Datsun Roadster: 2020 Challenge Build

Looking good!

Put all your speed holes in the final parts before cutting them out. I find it much easier to lock down a big square vs an odd shaped part for drilling.

2nd side also fits well. I will need to figure out a way to get the top two bolt holes spot on when I do the metal pieces. Both sides on the wood were close but needed "massaging" to fit.

Also this second piece was not even on the bottom edge with the first side. So I set the engine on the ground with both sides bolted on and measured how far off my highest corner was, and then cut the other corner on the same side down by that much to make it level. 

That means I had to "shim" up that side a bit to get the motor sitting level. But now it does, which is great.

Next I need to figure out how to make sure these plates are inline with the motor (same plane as the chain) as much as possible. The mount hole bosses are not all in plane, so that is going to require some washers. 

Overall however, I'm quite pleased so far.

gumby said:

Looking good!

Put all your speed holes in the final parts before cutting them out. I find it much easier to lock down a big square vs an odd shaped part for drilling.

Yeah, good thought!

Let this be the 50 hours in shot:

Fladiver64 said:

Are you planning on replacing the lower frame rails as well? Not sure the diameter of the lower frame rails but looks like 1" or so, How are you going to weld a 1 3/4 tube to a smaller tube. i t looks like the current system is a plate welded to the tube then the bar welded to that. To me that does not look like a strong connection since the only contact point is the edge of the tubing.

I think you could have a problem with tech as well because it states welding roll bar to frame is permitted. "Also, the roll bar may be welded to frame connectors that are fully welded in place and are 1 5/8 inches x .118-inch MS or .083-inch CM round and/or 2 inch x 2 inch x .058 MS or CM rectangular" I am not sure that if your frame is only 1" diameter, they are going to let that pass.

If you are moving the main hoop back because it fits the car better, wont you have to move the steering column back the same amount? Then extend the chassis from the steering column loop to the front suspension.

You might consider building a new center section, main hoop, lower frame rails from rear diagonals to length chassis needs to be extended, front diagonals, dash bar. Then create a sleeve system to put the existing front suspension in the new larger lower frame rails.

It seams like a lot of work but I think you are going to end up doing most of it anyway, so might be easier to start fresh.

I've been thinking about the frame plan pretty extensively, and also chatting a bit with Gumby because he has experience with this chassis first hand, and he happens to be a chassis builder as a day job.

In the end, I do think much of what you suggest will be the path I follow. Right now my current plan is to replace my lower rails (they are 1 inch, dunno wall thickness yet) with 2x2 square tube. As you suggest, that should actually improve the weld strength at these joints:

all 4 are critical suspension mounting points to the chassis, and I agree that they should be super solid.

You are also right I will have to move the steering wheel and pedals back about as much as the roll bar, but I will probably just extend the steering column and not move that front hoop, since the front hoop is pretty integral to the front suspension.

Where's your frame table that you've leveled so flat you've become a folk hero to the flat Earth movement?

Stampie said:

Where's your frame table that you've leveled so flat you've become a folk hero to the flat Earth movement?

Well, since the earth is flat and I need a flat surface, I'll just use the earth as a frame table.

But seriously I plan to use the garage floor.

In reply to Robbie :

I'm debating how fancy I need to make one or just redneck engineer it. 

In reply to Stampie :

Redneck that E36 M3 guys. Flat enough is flat enough for what were doing.

Love the engine plates. A few various sized "speed" holes, and they will look fantastic.

I vote for mounting the plates to a adj. slide assembly closer to current seat back (but far enough for plenty of room), and make a pivot point just under engine. BMW K bikes use a single shock; wouldn't be hard to fab a mount for a single coilover?

Ok, my 3D modeling is bad, but a hand sketch would be worse! But just food for thought. Now y’all make ‘er pretty!

Robbie said:

 

2nd side also fits well. I will need to figure out a way to get the top two bolt holes spot on when I do the metal pieces. Both sides on the wood were close but needed "massaging" to fit.

