Saturday, May 3, 2014

Reducing Rattles: Installing custom foam in the floor cavity

From the start it has always been our intention to drive the Dino when it was finished. As such we have employed processes and materials that offer greater durability and function than original provided that they be installed in a manner that is not visible from the outside. This practice is commonplace in the best Pebble Beach winning restorations and we were happy to incorporate them on our project.
In this post we will look at one of these upgrades. From factory the Dino floor was made up of two thin fiberglass sheets pop riveted to the chassis. One sheet makes up the inner floor while the other makes up the lower floor that is seen when looking under the car. Between them is open space which turns the whole area into a drum. To make matters worse, at Scaglietti, the floor is installed before the chassis is painted (meaning the tubes are bare steel) and the floor is not sealed in any way to keep rain water out.
For these reasons the Dino chassis is prone to terrible rust as the tubes can spend years in a bath of un-evacuated rain water. In our case the floors had never been removed and we were lucky to find limited rust when the car was disassembled. Once the car was painted the chassis was treated with an anti-rust primer and then painted with an epoxy paint offering much more rust resistance than bare steel.
With the chassis members protected it was time to turn our attention to the hollow space in the floor. Again with the car being a driver we wanted the floor to be more solid and offer less transmission of road heat and noise. To this end we investigated different foam materials and ran into sizing problems where no material was the correct thickness. Eventually we found a company that cut some closed-cell foam to our specification creating for us a sheet that was just over 1mm thicker than the gap between the floor panels. Closed-cell foam was used because it will not absorb water and the extra millimeter of thickness ensures a tight press fit without bulging the fiberglass floor.
With the foam purchased the next step was to make cardboard patterns from which to cut the pieces. Once all the patterns were made it was off to the large sheet to determine a layout that gave us the best yield (the material was expensive and we did not want to waste any).

Below is an image of all the foam pieces in place before the floor is installed. Between the painted chassis and the closed-cell foam the chances of rust are much reduced from before. To seal things even better, a thin coating of seam sealer was placed between the chassis tubes and the fiberglass floor being extra careful to not have any visible sealer on the outside thereby maintaining the most original look possible.

Lastly with the floor in place the new rocker panels had to be drilled for the mounting rivets. We determined that originally these rivets were placed very close to exactly 10cm apart so we laid out a string to ensure a straight line and made holes in the correct location staying faithful to the original spacing. To top things off we installed black powder coated rivets for a nice clean install that looks factory original but is much more durable than it ever was.

One thing to note is that the fitting of foam to the underside of the chassis is very much a marginal improvement in sound transmission to having the area hollow. Many people think that installing something like this makes the car Mercedes quiet inside and nothing would be further from the truth. The reality is that the inside of a Dino is a loud place to be regardless of what you do and the foam is used to dull some of the annoying rattles and frequencies that more cheapen the sound rather than take away from the original character of the car.

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