RE: Variable valve timming

["Aaron Ness" <aaron@makuta.com>]

Not familiar with the 16V setup, but the 8V (and my BMW) has the tensioner
on the "loose" side of the belt.  IOW, this side will have some slack
created when the crankshaft turns.  The actual valve timing is set by the
number of belt teeth on the side opposite the tensioner.  It has to be this
way because a belt only works in tension - you can't push a belt to drive
something.

Based on this, you could put an adjustable tensioner on the tension side of
the belt (the front of the block on an 8V) to vary the number of belt teeth
between the cam and crankshaft.  This would have to be supplemented by a
spring-loaded or other self-compensating tensioner on the slack side of the
belt to maintain tension when you retard the valve timing.  Then you have to
choose the spring carefully so it doesn't fail or you're gong to be jumping
teeth.

I haven't looked at how production VVT engines adjust the valve timing, but
this should work if you're up to the task.

Aaron
'87 528e
'82 Scirocco
'70 Beetle
'82 Kawasaki GPz550


> -----Original Message-----
> From: owner-scirocco-l@scirocco.org
> [mailto:owner-scirocco-l@scirocco.org]On Behalf Of Daniel Brideau
> Sent: Monday, June 18, 2001 10:33 PM
> To: scirocco-l@scirocco.org
> Subject: Variable valve timming
>
>
> When I put new timing belt on my 16V, I managed to install it
> "a tooth off".
> This happened, because I aligned the timing marks with the
> tensioner set in the
> loose position.
>
> Tightening the tensioner moved the timing, quite a lot.  The
> power difference
> was considerable.
>
> This got me thinking, how difficult would it be to make a
> tensioner assembly
> that could move?  If two tensioning cam-pulley things were
> mounted to a sliding
> plate, you could manage the cam timing 'on the fly'.
>
>
> My specific question to you guys is: how much force would be
> required to move
> the timing while the engine is at full speed?  I think quite
> a lot, but haven't
> taken the time to study the dynamics involved.  Some sort of vacuum or
> oil-pressure controlled servo would be needed, or perhaps an
> electric motor
> driven actuator.
>
>
> Any thoughts?
>
> Dan Brideau
> http://www.type53.com/
>
>
>
>
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