Frame construction

 

After spending a bit of time looking at the motor mounts I decided I didn't like the peaks sticking up, so I cut them off level and capped them while adding the mounting plates. There is no question these will support the engine.

 

I've also added diagonal bracing- the following picture only shows the front additional tubes. I later realized I went the opposite direction with them than most people though the end result will be the same as far as stiffening the frame. The tubes are actually pulled in a little closer to the engine this way but I will still have plenty of clearance with the engine, exhaust, and steering components, so I'll leave them this way for now.

Here's another picture of the bracing.

And I'm now beginning construction on the rear end. Because I'm using a Miata donor I'm designing in an independent rear suspension. This is a tubular version of the Miata subframe and is actually quite easy to build... after spending way too long plugging it into LibreCAD. I really hope it works!

Finally a warm evening to work!

Last night was the first warm evening we've had since last Fall and I was able to spend the entire evening in the garage working on moving some tubes around and making the engine mounts. I've decided to keep the engine offset 1/2" to the passenger's side and lower the engine 1.5 to 2"  below the bottom of the frame. This helps me avoid reconfiguring the top cross tube behind the engine and should help the hood clear the top of the engine more easily.

I decided to make triangular mounts partially because they'll look cool, should easily be strong enough, and allow access to the engine mount bolts if I avoid closing the bottom of the chassis in between the supports. I use 16ga 3/4" square tubing and am considering cutting the top peak off and welding the holes closed. I have yet to add 1/8" sheet to the insides of the mounts.

Recent Progress

More tubes have now been tacked in though progress is a little slower than I hoped due to weather being usually cool. Once it warms up a bit I'll be spending a lot more time in the garage. Here you can see the engine and transmission sitting roughly in place. I think I'll need to lower the engine another inch, move some tubes around a bit, and then fabricate the engine mounts.

The engine is spaced 1/2" to the passenger's side due to the rear differential being offset 1" to the same side. I'm hoping to minimize the drive shaft angle: a little angle is beneficial for keeping the U-joints properly lubed, but too much causes stress.

The design work and planning gets a lot easier when you can use a CAD program. Luckily my previous job taught me how to use AutoCAD. Unfortunately I do not have my own copy, so I had to take a little time to learn LibreCAD which is an open source free CAD program.

Here I mocked up the rear end borrowing some ideas from Matt Rodger's car as detailed on the LocostUSA forum. I also took some measurements on the current transmission output shaft and differential input shaft. Once I get the engine and transmission mounts completed (and moving tubes around a little) I'll be working on the back end of the car. At least the cool weather gave me a chance to iron out some ideas and develop some plans!