1991 Yamaha 200hp maintenance and shift shaft repair

[Capt. Bob]

T-stats, pressure relief valve and impeller replacement is standard DIY maintenance for many boat owners and the Internet is full of pics and You Tube videos but I have found only a small collection dealing with an older engine like mine. Since I don't have a rebuild thread I thought this may be of some service to a very very small group who might own an older two stroke Yamaha.

Started by removing the T-stats and pressure relief valve housings.

T stat housing in each bank:




Next I dropped the lower unit. The "hidden " bolt under the steering tab added a "third hand" since I was working without a net.

Lower unit:


Longer helper bolt in place and then being used:




Prop came off easily, 13 3/4" x 17":


Lower unit removed:

[Capt. Bob]

Once the housing cover was removed, you can see that the impeller cup rotated inside.
Not good.


Also note the 'wallowing' on the center hole of the cup.




Worn impeller


 

[Capt. Bob]

The new impeller is held to the drive shaft with a woodruff key. This infamous part is known to "mate" with the shaft and require a small explosive charge to remove so a dab of grease is recommended upon install of the new key. Yamaha likes the key to be "press fitted" so.

A large c-clamp "pressed" into service.



Key in place.



The impeller slides down, nothing special there but wait....
Yamaha uses a "locking/holding" device consisting of washers (2 flat, 1 wave) a nylon spacer and a stainless drive shaft collar.



Here they are in order of assembly. I tried to use the car as a background.



These go on top of the impeller but their real purpose is to remove backlash from the drive shaft itself. The impeller isn't going anywhere once it's inside the cup, inside the housing and bolted down to lower unit case. You cant find these parts on the 91 and older exploded parts diagram so I believe they were fitted circa 1992. A Yamaha mechanic stated their main purpose was to remove "rattling" from the drive shaft encountered at idle speed that disappeared at higher throttle settings.

Lastly, when installing the impeller in the cup/housing assembly, rotation of the shaft to "twist" the impeller blades into the cup while pressing down on the housing is clockwise. Very important.

Finished assembly.

[wingtime]

1) How old was the pump housing? Were you having a overheat problem?

2) GREAT FRIGGIN idea using the workmate to hold the lower unit while you work on it.  Way better than using a vise to hold the skeg.

[Capt. Bob]

1) How old was the pump housing? Were you having a overheat problem?

It is the original that was on the motor when I got it. I changed the impeller in 2012 (along with the T-stats and pressure release valve) and reused the washers/spacer/collar. I haven't used the boat in a while but have been exercising the motor every few weeks on the muffs. The last few times I ran the motor I noticed the t-stats were slower to open. The last time I ran the motor I noticed the "pisser" wasn't functioning. I shut it down before the t-stats opened. I tried it again the next day (thinking my house water pressure had been low) and the result was the same so I tore into the pump. I believe it was during those last two runs, when the pisser was not functioning, the cup spun in the housing.

2) GREAT FRIGGIN idea using the workmate to hold the lower unit while you work on it.  Way better than using a vise to hold the skeg.

Works really well. I bought that Workmate in the early 80s and it has had its share lower units on it. I've seen a couple of shade tree boat mechanics using one on You Tube.

[wingtime]

Now I have an excuse to buy one!

[Capt. Bob]

Installed the new t-stats and pressure relief valve. Again I used a thin coat of gasket seal to level out the eroded mating faces between the t-stat cover and block.

Pretty At least for a while.



Gasket seal, typical to both.



No pics of the pressure relief valve assembly but removing the bottom ignition coil assembly from the right bank makes installation much easier.

Now on to the shift shaft replacement.

[Capt. Bob]

Outboards (at least Yamaha and OMC anyway) started using stainless steel in several major components circa mid 90s. The infamous steering bracket is probably the most noticeable component that owners could see where stainless made a big difference in useful life span.

On Yamaha motors, another component that suffered but isn't as high profile vision wise is the shift shaft. The shaft does exactly what its name implies in that it allows the lower unit to engage the 3 positions of function, forward, neutral and reverse. If you ever have changed out an impeller in your water pump, you know when reinstalling the lower unit, you need to line up both the water tube and the shift shaft. If you have an old Yamaha motor, the next time the lower unit is dropped, you may wish to take a peek up at the shaft.

Shaft corrosion.



Over time, salt water eats away at the shaft and eventually it begins to twist when engaged leading to erratic shifting. When failure of the shaft (think snaps) you know what happens. You end up coming home in forward (lucky you), reverse (oh boy, sounds like fun) or with Sea Tow. Seems easy enough to detect and so just replace it. Used shafts are on eBay and relatively inexpensive but......

