Preparing the Datsun Roadster Frame
Preparing the Frame
The first thing to do is to prepare your roadster frame for the new SR. This will involve removing the existing radiator, engine, transmission, driveshaft, and exhaust system. You want the already-too-small engine compartment to be free of as many items as possible. Now is an excellent time to pressure wash and clean the frame before doing any fabrication work. You want your work surfaces to be as clean as possible, this not only makes things a lot nicer for fabrication work, and it also prevents you from becoming a giant grease ball by the time the project is done.
One of the first things that I do when I start working on a roadster is rounding off all the sharp edges on the frame and body. The stock roadster frame will quickly fillet you with all of its sharp edges. A few minutes spent at the start of this project will save you many cuts and bruises down the road.
Should I Remove the Body From the Frame?
This is a great time to make the decision to keep the body on the frame, or remove it for ease of fabrication. The first few SR swaps that I did into roadsters, I left the body on the frame. This was nice to use as a reference point to know where the firewall and sides of the engine compartment frame rails were, but it also made doing the modifications to the X-member and the other spots on the frame much more difficult.
Now when we do this conversion, we remove the body from the frame, and put it onto a body cart to keep it safe from damage, and to allow much better clearance to the frame.
Now doing the modifications on the X-member for the transmission mount, speed sensor, and opening up the exhaust holes is much easier than before. We also have the benefit of having a front half of a recently scrapped roadster (aka Buck) to bolt onto the frame for firewall, radiator core support, or frame rail reference. Since roadsters generally have the same engine compartment dimensions (such as firewall placement) this is a great tool for modifying the frame.
Frame Modifications
Assuming that we have decided to remove the body from the frame, we can start doing the modifications to the frame to fit the SR into the engine compartment.
Mount the stripped and cleaned frame on a set of heavy duty jack stands. I like to work with the frame about 24″ off of the ground, but find a suitable working height that feels comfortable to you.
After the frame is sitting on the jack stands, shim it as necessary to get it as level and square as possible. Use your magnetized level to check that the frame is level in more than one place. Give the frame a wiggle test to make sure that it is stable, and will not fall if something was bumped into it. You will be working at some unusual angles when doing the frame modifications, and it is very important that the frame is sitting solidly on the jack stands!
Once the frame is setup, scribe the center line on the front cross member and the X-member. This line will be very important, so be sure to use a good scribe and mark the frame carefully as we will reference this line many times during the conversion.
The front cross member can be difficult to mark, but I find that it is easiest to measure between the rectangular mounts (see photo) and to scribe a center line. The approximate dimension from side to side is (6 1/4″).