible cause gear play back, has happened before. Adjusted the selector cable on engine to remove knocking sound at Low rpm, was successful but temporary, have adjusted Multiple times. know my fear has happened. Now i will drop the leg and see how much damage??? How can we prevent this happening a 3rd time???

[99yam40]

hard to tell from what you wrote

but the new gears need to be shimmed properly into the gear case

[rodbolt17]

two common reasons for gearcase knock at low speeds(below 1000 RPM).
one is normal prop chatter and the only way to eliminate it is playing with prop designs.
two is someone failed to CORRECTLY install the collar and retainer assy on the water pump impeller.

quit adjusting stuff or you will destroy the case.
once adjusted its adjusted for life or until something mechanically wears out which means the worn parts MUST be replaced before adjusting again.

I currently have two gearcases apart that were destroyed by the owners/backyardigans.
one is a 90 Yamaha case that the shift shaft in the midsection failed but they kept monkeying with the adjustments until they tore up the rev gear and clutch.

the other is a 100 mercury 4cyl that the same monkey/backyardigan kept playing until it wiped out the fwd gear and clutch.
the merc had a simple worn shift cam.

had they brought them in at the FIRST sign of problems, the Yamaha would have just had a simple shift shaft replacement,it actually took me 45 minutes to pop the powerhead off yesterday evening. now its a reverse gear and clutch as well.

the merc would have required a few seals a couple orings and a shift cam.
now it needs 760 dollars worth of parts just sitting on the counter and about 6 hours labor, give or take.

REMEMBER. if its a MECHANICAL adjustment it NEVER needs readjusting unless something wore out.
or the backyardigan previously mis adjusted it trying to solve a problem they were clueless about.

[boscoe99]

What sort of damage did you have and what was the fix that you did?

What you describe as "play back" is technically referred to as "back lash". It can't be too little or too much. It needs to be within specifications. Were any of the gears replaced due to whatever damage it was that you suffered?

http://en.wikipedia.org/wiki/Backlash_(engineering)

As noted, there is nil adjustment that can be done with the shift cables. Back lash is adjusted internally by installing the correct thickness of shims.

As bolt notices, one source of a knocking sound in idle at low RPM is what is referred to as prop rattle or prop chatter. Usually caused by a heavy stainless steel propeller. Usually does not happen with an aluminum propeller. Yamaha, Mercury and others make propellers with different styles of hub kits for stainless propellers to mitigate this issue.

Also as he notes, if this is an F225 four stroke (you indicate a two stroke) then if the water pump is not replaced in a prescribed manner you can also get a knocking sound that might not previously have been there.

[rodbolt17]

actually, ANY of the Yamaha outboards that use the collar and retainer will exhibit drive shaft knock in gear at low speeds if the collar and retainer are not PROPERLY installed.
wont hurt anything its just annoying.
same as the propshaft chatter due to the prop design.

two strokes are typically noisier at low speeds and its harder to hear but its there.

cannot tell you how many OX66 motors and 4 strokes I have "fixed" simply by dropping the lower, correctly installing the collar assy and reassembling.
typically done after an untrained tech/backyardigan changed the water pump.
I have even seen a few that the collar and parts were sitting on top of the pump housing when disassembled or were missing completely.

[Barema Bullet]

back lashing

Thank you all for your input.

Sorry, it is a 4 stroke Yamaha, and when we first damaged the gear box, it was a complete right off, both fw n rev gears were destroyed and Dealer ship replaced with complete unit, yes back lashing is the correct term. Back lashing mainly occur once we put into gear and around 1000 - 1200rpm we would hear the knocking.

I am yet to pull the gear box apart to inspect the internal damage ( will keep you updated to the severity of damage) , in any case will need to replace the entire gear set and seals, most likely fit a few shims as well to get this perfectly fitted.

Will have a look at the collar assay and water pump to see if this is a contributing factor.

Cheers
Stephen

[rodbolt17]

its NOT back lashing.
back lash is a term to describe the amount of clearance between two given surfaces.
typically fwd gear to pinion will . .007" to about .014".
pinion to reverse is typically ..016 to about .045.

that KNOCK you are hearing below 1000 RPM is either a light engine miss, inccorect blade desighn on the prop or the collar and retainer assy is not assembled correctly.


think think real hard.

as a piston fires it acccelrates downward causing the crankshaft and the drive shaft AND the propshaft AND the fwd gear to accelerate.

