Date:         Mon, 30 Sep 2002 11:45:07 EDT
Reply-To:     FrankGRUN@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Frank Grunthaner <FrankGRUN@AOL.COM>
Subject:      Re: On I4 Engine Vibration/ hard mount of carrier
Comments: To: mdlind@RICA.NET
Content-Type: text/plain; charset="US-ASCII"

In a message dated 9/30/02 5:28:54 AM, mdlind@RICA.NET writes:

<< Jason, it has been suggested, properly I believe, that the TIICO motor
mount/engine carrier needs to be welded, not suspended on rubber bushings.
As it comes, it can float between the frame of the van and the engine. This
is because is has rubber mounts at both the engine and at the frame of the
van, allowing it to move independently from both the engine and the van. So
damping might not (probably isn't) even be part of this picture. >>

Myron, dampening (both positive and negative) is always in the picture. There
is a significant difference in the way VW did engine powertrain isolation in
the '83 (and subsequent euro production of NA and TD motors) that they did on
the '82's and the prototypes. One can think of the cradle mounting assembly
as a mini sub-frame (extensively used by many manufacturers to attach the
powertrain to the body). Usually, those subframes have the engine mounted
through active or passive motor mounts, and then mount to the frame through
another passive isolator. Sometimes they are bolted metal to metal. Its often
a question of the needed rigidity.

There have been anecdotal reports of better vibration isolation with the
welding of both the TIICO and the '82 Diesel carrier bushings. I'm not overly
familiar with the TIICO system but I'm depressingly familiar with the early
diesel approach. A key here is the generation of resonances. The elastomer
suspended carrier is not necessarily a bad design. But in comparing the rigid
carrier design to the elastomer suspended one, note that the crossbar has
been eliminated. If you run the elastomer system without the crossbar, very
significant vibration resonances can occur.

So the rigid mount puts all vibration isolation control on the motor mounts
which I suspect are designed for a different isolation response function as
compared to the '82. The earlier carrier design with stiffening crossmember
could have a resonance that was removed by hard dampening to the frame.
Possible. But just as likely the two stage isolation system could offer
better isolation.

Remember, VW engineered both systems for the vibration amplitude generated by
the 1.6L diesel. The 2.0L gas engine has a higher amplitude input to the
problem and the peak frequencies are also different because of the enhanced
rev range. I would argue that the better system would be the use of
sorbothane bushing material with active isolation motor mounts. In the end,
though, this is all speculation. The answer is readily obtained by measuring
the vibrational spectrum, then changing the bushings or carrier mount and
measuring the system again. Not overly difficult. Have a vibration
measurement party.

Frank Grunthaner