Converting a factory JK/JKU hardtop to modular

jscherb

Expedition Leader
#1
Factory hardtops are awkward - being one piece (ignoring the freedom panels for the moment) they're big, bulky and very hard for one person to lift off or install safely or easily. They can also be very stuffy inside - the side windows are bonded in place and don't open. I think there's a better way - going modular.

I've been designing and building modular Jeep hardtops for the past 6 years. It all started back in 2010 with my LJ "Safari Cab" hardtop project. The modular design of the LJ Safari has worked out extremely well over the years - being assembled from multiple smaller parts, it's easier for one person to install, remove and store than a traditional hardtop, and the modular design has also allowed a range of configurations, including swapping the hard sides/glass windows for soft sides that roll up.





Recently a company asked me to design a slider window retrofit kit for them to market for the JK, the idea is to replace the factory bonded-on side windows of the JK hardtop with opening windows. I finished up that project for the JKU and the next step was to do the JK 2dr version. To do that I needed a 2dr hardtop to work with, so I picked up a 2dr hardtop shell I found on Craigslist.



I decided that shell would also make a good candidate for an idea I've had for a long time, which is to convert a factory hardtop to modular. Converting it to modular would also make my window retrofit project easier because I could work on the hardtop side panel on my workbench rather than having to always work on the one-piece hardtop. So I cut the hardtop into pieces:





I came up with a design and DIY-process for converting factory JK/JKU hardtops to modular assembly, and the purpose of this thread is to share that process in case anyone wants to convert their hardtop.
 

jscherb

Expedition Leader
#2
The conversion is a pretty straightforward process that I think most people with a little DIY experience could successfully do. I wrote up all the necessary steps as a DIY guide, and then I executed the steps to test how the design and modification process worked.

Here are a few photos of the completed modular conversion.

Fully assembled. If I didn't tell you it was the finished modular conversion you would probably think it's just any old factory top - the conversion doesn't really affect the outside looks:



Side panels removed. Now you can tell it's the modular conversion :):



Since I don't have a 2dr JK to show it on, here's a sides-off concept:



Disassembled:

 

jscherb

Expedition Leader
#3
The modular top can in installed/removed in one piece, just like the factory top:



It can easily be installed by one person - all of the panels are light enough to be handled by most people. The roof panel is large enough that it could be a bit awkward for people not as tall as I am, but as you can see by me holding it with one hand, it's not very heavy:



Installing the top can be done in steps - install one side panel and then the rear panel, then install the other side panel, and finally install the roof (I'm doing this on the driveway instead of on a Jeep because I don't own a JK 2dr to put this top on).

 

jscherb

Expedition Leader
#4
Storing the modular top.

I checked to see how much space the top takes up against a wall - at the bottom the outermost panel in this stack is 15" from the wall. I think most garages have 15" to spare between the wall and a Jeep, so it should be easy to store in the garage.



Also the rear panel and side panels are all small enough to each fit under a single bed. Two sides can fit under one bed and the rear panel can fit under another. The roof will fit under a queen bed, so probably the top can be stored inside in many apartments and most houses.

Even though my hardtop parts don't have any glass, all of the above still applies to parts with glass and a liftgate.
 

jscherb

Expedition Leader
#5
Here's a view of the inside of the top, you can see where everything bolts together:



The basic idea of the project is to cut the factory top apart and add the bolt flanges seen above on both sides of the joints that have been cut.
 

jscherb

Expedition Leader
#6
A few concept images, just some ideas that could be done with the modular conversion...

With just the top panel installed, something like this J8 could be done (or like my LJ Safari)






A few JKU ideas:





The same with roll-up side panels:




Some 2-door concepts:







with roll-up soft sides

 

jscherb

Expedition Leader
#7
When I was doing the design for this conversion, I came up with a list of criteria that I wanted the conversion to meet:

1. The hardtop should have a factory look after the conversion. With all the panels in place, the hardtop shouldn't look any different than a factory top. On the inside, the conversion should be as non-obvious as possible and should look as if it had come from the factory that way.

2. The assembled modular top should be as strong as the factory top.

3. The top should fit exactly the same as the unmodified factory top - there should be no changes in dimensions or fit.

4. Running without the side panels should be possible.

5. The top should support optional roll-up soft sides.

6. Repainting should be at most a minimal touch-up with available MOPAR touch-up paint. A full repaint should not be required.

7. Cost of materials for the conversion should be kept to a minimum, between $100 and $200.

8. It should be possible to install/remove the top in one piece just like an unmodifed top, or install/uninstall it piece-by-piece.

