Chassis bolts

[NTG999]

I'm currently refitting the body to chassis of my Elan Sprint after repaint. I previously fitted a galvanised chassis in approx 1990 when I think I bought a kit of bolts. My questions are, the bolts where there is a choice, mainly the underneath ones and behind the dash should the bolt head be under the car or in the car?
I notice my old (non original) bolts are all slightly longer by 1/4" than the ones listed in BB and the manual, are the correct length bolts always long enough even with spacers?
Finally the 2x bolts in to the rear uprights I tapped and fitted 3/8" bolts back in 1990 but BB and manual list 7/16"
Thanks

[oldelanman]

the bolts where there is a choice, mainly the underneath ones and behind the dash should the bolt head be under the car or in the car?

There is no choice about which way round any of the hardware is fitted , at the front and rear uprights and behind the dash the bolts pass through plain bobbins in the body into threads tapped in the chassis, in all other locations set screws pass through holes in the chassis into threaded bobbins in the body.

are the correct length bolts always long enough even with spacers?

That depends on how big your spacers are, check that you have enough thread engagement with the standard hardware and fit longer ones if required.

Finally the 2x bolts in to the rear uprights I tapped and fitted 3/8" bolts back in 1990 but BB and manual list 7/16"

7/16" is correct. A 3/8" bolt will be a loose fit through the 7/16" body bobbin and could allow movement.

[HCA]

Finally the 2x bolts in to the rear uprights I tapped and fitted 3/8" bolts back in 1990 but BB and manual list 7/16"
Thanks

Are you sure they were ⅜? Do you mean ½" maybe? Tapping out to ½" is a fix for stripped threads in these bobbins...

[bitsobrits]

No threads in the rear upright bobbins they are smooth bore.

Fasteners diameter should match the bobbin. If the body bobbins are 7/16" then use 7/16" bolts. Or replace the bobbins with 3/8" diameter or use a sleeve if using 3/8" bolts.

Not sure why Lotus felt the need for 7/16" bolts on the rear uprights. I would reckon the strength limit here would be the body and or chassis, not the bolts. A 7/16" bolt has a shear strength only about 15% greater than 3/8". And the roughly 40% greater tensile strength of the 7/16" is rendered superfluous by the limit of the bobbin strength and thin sheetmetal of the uprights.

[HCA]

correction...

Are you sure they were ⅜? Do you mean ½" maybe? Tapping out to ½" is a fix for stripped threads in these uprights...

[oldelanman]

Not sure why Lotus felt the need for 7/16" bolts on the rear uprights. I would reckon the strength limit here would be the body and or chassis, not the bolts. A 7/16" bolt has a shear strength only about 15% greater than 3/8". And the roughly 40% greater tensile strength of the 7/16" is rendered superfluous by the limit of the bobbin strength and thin sheetmetal of the uprights.

I think those bolts we're used to mount the seat belts in early cars and seat belt hardware is/was 7/16" I believe so that may be why.

[NTG999]

That makes sense, 3/8" everywhere except 7/16" where potentially seatbelts mount, as pointed out other factors are limiting before the strength of the bolt is tested.
My chassis isn't tapped for the 'underneath' bolts so the body was secured with nuts & bolts through bobbins so I still have the choice of bolt head in the car or underneath...

[RichardHawkins]

NTG999,

As others have commented, originally the bolts/set screws were fitted into threaded bobbins and threaded holes in the chassis. As you have bobbins without thread and a bolt with nut to secure the body to the chassis, I was told as an apprentice to put the bolt in from the top with the nut underneath, so if the nut works loose and falls off, the bolt might stay in place and hold the two parts together. 50+ years later I am not sure of this advice, but I think it is probably the better option.

Hope this helps,

Richard Hawkins

[Elan45]

Just this week, I bolted the body of my pre-aiflow coupe back onto its original frame. Since my floor bobbins were original and still threaded, I ran the bolts in from beneath the the car. Looks cleaner from underneath and I suppose if the bolts are reversed and even just 1/4 inch hung down, that would be 1/4 inch less ground clearance. Some how I.ve got to figure how to load photos onto my computer and show them here.

Roger

[pharriso]

I was told as an apprentice to put the bolt in from the top with the nut underneath, so if the nut works loose and falls off, the bolt might stay in place and hold the two parts together. 50+ years later I am not sure of this advice, but I think it is probably the better option.
Richard Hawkins

One word.... Nylocks!