DeTomaso Mailing List: September 98, Message #150

As we all know, working on a Pantera to fix one small thing tends to lead
to much greater adventures. This is one such adventure, and, with
suitable advice and expertise, may have a happy ending (at least a few
weeks from now). Or maybe not.

It all started when I blew yet another set of supercharger drive
bearings on the way back from Vegas. Rather, I blew one of the pair,
as there was a bit of a misalignment between the supercharger input
shaft and the bracket holding the bearings supporting it. Grease from
the bearing was inside my deck lid, and I've seen that symptom before.

The misalignment was caused, it seems, by the bracket slipping downwards
from the force of the drive belt from the jackshaft. Wilkinson's
design relied on friction between the (aluminum) bracket and the 
(steel) bolt heads holding it onto the bellhousing to keep the bracket 
from moving. This may have worked for a while at his shop, but eventually 
the 100hp pulled through that belt worked things loose enough to pull the
bracket down.

So, after discussing it with Russ B. and Jack DeRyke in PCNC, I rigged
up a simple solution of a pair of screw slugs run vertically through
the bellhousing bolt bosses on the brackets. These, when adjusted,
press against the sides of the mounting bolts and thus prevent the
bracket from moving down.

All has been more or less fine since then, except for the nagging knowledge
that I'd never checked the bearings nor replaced them. They were probably
bad, as a minor misalignment would at least pop the grease seal on one
of them, and I'd already seen the grease. So, I obtained another set of 
bearings (almost got that number memorized) and prepared to pull the bracket 
and press out/in the old/new bearings for what I hoped would be the last time.

This evening was the night I pulled it apart. The pulley on the shaft came
off with its usual amount of reluctance, but the two spacers behind it
didn't want to come off at all, and they're not shaped to be able to get a
puller on them. Odd, because they used to fit snugly, but slill I could
get them off. So, I undid the bolts holding the bracket to the bellhousing
in order to pull the bracket and spacers off together. Funny, the screw
slug on the driver's side is touching the side of the bolt as it should,
but the one on the passenger side is actually floating about a millimeter
or two above the bolt. Huh? Curiosity rising (along with a sneaky
suspicion), I started to pull the bracket and spacers.

The bracket didn't want to move, either. Oh, well, I thought, just one of
the bearings is bad and cockeyed a bit. What I saw when I got that bracket
and its bearings off the shaft explained far too much for me.

One of the bearings had indeed popped its seal but still turned fine. The
other bearing appeared to be OK. The shaft, however, is a different story.

The shaft is scored badly beneath the bearings. It's about 0.5 to 1.0 mm
scored depth (on a 25mm shaft). The misalignment had gotten so severe
that the bearings were both cocked at an angle and they galled the heck out
of the shaft (why are the bearing faces harder than the shaft, anyway?)
where they touched it. This misalignment flattened the back face of
the forward bearing to where it didn't want to slide on the shaft at all.

I looked for a correlation between the angle of the scoring and any
way the blower shaft could get that far out of whack. Turns out that
one of the two (and only two) mounting bolts for the whole supercharger
assembly on the manifold was loose. This allowed the rear of the blower
housing to swivel just a bit to the driver's side, as the belt doesn't
pull straight down, but off at an angle towards the driver's side. This
movement explained the floating screw slug, and it also gave the needed
angle to score the input shaft. It seems that the two mounting bolts
for the blowers was another area that ol' Steve decided that friction
would be enough. The blowers fit quite loosely around the studs and
rely on the friction between the (aluminum) housing and the (steel) nuts
on top of the studs to keep the blowers from shifting.

So, here I am with a disassembled supercharger drive system, a damaged
input shaft, and (shelved) plans to drive the car this weekend. I have
a rather important event (to my girlfriend) to go to on the 19th, and
I was hoping to drive the car to it (class reunion - she really wants
to arrive in the Pantera!).

The happy ending? There isn't one yet. This is where you, the various
mechanics and other relatives of Murphy come in (me, I think I'm bastard
child twice removed, or maybe three times, I can't remember how many
times they removed me...). I need advice.

Is this shaft damaged beyond repair? Can it be metal sprayed and machined
back to tolerance? If so, can this be done with the shaft still in the
supercharger housing (read: royal pain to disassemble, and impossible
to reassemble properly)? I remember someone (Jack?) mentioning a metal
depositing and machining process for restoring scored rear axles, could
such a process work for this shaft?

I'll take any kind of ideas from anyone, as this blower is basically 
unobtanium at this point and I don't really want to give it up permanently
 - it's addicting. I'm really hoping to get this car back on the road
before the rains come this fall. The car is pretty, yes, but I think it's
prettier on the road than decorating my garage (although it does that
well enough, too).

Help!

-tom, not looking forward to running just a Holley on an engine set up for 
low compression, large cylinder volume, and a supercharger cam grind 
(but it ought to _sound_ interesting, even if it gets outdragged by a kid 
on a skateboard...)
'73 euro GTS #6382