[Shotimes] Cams and Crowbars and Cranks, oh my!

[Jim & Debbie Leyden]

Makes perfect sense to me.  But I learned my trade in the Machine Tool
Industry.  The advent of Geometric Tolerancing helps this problem quite a
bit.  But true high precision quality is really a function of careful part
selection and matching to keep the completed assembly at the center of the
bell curve.

Jim




-----Original Message-----
From: shotimes-admin@autox.team.net [mailto:shotimes-admin@autox.team.net]
On Behalf Of Zach Leahy
Sent: Monday, June 06, 2005 1:41 PM
To: Dave Pillsbury
Cc: Rich Bruso; shotimes@autox.team.net
Subject: Re: [Shotimes] Cams and Crowbars and Cranks, oh my!

I think it is probably an RSS (Root Sum Squared) result of tolerance
stack ups.  I bet the nominal value is about a 2500, but it can
obviously swing a lot farther one way or another.  It does not mean
that everything is machined exactly the same, but that the overal
stackup of tolerances is the same.

Basically an RSS value will form a bell curve, where it seems 2500 is
right in the middle, but it is possible to deviate farter away to the
extremes, but more likely to be near 2500.  There are probably several
meachining tolerances that play a role and while one may be +.002 the
mating part may be -.002.  RSS, good stuff, makes building highly
accurate things posssible.

Did that make any sense to anyone else?   It made sense to me, but I
am the one writing it, and see this kind of stuff at work

Z

On 6/6/05, Dave Pillsbury <showerks@comcast.net> wrote:
> I've got dozens of 2575. Strange thing about running the shim spectrum.
> I've seen from 2300 to 2600 in one engine. To a straight up 2500X24
> shims in the last customer car we did. I thought that one was strange as
> hell. Until I cracked the engine on my 95 and took a look at the shims.
> 2475to2525 is the shim spread on it. but the 89 engine here was
> 2375-2600 and the 2300-2600 engine was my 90 the 94 ATX that I robbed
> the shims out of had very little spread too. It's either a simple fact
> of quality got better and there was less valve shim difference or the
> early engines were built better. By the way the last 94-95's I've done
> were all way out of spec!
> Dave
> 
> Rich Bruso wrote:
> 
> >   Well, it looks like Lola's previous owner's mechanic did me another
favor.  I got the car in '01, and in '02 (on my wedding day, no less) my
clutch went out.  Upon inspection, it turns out the mechanic kept tracking
down 9 1/4" clutches, so I got to spring for the larger bolt circle flywheel
then.  Fun.
> >   Anyway, the same guy apparently used some sort of percussive
maintenance tool to reinstall the pulley.  I've managed to strip one puller
bolt and bend two.  Fun.  It appears the key is still intact, and I know the
timing belt pulley hasn't slipped at all (good news there)  I'm just
wondering if anyone has any experience with trying to pull a munged up
pulley off without collateral damage.
> >   Also, after meticulous moving, checking, and rechecking, I've come
down to some wonderful valve lash numbers on all but one each of the #2 and
#3 exhaust valves, both of which really need a 2575.  2600 is too tight, and
I'm out of 2550's.  Let me know if you have any spares you'd be willing to
get rid of.
> >   Strange note.  My spare motor (out of my old Titanium '89) had both a
2650 AND a 2375.  Quite a range of shims in that motor.
> >
> >
> >-Rich Bruso
> >89 Black (Lola)
> >89 Silver (parts)
> >Sierra Vista, AZ
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