9. No special tools or techniques should be required that wouldn't be accessible to an average DIY-er in a home garage.

10. The conversion process should be designed to ensure all of the above and ensure an accurate fit and alignment of the modified parts without the need for any special skills or prior fabrication experience.
 

jscherb

Expedition Leader
#8
The basic conversion steps:

1. Cut the factory top apart.

2. Add bolt flanges to one side of each joint between the panels. I did this by fiberglassing the flanges directly to the panels with clamped-on forms.

3. Add matching bolt flanges to the other side of each joint. To make sure we end up with flanges that perfectly match those in step 2, I created these flanges separately and bonded them to the hardtop panels - this method makes the process very accurate and easy.

4. Final touch-up.

Obviously this leaves out lots of details, but at the highest level, it is what the project is about. All of the details will follow in this thread.

The materials I used are as follows; I'll cover each in detail when I get to the step where the material is used but for now here's a list:

- 1.5 oz. fiberglass mat
- 2" wide fiberglass tape
- West System Six-10 epoxy, with extra mixing nozzles
- 5-minute epoxy, such as Devcon from a home center
- SMC-compatible resin (1 qt)
- General purpose polyester resin (2-3 qts)
- White tint for resin (optional)
- 5/16" weld nuts/tee nuts, and 3/4"-long bolts + washers for each (t-nuts optional)
- Weatherstrip to seal the bolt-together joints between panels

Not every one of the materials in the list is strictly necessary, I'll cover what's required and what's optional when I get to those steps.

Other things you'll need:

- Masking tape. Mostly I used Scotch blue 2"
- Acetone. For cleanup after fiberglass work, it's a solvent for the resin.
- Waxed paper
- 80-grit sandpaper and some finer grits

I'll cover the tools necessary as I use them. Mostly hand tools, a sanding block, drill and bits, some clamps. Most of the tools the average DIY-er is likely to have with the possible exception of clamps that are long enough to span the panels.

Cost - Materials should run between $100 and $150 depending on where you buy things.
 

jscherb

Expedition Leader
#9
Materials

In the next step flanges will be added to one side of each module joint using simple wooden forms which will be clamped in place. Before getting started, a few words about materials.

The JK factory hardop is made from Sheet Molded Compound (SMC), which is a variant of fiberglass. Unlike ordinary fiberglass, SMC contains a mold release compound to facilitate molding in press-type molds in volume productions. SMC variants also usually contain a filler material, often calcium carbonate but sometimes talc or powdered limestone. Because of the integrated mold release, ordinary polyester resin as used in fiberglass work won't reliably bond to an SMC part. Depending on the exact SMC forumlation and other factors sometimes polyester resin will bond, but most often it won't be acceptable in a structural application like the flanges needed to bolt the hardtop back together.

Adhesives/resins

One choice for building the flanges is epoxy resin. Epoxies formulated for fiberglass layup use, such as West System 105, work similarly to polyester resin, and bond very well to SMC. They require fairly precise mixing to achieve proper cure and maximum strength, so the West System resin is available with metered pump-action dispensers to make precise ratios easy to achieve. Epoxy resin costs about $75 per quart.

The second option is an SMC-compatible polyester resin. An example of this is Evercoat 864, which is a polyester resin with Methyl Methacrylate added to counteract the SMC's embedded mold release. Unlike ordinary polyester resin, which uses liquid Methyl ethyl ketone peroxide (MEKP) as a catalyst, Evercoat 864 uses a cream hardener similar to that used with body filler. It's a little hard to meter the exact amount of cream hardener for a given amount of resin, but the ratio is less critical than with epoxy. Evercoat 864 is about $50 per quart, and a lower-priced competitor from USC called All Resin is about $30 per quart.

A third option is a hybrid technique I've come up with that uses both an SMC-compatible resin and ordinary polyster resin. It turns out that ordinary polyester resin will bond to SMC-compatible resin, so this technique involves doing the first layer of the fiberglass layup with SMC-compatible resin to ensure the new layup bonds to the SMC part and doing subsequent layers on top of the SMC-compatible resin base with ordinary polyester resin. Since ordinary polyester resin is about $12 per quart, this is a cost-effective way to build fiberglass structure on a base SMC part.

Adding all of the flanges to the hardtop parts will take two to three quarts of resin, so epoxy would cost about $150-$225, SMC-compatible resin would cost about up to $90 (using the less expensive USC All Resin), and the hybrid technique will cost maybe $60 for resin.

