Fiberglass White 4000 Hood Repair 

 

Have we ever seen or have we been a truck driver who has damaged the fiberglass engine hood and has smashed the front guard including  the light surround and wheel arch? well it does happen and I have fixed quite a few over the years.  fiberglass white 4000 engine hood

They may look bad  and can be and usually much cheaper to fix then getting a new one specially if the truck is not insured, but remember though for a diy’er it could be out of their league to fix unless your quite knowledgeable and even then one might ask why fix it.

These smashed hoods can be pretty easy to fix and can apply to many different fiberglass panels and applications, even if you buy a second hand hood these usually have scratches or even damage already and can cost around $1000 to $1500 not including freight depending on where they are.

First we need to remove the hood from the truck and set it up off the ground and made level and also we can work under it safely, then get a pressure cleaner or jet hose and give under the hood a good clean where damaged when dry remove any items e.g. radiator grill, headlamps, blinkers, logos etc in relation to the area damaged/broken these could be bolted through.

Then release any fiberglass sections that are kinked under another panel or raised above the surface, this happens from the impact breaking the fibers from stress flowing through the panels and finding weak points in the laminate, these jagged fibers can be enough to hold a panel from springing back to be in line with the other section.

If a section say the back of the wheel arch to the rear of the guard is not attached no need to concerned about this as pieces like this can be put back when it’s time to glass the rest of the hood, now if we look underneath the hood you should see it’s coated in a Black Under Body Deadener paint.

Now we need to put our PPE on including googles, mask etc and with say a 100mm grinder with a 24 grit grinding/sanding disc we now need to clean away this till we get down to the fiberglass, do this allowing at least 60mm either side at this point of the broken area where possible, we will now see more of the damaged done by the impact any de-laminations to the laminate  de-laminations are usually a pale cloudy white colour and splits the laminate thickness making it weak.

Now if we have a larger detached panel we can put this piece back in place by working from the outside, you will need two (2) pieces of flat thin pine or ply (if the panel is in a flat section) say 25mm 1″ wide x about 75 mm 3″ long drill a hole in each end roughly so a screw can go through easily (Example).

missing panel screw down points example

Now on the main body of the hood where this panel goes and place the timber 90 degree and midway to the crack and drill a small hole for the screw to be screwed into the glass panel on the hood, screw this in and do up firm do this along the length maybe just one more or another down the front or back of where the section goes.

Note: Some small panels if they line up well could be temporary held in place with a bit of car filler in spots then grind out between and put a single coat of csm, let dry and grind out the filler and continue with the layup.

Put the missing part in place up and line it up and under the straps you have screwed in and drill the same small hole through the glass panel and screw the panel in place so the cracks line up with the hood, now if your part is relative big and is on a curve you could use something like a ice cream lid plastic so as to go around curves better and pan head/flat head screw as not to pull through the thin plastic.

By the way look out for delaminated areas although you will most likely see theses when you do a grind from under the hood, if you do have one or two then carefully using a chisel take these out till you see solid glass and not a cloudy section still, saves a lot of grinding especially on a large area, although you will still need a light grind on the surface area and feather off the outside section.

We now need to do a grind around and between the straps like below, we can now mix up our resin depending on your situation but for a boat or truck hood etc. I would recommend using un-waxed resin ( isophthalic ) by the way using epoxy on a engine hood ( unless it is made from epoxy or it is made from some injected resin with glass fiber running through it as epoxy will stick to just about anything) can be expensive and messy if you never used it before, and  this allows us not to bother grinding again to remove wax if we have interruptions while building up the laminating and if your article is epoxy use it instead and follow the directions.

Now working from the outside and wearing appropriate Safety PPE we can start grinding out the bond area we need before glass up we now need to change discs to a 16 grit disc as we need to make the bond area porous so to speak, the width of the grind should be at least 75mm-100mm or 3″- 4″ and should be dished shaped  )  and go ¾ of the way through at the crack (using this as your centre) and grinding out to a feathered edge to the outer edge of your bond where this should have a mark.

Whilst using the grinder with such a course disc do not apply to much pressure to the laminate while grinding as it will be easy to grind through the other side, just use the weight of the machine to start with unless you have used grinders before, remember the laminate in a truck hood may be only 7-6mm thick or ¼” in old terms or less.

After preparing all the outside bond grinding areas it’s time for cutting up our fiberglass mat we will need at least 3 layers of 600gm CSM (chopped strand mat) or 2 x 600 and 1 x 450gm cut into strips ( this will depend on your engine hood or product your working on ) now with the strip size in width will depend on how wide your bond area is.

If our bond area is say a 100mm wide or 4” old term and 1mt long ( fiberglass roll ) unless using off cuts and laminate thickness is around 7mm then will look something like this.

  • First layer 40mm
  • Second layer 70mm
  • Third layer 100mm or a touch less if your top coat is Gelcoat or Flow coat, truck engine hoods are usually grey and sprayed in 2 pac top coats to your desired colour so a two pack finish coat is more desired.

 

END of PART 1

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