REFLECTOR: Cylinder repair follow-up

Laurence Coen lwcoen at hotmail.com
Mon Jun 29 11:23:18 CDT 2009


John,

The ID for the 6A-335 liner is 4.500" and the 6A-350, which I assume you 
have, is 4.625".  This means that the 4.465" would be way undersized even 
for the smaller engine.  The min/max ring gaps are .013"-.023".

Increasing oil flow through the oil cooler will reduce the oil temp. 
Minimum oil operating pressure is 47 PSI.

Larry Coen
N136LC


--------------------------------------------------
From: "John Dibble" <aminetech at bluefrog.com>
Sent: Monday, June 29, 2009 10:02 AM
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Subject: REFLECTOR: Cylinder repair followup

> With further investigation of my recent failed cylinder and related
> issues, I have concluded that a combination high oil temp and tighter
> cylinder clearance is the cause and would like comments on how to
> proceed.  First is the oil temp.  My oil temp had been pretty good the
> past year or so.  Then 4 months ago I added 3 washers behind the bypass
> spring to raise oil pressure.  I didn't notice temperature issues then,
> but it was a much cooler time of the year.  As I understand it, the
> reason the pressure was low, was due to engine wear which allowed oil to
> pass through the lubricating areas more easily.  I suppose if the wear
> was uniform, then the lower pressure would not matter, but it's most
> likely that some areas didn't wear as much and need the higher pressure
> for lubrication.  By raising the pressure with the washers, there is now
> more oil being pumped through the engine than before which means more
> oil is also going through the cooler.  That explains the higher oil
> temps since the available cooling air is unchanged, so the oil can not
> be cooled as much as before.
> The 3 washers gave about a 10-12 psig increase in pressure.  However,
> the higher oil temp eliminates most of that increase ( maybe not really,
> since the reason for the decrease in pressure at higher temps is that
> the oil flows more easily and good lubrication is still being
> achieved?), so I'm thinking of removing some or all of the washers.
> What I'm wondering is what is the minimum oil pressure that I can fly
> with?
> The other issue is cylinder clearance.  I've had 2 PZL sleeves replaced
> with American sleeves (I understand that is all that is available).
> Each time I sent the cylinders for repair I was told that the PZL liners
> were beyond the tolerance.  It seems strange for that to have happened
> in as little as 350 hours.  Besides my remaing PZL cylinders have 700
> hours and are working fine.  For that matter the 2 PZL liners that were
> replaced looked in good condition with no scoring.  I replaced them only
> because I was told they were beyond the tolerance limit.  In retrospect,
> I think I should not have replaced them as I feel that the new liners
> have a too tight tolerance.  The i.d. of the new liners is 4.465" and
> the mechanic said I could have them bored out 0.003".  I'm thinking of
> doing that as I think I need greater clearance for my operating
> conditions.
> I suppose I could also install a second oil cooler.  Seems like that
> would be more work.  Anyway, I'm looking for suggestions as to which way
> to proceed.
>
> Thanks,
>
> John
>
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