MustangEater82

iTrader: (1)

1st what is a typical diameter for fastners used in bolt ons? Also are the holes already in them or do you drill from a pilot or scratch?

The question I have is one of the main concerns, I have read is bolts stretching or coming loose. Is this really the only concern for bolt ons?

I may have access to some extremely high quality hardware and can have the holes be very close tolerance to the fastner. +/- 0.003

Is this the downfall of bolt ons? Or is there more?


I do not have a welder, and I would like to spend a lot of time perfectly leveling my car, and drill and bolt I. Subframes.

DJP87Z28

My opinion on bolt in SFC's is not the fasteners but the soft metal they are bolted to. That is why welding is the preferred metnod.

SCCAjunkie

The issue, from my understanding, is elongation/deformation of the bolt holes. While I close tolerance hole would possibly help, it's all moot the moment the first deformation of the hole occurs.

If I had to guess, I'd *think* that the major issue is bolting the SFCs onto a stock (thin) floorpan/frame stamping, coated with undercoating or otherwise being not perfectly clean, bare metal. Anything in between the SFC mount pad the the surface it's bolted to would act as a sort-of lubricant between the surfaces, allowing for shear stresses to be placed on the fastener. Given that the fastener is likely to be stronger than the steel stamping, the shear stress loads one part of the hole and bumps metal. The second this happens, play develops, and any future stresses are multiplied due to momentum of movement in the hole, in addition to the forces present.

If you could get a perfect surface mating between the parts, and rely on static friction to absorb/distribute the shear stresses, the bolts would see pure tensile loads and not side-load the holes. Keep in mind the shear loads are still present, so you need ample friction to distribute it.

Not knowing how the clamping bolts are installed, I'd also worry that if you're drilling all the way through and putting a nut on the other side of the frame rail itself, you wouldn't be able to exert enough clamping load to obtain the friction needed without collapsing the rail. If you are only placing the nut on the other side of a single surface, you'd need enough fasteners and a backup plate to ensure complete surface contact to get the friction you need.

The point is that by the time you've done everything needed to approach the level of surface preparation needed, you've prepped them for welding. If you're really concerned about the precision of leveling the car and using tight tolerance holes, I don't think bolt-ins should really be a consideration.

At minimum, I'd install the bolt-ins, *carefully* put the car on a trailer, and take it to a shop that will weld them in.

MustangEater82

iTrader: (1)

I was considering that as well but a weld just is just the same soft metal. The key is to get the metal to be up flush from the subframe and the bolt just holds them together, same way a weld does. And if its going into sheetmetal, I was considering a doubler.

MustangEater82

iTrader: (1)

One of the reasons why I was asking about bolt one and predrilled holes, is I was considering doing several smaller fastners, possible even with soy personal when going through stamped metal.

Main reason, I do not have a welder, I wouldn't consider myself a skilled welder but I understand it. And well I have an aviation background and just the route I am used to, row of fastenrs, close tolerance no angularity holes.

Dyno Don

iTrader: (7)

Without a sleeve in between, all you will be doing by tightening is squeezing the parts and they will come loose.

MustangEater82

iTrader: (1)

Huh?

87350IROC

iTrader: (2)

Agreed. The frame rails are really thin steel. The frame rails will probably crush before you can get the bolt tight enough for proper joint stiffness.

Pablo

iTrader: (1)

Everyone keeps talking about elongation of bolt holes but has anyone ever seen it? When was the last time you saw your LCA mount bolt holes elongate? Or your K member bolt holes?

I have been on TGO for over 15 years and I've never seen anyone post actual first hand experience or pictures of bolted LCAs elongating holes. Sounds like an urban legend to me.

Can something like that happen? Maybe, or maybe not. Obviously installation is the biggest factor.
There wasn't a single weld on the aircraft I used to work on (well there was one and it cracked all the time) and they seemed to hold up pretty well considering they are mostly made of aluminum. That means it's all rivets, bolts, and screws.

Just something to think about.

