Fitment and Seat mount fabrication (Seat / Harness install part 2)

Disclaimer: I make no warranties on the safety of these mounts. Any claims I make here are unprofessional opinions. You must make your own independent judgment on whether to follow these instructions or not. I will not be liable for any injuries any persons or damage to your property resulting from anything you read from this blog.














Sub-disclaimer: personally, I would not use this mount for road racing. I'll state the reason why later.

The stock seat's mounting hole centers are 330mm apart. The sprint's mounting hole centers are 345mm apart. I started modifying the holes on the stock sliders/rail to make it work, but after a bit of drilling I realized it was not working. The 15mm difference in width does not allow for the bolt head to fit inside the slider properly. When the holes on the rail are widened enough to accept the Sparco seat, the bolt head will hit the slider. Others have narrowed the bolt heads to make it work, but the smaller bolt head, inability to use washers, and the widened holes on the already thin gauge steel on the sliders drove me away from using it. Therefore, I decided to make a simple adapter. Before I get started, measure twice and cut once! Saves a lot of time. Also, drilling by hand inevitably brings some error so be prepared to enlarge holes. Don't mess up too much. Things needed: -Two steel square or rectangular tubes. Make sure the steel is decent grade, ideally a cold-rolled steel like 4130/4140. The wall thickness should be pretty good, like 11 gauge (.125"). The tube must be at least 1 inch high. -four M8 bolts with a small head, shorter than 16mm. (I used a hex bolt) Use 10.9 gradr or higher. Thread pitch is 1.25mm -four M8 nuts with same thread pitch (10.9 or higher) -assortment of drill bits (small, medium bits leading up to 3/8") -dremel with grinder and cutting wheel -tape measure and straightedge

Preparation
Cut the tubes. Cut the tubes the same length as the sliders are. Should be around 14". Mark these tubes on all sides with a sharpie so you don't get confused. Arrows and writings will do: front, outside, inside, left and right. If you can't find a sharpie, masking tape and pen(cil) works too.

Tube - Slider mounting holes
Refer to this diagram if you are confused at any point.

Take a tape measure and measure the distance between each hole centers on the slider. Measure the distance to the ends of each hole and plot it out on the tube. To do this, measure the distance between A and D, then C and D. Add the two numbers and divide by two to find B and D. Using the distances, mark two dots for each distance on the tube. Draw a line using a straight edge and make lines like A, B and C. Stick one end of the slider and tube when finding an anchoring point for the tape measure, unless you can cut tubes perfectly. The picture is obviously not to scale, and keep in mind that for one hole C and D will be very close together. Mark the center point on the centerline of the tube along the longitudinal axis. Then, move the center points 2mm towards the center of the seat. This line is E2. The intersection of this line and the lines marking A, B, and C is where you will be drilling and where the sliders will bolt in. The hole sizes should be 8-9mm, or 3/8".


Tube - seat holes
Flip the tube over. Find and mark the longitudinal center axis. Draw another line parallel to the center 5.5mm apart, towards the outside of the center of the seat. At least 15mm behind the front hole you drilled on the other side, mark center points for two points that are 271mm apart. Find those points on the 5.5mm offset line and drill with the same size as the previous step.
Access Holes
You will need to find a way to put your hex key for the bolts that go into the seat. Using the holes you drilled on the seat side of the tube, drill straight down. Use the 3/8" bit so you can drill a small spot to find the center point. Then work your way up from a small bit to 1/4", or however big your hex key is.

Test fit and installation
After all these holes are drilled, test fit all the components and see if everything lines up. In my case, it fit at first try. Since rail-floor mounting holes are over-sized, if you followed proper directions this should work. Torque everything very well and install. If something doesn't line up and the error is minimal, dremel the holes a bit bigger. Use grade 8 washers whenever you can fit them.

Copyright 2009, 2010 (c) by Jerry Lee.