PS PUmp rebuild?

[Phil Rose]

At 11:28 AM -0700 5/9/05, Bernie Benz wrote:
>No!  Is best to isolate the leak to a specific cylinder head before pulling
>the pump, as you may not have to pull the pump

Good advise.

>  or at least will know just
>which one needs to be opened and the O-ring replaced.

Bad advice! Once it's decided you need to remove the pump to replace 
one, yopu ought to replace _all_ those cylinder-cap o-rings. If 
you're in the midst of a pit-stop and thus a few minutes extra time 
is critical, then perhaps just replace the one that leaks--but 
ordinarily it's a penny-wise pound-foolish way to go. These o-rings 
most likely share a common "history"--meaning age and/or poor 
technique during installation. There's no reason to expect that the 
other o-rings are not near the failure point.
>These O-rings don't
>wear out, just fail because of poor installation.
That's not necessarily fact--just your considered opinion. My opinion 
is: O-rings, like any synthetic polymer material, are subject to 
age-related embrittlement (this derives from the inevitable changes 
due to a phenomenon called "free-volume relaxation"-- sometimes 
called "enthalpy relaxation"); and that changes the rubber's modulus 
and its ability to recover from compressive deformation.  Couple that 
with constant thermal expansion/contraction and the material can have 
poorer and poorer sealing ability over time. This scenario doesn't 
even account for possible effects from contact with the hydraulic 
fluid.

>I agree with Bernie that there can easily be damage (from excessive 
>stretching) caused by inadequate lubrication during installation. 
>But if one of those 8 o-rings suffers from poor installation, what 
>are the chances for the other seven?

Phil


-- 

Phil Rose
Rochester, NY
mailto:pjrose at frontiernet.net