87350IROC

iTrader: (2)

The LCA's have a steel sleeve in the middle of the bushing to prevent the mounting tabs from crushing. That is why you can torque the bolts to 100ft/lbs. 100ft/lbs is enough to ensure all of the load is taken up by the friction in the joint, and not shear in the bolt. It is a properly designed joint.

If you don't have a sleeve in the frame rails, I'm not sure you could tighten the bolts enough to ensure all the load is taken by friction, before the frame rail starts to crush. I have no doubt, if you designed a proper bolted joint, there would be no problems with the holes egging out.

Yes, aircraft are typically very well designed. The interesting thing is that from a static strength standpoint, aircraft structural analysts assume there is zero torque on the bolts. In other words, all the load is taken by shear in the bolt and bearing in the structure. This works because aircraft have a crap load of fasteners to share the bearing stress. Have you even seen how many fasteners are on an aircraft skin panel? This does not work in the automotive world where very few fasteners are used. Automotive analysts rely on bolt torque as the means of passing the load.

Look at all those fastener holes for such a small panel.

Pablo

iTrader: (1)

I might know what an aircraft panel looks like I've actually made a few of them.
A hole egging out is going to egg out because of the same force that causes working rivets. Many bolts on acft are shear bolts but not all. Either way, they all have a torque spec, german torque doesn't count (goodentight). So there is going to be residual torque stress on them no matter what. That whole mess of hi loks on that panel takes the torque wrench out of the equation though! It would seem to me that they work by friction between the surfaces dontcha think? That's all incidental to your point as it's incidental to my post.
If you'll notice, I never mentioned anything about crushing frame rails, only that there was not one instance of anyone "egging" out hole on SFCs that I've ever seen posted on TGO.
There are probably a number of ways to bolt in an LCA and avoid the issue of crushing, so you are having an argument with yourself on that one.
I cited the aviation example to point out that bolted joints can be quite trustworthy when done properly. There seems to be this idea that everything must be welded in order for it to be strong, and indeed, in aluminum acft components, welds seem to frequently cause the most trouble with cracking. Again, neither here nor there, just that the execution is far more important than the method.

87350IROC

iTrader: (2)

Excellent.

Yes of course all the bolts on a plane are torqued. I was not being very clear in my point. My point was that for aircraft structures, the stress analyst ASSUMES there is no bolt torque and therefore the entire load is taken in shear by the bolts. In other words, from a static strength point of view, the plane will fly just fine with all the bolts "loose". That of course makes for a conservative result which is good when you're carrying 300 people 500mph at 40,000ft. From a fatigue point of view, you must assume some bolt torque, but its well less than the spec. Over the course of an aircraft's 30-40yr life span, the fastener toque will relax some. This is all for large civilian aircraft. I wouldn't be surprised if the military guys use less conservative assumptions. I just don't know, my combat aircraft days I was merely a dynamics guy.

But back to the point, I as well have never seen an egged out SFC or LCA hole. But I haven't looked either. I have however seen an egged out sway bar end link hole. No doubt caused by a loose fastener.

So in the end, I agree with everything you said. If it were me and I was dead set on running bolt in SFCs I would find a way to add a sleeve to strengthen the frame rail.

MustangEater82

iTrader: (1)

Lol ill be honest I was considering doing a row or two of staggered highloks.

I was talking with some buddies, with a weld the stress point then is the weld and it creates a lot of stress in a localized arwa as well.

DJP87Z28

Welded SFC's (tube type) for 10 years now and still solid. Different stress on a car then a aircraft. I would still go with welded SFC's and my bolt in Rear LCAs & Panhard bar are still untouched for the same time frame.

MustangEater82

iTrader: (1)

Actually they see a lot of similar stresses. Not the same way, but torsion, shear, tension, compression.I. in fact an airplane sees more. Old steel bridges were built with rows of fastners on trusses, not welded.

