A Couple of Dumb(?) Questions

[Matt K.]

Hello All - hopeful future Gen 3 Coupe builder/owner here. Been following the build threads for a little while, and done a little searching, but haven't come across anything related to the following:

1) It looks like some builders put silicone sealant between the steel structural members and the aluminum panels. For those that don't, how do you seal up the drilled (or drilled & tapped) holes where you put rivets/screws in so as to prevent rust streaking when you wash the undercarriage?

2) Has anyone put any type of bumper at the rear and/or front of their cars to help prevent minor collision/incidental parking lot damage? I've seen how the older Corvette fiberglass bodies can "split" during an impact. Do the coupe bodies do the same? I'm thinking that if I do build a car, I'm going to drive it regularly, and I'd like to mitigate the "minor" damage risk as much as is practical.

Thanks in advance!

Matt

[bil1024]

Silicone is required for extra strength, I see no reason not to use it.

I know some builders have welded in Metal bars on the frame, sandwiched right behind the body and nose/rear, some states do require this

[John Dol]

Matt,

Silicone also helps reduce metal rattles.

Look at Karen Salvaggio’s racing coupe she had a rear bumper on hers.

John

[edwardb]

1. Factory Five's instructions (and videos) show using adhesive plus the rivets. I guess it's builder's choice, but is how it's intended to be assembled. As already stated, adds strength, sealing, and any chance of rattling. They recommend using plain old silicone RTV. I've found it works very well and holds surprisingly well. I've had to remove a panel or two in the past and it's very hard to get them off without damage. Some prefer different adhesive, e.g. urethane. A little more expensive but certainly stronger, although I'm not personally sure it's necessary. Some don't want silicone anywhere on their build for fear of contaminating the finish down the road. I haven't had an issue with that either. But like many decisions on the build, do what you're comfortable with. As you're installing the panels, run the bead of adhesive, whatever you use, down the center of the row of holes. That will seal them up when you put the rivets in. I've never seen any rust streaks on the underside.

2. Bumpers on the Coupe body are going to be challenging. No doubt something could be rigged up to pass a legal inspection. But I question how much good they would do. There is a fixed frame in the back where something could be added, either under the glass or provide mounting for exterior bumpers. But the front with the full tip nose is going to be difficult. In the end, without major modifications (and I have no idea what that means...) is only going to be as strong as the pivot mounting. In the end, IMO minor accidents and/or incidental parking lot bumps are going to damage the glass. Nature of the beast. Just don't be bumping it.

[Matt K.]

Thanks to all for your responses. Very helpful!

Matt

[John Dol]

https://www.bing.com/images/search?v...=63&ajaxhist=0

Rear bumper

[Matt K.]

Excellent. Thanks John.

Another question: Do you guys know if anyone has ever attempted to use the Scotch VHB tapes for attaching the aluminum panels to the steel structure (or to themselves, for that matter)?

[edwardb]

Excellent. Thanks John.

Another question: Do you guys know if anyone has ever attempted to use the Scotch VHB tapes for attaching the aluminum panels to the steel structure (or to themselves, for that matter)?

I think it's been asked a couple of times. Usually with the same response. Why?

[Matt K.]

My thoughts:

PRO's:
- Eliminates silicone sealing/bonding requirement
- The claimed tensile (and shear) strength of a "good" tape bond is higher than that for silicone sealant
- Significant(?) reduction in the amount of time spent marking hole locations and drilling for rivets
- Reduced mess

CON's:
- Probably more difficult to remove panels, if need be
- Lower temperature capability (reduction in bond strength at higher temperatures)

[edwardb]

My thoughts:

PRO's:
- Eliminates silicone sealing/bonding requirement
- The claimed tensile (and shear) strength of a "good" tape bond is higher than that for silicone sealant
- Significant(?) reduction in the amount of time spent marking hole locations and drilling for rivets
- Reduced mess

CON's:
- Probably more difficult to remove panels, if need be
- Lower temperature capability (reduction in bond strength at higher temperatures)

I don't think that's a very good comparison. I would not recommend building with only silicone sealant, as in no rivets. Even if the tape bond is equal to the silicone bond, it's nowhere near the adhesive bond plus mechanical bond when rivets are added. Additionally, while the fit of the laser cut panels is very good, I would question how possible it always would be to get a "good" tape bond, as in full contact. Some shapes are irregular, panels don't always match exactly on the same plane, sometimes there isn't a lot of contact, etc. A bead of adhesive and a row of rivets will easily overcome all of these.

Marking, drilling, riveting takes a while I guess. But it's a relatively small portion of the overall build time. Using clecos as you go is an old school process but works really well holding panels in place while you're doing the drilling, and then again getting them located and riveted back into place with the added adhesive. A shop vac makes quick work of whatever mess there is. Good to see you're thinking outside the box. But I'd recommend in this case going with the proven process.

[Matt K.]

Edward- Thanks sharing your experience-based thoughts. Looking forward to continuing to watch and learn from your Coupe build.

Matt