Thread: Yamaha V-6's F250 4 Stroke Hydraulics Rebuild

Busy, busy, busy…..

After the main hydraulic housing drained it is time to clean it out.



First thing is to clean very well the flanges that mate to the housing. The o-rings are so thin a very clean & smooth housing is necessary for a watertite seal.



This is the motor to pump adapter. The groves are not quite center, so make sure it is in the correct direction before installing the motor.



The insides of the reservoir and the bottom of the Tilt cylinder both has a oil/water sludge, I clean them out very well then wipe out as clean as it will get.



I like to fill the reservoir with fresh fluid at this point along with the Tilt Cylinder tube leaving enough room for the Tilt piston mentioned earlier as well as the base rod components on the Tilt Ram Rod. I usually leave it like this overnight as air will bubble out if given time to work its way up. A new filter screen is added here too. A small brass adapter goes under the new filter screen, I didn't get a picture of it but its sticks thru the filter screen so you can't miss it.



Before we can install the Ram Rod the Reservoir must be installed so here I clean the inside and out as well as the flange, install a new o-ring, and install the reservoir to the main housing using Nickel based Never-Seize.



To replace the Seals in the Tilt Ram Cap you first must remove the valve assembly on the bottom of the shaft to allow the Cap to slide off. The Trim cylinders do not have fluid above the piston but the Ram does so a Wiper O-Ring and Backer Ring is installed in the cap as well as a Dust or Wiper Seal. A single Torx screw holds the Valve springs & Check Balls in place. Shims are under the spring retaining plate and must be return before installing the retaining plate.



Once you have the Torx screw, washer, springs, check balls (4 total here), & shims out of the way you can put the Eye of the Tilt Ram Rod in a vise to break the Valve Head from the rod. I use a spanner wrench for working on larger hydraulic cylinders for the task. As you can see I use a 1/2in drive to 3/4in drive adapter for this big spanner. I place the spanner pins in the holes where the springs were removed and it's standard right hand threads. Blue Loc-tite is used so it will take a bit of time to unscrew.



I use a seal pick to remove the o-ring & backer ring if reusing the old cap but here I'm installing a new one. The picture holding the cap is to show the orientation of the o-ring & backer ring. Again I use a socket & extension to press in by hand the outer wiper seal.



I use contact cleaner to remove any oil from the threads before adding the blue loc-tite and screwing together the sub-assemblies.



Here I'm replacing the lower o-ring and backer ring on the valve assembly piston. You can see the springs and balls on the paper towel.



The balls go in first. One in each hole followed by the spring assemblies. The shims are added under the retaining washer, then the retaining washer, followed by the Torx screw washer & screw. Blue loc-tite is used on the screw too. Now you are ready to install the Ram Rod into the cylinder body.



I will cover bleeding in the next post.

It's important to bleed as much air out of your repair as you can so after re-installation the hydraulic unit will lift the engine thru the complete range of motion. Most hydraulic units have a release valve in the form of a screw on the side of the main body.



After closing the unit up and topping off the reservoir with fluid the release screw is opened to allow fluid to bypass as you push the Tilt & Trim Rams down by hand.



Push down the Tilt Ram first. Once it is close to all the way down you will hear a air pocket being pushed out. Once the Tilt Ram is fully compressed I use a strap to hold it down while pushing both Trim Piston shafts down. One side usually goes down before the other, like the Tilt Ram when you get close to fully compressed you will hear air being pushed out. Now each time you push out air the volume of fluid in the Reservoir goes down. You always add fluid to the Reservoir with all the Rams fully extended. Close the Release Screw Valve at this point. Very Important!



You add fluid each time you run the Rams back out with a battery. I just use leather gloves to hold the wires to the battery terminals. When touching the battery terminals you must be forceful of a lot of arcing will occur. Its hard to see in the picture here but I have added fluid till the point its running out of the fill hole. At this point install the cap and repeat the bleeding process by loosening the Release Valve Screw, pressing the Rams down, tightening the Release Valve screw, raise the Rams with battery power until you hear very little air come out from under the cylinders. The bonus is this pushes air out of the pump itself to help it prime. After re-installation in the engine I usually have to use the engine weight a couple of times to compress the Rams for a final bleeding.

Good work as usual. Hard to beat the holding power of some good F clamps. I have some Bessey brand that are stout for sure. It is amazing what they will do

Wow, never even thought about rebuilding them till they leak. Great idear. I guess you found me some more projects Rojo. And just when I thought I was getting ahead!

Great info and write-up John. Will come in handy in the future for sure Thank you sir.
Ed, you still have the boat hull to do, Right??? Can't get it in the water till it's finished.

Originally Posted by Slab

Wow, never even thought about rebuilding them till they leak. Great idear. I guess you found me some more projects Rojo. And just when I thought I was getting ahead!

I bought my Spanners from Marine Tech Tools. Theirs has replaceable pins. Stay with OEM parts, aftermarket seal kits are not as good in my opinion. The 4 Cylinder engines take a smaller spanner than the V-6 engines. I also ordered extra pins.