Bolts, classing, hardness, and strength...
 

So at some point in the near future I'm going to be removing my timing wheel to do some minor modifications. I've decided to go ahead and purchase new bolts head of time for when I re-install it, as I hate re-using fasteners in super-critical applications like this, especially when they're only 40-50 cents each.

For review, I'm talking about the four 6mm x 70mm bolts that hold my 36-1 wheel and its aluminum hub (and the crank pulley) onto the front of the crankshaft:

http://img152.imageshack.us/img152/1...hedleftzj3.jpg

(ignore the large bolt in the middle in that image- I only put that one in when I need to turn the crank with a wrench. It's not part of the main structure of the system)


I have a couple of options here. I can either get zinc-plated class 10.9 hex-head bolts (which is what I have in there now) or I can get unplated class 12.9 socket-head bolts.

I like the idea of using bolts with a higher yield strength, which I'll be able to torque to a higher preload. I'm slightly concerned that the 12.9 bolts' greater hardness may cause them to be more likely to fail catastrophically in what has got to be a brutally high-stress environment. And I'm slightly more concerned that using unplated hardware in this environment is just an incredibly stupid idea in general.

Do the Mech-Es among us have any thoughts on the matter?

Do they still look that good? I don't see the problem with re-using a good bolt. What are they torqued to? Surely not too much. As to what I would replace them with, I would stick with what you know and just buy new duplicates of what seem to be doing their job, if they are only $.50 each.

I'm not re-using them. Bolts like this get torqued once, then thrown away.

The ones that are in now look fine. Can't say the same for the wheel itself (covered in rust) but I see no indication that the hardware has suffered in the least.

I'm definitely leaning towards replacing with same. Just trying to convince myself it's the right thing to do. Several folks speculated when I first did this that the bolts would fail leading to the destruction of the crankshaft (and / or a spiked, spinning wheel coming out through the top of my hood) and for some reason I'm still paranoid about it two years later.

the post where I go into far too much detail.
 

bolts clamping two flat pieces together are primarily in tension, not shear. They do their work by acting as super high rate springs when you torque them. the main force preventing relative motion is friction between the mating part interface.

clamp load obviously increases with bolt torque.

and increases in bolt tensile strength mean higher clamp load capacities.

the FSM says 8.7-13 ft-lbs for the four pulley bolts.

based on these charts:
US & Metric Bolt Torque by Grade
http://www.rpmmech.com/docs/tightening_torque.pdf

it appears they're using a lower grade bolt. If you want to "uprate" that, an 8.8 should be plenty, but I wouldn't torque it past the 13 ft-lb limit for fear of stripping threads.

You can look at the second chart to get a feel for the clamp loads involved if you want. multiply the clamp load by the number of bolts for the total clamp load. what's that work out to, 3-4000 lbs clamp load?

so even with a higher rated bolt, you're not getting more clamp load at the same torque, just more factor of safety.

If 4 of those bolts can't hold 13lb-ft each, something is seriously wrong. I'd stick with what you have, unless you can get something with a higher rating just as easily.

I doubt that it is a very high stress environment at all. Especially when all for bolts are torqued similarly. No relevant sheer will be acting on them on startup. The aluminum spacer and toothed wheel aren't heavy enough to cause any. Since crank pulley and toothed wheel will spin at same velocity, again, no sheer. New bolts (for your piece of mind), torque to spec and forget.

If you actually need to throw them out after each use, you're tightening them too much, or being paranoid. You'll start sacrificing too much elasticity when you go to a higher grade. Get the standard 8.8, long enough to engage all the threads, and torque properly. I think fsm says use loctite, but you shouldn't have. Might help put your mind at ease though.

This.

Sometimes, the things I build have a tendency not to work in rather dramatic ways. It doesn't happen often, but when it does, I prefer that it not result in the destruction of my engine.

New 10.9 bolts it is.

also joe, the longer the bolt, the higher its stretch capacity. if those bolts are longer than the original ones in the pulley, then you're even better off.

On my old application with a 60-2 wheel I drilled and pinned the wheel with roll pins. They are very strong and take all the side load stress off the bolts so you don't have to worry about vibration working on them. The bolts then just hold the wheel on.

I can't tell from that picture what keeps the wheel centered?

The inside of the aluminum hub self-centers on the large crank bolt. The wheel self-centers on a raised section in the middle of the hub (beneath the large bolt and washer in the above pic.) Details here.

If by socket bolt, you mean one of these guys here
http://t2.gstatic.com/images?q=tbn:L...c/bolts-b1.jpg

Then I have experienced socket bolt failure in this application. It occurred on the dyno. The head of one bolt sheared which allowed the timing wheel to begin separating from the crank pulley--creating an awful noise that sounded a lot like a really bad lower engine problem. 2 other bolts loosened up. Bolt 4 was tight.