NOW as #1 is sloweing down due to #3 coming up on compression stroke but has NOT yet fired the crankshaft and the drive shaft and the propshaft AND the fwd gear all slow down as they are all mechanically joined.

HOWEVER the cluctch is splined to the PROP shaft now the inertia of that big stainless steel prop rotates the PROP shaft and shift cluctch AWAY from the dogs on the fwd gear.

now #3 fires and the acceleration starts all over AGAIN and the crank speeds up the driveshaft speeds up the fwd gear speeds up and KNOCK the slack comes out of the clutch dog and gear dogs.

now the second cause is related to the first cause but is in the lash between the pinion gear and fwd gear.

these gears are a spiral bevel cut and underload try to seperste.
means the fwd gear needs to go fwd but it cant.
means the drive shaft HAS to go up against the thrust bearing.
as the shaft speeds up and slows down it starts bouncing, KNOCK, KNOCK.

the drive shaft typically has .01-.016 play up and down.

that's why you MUST pull up on the shaft when seating the collar assy.

or it goes KNOCK KNOCK KNOCK when your done.

a slight engine miss can cause a knock in the case due to the above.

.
once the in gear prop load(thrust against the water) goes over about 1000 RPM this constant accel/decell is so rapid that the lash never changes and the clutch must follow the gear.

if you install gears in a used case remember when setting gear back lash, loose lives.
may have a whirring noise but it lives.
to tight a lash dies a quick and violent death.

[boscoe99]

Two subjects appear to being discussed at the same time.

I was addressing the replacement of a damaged gear set. In which case shimming is required to set the correct amount of gear back lash.

You are addressing the need to preload the drive shaft in certain Yamahas so as to prevent drive shaft bounce.

[Barema Bullet]

Boscoe99,

the leg was a right off, and dealer ship supplied complete new lower unit. this new unit is now damaged, and i am in the process of pull the gear box out, to determin how much damge has been down to the new leg, (10month about 500hr on it).

[rodbolt17]

unless you hit something, failed to keep a check on the gear oil or filled it full of water, my bet is on either drive shaft knock or prop chatter for the above stated reason.
gear backlash is set when the unit is assembled and from there on out stays JUST like it left the factory,in this case.

the ONLY way to change gear back lash is to physically disassemble the unit remove the fwd and rev gear bearings remove the driveshaft bearing housing and physically change shims.

so UNLESS someone has disassembled that case the backlash is just like it was when it was assembled.

NOW if the water pump is wearing out you may have to replace the pump and CORRECTLY install the lock ring assy.
that lock ring assy, its sole function in life is to keep the driveshaft bearing tight against the bearing housing to eliminate???????
KNOCK at low RPM. that's its ONLY function in life.
if you don't mind the driveshaft knock you don't have to reassemble the collar assy and it can be tossed in the creek.
however to many techs FAIL to properly install it.

[Barema Bullet]

ROdbolt17,

just to clarify, the 'lock ring assy' have attach a file. is the highlighted spacer and collar what you are referring to.
If this is not re-install correctly By pulling up on the drive shaft it can course the Knocking sound and intern start damaging the gears over time (heavy loads and long runs etc)

cheers

[rodbolt17]

toss the lock collar assy in the creek and it will cause NO damage.

get that through some thick skull.
its only there to take out the knock at low speed.
but the knock creates NO damage.

what part of the description are you having trouble understanding?

I understand language barriers, if you would prefer my wife will translate this to Spanish.

[Barema Bullet]

understood.

No drama, just clarifying the possible cause, and now it is down to hitting something before the knocking appeared at low rpm, or a damage seal, but no evidence in any of the oil sample of water.

Or just ware and tare from running loads all the time.

Hmmm ?

cheers

[Barema Bullet]

Got it apart now, both forward and rev gears damage and the Pinion gear along with Pinion bearing(1 roll shattered). Now to look at parts to rebuild it.
this is going to be fun.

[rodbolt17]

there are two different methods to shim the unit, one for the US market and another for non US market.
typically, as long as the gear oil is checked monthly and changed every 100 hours gear cases will go past 3000 hours.