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reinforced chassis?

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clshore Carter Shore
Beverly Hills, FL, USA   USA
The H brace ties the upper scuttle to the frame, preventing both lozenging and bending loads into the A pillars.

This area is often reinforced by a 'pierced hoop' structure on space frame Sports Racers and formula cars.
A pierced hoop is a sheet metal structure, reinforced at the edges by flanges or small diameter tubes,
having numerous lightening holes to save weight.
You can see two examples of pierced hoop on the cover of the Costin & Phipps book:
(Yes, the same Costin who later formed Cosworth with Keith Duckworth)

https://www.scribd.com/doc/27581157/Racing-Sports-Car-Chassis-Design-0837602963

They are used rather than simple triangulation tube braces in areas where the space will be occupied
by cargo, occupants, etc,

Obviously too complex and expensive to build for a low cost Sports Car like a Spitfire, the H casting was a simpler cheaper solution.

It's certainly possible to fabricate a replacement for the H brace in tubular or plate steel/aluminum (maybe even Carbon Fiber!).
But solving what problem exactly?
The forces involved are low, and the H brace already exists, fully proven and available for bolt-in to anyone with an eBay account.

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spitfire50 Avatar
spitfire50 Paul Mugford
Rochester, N.H., USA   USA
In reply to # 1505414 by hearditallbefore Top tip from a commercial restorer here in the UK.

Drill a hole at the lowest point of the chassis rails under the diff, the bit where they all rust, check inside chassis with a little cameraphone borescope, (€10 on eBay etc), if it’s only surface rust, alls well, just pour in some rust treatment if you feel it’s worth it and pop a bit of weld over the hole and grind flat.

Doesn’t take long, but settles a nagging doubt. Generally, they are either good or rotboxes inside.
Andy,
Why weld the holes shut? It seems you have made a drain in an ideal spot. Why not leave it there?
Curious,
Paul

hearditallbefore Avatar
Portsmouth, Hampshire, UK   GBR
In reply to # 1505457 by spitfire50
In reply to # 1505414 by hearditallbefore Top tip from a commercial restorer here in the UK.

Drill a hole at the lowest point of the chassis rails under the diff, the bit where they all rust, check inside chassis with a little cameraphone borescope, (€10 on eBay etc), if it’s only surface rust, alls well, just pour in some rust treatment if you feel it’s worth it and pop a bit of weld over the hole and grind flat.

Doesn’t take long, but settles a nagging doubt. Generally, they are either good or rotboxes inside.
Andy,
Why weld the holes shut? It seems you have made a drain in an ideal spot. Why not leave it there?
Curious,
Paul



Keeps the wet from getting to the main box sections.



Swatting the yellow jackets away from the Triumph apple of truth…

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clshore Carter Shore
Beverly Hills, FL, USA   USA
A little rubber or plastic plug would work, or even thread it for a small plug, installed flush.

79bluespit Avatar
79bluespit Rick Lazio
Burlington, ON, Canada   CAN
some racers inject HD foam into the frame. it works very well i hear. will it be a moisture trap? i dunno. but if stiffening up the frame is your only objective this could be your answer.

clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1506130 by 79bluespit some racers inject HD foam into the frame. it works very well i hear. will it be a moisture trap? i dunno. but if stiffening up the frame is your only objective this could be your answer.

The foam works by preventing buckling or deformation of the thin sheet metal walls on unibody cars.
On aircraft monocoque structures, such metal deformation is commonly called 'beercanning'.
It also prevents water intrusion by sealing the wall surfaces.

But on a structure like our chassis, where the walls are more substantial, and the enclosed cross sectional area is small,
such stiffening tricks are essentially ineffective.
But prevention of water intrusion is an excellent result all on it's own, and fully worth the effort..

79bluespit Avatar
79bluespit Rick Lazio
Burlington, ON, Canada   CAN
Also, the foam used is not your hardware store 2lb closed cell stuff. Its specifically engineered for this to cure in an enclosed space, adhere to metal with great force and be very very rigid. So perhaps the engineered foam for this application can inhibit rust. If someone does this, one example of foam you can use is Infiniti Q chassis foam as its enguneered for this purpose. Special order of course. The Q car and only a handful of other new premium cars use this for chassis stiffening. In addition, the spitfire body which is structural, as carter mentioned should reap the highest benefit for stiffness.

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clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1506289 by 79bluespit Also, the foam used is not your hardware store 2lb closed cell stuff. Its specifically engineered for this to cure in an enclosed space, adhere to metal with great force and be very very rigid. So perhaps the engineered foam for this application can inhibit rust. If someone does this, one example of foam you can use is Infiniti Q chassis foam as its enguneered for this purpose. Special order of course. The Q car and only a handful of other new premium cars use this for chassis stiffening. In addition, the spitfire body which is structural, as carter mentioned should reap the highest benefit for stiffness.

Good info Rick, thanks for providing the insight and details.
Now If only I could get a new Spitfire 'body in white' to do the foam treatment to ...

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
I saw something like this being done to a Lotus Elan frame. The alternative was to build a space frame, but it was claimed this foam filled frame was lighter and stiffer.

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Fictioneer Avatar
Fictioneer Doug Hirt
Colorado Springs, CO, USA   USA
This is an interesting discussion. I had read that RATCO, the company that makes chassis frames for TR4s and 6s, fill their frames with foam. I had wondered about that at the time thinking it would trap moisture, but I guess they know what they're doing. I had been thinking "ACE hardware foam" not "industrial grade foam" designed for this very purpose. This sounds like a good way to stiffen up a TRs body as well seeing as they are so flexible. Does anyone see any downside in putting this into the sills of a TR4A?



"Mr. Filby, do you think he'll ever return?"
"One cannot choose but wonder. You see . . . he has all the time in the world!"

79bluespit Avatar
79bluespit Rick Lazio
Burlington, ON, Canada   CAN
I can't see a downside if using the correct foam. The fear is moisture trap. But the specific foam for this adheres to metal to a high degree.

The issue that immediately comes to mind is that most if us sprayed the inside of sills and cavities with rust proof. I know I did. A nice oily mess in there. One where foam may not adhere to. But maybe someone with an engineering background can chime in re stiffness in this case. Perhaps it will stiffen rust proofed cars, but to a lesser degree.

hearditallbefore Avatar
Portsmouth, Hampshire, UK   GBR
PU foam is highly adhesive.
Its commonly used in the marine industry as a sealant on steel hulls and bilges.



Swatting the yellow jackets away from the Triumph apple of truth…

clshore Carter Shore
Beverly Hills, FL, USA   USA
For DIY, the resin and activator are mixed as a liguid and immediately poured into the prepared object.
You must provide expansion vent holes so that the excess foam can escape, and calculate the amount needed to
completely fill the enclosed volume.
It's important to orient the object such that the liquid can run to the bottommost extents, without trapped voids.
The foam activates and expands rapidly to fill all available space inside.
Once expanded it cools and stiffens.
The excess is trimmed away from the vent holes, typically sawn and sanded flush.

An additional side effect of the process is noise reduction, the panels cannot resonate, and vibrations are damped by the foam.

65or66 Gold Member Jim B
Lake village, IN, USA   USA
1965 Triumph Spitfire MkII
1973 Triumph Spitfire 1500 "Jusanudda Munny Pit"
I'm thinking...if I sit in my Spit, my body coated with Vaseline, and have my wife pour about a gallon of the stuff in around me, I'll have the stiffest...oh wait, that's not going to work, is it?

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