[Steam-engine] Pouring Crank bearings.

[Robert Smith]

Hi All -- 

In my experience, the primary goal is to get the crankshaft properly
positioned in the bearing shell before pouring.  There are two primary
concerns to address.

1.  If you are pouring only one bearing be certain that the crankshaft
is in proper alignment with the existing, offside bearing so that the
crankshaft does not 'bind' while running in the old bearing.  This
concern should be cause for frequent checks of excess heat and other
signs during the first several hours of running after the repour.

2. Next, one must assure that the clearance volume in the ends of the
stroke is properly balanced at each end of the cylinder.  Now, on nearly
all engines that I have encountered, the piston rod is threaded into the
crosshead and secured in the proper position by a large locknut.  Thus
the position of the piston can be adjusted so that the clearance volume
at dead centers can be equalized at each of the dead centers.

Note: The clearance volume is important in determining the
characteristics of the 'compression' phase of the operating steam cycle
( see the steam diagram) during the period between exhaust valve closure
and dead center.  It is not really sufficient to just avoid hard contact
between the piston faces and the cylinder head at either end of the
stroke.  The clearance distance should be equalized at one end of the
stroke vs. the other.  The really 'proper' way to do this is to take a
set of steam diagrams on the newly serviced engine and adjust as
appropiate.
I did see one operator once make this adjustment by unscrewing the
piston rod at the cross head to lengthen it and the feeling for
mechanical interference at top dead center by rocking the flywheel back
and forth around the dead center position until he found the point of
first contact.  He then told the mechanic working with him who was
making the actual adjustment to, "OK, now just back it off about three
turns and lock it down"!!  Made my  hair stand up.  But, as James so
ably points out below, most engines are probably fit up so sloppily that
it hardly matters!

    Happy steamin' to all,

    Bob Smith


----- Original Message ----- 
From: "James Mackessy" <jmackess at twcny.rr.com>
To: "Steam-engine mailing list"
<steam-engine at lists.stationary-engine.com>
Sent: Thursday, January 19, 2006 1:24 AM
Subject: Re: [Steam-engine] Pouring Crank bearings.


> Hi Andy!
>      While all of the things you mention are valid concerns,  the real
> learning starts when you
> just pour the babbitt. You are right in stating that these were simple
> machines, and if you
> take reasonable care in getting the position close, things will come
out ok.
> Many old engines
> are out there running with things way out of whack due to wear, and
they
> seem to do fine.
> If it doesn't come out right, melt it out and do it again. It's not
like
> it's cut in bronze;-). I don't
> know what the original location tolerances were, but I bet we'd find
it's
> not as close as we thought.
> Best Regards;
> Jim Mackessy
>
> _______________________________________________
> Steam-engine mailing list
> http://www.stationary-engine.com/mailman/listinfo/steam-engine