RSR Type Engine mount cross bar

[Walt Fricke]

Sherwood - I've got both the nut and nutless types. The longer bolt specification seems bizarre, but I've never paid any attention to the difference.

For the ones with the nut, I'd weld the nut on. Counter hold was there if needed, but quicker all around. This is for race cars, where speed of R&R is important, as it happens way more often than the 10-20 years between removal for a street motor. I've worried about fatigue fractures, especially with the nutless variety. I've seen the pictures of them. But somehow it hasn't happened to me.

I think a little gusseting of the nut or threaded area - there is plenty of room for that - would make that part bullet proof.

Which seems rather more useful than welding flanges. Weight is a wash on yours? In which case, why not stay with the solid stock? Are stock pieces prone to failure?

The one genuine RSR failure I saw on a guy's genuine RSR was concluded to be a manufacturing defect. It looked like those holes might be stamped, and something missed somewhere and left a mark on the solid connecting part above a hole.

The adjacent motor console can stand a whole lot of Swiss cheesing with no problems. I don't recall that the factory did that for the RSRs, though.

[911pcars]

Walt, Agree. Welding a nut in place is a good idea. I suspect your lack of end failure might be due to more frequent R&R of your track drivetrain. Typically, threaded fasteners in intimate contact between lengthy service intevals or are assembled dry in corrosive environs tend to remain in more intimate contact. Add in massive torque from an impact gun or 4’ breaker bar to R&R that bolt and there you go.

[panzerfaust]

Originally Posted by Walt Fricke

If this is what you see done in sheet metal reinforcements, isn't this material too stiff to be done easily? Wouldn't you need a hefty die and very strong press?

I'm nut sure why making it more rigid in the fore and aft direction is all that important. Porsche just made holes for the RSRs, didn't it. Solid transmission mounts will hold resist those forces.

Does swaging holes in sheet metal make if more resistant to bending when under compression? But here compression on one side is resisted by tension on the other, isn't it?

I'm not following the "lighter and stronger" part, though, assuming the holes are the same size. Isn't tensile strength more or less governed by the smallest cross sectional area? Which is at the 0 and 180 degree point on each hole? I've tried to keep those consistent hole to hole, though I have no idea what a reasonable minimum would be.

Since my home brew ones haven't failed, the old 356 guys would say I probably made them too small. Keep going until things break, then go back t the next smaller size seemed to be the mantra from the Swiss cheese era of lightening.

unless you are handy with an hammer and anvil of course you would need a die, either a press or screw type male-female form. It gets expensive if the holes are different size and you arent geared up for it with tooling like a metal fabrication shop.

each time you create a fold or a crease you in increase the cross section all though material is the same thickness. think of a sheet of paper, strategically crease it and you can stand it on its end. adding swaged holes is common practice in aircraft construction when weight is a critical factor.

" Keep going until things break" ha! i like your approach. Colin Chapman style.... he did win a lot of races didnt he? :-)

best

ps did the RSR 3.0 went a step further and added below an I-beam section?

[Walt Fricke]

Actually, that "keep going until things break was kind of disappointing to me. I was at a vintage race at Steamboat, admiring well drilled rear brake rotor hats. I was hoping to hear some kind of formula. R&D by breaking was a bit above my budget.