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"Thanks to the Interstate Highway System, it is now possible
to travel across the country coast to coast without seeing
anything." -- Charles Kuralt
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Date: Fri, 20 Feb 1998 18:56:58 -0800
From: Joe Curry <spitlist@gte.net>
Organization: Curry Enterprises
To: Peter Zaborski <peterz@merak.com>
Subject: Re: Tach Question
References: <903A11BB7D30D11199B800A0C95C6EDD3E4B12@EXCHANGE.merak.com>
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In the Spitfire Mechanical tach drive on the distributor, there is a
nylon worm gear that transmits the rotation of the distributor to the
tach cable. That is one of the weak links in the whole system. Binding
cables can cause this gear to wear out. I assume the one in the TR6
(like the GT6) is of the same technology. Perhaps this is where the
trouble lies.
Joe Curry
Peter Zaborski wrote:
>
> > -----Original Message-----
> > From: jaltman@altlaw.com [SMTP:jaltman@altlaw.com]
> > Sent: Friday, February 20, 1998 4:54 PM
> > To: 'Peter Zaborski'
> > Subject: RE: Tach Question
> >
> > Thank you. I was reading about 3200 until I replaced the tach cable
> > and now
> > it reads about 3600. I wonder why a new cable would cause that?
> >
> It is indeed strange...
>
> For the record, my car does show the ratio of rpm to roadspeed Bob
> indicated in the message I quoted below.
>
> Now back to your problem. We know the dist spins at a speed which is
> directly related to the crankshaft speed (this is via solid gears). The
> cable is attached to the dist and the other end to the tach.
>
> Here are two more things to consider...
>
> 1. Why did you change the cable in the first place? If you put it back
> in does the engine speed go back to where it was (ie. from 3600 back to
> 3200)? If so, perhaps the old cable was rounded and therefore slipping
> in the square drive part of the dist (where the cable plugs in).
> Alternately, maybe the dist end of the cable is rounded and the slippage
> was causing a lower speed than actual to be displayed on the tach.
>
> 2. If the new cable is actually transmitting the correct (ie. full,
> non-slipping) rotation to the tach and the old cable was rounded and
> causing slippage somewhere in the linkage, then perhaps the tach is out
> of spec and needs to be recalibrated?
>
> If everything was fine with the old cable (ie no slipping) then I cannot
> see how a new cable would cause the tach to speed up. There is no
> gearing in the cable it is just a solid piece of steel.
>
> These are my thoughts...
>
> Peter Zaborski
> 76 TR6 (CF58310 UO)
> Calgary AB Canada
>
> > Jim Altman jaltman@altlaw.com Illigitimi non Carborundum
> > http://www.altlaw.com/ 69-TR6#CC28754L W4UCK
> >
> >
> > -----Original Message-----
> > From: Peter Zaborski [mailto:peterz@merak.com]
> > Sent: Friday, February 20, 1998 6:50 PM
> > To: 'jaltman@altlaw.com'
> > Subject: RE: Tach Question
> >
> >
> > Jim this may not be exactly what you want but I saved it from a much
> > earlier post by Bob Lang...
> >
> > RPM's Gear Speed
> > 2000 1 10 MPH
> > 2000 2 20 MPH
> > 2000 3 30 MPH
> > 2000 4 40 MPH
> >
> > All speeds are very good first order approximations.
> >
> >
> >
> > Extrapolation would suggest that 60mph results in ~3000rpm.
> >
> > HTH,
> >
> > Peter Zaborski
> > 76 TR6 (CF58310 UO)
> > Calgary AB Canada
> >
> >
> > > -----Original Message-----
> > > From: jaltman@altlaw.com [SMTP:jaltman@altlaw.com]
> > > Sent: Friday, February 20, 1998 4:33 PM
> > > To: 'Triumph List'
> > > Subject: Tach Question
> > >
> > >
> > > Lets try this again. Would one of you 6 drivers please note your
> > tach
> > > reading at 60 MPH and let me know what it is? Please. No OD.
> > >
> > >
> > >
> > >
> > > Jim Altman jaltman@altlaw.com Illigitimi non Carborundum
> > > http://www.altlaw.com/ 69-TR6#CC28754L W4UCK
> > >
--
"Thanks to the Interstate Highway System, it is now possible
to travel across the country coast to coast without seeing
anything." -- Charles Kuralt
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