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I get asked all sorts of questions but perhaps the most common is what can you fit drive train wise in chassis "X"? Until you have built you first chassis it's hard to see just how easy it is to make changes to my basic designs.  The following should give you a good idea on how I would deviate from the plans.  In this case I am going to take a 2 seater design with a rear mounted radiator and change it into a 3 seater with a front mounted radiator.

With the drive train in position I started on the upper cab.  Since I want to put a 3rd seat in this chassis I deviated from the plans by making the A to B pillar bars 2 inches longer than called for. While bending these tubes I did discover a typographical error in my plans.  If you purchased the HR2 Pickup plans see the following .pdf file for the correct numbers.

The box is my radiator mock up.  It is approximately 25" wide, 20" tall and 7" thick.  This is narrower than my existing radiator by one inch so I'll have to either get a smaller radiator, notch the front tubes or mount the radiator in back. More on this later.

The longer span between the A and B pillars gives me the extended cab look I am after.

A head on view of the A to B pillar.

The next step was the double A pillar bar.  The cross bar in the picture is to hole the two A pillars in place side to side until I get to the roof.

After some additional thought this tube may or may not be in the final version.  After mocking up the rear seat I may need the extra room for entry into the front seats.  To answer that question the front seats need to be positioned which means the front floor needs to be designed.  When you are working on this part of the buggy you need to keep transmission/transfer case removal in mind as well as exhaust routing, front driveshaft routing, legroom, etc, etc. 

I used some scrap tubing to mock up where the front seat mounts were positioned in relation to the outside of the seats. For this chassis I am planning on using square steel tubing for the main floor structure to make mounting panels easier.  I also want the whole inner structure to unbolt for maintenance access.

The floor will step up from the foot wells a few inches so I would need a tube on the side of the chassis to mount the cross tubes for the floor.  I found a stack of material that was the correct height and tack welded it to the frame.  This gave me a great reference plane while I worked to notch the final tube into position.

Next I tack welded some steel channel to give me a reference plane for the floor cross tubes making sure I had enough clearance to rotate the transfer case if needed.  I am utilizing some scrap 1.25 x 1.25 steel tubing for the two cross tubes; two 4" pieces on each side and  a center piece filling in the rest of the gap.  Two tabs per side will be welded to the frame and bolted thru the removable center section.

Here's the front bar tacked into place.

It is always good to double check things. After throwing the rear seat back in the chassis I am thinking the seat still needs to go back a few more inches. The seat shown is a PRP preemie seat (22" Tall X 17" Wide X 20" Deep) which fits my 5 year old perfectly.  However, since I want this chassis to accommodate the family for the next 5 years I want enough room in back to go up to the pre-teen sized seat (28" Tall X 19" Wide X 23" Deep) which is basically a couple more inches in all directions.

Now you will see the importance of keeping the frame lightly tacked together.  With my drivers seat and 3rd seat in place I cut the welds on the motor mounts and rolled the motor/trans back a few inches to make room for my existing 19" tall x 26" wide x 7" deep Ron Davis dual pass radiator. Next I cut the welds on the front shock hoops and rotated them outward until I had enough room for the radiator.  At the same time I positioned the front axle so it was centered on the frame and figured out where the shocks would have to mount assuming 7" of up travel.  Based on this I found I needed to lower the shock hoops about 2 inches.

With the shock hoops lowered I then re-made the two bars that tie the A-pillar into the shock hoops (note the new downward angle which actually matches the plans better).

The front axle will actually sit 8" back from where it is shown, I just have to raise up the chassis but want to wait till I can throw some more welds at it.  Another thing I learned from this mock up was that I may be able to get away with a single driveshaft (no carrier bearing).  You can see the tube in the first picture goes straight back with very little angle to the transfer case output.  I am hoping this means I can run in 4 high without a lot of driveshaft vibrations and rumbling.

I thru a tire into the mix just to see what a 110" wheelbase would look like (remember the front axle needs to move back 8").

Back to the passenger cabin.  Using some masking tape I tried quite a few bracing configurations before coming up with this one which seemed to maximize rear passenger headroom while still keeping the roofline low.  The rear seat is tucked up close to the two front seats with the intention of using the space between the two front seats as legroom. there is enough room that I can move it back 3-4".

Once I was happy that I could get my 3rd seat in the chassis I started to brace the chassis side to side by installing a dash bar and upper roof bar (front).  The double A pillars also got moved forward an inch for more entry room.

Once I get a few more of the cross bars in I can throw better weld the chassis so its easier to climb around in.  As it is I have had to use ratchet straps to hold the A to B pillars in place at their correct angles.

On the tool front, my harbor freight angle finder has been augmented by a digital version.  I highly recommend one of these vs. the one on the left for the better measuring consistency.