<VV> bad crank

[djtcz at comcast.net]

From: djtcz at comcast.net 

snipped and bottom posted 

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-------------- Original message -------------- 
From: Bill Meglen <tirediron at charter.net>
Subject: <VV> Engine noise diagnosis on full rebuild

A friend, a professional mechanic with a Corvair background is working on a
another friends car a 1964 convertible, late 110 engine rebuilt 140 heads.

Rebuild included new crank, Isky cam, lifters, valve train, bearings and
fasteners. It ran fine then at about 490 miles developed what sounded like a
collapsed lifter. The owner found that the noise  diminished at higher rpm.
So he abused it and the clatter morphed into a knock. Initially a lifter was
replaced and showed excessive wear. Complete tear down found a bad crank and
resultant (?) loose main.  Consultation with Clark, tech led to the
conclusion that the crank from another vendor was at fault.  New crank
obtained from Clark?s. All bearings replaced again. Mains, and rods
plastigaged and everything carefully measured during assembly. Oil passages
carefully cleaned.   The oil pressure relief valves seemed operative but one
was replaced to be safe. Cam was ?run in? again. Engine ran good, oil
pressure 25# at idle 40# at operating speed. Engine has a metallic sounding
tinny noise isolated with a stethoscope to only one bank of engine but not
identifiable to a specific cylinder.  Engine seems to run great.

Recollection on original tear down was that the base engine showed no
evidence that it had been rebuilt. Appeared to be an original unmolested
engine. Very little wear, so indicative of a low mileage engine.  Some
recollection that there was unusual wear on the same lifter that was
ultimately replaced.

While oil passages were cleaned well, oil pressure is good, and relief
valves seem operable there appears to be no way to verify that oil is
reaching the lifters and all parts of engine  needing lubrication.  We all
stumped and only speculate that oil deprivation might be at fault.  Still c
onfident that there was a bad crank but concerned that the problem that
initiated the failure may be in addition to the crank issues.

Welcome any ideas on the problem and its resolution.  A lot of money, time
and anguish is invested in this project.  It appears that everything was
done right but...?


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I'm sorry for your friends' troubles.  When starting from New engine joy and excitement it's a long fall to the ground. I hope the recent rebuild works as hoped.

Some would say categorically that the worn lifter took the lobe on that formerly new Isky cam with it. They might be right.  During rebuild II was the cam nose/max lift measured and recorded?  How did the lobe appearance and dimensions compare to each other (original and Isky cam)?  An in-car valve lift check can (and should) be done with a dial indicator on each  valve spring retainer(s) while rotating the engine.  Was each valve checked for coil bind and retainer/guide interference at full lift?   Did the cam and lifters get treated to moly paste at each assembly?
http://www.dustyengineering.com/cordoba/images/IM001588.JPG

One main bearing was worn, but the rod survived or thrived?  That is kind of odd.  Like most engines, Corvair  rods get oil last.
pump>block>main bearings> into crank> rod bearings.
cam lobes and lifters get splash and table scraps
http://oldcarandtruckpictures.com/Corvair/1960s_Corvair_air_cooled_cut-away_engine.jpg

What did the worn main look like?
http://mahleclevite.com/it_bearingfailures.asp
What happened to that crank journal?

What crank "badness" is being suspected that can not be measured?
Was Clark's crank checked for the same badness and found acceptable?
Good Plastigage readings on ALL bearings and a free turning crank are >>usually<< sufficient, except when it isn't.  I am personally unwilling to take the risk of not measuring every crank journal for diameter, roundness, and taper and check every bearing (at least with plastigage).  The money I've spent on the tools would haved bought a batch of lottery tickets, but I think I won anyway.

Were the case bores (mains and cam) measured for size and roundness?

Where is the failed main, relative to the lifter problem?  
Is the worn GM lifter around to check out?



Dan Timberlake 
Westford, Massachusetts, USA