The theory/speculation is that the bolts were much harder than the soft aluminum trigger wheel underneath. As the bolts hammered on the trigger wheel, it wore material away, allowing vibration to eventually destroy the 1 bolt and back out the other 2. As I found out later, I am not the only person who has experienced this, and the ultimate solution is install a large steel washer ring behind all 4 bolts.

So my experience is that the bolts themselves can fail, but the key factor is in the mating surface--not the bolt itself.

The TEC2 folks from 2001 had the same experience as Ben with the same solution (larger washers).

Interesting stuff.

Yes, those were the socket bolts I was considering as an alternative to the ones I currently have. In fact, if you look at the pictures I took during the mock-up of my original build, there is a set of them sitting in the stackup. I wound up not using them as the particular ones I'd bought were too short.

In my case, the mating surface for the bolts (apart from some common cut-washers) is the 36-1 timing wheel, which is made from mild steel about 3/16" thick. This wheel sits on top of the almost completely solid face of the aluminum center hub, which in turn sits on top of the crankshaft pulley, in the place where the large steel washer with five holes sat in the stock configuration.

I'm not concerned about deformation of the mating surfaces.

My only concern (and this is purely speculative) is that any imbalance in the hub/wheel combination will, at high RPM, attempt to place a bending load on the assembly (IOW- force it outward to one side.)

If the bolts, which are in fact quite long, are able to stretch, then the assembly will be able to yield to these forces and displace itself from centerline, this increasing the load, etc.

I'm just being paranoid, I admit.

Seems like a valid concern. But I can't imagine why your assembly would be out of balance.

Isn't the whole configuration slightly out of balance anyway due to the forces required to drive the accessories?

Should be able to take it to a decent shop and have the whole assembly balanced. And by whole assembly, I mean pressure plate, flywheel, crank, timing sprocket, pulley, aluminum hub, and timing wheel, with all hardware.

The biggest forces on it are not imbalance, but probably crankshaft torsional vibration. (which the ATI damper reduces BTW).

I vote for vibration and since I had one on a VERY high NVH motor (DIY Turbocharged 0Olds Quad4) with an aluminum crank pulley, I still vote for a positive lock in the rotational axis with something.

I used roll pins with very good results after one failure from bolts loosening and deforming the surface under the bolt face.

I was a TEC2 user as well.

Be scared! BE VERY SCARED! You will have a ninja throwing star sticking out of your hood in a month. :laugh:

Yeah, well, given that the crankshaft is sort of inside the engine just at the moment, I kinda don't see that happening. :D

Provided by the stock pin pressed into the hub thingy that sits in front of the crank. It's not quite an interference fit, but it's snug.

Heh. It's been fine for close to two years, but it's funny that This Thread should come up today. :rolleyes:

Yeah, that ENTIRE engine would be in the scrap metal pile. I overrevved an engine by just a few thousand RPM's once (11,000) and thought a head rebuild would be enough (all 16 valves bent), and it did for about 6 months, until a crank bearing spun in the block at random one day. I'm sure it was attributed to the high revs. Later found out that there was other block damage that rendered it useless for a rebuild from some guy I sold it to.

I also doubt 15,000, had to have been a sensor issue. I doubt even a 5th to 1st shift would allow that high of a rev without just sliding the tires or breaking something else first.

n/m, actually read the thread now. Obviously it wasn't the claimed 15k.

And yet: Do it then.

That engine isn't going into this car. I have something... special in mind for it.

Sounds like you've got a pretty solid set up. The wheel I have has an aluminum center section. I don't see your set up suffering from the same problems that mine did. When my motor comes out of the car, I'll have a machinist cut a giant washer ring for me, but for the mean time I replaced the bolts with new, slightly longer and installed the largest washers that would fit. I also used red loctite. I had used blue loctite originally.

My socket cap bolts failed again. Two of them broke, mid shaft. Seriously.

The resulting noise made me think that something in the motor collided into something that it should not have. Luckily for me, that wasn't the case. I'm not saying that these bolts belong in Dante's 9th layer or anything, since they did last several thousand miles, but I wouldn't lose a minute of sleep if they found themselves condemned to the 7th or 8th layer.

I'm going to come up with something better.

Wow.

Knock on wood, but the 10.9s on my hub are holding up nicely. Again.

Ben,
is any area of the wheel coming in contact with the thread of the cap head screw?Could they have vibrated loose prior to failure.You may want to try stripper bolt or shoulder bolts,or even aircraft hardware.
http://www.mcmaster.com/#shoulder-screws/=6oz54m
(G)

Ben -- giant washer + hex head bolts = win.

i still say the worst day of my miata related life was when my harmonic balancer fell of do to 2 sheared bolts and 2 bolts that worked free. do the shit right joe walking back to pick up parts and installing them improv style after work to get home is no fun.

