How to install new bonnet / hood sound absorber on a Porsche 944

THE WHY?

The benefits of installing new sound absorber to the underside of your hood / bonnet are reduced noise. It also keeps the heat inside the engine compartment preventing damage to external paintwork and keeps the engine at the optimal operating temperature aswell as insulating it from the sun and snow.

THE TASK

Before you can start you will need to remove all the old sound absorbing material, see my other post for a how to. This is very important as poor preparation could end up costing you a lot of money.

You will then need the following items:

a. Methylated spirits
b.Wax paper or baking parchment
c. 3M Scotch Weld 80 Spray Adhesive (£15)
d. Scalpel
e. 2 x sound absorbing pads from Porsche or here (£30-40 per side)
f. Large sheet to cover engine bay
g. Masking tape
h. Old newspapers

 

 

THE HOW TO

(Amateur mechanic Job Time approx: 1-2 hours)

As stated above you should have completely cleaned the old sound absorbing material from the underside of the bonnet /hood. If not see here for a how to.

Now begin by covering the engine bay with a large sheet, this will prevent any glue getting on the engine. Next use newspaper and low-tac masking tape to mask off one of the sound absorbing areas as shown below.

Give the exposed area a quick wipe over with methylated spirits to remove any grease, allow a moment for the meths to evaporate. Now depending on what sound abosrbing material you've bought the process here may differ. If you've bought genuine Porche sound absorber I believe it has it's own adhesive backing. If like me you bought 3rd party sound absorber you will need to use a special heat tolerant spray adhesive called 3M Scotch Weld 80. Spray the exposed area giving it a generous coating, then tear off two large sheets of wax paper / baking parchment and stick these over the glued area (as shown below) making sure you leave about 2-3 inchs of exposed glue along the top edge.

Now pick up the corresponding sound absorbing pad and coat the back of the pad in the same 3M adhesive. Once you've done this take the top edge of the pad and carefully line it up in the correct position and stick it to the underside of the bonnet. This glue is not repositionable so precision is the key here. Once you are sure you've got it lined up correctly remove the upper most sheet of wax paper and carefully smooth down the pad making sure you massage any air pockets out to the edges. Then remove the lower sheet of wax paper and smooth the final piece down. You may find that the bottom edge overlaps the area, but before you trim it make sure you remove all the surrounding masking tape and newspaper. Now simply trim off any excess with a scapel and press down all the edges. If you've got any bubbles use a pin to make a smal hole in the centre of the bubble and massage out the trapped air.

 

Now mask up the other side and repeat the process.

Now the finshed article with transfers applied

 

Here is a link to the 3rd party manufacturers instructions in case you are still unsure or need further detail.

How to remove sound absorber from the bonnet / hood of a Porsche 944

THE WHY?

The benefits of removing and replacing the sound absorbing material from the hood is that it prevents the engine heat from damaging the exterior hood paintwork, it absorbs some of the noise from the engine and also stops the old material depositing itself all over engine bay.

THE TASK

This is one of those jobs that there's no easy or quick way of doing, it purely comes down to sweat and elbow grease. Saying that anyone can tackle it, you just need patience and determination. Allow about 8 hours to remove all the sound absorbing material.

You'll need the following:

Plastic edged scraper (I used a white body filler spatular)

A large plastic or disposable sheet - to cover the engine bay

Cellulose Paint Thinners (I used 4 bottles of this!)

White Spirit

A mini roller and tray (use the cotton roller, not the sponge type)

Something to scrape the gunk into - I used a dustpan

Some latex gloves to keep the gunk off your hands

THE HOW TO

(Amateur mechanic Job time : Approx 3 hours per side)

Firstly cover the entire engine bay with a sheet otherwise it'll be a nightmare to clean all the old gunk off afterwards. Now unlike mine yours might still have all, some or bits of the original sound absorbing material clinging to it, so remove as much of this as you can until you're left with about 1mm of the combined glue and foam layer.

Now the fun begins. You need to soften up the dried glue and foam layer by rollering on the cellulose thinners in 30cm sections several times over and then quickly scraping this off with the plastic scraper until you are left with just the glue. Repeat as necessary. If you look at the image below the right hand section is after the cellulose thinners has been used and the left hand section is still to do.


Now, once you're left with just the glue on both sections we switch to the white spirit and use the same method of rollering it on. You can afford to do larger sections with the white spirit as it doesn't evaporate as quickly as the cellulose thinners. The picture below shows the glue completely removed from the left panel using the the white spirit.

And now the finished article....



Now, see my post on how to install new sound absorbing material here