TTOP350

iTrader: (8)

I know its not a frame connector and its a bit diff loading but I have a stock TQ arm that I bent an stretched the holes out.. Yes, they were Torqued properly.
How? I'll never know 4 sure but Im sure the 4.11s, ETstreets and some crown royal had something to do with it..
I'll say these cars do twist a lot when going up driveways and things at odd angles..
I've taken bolt ons off after they have been on for many years and there is evidence of "stretching" or "compressing" metals but its not enuff to get excited about. However, I think it could lead to more squeaks and rattles.
I weld them all in just for piece of mind..

wretched737

Why not bolt it in like you want to, than have a shop or friend put a couple stitch welds around them to lock them in for good? best of both worlds no? I'm not sure where you are located but i am sure it is worth looking for a local member to do them for you

Tony V

iTrader: (5)

I've got Jeg's bolt-ins. Works for me as this thing is mostly a track car and the bolts go through the forward pads of the door bars. (S&W 8 point roll bar).

I've thought about welding them in...

SCCAjunkie

I personally have seen egged-out holes on SFCs, on both a Firebird and on a Mustang (Fox body). I had pics of the Mustang, but I can't find them. I cannot vouch for the installation quality though. While I'd certainly agree that execution is the major issue, I'm not sure I see a way in the case of our SFCs that can overcome the physical limits of the material and nature of mechanical joints.

I don't have a background in aircraft, but in my experience, bolts would not be used to make this type of attachment- rivets would. If bolts were to be used, the location of the junction would certainly be reinforced well beyond anything remotely like what we're dealing with. Also, aircraft joints have fasteners where you're not using the threads as a bearing surface...

Welded joints can certainly be issues as well due to heat effect, but once again you're looking at distributing the forces out over many linear inches of weld, versus concentrating it in one small region, where the hole itself may be a stress riser waiting to happen (not to mention the tearing action of a "dull bit" and other issues).

In the end, I would agree with Pablo that the execution is more important than the method, but I see more ways to screw up a bolted connection than ways to get one right...

87350IROC

iTrader: (2)

Agreed. But that is true of any science.

And yes aircraft fasteners use tight tolerance holes and shouldered fasteners for shear loads. But I would do the same if I was expected to the fasteners to see shear on an auto. Case in point, LT1 T56 pressure plate bolts are only torqued to 17-20 ft-lbs IIRC. I don't know why, but that is the spec. The correct bolts have a long shoulder that extends into the flywheel to take the shear load. They are a tight fit. I haven't done the math but I'm sure GM has and determined there is at least a risk these bolts will see shear loads.





At the end of the day though, the risk with bolted joints in the frame rails is that the frame rails will fail, not the bolts.

SCCAjunkie

Agreed, but it's not bolt failure that worries me. The teeth on a bolt making contact with a thin metal section seems a lot like a chisel point to me.

But we could do this all day.

To the OP- I don't think you're going to have a failure via either method per se. I simply think that bolting the connectors in offers a less secure method of preventing movement versus welding the same. At the end of the day, what good are SFCs that don't prevent as much flex as they could? It sounds as if you're serious about correct installation regarding the chassis alignment, so why go to all that trouble if a year from now there's a decent chance your connectors will move the 3/32" that you spent all that time trying to correct?

87350IROC

iTrader: (2)

Agreed, which is why I said "At the end of the day though, the risk with bolted joints in the frame rails is that the frame rails will fail, not the bolts." at the end of my post.

I agree, for the casual user, welding is the way to go.

MustangEater82

iTrader: (1)

Proper hardware would have the grip of the bolt in the hole, not that threads.

87350IROC

iTrader: (2)

Right but the frame rail is still really thin. The bearing stress would be very high if the friction in the joint was not high enough.

83 Crossfire TA

iTrader: (2)

What it really comes down to is that a bolted joint could be designed to work, but it would have to be bolted to a welded plate that distributes the load to the existing frame/body, kind of like the reinforcement plates inside the frame rails where the transmission cross member bolts on. This will end up being a lot more work and the only reason that I can see that it would make sense is if you needed to be able to remove the connectors for some reason (maybe something with a funky exhaust or some legal/rules issue)