Jim K
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Re: LCA bolt failure?

Post by Jim K »

Or, using a 'T' x-section, box-bar, H-section..... OR, even better: a new M3, Mitsu Evo etc, hahahah! 8) :lol: Speaking of ...stiff -in more ways than one! :oops: :mrgreen: :wall:
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Re: LCA bolt failure?

Post by Maurizio »

Buy a Hartge 1series :twisted: the attempt to evolute the ar75 Nah the crappy (image) alfa´s are more fun :lol:

Not optimal, but already better.
Quick drawn ... preferably on both sides of the strip (around the bolt).
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Re: LCA bolt failure?

Post by Jim K »

Hahah! I thought of that when I made the strip, but there is no way to tighten the nuts... No access as you can't fit a wrench or ratchet. The oil pan is in the way. :(
Maybe we have to design something 'U'-shaped to fit on the rail with a hole for the long existing bolt.. The bottom (horizontal) part of this will have 2 threaded holes for short bolts to fix the transverse ~8mm thick stiffener. We now have the advantage of a removable flat single-plane stiffener connecting the rails with 2 bolts per side. Think about it! :idea:
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Re: LCA bolt failure?

Post by 75evo »

Jim,

Do you remember the boxed section of a 75 which Maurizio (and I think Mats) did not quite like? I think it was a Dutch race car. There were photos of it on a chassis lift. The whole rail was replaced with what looks like a very very stiff steel rectangular section, of much thicker gauge than the flimsy stuff the chassis is currently made of. Then box it (removable) at the front (around the oil pan area0 and the rear (around the bell housing area).

But it doesn't look like a cheap solution. Looks like major surgery.
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Re: LCA bolt failure?

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I will look into improving the situation in the most practical way. On the other hand and to be fair, I am thinking Alfa didn't design the car for hard trackday use and extreme braking with big brakes and semislick tires, but -I guess- a small percentage of ...torment by owners going a bit over strict everyday use. 8) Its up to us then to improve as necessary for what we intend to use it for.
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Re: LCA bolt failure?

Post by Maurizio »

So Jim, the main question then is are you willing to open up the chassis member. Material is not the money here, time is...

As 75evo (I forgot Nizam?) is suggesting is not a bad Idea.
The picture in question:

Image

This is how a dutch firm, race team does it. The picture was from a hobby/street car of one of their mechanics, which was for sale. It wasn't done very nice, the box frame doesn't really nicely inject the forces into the original chassis.

So main: The box section stiffening I didn't like because it was to much (heavy) material added in the wrong places.


But the basic idea is good, here alfa already went wrong in the original chassis member design ...

Image

So in theory Left is what alfa did en Right is the correct way in terms of rigid lightweight design.

The vertical strips in the H are making the stiffness and the distance between them is the biggest contributor, not the thickness of the strips. The horizontal is making sure the forces are injected in both the vertical ones in simple pull and push forces. Try to avoid bending when injecting forces.
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Re: LCA bolt failure?

Post by Jim K »

The picture may show an effective but ugly solution. This I will not do, but I'll make a drawing of what I propose after I see a 75 in the air at the garage so I can make sure of what's involved. There are a few little snags for what I'm thinking of doing.
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Re: LCA bolt failure?

Post by MR2 Zig »

Kevin is right on the fine thread pitch for this. You can put more torque on a fine thread fastener than you can a coarse thread. I don't know the specific reason (thicker section under the thread, shallower ramp angle of fine thread, more contact area of fine thread, etc), but the fine pitch bolt takes more torque and is a little more resistant to loosening due to vibration. For the best results have 2 threads of the bolt extending past the nut when it's all torqued up.

A too long bolt can be shortened as long as there is enough thread so that the nut doesn't bottom out. If you shorten a bolt, grind with a nut or thread chaser on it. Don't let the bolt get so hot that you start seeing color (colour) in the freshly ground steel. That much heat kills the heat treat of high grade bolts. Dunking the bolt in water works well.

I hope that helps,

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Re: LCA bolt failure?

Post by MR2 Zig »

To get the stiffness out of your existing brace weld a length (from one frame rail to the other) of 1/4 x1/4 x 3/32" angle iron to the bottom of your flat bar. Stitch weld both ends of the "L" to the flat bar with the corner of the "L" pointing towards the ground.

This should do what you want until you can come up with a better solution.

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Re: LCA bolt failure?

Post by Duk »

Is there a 'crush tube' inside the chassis rails that the LCA bolts pass through?

Chassis flex is 1 thing, but bolts coming loose because of load (chassis rail being compressed/distorted) is another.................. :shock:
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Re: LCA bolt failure?

Post by 75evo »

I believe there is a tube in the rail. If not if you keep on tightening the LCA bolt, it will crush the rail.
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Re: LCA bolt failure?

Post by Maurizio »

75evo wrote:I believe there is a tube in the rail. If not if you keep on tightening the LCA bolt, it will crush the rail.
Yes there is an aluminium tube in the rail, but this is not enough to let the two vertical walls work together for optimal stiffness. It's strange alfa didn't recognise/improve this, at the 105 series: steering houses break due to the same construction principle...
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Re: LCA bolt failure?

Post by Jim K »

Thanks for the input guys! Yes, there is a crush tube in there (iron not alloy). The fact that the self-locking nut disintegrated (never found it) with the bolt thread intact, can mean the nut was $hit quality, simplifying the problem. I have a few of those and will have them tested at the materials lab by a friend. In the meantime, I will have to look at what Alfa used for nut/bolt as I don't have any around, having changed all 3 cars to Allen bolts+locknuts. I don't have any originals around, will look at the Alfa garage. Maybe the problem is simpler than I think, having only to do with bolt/nut quality? -I sure hope so!
I asked again for long Allen bolts and they are not available >120mm in fine thread (1mm) but only in 1.5 and 1.75mm. I searched the net, same story.
I'm surprised you guys haven't run across the same problem with your cars!
Here's a sketch of what I consider a simple and effective (?) fix to the problem. Ideally, there should be two such assemblies for the front and aft LCA bolts and maybe a rigid connection of the two bars underneath?
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Re: LCA bolt failure?

Post by Maurizio »

Jim,

First for the threads, here in Holland most guys use threaded rods, you buy them per meter. You can get them in 12.9 quality. Nuts on both sides.
Not cheap but you can do two cars with a meter if you cut carefully. If you want to go cheap you could do only the front ones :lol:
The strength difference between course and fine thread is not really big just go for the better quality iow 12.9 and matching nuts.


Then some remarks on your stiffener sketch.

So I see again a U shaped (two folds) in each bracket, so you do not generate any stiffness. Thickness of the U's?
What I'm not sure of... are you going to weld these into place onto the outside of the chassis members?
If so I'm still not convinced it is the best idea, but is already ok-isch.

To get this more to my liking :mrgreen:
Would you consider opening up the chassis member and put in a solid square block, instead of the alfa original crush tube? And weld it into the chassis member?
If so... we have to work this out a little better 8)

Then for the bolts to secure the connection strip between the two members...
What thread diameter are you thinking about?

General bolt connections:
For a good bolt connection you need at least 3~4 bolt diameter free length, between head and the first engagement of the thread. Long story short, compensate setting behavior and leaving enough elastic pretension in the bolt. What you are sketching here isn't going to stay in place very long!

I'm not sure if this is understood correct, will make a sketch tomorrow night.
Don't have the right drawing tools / time right now :oops:
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Re: LCA bolt failure?

Post by Duk »

How about titanium bolts?
I found some on ebay in 1.25 pitch.
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