Re: slackening V6 tensioner

[dlou <dlou@domain.elided>]

>From: ethan schartman <eschartman@domain.elided>
>Subject: slackening V6 tensioner
>
>> From: Joe Elliott <jee@domain.elided>
>> Subject: V6 belt tensioner
>> 
>> What is it about the mechanical detensioner that
>> makes it slack off 
>> if you turn the engine backwards?
>
>in normal operation...
>
>except for the first time (possibly), i have not had
>problems with reverse rotating the engine because i
>never parked it in gear 

Aye, now there's the rub.  If you use the parking brake, you'll
risk the seals on the rear caliper.  If you use neither, you'll
be an insurance liability ("Mr. Defendant, before your car hit
my client, did you engage the parking brake?  Put it in gear?")

Maybe we should chain our V6 cars to parking meters?  Perhaps get
wheel clamps like London and Denver use against repeat parking
violators?

It would seem that the original question was directed
towards the differences in the mech detensioner vs. the hydraulic.
Besides the possible differences in spring tension (which was addressed)
my theory is that there are different modes of operation.  The
mech detensioner responds to temperature while the hydraulic responds
to oil pressure.  Thus, it would seem the following truth table applies:

(H= high spring pressure, L= low spring pressure)

               Hydraulic    |    Mech
----------------------------+--------
cold, off    |    H         |     H
-------------+--------------+--------
warm, off    |    H         |     L
-------------+--------------+--------
cold, idle   |    L         |     H
-------------+--------------+--------
warm, idle   |    H         |     L
-------------+--------------+--------
cold, revved |    L         |     H
-------------+--------------+--------
warm, revved |    L         |     L

Also, there's the differences in spring design.  The mech tensioner
uses a single (bimetal?) spring providing tension around it's rotational
axis.  The hydraulic tensioner uses 2 (solid steel?) springs
providing tension along their linear axes.

-Dennis
Sunnyvale, CA
'85 GTV6
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