That's kind of what I was thinking too. Greg doesn't know it yet, but he's going to machine a giant washer for me. :giggle:
The problem is that there's no room for hex head bolts due to the small ID of the trigger wheel overlay where it fits inside the pulley. So giant washer plus fancy socket cap shoulder bolts hopefully will be win.

Or I will get one of our 36-1 wheels off the shelf and run it similar to Joe Perez.

Can you open up the ID of the trigger wheel adapter on a lathe? That's what I had to do in order to fit that stuff. Just a little bit.

Oh, and you can just use the factory giant steel washer ring.

Thanks Jay, that sounds like a good plan. I'll take the pulley off and have a look at it as soon as I can.

Not sure I follow you here. What change(s) do you propose I make to my current setup?

no changes i am essentialy agreeing with your new bolt philosophy if you have any doubt in the intergrity of what you have. maybe some nord locks or lock washers for peice of mind but other than that you have just about all you can get.

So, here's pics of Joe's nightmare. Only it's my nightmare.

Jay, the factory washer-ring must be an NA thing because it wasn't on my car.

Taking this as an assembly to a machine shop in the morning. I'm going to have them drill the assembly, tap the pulley boss for larger hardware, and mill the bolt areas of the trigger wheel "cup" for larger hardware. Figure I'll stud the boss, then use nylocks or other self locking hardware on the trigger wheel.

Don't mind too much the red color in the first pic. It's just a camera phone capture, and it's overly sensitive to the little bit of georgia red clay that's on the motor. Yeah, the dirt here is red.

Before you go through all that, let me tell you what I did.

I have the exact same set up with an Electromotive, and I hated the allen head bolts. I got rid of them and used some bolts from a Yamaha dirt bike motorcycle. The head is an 8mm instead of the stock 10 mm. It has a washer boss on the bolt, and it installs easily with a socket. They are a very high quality bolt as well. I use them over and over, and the threads stay clean and straight.

Get a new crank timing belt pulley, and try those Yamaha bolts. I have had that damn pulley on and off a 100 times and have not had any problems. It is also much easier to install than the allen heads. I am willing to bet that you are not torquing them correctly. It is hard to do with those alan heads. I will get you a picture of the bolt for you today when I get back to the house.

Yes I was assuming NA. Didn't realize this changed for NB.

From your pics, this is pretty much what happened to all Vishnu adapters -- the bolt heads abrade the soft aluminum, which takes the preload out of the four little bolts. They then loosen and eventually snap.

Larger bolt underhead area (replace tiny allenhead bolts with integral washer hex head) and a steel backing (NA washer ring, in my case) fixed it for me. No need to mess with larger dia bolts and such, in my case...

Ben, this is what I use.

m2f--I bet you I did torque them down correctly, with a allen head socket on a midget ratchet. Also loctited them.

If you can find me a part number or application for those bolts, that would be great. There's 3 Yamaha dealers within a short drive. Extracting broken bolts out of the pulley boss is easy enough.

Down the road I'll probably switch over to a DIYAutoTune.com 36-1 mild steel wheel, which will never have this problem. Only hold up is I'd need to fab a sensor bracket, which takes time that I don't have this week. I'd like to make the car self locomote by the weekend because there's an event at Road Atlanta Thurs-Sun. I also want to powder coat the mild steel which would take a few days.

Well stuffs is at the machine shop. Saying good bye to 6mm hardware and hello to 8mm hardware with a much larger shoulder. That should help. With a steel backing, we should be in the win category again very soon.

Do you still need a giant washer?I have some 4140 setting next to the lathe right now,Just PM me dimensions,and It is Yorn....
(G)

Yeah, thanks Greg. Can't get exact dim's right now since the parts are at a machine shop. I'll let you know in a few days. :)

No problem,Ive got a variety of materials,316 SS,Al Bronze,4140, 7075 Aluminum...
Just let me Know
(G)

A word of warning. The 6x15mm bolts provided by Vishnu are a full 8mm too short. They barely bite into the pulley boss, so there's no doubt that they'd snap off.

I'm now up and running again, with 8x20mm hardware. The next jump up was 8x25mm, so after Rev Greg cuts me a washer-ring, that's what I'll run.

Im available to measure your parts to get the exact Numbers,let me know so we can meet up.
(G)

Thanks Greg--but I can either come to you or send you a drawing and/or spare parts. I don't want to ask you to come to me for a favor. :)

Iam ready when You are,Ben.I will Pm you my info.so we can meet up.
(G)