In addition the the resin, fiberglass will be required. I'll show using a combination of fiberglass mat and cloth tape to build up the flanges, but you could be successul using all mat or all cloth if that's the way you wanted to go. I'll explain why I'm using a combination when I show those steps.
 

jscherb

Expedition Leader
#10
Sourcing materials

I buy all of my fiberglass materials from US Composites (http://uscomposites.com). I've been very happy with their price, quality and selection over the years. They carry the necessary fiberglass mat and fiberglass cloth tape, polyester resin in quarts and gallons and if you decide to tint your resin white they've got the white tint as well. I'd recommend buying one yard of 1 1/2 oz. fiberglass mat ($3.40/yard in 50" width), a roll of 2" fiberglass tape ($16.60), and a gallon of polyester resin from them. You'll only need 2-3 quarts of resin - their #435 resin is $11.75 per quart but gallons are $30.50, so you might was well go for the gallon.

US Composites doesn't carry West System Six-10 epoxy, so if you decide to use that brand it's available lots of places online and also at West Marine stores and on eBay. It's $20-$25 per tube, you'll need one tube. The extra mixing nozzles (part #600-2) may or may not be found on eBay but can be found online or at West Marine ($4.39 for two)

SMC-compatible resin - I picked up the USC All Resin that I used at my local auto paint jobber, Elmira Auto Paint. It's commonly used in auto body shops to repair Corvettes and other vehicles with SMC parts, so you can check locally if you have an auto body/paint supply place. Both USC All Resin and Evercoat 864 are also available on eBay and online retailers. You'll need a quart.

If you decide to use t-nuts as I'll show for attaching the parts together, you'll need about two dozen of them (8 more if you're doing the additional mod for soft sides), and they can get expensive at the local hardware store or home center, so I usually buy hardware like that in quantity from McMaster-Carr (http://mcmaster.com/). They'll also have the weatherstrip you'll need to go between the module joints.

I picked up the 5/16 x 3/4" bolts needed in the bulk bins at Tractor Supply for less than $3.00 for the quantity required.

Everything else can be found at a local hardware store or home center.
 

jscherb

Expedition Leader
#11
Preparing to cut the factory hardtop apart

This step is pretty straightforward, the factory has provided us with lines to cut along.



Before cutting the hardtop, make up a gauge bar to hold the two sides apart at the correct distance, this will come in handy later. Remove the push fastener that holds the bottom of the weatherstrip in place as shown in the photo below. It comes out pretty easily, but if you have a fastener removal tool like the one in the photo it's even easier and the fastener won't be damaged.



Next, a cut piece of wood long enough to span the two holes and drill holes in the wood for bolts to go through the holes you just removed the fasteners from. #10 bolts work fine here. The wood doesn't have to be very strong, I'm using a piece of pine that's about 1/4" thick and 1" wide.





Once the gauge bar is made up it can be removed and put aside for later.
 

jscherb

Expedition Leader
#12
Cutting the top apart


The best tool for cutting fiberglass is an abrasive disk. You can use a saw, for example a fine blade in a jigsaw, but the impacts of the teeth on the fiberglass can make micro-cracks which could grow larger over time, so it's always best to cut fiberglass with abrasives.

I use a 4 1/2" angle grinder with a 0.045"-thick cutting disk. This disk is less than 1/16" thick, so it doesn't make a very wide cut, in fact it's probably thinner than the line the factory has provided for us to cut along. I say probably because the width of this line can very from top to top, it's one of the variables during assembly at the factory.



I found it convenient to put the top on a workbench, letting the sides and back hang down, but cutting can be done on the floor. You'll definitely want to remove the rear lift glass before cutting. The bonded-in-place side windows can remain, although the top in these photos I'm working with has had the windows removed (they were removed by the person I bought the top from, I don't know why).



Start by cutting the side-rear joint. It's easy to keep the cutting disk in the line, just take your time. I'm wearing a dust mask for protection.



The mounting flange won't be cut all the way through because the cutting disk doesn't go deep enough, here's an inside view taken after I had just started the cut from the outside. Cut the flange from the inside.



The top line of the side panel can be cut next. I cut from each end towards the middle, and since the top was hanging on the workbench, I supported the side panel with one hand while I finished the center of the cut with the other. Be careful not to cut the weatherstrip at the front.



Once the other side panel has been cut off, the rear panel can be cut off, again I cut from each side towards the center and then supported the panel with one hand while I finished the cut in the center.

