<VV> loosening tight bushings, etc
djtcz at comcast.net
djtcz at comcast.net
Tue Nov 27 19:15:05 EST 2007
First, I'd look in the starter hole to see/feel if a 0.03 inch gap appears between disk and pressure plate when depressing the clutch. I'm thinking a strong gap only between disk and flywheel would be one semi-conclusive sign of a disk in backwards, although the marginal disengagement without grinding more or less eliminates that one.
I too would (optimistically) try to loosen the bushing before pulling the drivetrain.
I'd depress the clutch while cruising in any gear and rev or idle the engine a bit for 10 or 20 seconds to spin the crank around the input shaft, then engage the clutch and drive around for 10 minutes to let things cool off, and repeat the declutched revving. I'd hope A few dozen well spaced cycles would start to show an improvement, if a "tight" bushng was really the problem
Prolonged rubbing even with oil-lite or heavily leaded bronze heats things up. The bronze bushing has a relatively high coefficient of thermal expansion, so when it gets warm it tries to grow in diameter. As it is a press fit in the crank, the expansion forces it to squeeze inward, and tighten, and the vicious cycle of cascading thermal runway begins.
I worked for a precision machine tool spindle company for several years, and the labyrinth seals were designed to have about 0.010 inch radial clearance with the shaft, and were made of a nice leaded bronze. Other engineers there slept well at night believing "the bronze was a bearing" and would survive in the event of a touch down. But from time to time spindles would be warranteed when "the sparkles came out". I have several samples of the bronze inserts from those spindles with scuffed, or welded ID faces, even light blue blue color radiating outward, with deep heat checks, and whose outside diameters are unmarred and still have the fine turned finish, but are several thousandths undersize.
I believe the failure started when the bushing rubbed (because it was not really well centered), got hot, swelled up in the cover and gripped the spinning shaft even harder, then got REAL hot swelled even tighter and maybe brazed itself to the shaft. When the spindle screeched to a halt, the bushing got a chance to cool off, but the material had "upset" so the OD was now shrunken, not worn smaller. The result was a "spinning" bronze insert.
-------------- Original message --------------
Date: Tue, 27 Nov 2007 07:28:22 -0800
From: "Steve Brennan" <Alohaz at ca.rr.com>
Subject: <VV> Pilot Bushing Installation
To: <virtualvairs at corvair.org>
Cc: 'Chris & Bill Strickland' <lechevrier at earthlink.net>
Content-Type: text/plain; charset="US-ASCII"
Your point Is well taken, Bill, as I remain confused as to whether I need to
drop the drive train and replace the pilot bushing or just drive the car so
that it can fix itself. Bill Meglen first raised the issue of a seized
bushing, and when he replaced his, he found it showed signs of spinning in
the crankshaft. If this is the case, I'm not sure what damage might be
done by my driving the car while hoping the problem fixes itself.
Have others out there found that a tight bushing fixes itself in due course?
1962 Spyder Coupe
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