PS PUmp rebuild?

[Schaible, David]

I had the shaft seal go and did not mess with the caps on the first
rebuild, then possibly from "faulty installation" or fatigue,
embrittlement or whatever at least one of the caps went (after 250k mi)
several months later, at which time I replaced all of them, the o rings
I removed from the caps seemed fine, not brittle or oddly compressed
etc. pump has been trouble free since.........one case scenario for the
record.  fwiw



David Schaible
 

 
 
JRS Pharma LP
2981 Rte 22
Patterson, NY 12563
845.878.3414
 
ALL STATEMENTS IN THIS CORRESPONDENCE ARE CONFIDENTIAL UNLESS OTHERWISE
NOTED
 

-----Original Message-----
From: Phil Rose [mailto:pjrose at frontiernet.net] 
Sent: Monday, May 09, 2005 4:46 PM
To: Bernie Benz
Cc: PeterBergin at aol.com; 200q20V mailing list
Subject: Re: PS PUmp rebuild?

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
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