Shaft construction doesn't lend itself to remove and replace like the impeller. We're all familiar with the operation of the helm binnacle and the control cables for throttle and shifting. Both cables attach at the motor and the shift cable operates an "arm" that moves the shaft. The shaft is mounted to this arm via a cotter key through the shaft upper bracket which in turn is held in place by a larger "lower bracket" mounted with two bolts to the power head.

Shot of arm/shaft attachment.



Note, removal of lower carb for access.

To remove the shaft on these older (and I'm guessing newer models too) the power head needs to be unbolted and raised.

Here's why.



Shaft is welded to the upper bracket and is held into the lower bracket by a cir clip.



Lifting the power head and removing the lower bracket allows access to the clip and removal up through the mid housing. Note that the shaft has been cut in the last pic. This allows the shaft's main length to fall out the bottom of the mid unit and removal of the upper bracket without power head removal. I don't really care to think what condition the power head attachments would be in after all these years so not having to mess with them is a big plus. Note, new upper arm is pictured below bracket assembly. This is the trick part.

Tomorrow, new upper to lower bracket assembly.

   

[wingtime]

I will say the Mercury and Yamaha shift shaft that turns to shift makes taking the lower unit on and off easy.  The OMC push pull shaft can be a pain in the butt when you drop/install the lower unit, however at least it is easy to see it and service it when you change out your water pump.  So I can't really say one style is any better than the other.

You were very close to a tow with that shaft!  Good job and thanks for the informative thread!

[Capt. Bob]

You were very close to a tow with that shaft!

Indeed.

I've been thinking about the shaft breaking for some time and when I dropped the LU, took a peek, thinking changed to doing.

The product I'm using is called....wait for it......a..........shift shaft.

Here's the link. https://www.shiftshaft.com/
I stumbled across this site a few years back and wondered if they were still around. Yes they are.
Not cheap but one pays for convenience so. I popped for the shaft and so far have been pleased. The material and welds appear very well made. If the stars (and the shaft) align and the shift works, I think I bought a few more years for my motor. That stated.........

A earlier photo showed the shaft cut. Here's where I made the incision.



The shaft passes through a rubber "gaiter" (located at the end of the socket). I worked a sawzall blade under the gaiter and was able to slice through the shaft very easily. It then fell right out of the mid unit. I was then able to remove the lower bracket and pull it clear of the power head.

Placing the bracket assembly in a vice, I removed the cir clip and separated the two brackets. I took a moment to clean the zerk and shot a little lube through it.



At the top is the lower bracket that mounts to the power head.
Below and to the right is the new upper bracket and the nylon bushing (reused from the original upper).
Below that is the clip and washer that retains the upper to the lower.
And directly under the lower is a spring and ball bearing. This assembly rides in the hole just to the right of the larger hole in the lower bracket with the zerk fitting.



The vise holding the lower bracket with the new upper in place.



Notice that unlike the original upper which had the shaft welded to it, the new upper allows the shaft to be inserted from the bottom, passed through the mid and is held in place with a cotter key.



I mounted the lower/upper bracket assembly earlier this eve to the PH and tomorrow hope to align and secure the new shaft and re-install the lower unit.

It could happen.

[RickK]

Nice documenting there CB 

[Capt. Bob]

As Wing stated, the shift shaft configuration in a Yamaha helps with the alignment when reinstalling the lower unit but since I removed and replaced the shaft, I was concerned in realigning the new shaft with the LU. Unlike the original, the new shaft has splines at each end that require engagement so...

I first installed the shaft over the lower unit spline and marked its position with whiteout.



Next I installed the shaft up through the mid section and engaged the splines in the upper bracket.

After first try.



When I tried to install the lower unit, it hung up on the new shaft so I uncoupled the upper bracket assembly from the shift cable "arm". This allowed me to rotate (I wiggled it) the upper bracket and that moved the shaft while my son put pressure upward on the lower unit. This method worked and the shaft engaged allowing the LU to slide into place.

In this photo, the splines of the new shaft are visible with the retaining cotter key in place. The key to the left is the one I removed to allow the movement needed to align the lower end of the shaft and the LU.



I'm guessing that this will only need be done on the first install. After that, realignment of the shaft and lower unit should function as it originally did.

With the carb reinstalled, I started the motor and checked the "pisser".



T-stats operational.



So, cooling issues resolved and shifting as designed. I now have a stainless shift shaft like the big boys.

 

[RickK]

Good job there CB.

[jdupree]

Good job Bob!  Looks like you have a new motor

[Woodeneye]

Encyclopaedic as usual.

Welding a steel shift shaft in? WHAT were they thinking?