 

 

 

 

I would make up some sacrificial bolts, grind the heads down to a point. Then mock up your engine on the laser straight garage floor, so that it is level and at the height you want. Clamp the two side plate to the motor, using hte floor to keep them parallel, with slight clamping pressure you can move the plate around until they are exactly where you need them. Tighten up the clamps and give each bolt a smack with a hammer and all the holes are marked exact.

03Panther said:

Ok, my 3D modeling is bad, but a hand sketch would be worse! But just food for thought. Now y’all make ‘er pretty!

Nice! I totally see what you are saying. And maybe I will look to add springs and shocks in the future. But for now, I actually really like the beautiful simplicity of the rubber puck suspension. 

I did have an idea to use the (factory double adjustable) front forks from the bike to make long rear springs like a Baja truck.

In reply to Fladiver64 :

My issue with that is the mount bosses are not all exactly in the same plane. I'll see if I can get a good pic, but I have about 1/4 inch of washer between the plate and one of the bosses on either side.

I guess I could screw one of the bolts out a bit so the point protruded to the level I want.

51 hours in. Really no going back now.

Also, I set the engine on the subframe and the plates are looking good. I need a few more tweaks still, of course, but I'm happy.

Oh hell yes!

Also the existing bottom rail is 1 inch tube with .095 wall thickness.

So after some quick area and moment of inertia calcs, it looks like 2x2x.060 square tube will be about 66% heavier and nearly 10 times stronger than the existing bottom rails.

Even adding 6 inches to the bottom rails here's what the weight change looks like:

2x 72 inch 1 inch round = 11.0 lbs

2x 78 inch 2x2 = 20.5 lbs 

So I welcome the extra strength for a very modest weight penalty when extending the wheelbase 6 inches.

In reply to Robbie :

The other thing is, that's weight added at about the minimum height you could add weight to the car; so it should help lower its c.g.

Things are looking serious now!  Any idea where the engine is going to wind up relative to the Datsun body?  Parcel shelf?  Entirely inside the trunk?

Looks a lot like the airbox is going to be the "back seat," which could lead to some amusing stuff.

¯\_(ツ)_/¯ said:

Things are looking serious now!  Any idea where the engine is going to wind up relative to the Datsun body?  Parcel shelf?  Entirely inside the trunk?

Haha I wish... The front of the engine will probably end up about about elbow Level if the driver were in normal seating position.

Call that maybe 18 Inches from rear axle centerline to back of seat. I will have more than that. It's not ideal.

In reply to Robbie :

So the engine becomes the rear seat passenger, you're in the front seat, and the new, probably very small, air deflector wind screen thing is right in front of you.  It'll probably be fine.

Plus you've got the entire engine bay to stick your legs into.

In reply to Robbie :

That is what i would do, so all of your points are on same plane. Then just adjust with spacers for final install.

Good progress even if it feels like going backwards. Your build is in a similar place as mine, the more I work on it the less there is of it.

Keep up the good work

I hadn't read the thread for a while and just got caught up reading mostly from the end towards the beginning. Nice to see the plan coming together. I like where this is going.

Robbie said:

Also the existing bottom rail is 1 inch tube with .095 wall thickness.

So after some quick area and moment of inertia calcs, it looks like 2x2x.060 square tube will be about 66% heavier and nearly 10 times stronger than the existing bottom rails.

Even adding 6 inches to the bottom rails here's what the weight change looks like:

2x 72 inch 1 inch round = 11.0 lbs

2x 78 inch 2x2 = 20.5 lbs 

So I welcome the extra strength for a very modest weight penalty when extending the wheelbase 6 inches.

If you did 1.625 .120 wall wouldn't that give you a better start on a nhra cage/roll bar?

In reply to Stampie :

I don't think better. It looks like both are acceptable frame members for which to mount bars and cages. But, 1.625 x .120 tube would be about 25% heavier and about half as strong as 2x2 x 0.060. Plus, flat surfaces = much easier to cut and weld.