Power Steering Fix

 

 

Introduction

 

The following is a modification that I have been getting a lot of questions about.  There is a great many myths about what causes the power steering problems for people racing 5th Gen Preludes.  Much of this stems from people believing in certain "experts" that say it can't be fixed, or even denying that it doesn't exist.  Well sorry guys it not only exists, but I fixed it.

 

For those that are painfully familiar with the problem you will notice that it is rpm related.  Take a corner at 7000 rpm in 1st and there is no power steering.  Take the same corner at 4000 in 2nd and there is power steering.  Pretty simple experiment.  After hanging out on a lot of Honda boards for a few years I found many references to the same problem on other Hondas.  The problem wasn't cavitation as most domestic experienced racers will assume.  When an engine meant to run at 6000 rpm is run at 9k rpm as is the case in many racing applications, the steering pump spins too fast and the fluid cavitates.  The H22 IS designed to run at 7500 rpm (where I'm running it) so I can't imagine that Honda wouldn't have foreseen this problem.  I tried several different funky fluids in the system to confirm this and no improvement.  Cavitation wasn't the problem.  The problem is also not electronic.  Sorry gizmo junkies but there is NO electronic connection in the system what so ever.  There is no speed governor involved and you can pull fuses till you are blue in the face and not fix it.

 

The problem is a valve!  A simple, unassuming valve.  Honda built us these beautiful engines that can doddle along at 2000 rpm or sing melodious symphonies at 7000 rpm all day long, but they couldn't make a power steering pump that would work at both.  Make a pump that works at 7000 rpm and you don't have power steering at 2k.  Make one for 2k and you get cavitation, or worse yet, high pressure leaks or even blown lines at 7000 rpm.  The solution?  Make a pump that work well in the mid range then put in a high pressure relief valve for high rpm.  Once the pressure in the system reaches some predetermined point the valve opens and bleeds off the excess pressure preventing all the nasty problems of high rpm.  What happens though is that the valve allows too much flow and the Solo-2 driver experiences a loss of power steering every time this occurs.  This I had read online, but always in "A friend told me" or "I met this guy at the track".  Not exactly reliable sources.  So I started reading and low and behold Section 17-28 of my 97 Honda Prelude factory service manual: The Flow Control Valve; if necessary, relief pressure is adjusted at the factory by adding shims under the check ball seat.  If you found shims in your valve be sure to reinstall as found and do not modify!  Ladies and gentlemen, if you didn't already know this, let me inform you now. NEVER TELL AN ENGINEER "DO NOT MODIFY"!

 

Step #1

Getting out the damn pump.

Page 17-25 of factory service manual

 

 

You don't have to remove any lines.  The valve is in the bottom of the pump, you just need it free enough to turn it over.

 

Step #2

Removing the Flow Control Valve.

Page 17-26 of the factory manual

 

Here is the flow control valve and it's associated components as I remove them from the pump.

 

There is a allen head (hex key) cap screw in the bottom of the pump that holds it in place.  Get a friend!

 

All you need to do hear is take out the cap screw and the valve should come right out, but there are some complications;

The cap screw is relatively tight and with the pump loose it's kind of tricky to hold on to while using a wrench.  Having a friend hold the pump while you wrench is much easier.  There is also a spring which likes to shoot out and fall into the engine (luckily mine fell all the way through to the driveway).  This is also a wet part of the system and fluid will go everywhere.  The closer to completely upside down the pump is the better.  You may also need to reach in and grab the valve assembly with some needle nose.  Be Careful!  There is a tiny screen on the end of the assembly.  Damaging it with a pair of pliers could be expensive.  They don't sell this little puppy separately.  Screw this up and you have to buy a whole new pump!  Lastly pay attention to the way the valve sits in there.  Putting it in backwards will mean no power steering at all.

 

Once out let the pump sit there and drip into a rag and move on to step 3.

 

Step #3

Valve disassembly.

Page 17-28 of factory manual

 

So now you have your spring and valve assembly sitting on a clean rag on a table.  Set the spring aside for now with the cap screw.  There are a lot of little components that come out of this bad boy and I don't want them to get confused.

 

You'll see that one end of the valve unit has a two flat sides for grabbing with a wrench, and the other end has a nut.  Note the screen in the nut.  As mentioned before don't damage it, it's very fine and is the only real protection the unit has against debris.

Remove the nut.

Once again, move slowly the components inside are spring loaded.  Literally!

 

Gently turn the unit over and remove all the bits inside.  The resulting pile should look like this.  Make sure the little ball doesn't roll away.  Loose it and there is no power steering!

 

See the little ring washers next to the bolt in the right of the picture?  That's the offending part!  Every spring comes a little different.  So some schmuck at the factory test each one for the pressure it releases at and adds shims until it's right.  Note the tiny spring with relatively huge coils?  It's quite stiff and only needs to deflect a tiny amount to allow the ball to become unseated and allow pressure bleed off.  What the shims do is decrease the preload on the spring.  By removing them we will increase that pressure again.  Of course the factory set that pressure for a reason, but being an engineer I know two things:  1 - The factory leaves a pretty big margin for error and the tiny increase we are making shouldn't hurt the system.  2 - I'm a racer and winning isn't every thing, it's the ONLY thing.   So the shims come out!

 

Step #4

Reassembly.

 

Carefully put everything back inside the valve unit in the same order they came out.  All except the shims! 

Tighten the little nut - 9 Nm (6.5 lbf-ft)

 

Set the shims in a safe place for later (like say a trip to the dealer for a warranty pump replacement...)

 

Replace the valve unit back inside the pump, along with its spring and tighten the cap to 49 Nm (36 lbf-ft).  Remember to get it the right way around!  The little nut with the screen in it faces out.

 

Reinstall the two mounting nuts, but only hand tight.

Replace the adjusting bolt and belt.  Then tighten the adjusting bolt to until the belt has reached is specified tension.  Don't have a belt tensioner?  Get it snug then drive the car to a local mechanic to have it checked.

Once the belt is tensioned tighten down the two mounting bolts to prevent the pump from coming loose over time.

 

Once everything is in, cross your fingers and start the motor.  Check for obvious leaks.  If there are none, you are ready for a test drive.  Take it easy at first an give the system some time to get out all the air bubble you introduced by opening the valve.  You may need to add some fluid later, but I found that so little came out, I couldn't even see a difference.

 

 

Results.

 

I found that the difference wasn't huge, but it did improve.  I now have enough muscle to deal with the loss of powering steering 90% of the time, so I've had no motivation to do any more.  The next step would be to increase the preload even more.  This would be done by make some tiny shims to go at the other end of the spring, deep inside the valve unit.  I haven't figured out how to even make said shims.  There is another danger.  Once the spring goes solid, it can not open at all and could lead to system damage due to excessive pressure.  So modification beyond this point is hazardous.

 

If you did all this and found your valve didn't have shims, well sorry your up the creek.  You could always look for a pump at the wrecking yard and mess around with it.  It's also been suggested that it may be possible to swap in a 4th Gen pump, which isn't supposed to have this issue.  I have no idea if this is true, or if the swap is possible.  If you try it let me know I'd like to hear about it.

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