The midget front suspension is based on a vertical 'kingpin' about which the
upright and stub axle rotate. The kingpin is attached to the shock at the
top, and the a-frame at the bottom. Since the kingpin is hardened steel,
and the upright is forged iron, there are brass bushes installed as bearing
surfaces for the kingpin to rotate inside of. The brass bushes are quite
soft, and wear fairly fast if not greased OFTEN (about every 1,000 miles, or
monthly). the brass bushes must be pressed into the uprights, and so
distort as they are installed, so they must be reamed to a final fit after
installation. Since they are a different diameter top and bottom (there are
two in each upright) the reamer must be stepped, so that both sizes are
reamed at the same time, keeping them in line with each other. Single size
reamers can be used, but only luck coupled with incredible skill would keep
the bearing surfaces truly in line, so a special tool has been created. If
you have the tool, the job (reaming only, not the whole rebuild) takes about
ten minutes per upright.
The other problem area with kingpins is the lower trunnion joint. This is a
truly excrutiating piece of engineering, where a low clearance threaded pin
goes through the A-frame and the trunnion on the bottom of the kingpin, and
seems to always be seized, so that instead of pivoting on the threads, it
wears everything in sight. These are tough to remove, so I tend to buy
rebuilt uprights, with kingpins installed, from Moss or someone like that.
Got a pair last time I was in England for about 15 pounds exchange, and
they've been perfect.
To test for wear in the kingpins, first make sure that you can get grease
into them. Then, use a big prybar to check for any vertical play. Then,
check for any side to side play. If you can see or feel any without
instruments, then you probably need a rebuild. A little play is ok, but
we're talking .050" or so.
Brian
At 07:31 PM 27/10/97 -0500, you wrote:
>Clue me in! I'm new to all this and am ready to disassemble the front end of
>my Sprite. What is the point of reaming the Kingpins? Is this something
>that has to be done with every front end rebuild? Help!!!!! What are you
>guys talking about?
>
>
>---David
> 1967 Sprite MkIV, Victoria, aka, Vicky
>
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