<VV> Re: tight crank

[kovacsmj]

Joe. The issue may be that the tight spot will wear in after a few
thousand rpm, but there is the chance that the journal and bearing will
heat up and start to swell, therefore making the fit even tighter. This
seems to indicate that a bearing and journal touch.

 This could lead to a bearing failure. The journal and bearing are
supposed to ride on a very thin film of lubricant and not touch. The few
other engines I built allowed the crank shaft while alone in the
crankcase to rotate with virtually no effort through 360 degrees. 

Getting all the information is most of the solution.
 
MIKE KOVACS
 

-----Original Message-----
From: virtualvairs-admin@corvair.org
[mailto:virtualvairs-admin@corvair.org] On Behalf Of N. Joseph Potts
Sent: Monday, July 12, 2004 9:40 AM
To: djtcz@comcast.net; virtualvairs@corvair.org
Subject: RE: <VV> Re: tight crank

Here's an idle question from a "virgin" (one who has never split a
crankcase): what happens in a situation like this if one just puts the
engine together and runs it? I can readily imagine (someone as stupid as
me)
doing this, hoping it will just "wear in," the way one is supposed to do
with shoes that ALMOST fit right. An example from a Corvair might be my
newly rebushed transmission-linkage tube. When I put it together, it
seemed
intolerably tight. Within a week of use, it got to feeling "just right,"
and
it still does.
     If I ever do rebuild an engine, I see a fair chance I'll be faced
with
this choice, and I'd like to hear from anyone who has enough guts to
admit
he has tried this.

Joe Potts
Miami, Florida USA
1966 Corsa coupe 140hp 4-speed with A/C

-----Original Message-----
From: virtualvairs-admin@corvair.org
[mailto:virtualvairs-admin@corvair.org]On Behalf Of djtcz@comcast.net
Sent: Sunday, July 11, 2004 10:52 PM
To: virtualvairs@corvair.org
Subject: <VV> Re: tight crank


> OK, Time for the engine builders to put the thinking caps on!
> However, upon assembling the crankcase halves, the crankshaft has a
> tight spot for about 90 degrees. Looking from the rear of the engine
the
> tight area is between 12 and 3 o'clock. The tight spot remains despite
> loosening and retorqing the crank halves and careful adjusting with a
> dead blow hammer on the crankcase halves. Defined tight spot = I can
> turn it thought the 90 degrees with moderate hand twisting on the
> distributor gear end, but if I stop in the middle (45 degrees) it
takes
> a bit more effort to start it to turn again. It starts with a little
> jerk and then loosens up as it goes past 90 degrees. The other 270
> degrees are almost frictionless like past engines I have rebuilt. This
> is telling me the journal may be touching a bearing for about 90
> degrees.
>
> Based on other experiences it may be telling me that one main journal
> is a bit out of concentricity with the others. (Unlikely?). Or perhaps
> one of the bearings is not quite seated properly. The worst scenario
is
> a bent crank shaft. (The plan is to disassemble and examine the
bearings
> to see if I can determine which journal is touching the bearing. Based
> on this I may swap the bearing halves or the 2 and 3 bearing to see if
> this brings a better result. I'll also check it without the cam shaft
to
> eliminate that but I doubt that is the problem as the cam turns at a
> different ratio.

> I will also replastigage at 6 places on each journal to see if I can
> find a tight spot like .0005 in one place and .0015 in another on the
> same journal. I don't have equipment to set up and run out the
journals
> to find an out of round or a concentricity problem.
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