>Date: Wed, 26 Jan 94 10:49:34 PST
>From: RadsickT <radsickt@lablink.ple.af.mil>
>Subject: GT6 progress
>
>Hello all,
>
>I finally decided on a plan of attack for the GT6mk3. I asked a
bunch
>of questions a while back about hot-rodding the GT6 engine, but I
have
>decided on this plan instead:
>
>1)Get frame and suspension together
> -use old shocks and springs for now
If parts are out, check shocks by moving through full travel by hand.
Should work smoothly from stop to stop. On my GT6MKIII, one shock
lost action in the last 1" of travel, causing wheel hop only during
hard turns in one direction. Took me quite a while to find problem,
since shocks seemed OK when car was bounced.
Also: leaves of rear leaf spring are separated by little pucks that
serve as contact points. They are circular, and are supposedly
retained within a circular impression in the surface of the leaves.
These little pucks tend to go away, causing the rear to sag and the
springs to squeak due to metal-to-metal contact. Take the leaf spring
apart by cutting the pin through the bracket, and use a bolt in its
place when reassembling. Fab new contact pads from some type of
plastic. Since I didn't care about appearance, I made the pads large
and rectangular to stick out the sides of the spring and surround the
bracket so they could not escape.
My GT6MKIII came with a rear suspension that was common with the later
Spitfire; no rubber yokes, no outer pivot, and the leaf spring was
mounted on the diff such that it was free to rock, except for one
leaf. The earlier Spitfire lacked the rocking spring, causing outer
wheel tuck-under in hard cornering. The earlier GT6 went with the
double-pivoted axle and the completely revised suspension design to
avoid this. Unfortunately, the design require two pivots in each axle
PLUS a little play lengthwise. Rather than go to the expense of two
U-joints plus a splined slip joint, they used rubber yokes, which will
also allow some axial movement. Such yokes are notorious
troublemakers. If you have them and wish to maintain that suspension
design, there is someone that makes a replacement axle with two
U-joints and a slip joint; perhaps someone here knows where to get
them. On the other hand, you can convert to the later Spitfire design
and still be somewhat legit, since Triumph went to it also.
By the way, the U-joints in the GT6 are available at most parts
houses, but tell them it's for a Spitfire. For some reason their
books list the GT6 as having the same U-joints as the TR6 (which won't
fit) and you cannot get these organizations to make corrections to
their listings.
> -paint frame, a-arms, etc with black urethane enamel
> -get new stainless steel brake lines fabbed (or do myself?)
>
>2)Get diff rebuilt/ rebuild tranny myself
On mine, the entire differential carrier broke in Yeehaw Junction,
Florida. They are definitely overstressed by the 6-cyl.
>3)Rebuild hubs, brakes, bearings, etc.
>4)Put everything above on the frame so I have a rolling unit.
>5)Put body back on frame so the Security Police don't yell at me
>6)Prep body for paint
You should know that the body of the GT6MKIII has a couple stress
points that tend to cause cracks. While you have it off, you should
reinforce these areas, perhaps by brazing some sheet metal on the back
side. One such area is at the corner where the headlight housing and
the flat area of the hood meet. Another, though not as visible, is at
10:00 and 2:00 on the surface that the cardboard tranny cover attaches
to the firewall; cracks develop through the bolt holes, and the entire
body seems to get flimsier due to the reduction in stiffness. I also
had a crack develop near one of the bonnet hold-down latches, but that
may have been caused by a previous owner screwup.
>7)Paint w/ metallic BRG Urethane Enamel
>8-infinity) assemble car
>infinity+1) cheaply rebuild old engine to stock specs
A definite don't-miss: The thrust bearings on the Triumph 6-cyl are
little semicircular items that are separate from the main bearings,
and are retained only by being trapped between the crank, bearing cap
and block. After a little wear, they get a little slop in them.
Since the GT6 sits with the engine pointing nose-up slightly, the
crank tends to slide rearward. Every time you use the clutch,
however, the action of pressing the throwout bearing against the
pressure plate slides the crank forward. Therefore, worn thrust
bearings result in longer clutch pedal travel.
Once worn enough, the action of the crank sliding forward causes the
front thrust bearing to slip out between the crank and the bearing cap
and land in the crankcase. When the clutch is released, the crank
then slides rearward until crank meets block, and the other bearing
falls out. The instantaneous result is an inoperable clutch, a
destroyed crankshaft and a fairly boogered-up bearing cap.
The preventative fix is to take the block to a machine shop and have
the thrust bearing recesses cut a whole lot deeper, and fabricate new
thrust bearings from bronze that are thicker so they cannot possibly
fall out, irregardless of wear. Alternative methods involve putting
flush-head screws through the stock bearings, are probably not as nice
but may be preferable for ease of doing.
Also: lubrication of the rocker assembly is via oil that has already
gone around the rear camshaft bearing (actually, this has been a
common method for many cars). Not to put too fine a point to it, this
sucks. When the camshaft bearing becomes a little worn, less and less
oil makes it up to the rocker, and the wear rate skyrockets.
The fix is easy, though. On the left rear corner of the head, there
is a small bolt with a copper washer. Its purpose is to plug the hole
where the oil passage from the camshaft bearing to the rocker assembly
was drilled in the casting. Remove this bolt plus one of the pipe
thread plugs in the main oil galley along the left side of the block,
and fab a line to connect the two openings. This will feed oil
directly to the rocker assembly, as well as provide a second supply to
the rear camshaft bearing. You should note a significant improvement
in the rocker assembly lubrication. You will not be able to get TOO
much oil up there, simply because the passages, and especially the
small bolt hole, are too small.
>infinity+2)look into performance engine, springs, shocks etc.
You might want to start with the TR6 engine. Same block, longer
stroke, can be installed with little grief (but not zero -- there are
some things to consider) and they are more common.
--
--- Kirbert
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| Kirby Palm, P.E. |
| palmk@freenet.tlh.fl.us |
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|