 

jscherb

Expedition Leader
#13
Prepping the joints for the flanges.

The hardtop was cut apart using a cutoff disk along the factory joint lines - since these joint lines are usually wider than the cut made by the disk, and since it's likely the cut isn't perfectly straight anyway, the cut edges should be touched up with 80-grit sandpaper in a sanding block. The SMC sands very easily, so don't give in to the temptation to use a power sander here - it won't take long with a sanding block and the resulting edge will be much straighter and more accurate that if you do it with a power sander. Remove all of the recessed area where the cut was made.



Next, about 1" on the inside of each edge where the flange will be attached needs to be roughed up a bit with 80 grit sandpaper. This can be done by hand, again it doesn't take much work and all that's needed is to rough up the surface to give it some additional roughness for the new resin to grip to and to remove any dirt or impurities that may be present. I used tape to guide my sanding to limit the sanding to just 1" so the finished inside of the hardtop looks nice.



There's one more area that needs to be taken care of - when the roof is cut apart from the back panel, there's a small hollow section on each side:



Part of this needs to be removed so the new flange can be bonded to the roof. I marked the area to remove with 1/2" masking tape,



and cut along the tape.



The section that was cut out can be saved and fitted back and epoxied into place later for a more finished look. Fitting it back in later is optional, depends on how you think it looks when you're done adding the flanges. I didn't do that, I thought it looked fine on mine without it.
 

jscherb

Expedition Leader
#14
Forms for the flanges.

The photos in this post show the forms to make the flanges in this first step. Flanges will be added on the top and back edges of each side panel, and on the back edge of the roof panel in this step.

For the side panel forms, I've used 1x4 pine for the top edge, and 1/4" plywood for the back edge - the back edge is curved so 1/4" plywood will bend easier to follow the curve. The wood is screwed together at the corner, and held tightly to the side panel with clamps. I've also taped waxed paper to the forms, this will serve as "mold release" so the new fiberglass doesn't stick to the pine. Since the windows are out of these side panels I'm able to use mostly short clamps, although I did need one longer clamp at the front end of the panel. If the windows were in place longer clamps that could span the panel would be needed all around. You might be able to do the job without clamps by wrapping strong tape like duct tape around the form and the panel, but I haven't tried that.





Once the form is clamped to the panel, it's a good idea to seal the joint between the panel and the form on the outside of the panel with masking tape so when you add resin to build up the flange it doesn't leak all over the outside of the panel. This photo is from below showing the tape sealing teh joint.



Similarly, a simple straight form of 1x6 pine is added to the back of the roof, and the outside of the joint is taped as above. Waxed paper is wrapped around the board. This form is easiest with long pipe clamps.





I've also added a line of masking tape about 1" from the joint on the inside of the panels. By using tape to define the edge of the fiberglass I'll be adding the end result will be a more finished look rather than a random edge to the resin/fiberglass that's been added.
 

jscherb

Expedition Leader
#15
Adding the flanges, layer 1.

To bond successfully to the factory SMC, I'm using USC All Resin, which is SMC-compatible. You can refer back a few posts to the section on materials for more info and alternatives.

I'm using 1"-wide strips of 1.5 ounce fiberglass mat as a first layer. Mat is a random collection of glass strands held together with a binding material that dissolves when soaked in resin. The reason I'm using mat as a first layer is that it will provide the best bond to the hardtop. I'll lay the mat flat on the hardtop, and it should be cut to width so that it can butt against the form and reach almost all the way to the masking tape. I'll use only one strip, laid directly on the hardtop.

The strips of mat laid in place:



The strip on the hardtop will be saturated with SMC-compatible resin, and the strip on the form can be done with ordinary polyester resin.

After those are laid in place and saturated with resin, I'll add several layers of 2"-wide fiberglass tape on top of the mat, folded into the corner. The fiberglass tape will provide a nice finished look to the flange if done carefully, and will be very strong. Also, the fiberglass tape layers will be applied using ordinary polyester resin rather than the expensive SMC-compatible resin.

2" fiberglass tape, which will be applied as layers 2-4 after the mat has been soaked with SMC-compatible resin:



BTW the best way to cut fiberglass mat accurately is with a roller cutter and a straightedge. I do it on an old piece of vinyl flooring.



Before mixing the resin, it's good practice to get all of the fiberglass ready and laid out nearby in the order you'll need it - you don't want to be racing the clock by having to cut the fiberglass after the resin has been catalyzed.

 
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