Engine Covers & Fairing Repair – Materials and Methods

[charlenesays]

Hi fellow V11 riders,

I’m diving into a custom fabrication project for my Moto Guzzi V11 Le Mans—specifically around engine side covers and fairing repair using acrylic or ABS plastics. Thought I’d open a discussion here to share what I’ve tried and learn from others working on similar mods.

Project Background:

• Right side engine cover has a cracked section from a tip-over.

• Left fairing intake trim had a missing insert.

• I plan to fabricate replacement parts using either ABS or 2 mm acrylic, shaped to match OEM contours.

Current Setup:

• CAD sketches based on molds and photos.

• Prototype parts cut on a CNC router or laser based on the material.

• Sanding and smoothing by hand before finishing.

Questions I’m working through:

1. Material suitability: Is ABS sheet stronger and more heat-resistant around the engine versus acrylic?

2. CNC vs heat forming: Best practice for cutting complex curves—do people prefer pre-shaping acrylic via heat bend or go straight to CNC routing?

3. Mounting method: How are you bonding your fabricated parts? I plan to use high-temp epoxy or solvent welding, but curious about vibration and durability on engine vibration zones.

4. Paint prep: For panels near heat or vibration—how do you prep fabricated plastic to match OEM finish and hold up in the elements?

Would love to hear input from anyone who’s fabricated or repaired V11 parts—or has experience with custom motorcycle plastics more broadly. If you're using a blend of fabrication methods or have photos of past repairs, I’d be excited to see!

Looking forward to your ideas.

[Pressureangle]

Arr, the ol' Pirate's bane. 

Plastics have been lamented since they first arrived.

Every type of plastic has it's own very specific requirements for bonding. Some bond to nothing, not even themselves. 

ABS plastic is problematic but not impossible. I worked at a heavy equipment shop, and to repair punctured fuel tanks (who puts a fuel tank under the loader where branches can stab it, anyway? *volvo*) we purchased a hot-air plastic welder. It worked fabulously on Polyethylene, and after some testing and practice just as well on ABS. It's critical that you discover the method to test and verify plastic type or you'll find not everything is actually made of what it's commonly called. I don't know the specific on V11 plastic, but I do have a couple pieces that could use some help. The idea with the air torch is that it's hot enough to melt the plastic while controlling exactly how soft it gets, and without risk of changing the chemistry of the plastic with flame or overheating. Mostly you simply choose the correct type of plastic welding stick and heat the base and stick together, melting the failure together. In practice, it's a delicate balance and while not hard to make a solid repair it is much harder to make a *pretty* repair. Preparation helps just as it does with metal welding, creating space in the crack to increase surface area without affecting the finish on the visible side. Using a small battery powered drill to spin the filler stick also makes things much more solid, but takes an even more practiced hand.
iirc the welder kit cost something like $700 in 2005, but I'm sure inexpensive chinese kits can be had within a budget now. Hm...

[Lucky Phil]

4 hours ago, Pressureangle said:

Arr, the ol' Pirate's bane. 

Plastics have been lamented since they first arrived.

Every type of plastic has it's own very specific requirements for bonding. Some bond to nothing, not even themselves. 

ABS plastic is problematic but not impossible. I worked at a heavy equipment shop, and to repair punctured fuel tanks (who puts a fuel tank under the loader where branches can stab it, anyway? *volvo*) we purchased a hot-air plastic welder. It worked fabulously on Polyethylene, and after some testing and practice just as well on ABS. It's critical that you discover the method to test and verify plastic type or you'll find not everything is actually made of what it's commonly called. I don't know the specific on V11 plastic, but I do have a couple pieces that could use some help. The idea with the air torch is that it's hot enough to melt the plastic while controlling exactly how soft it gets, and without risk of changing the chemistry of the plastic with flame or overheating. Mostly you simply choose the correct type of plastic welding stick and heat the base and stick together, melting the failure together. In practice, it's a delicate balance and while not hard to make a solid repair it is much harder to make a *pretty* repair. Preparation helps just as it does with metal welding, creating space in the crack to increase surface area without affecting the finish on the visible side. Using a small battery powered drill to spin the filler stick also makes things much more solid, but takes an even more practiced hand.
iirc the welder kit cost something like $700 in 2005, but I'm sure inexpensive chinese kits can be had within a budget now. Hm...

I've successfully repaired quite a lot of motorcycle plastics over the years with nothing more than a small soldering iron and some plastic filler of the appropriate type. The Ducati stuff from a few years ago wasn't possible to weld so I "Veed" out the crack on the inside and used "Scotchweld" ( these days I might use JB weld) in the Veed out section followed by fine copper flyscreen cut to size across the crack and another layer of Scotchweld to embed the screen which worked just fine after the appropriate filling and sanding of the outside face.

Some plastics don't weld BUT they do respond to a "braze" repair with the appropriate filler plastic. So you can use filler plastic to bond to the base plastic in a method the equivalent to brazing where it doesn't melt to the base material but still bonds well same as brazing. If you look in my Daytona build thread I explain how it's done on the airbox in some detail from memory. I think the original airbox is made from HDPE which isn't weldable but I managed to do the braze repair with LDPE from memory. That's part of the reason I post stuff for "records" when I forget the details. A pro plastic welder I showed the job to told me it was impossible to weld and said he couldn't help me. He was totally dismissive when I told him about this style of repair after I had done mine but a bit embarrassed when I showed him the results of my brazed method (which I didn't invent just researched). I felt like telling him he might need to find another line of work or at least update his training but managed to "hold back". Very out of character for me. 

Edited Thursday at 11:22 PM by Lucky Phil

[Pressureangle]

10 minutes ago, Lucky Phil said:

I think the original airbox is made from HDPE which isn't weldable 

Volvo earthmover fuel tanks are HDPE. It is very easy to weld repair, given the right equipment and filler; I cut pieces from ruined tanks as filler and patches.

[Lucky Phil]

22 hours ago, Pressureangle said:

Volvo earthmover fuel tanks are HDPE. It is very easy to weld repair, given the right equipment and filler; I cut pieces from ruined tanks as filler and patches.

I checked my Daytona build thread and the airbox material is made from cross linked polyethylene. I used Low density polyethylene rods to fix it but as I said it's more like brazing and you need to not actually melt the base material only the filler rod.

EDITED materials for clarity and eliminate confusion.

 

Phil

 

Edited Friday at 10:22 PM by Lucky Phil

[Pressureangle]

6 hours ago, Lucky Phil said:

The airbox material is made from cross linked polyethylene. I used straight polyethylene rods to fix it but as I said it's more like brazing and you need to not actually melt the base material only the filler rod.

 

Phil

 

ah, I've seen that but never had to repair it. Standard hdpe tanks are simply  blow-molded. This stuff is a bit 'stringy' on the edges, yes?

This is precisely why I said you need to know *exactly* what material you have before you start. Good stuff.

Edited Friday at 01:29 PM by Pressureangle