actually bolts provide clamping force, not torsional force. if they provided torsional force then you would not have to worry about things like lock washers and safety wiring bolts so that they do not back out.

 

Exactly, and in this case the clamping load applied to the damper/pulley, cam pulley and crank flange keeps the parts from rotating in relation to each other.

 

so the keyway does have load placed on it and is what drives these items. without the keyway driving these items they would move independently of each other.

 

Just a quick update on the whole Keyway vs. Bolt issue.

The keyway is for alignment- allowing clocking reltionships for the camshaft drive and locating timing marks etc on the pulley. Without out a locating device how could you maintain relationships between driven components?

Do you really think a 5mm square piece of low carbon steel was designed to take the drive load (fore and aft) of every drive component on the front of the engine?

There has to be a little "slop" in the keyway, other wise it would be a "press" fit onto the crank. So- if the bolt is not tightened to 220lbs ft, say 70 lbs ft, all you have to do is exceed the clamping force of the bolt with drive force and the puley will slap back and forth against the keyway. Eventually the keyway will wallow out to a huge size, break and generally make a mess of things. Still think the 220lbs ft is too high a torque? Would you torque your wheel lugs to 1/4th of their recommended tq?

We have had a customers who knew more than we did tighten the crank bolt to 50 lbs ft or so as they were "sure that was way too tight for that bolt". We documented the name, time, comments etc. Several months later I have to remind them of their superior judgement when they want a replacment pulley for free because the keyway wallowed out- go figure.

Our demo 2002 C230 has 20K+ miles on it with an alloy pulley that has a perfect keyway, no broken hub etc. We torque to 220 lbs/ft.

 

Kleeman, when the pulley was in the design phase, did you do any failure analysis?...ie torquing the bolt until the bolt or pulley failed? At my job we run into fastener issues on occassion, and before we proceed, we usually see what it takes to break it, before proceeding on the assumption that a torque is too low or too high. My only concern is the softness of the aluminum...in my experience, 220ft-lbs does seem very high for an aluminum component, but right in line with the torque you'd normally apply to a steel sprocket or pulley attached to the end of the crankshaft.

 

Not what I said at all.

I'm not going to waste more time on you. It's hopeless, go back to school and learn how to read.

 

Ahh, finally a voice of reason. He gets it!

 

As Kleemann said, no matter what instuctions you provide for installation some people are going to do that they want like me. So the issue is to make it at least as strong as stock and that requires the hub to be steel. If everyone installed it perfectly then the alloy pulley would be fine. Even torquing a bolt dry to 85 ft-lbs is not really 85 ft-lbs.

 

dcx, you seem to be so sure that you are so well educated on the subject. show me proof to support your basis. the reason I argue with you is because i have seen motorcycles break there keyway, and then not start. the reason they do not start is because they loose their timing becuse the ignition is triggered of of the flywheel. now the bolt is still at the recommended torque, however the flywheel has moved. now if the key doesnt drive the flywheel then what does? the bolt is just there to keep it from coming off. lets use another example. the oil pumps in some motorcycles use a keyed sprocket to drive the shaft, however there is no bolt to hold it on, only a circlip that fits into a groove. this is the only thing keeping it from falling off the shaft, no clamping force here. the key is the only thing driving the sprocket.if the key doesnt drive the sprocket, then what does since there is no bolt to provide clamping force to the sproket to keep it in place? just some examples of keys doing the work that you and kleeman claim they cannot do.

 

nov0798, I think dynodog and Kleeman have made the point that the keyway is for alignment, not to keep the pulley from spinning on the crank. The clamping force of the bolt is what keeps it from spinning. The key is way to small to take that amount of force as Kleeman pointed out. There are some components DESIGNED to use a key to transmit force, but this is not one.

 

Already showed you proof, I run engines every day with only a cam bolt holding the cam from turning. And remember the supercharged engine with no key? It's a production engine(w/o blower)- the new Hemi- none of them have a key in the snout. Already told you that, you did not listen. I just set up a dual overhead cam engine tonight with new cams and no dowel or key to hold anything, just the bolt. Works just fine.

Yes, keys can be used to drive things, a designer can do whatever he wishes. That does not make it a good design. Keys are usually used in low power applications with relatively smooth power to transmit: pulleys on electric motors, your oil pump example etc. They have to be sized accordingly too. (little keys won't do big jobs) (we're talking about a little key remember)

You just sighted a great example: if the key was all that was needed, why did it fail on your motorcycle flywheel? It should've been fine without the bolt, right? Most likely something else was wrong, probably the bolt was not preloaded properly for some reason or it was just too small. Torque measured to turn a fastener means nothing if the thing is bottomed in the hole or the surface it is against is galled and the friction is high. Fastener preload (stretch) is what applies the load and keeps the fastener from loosening and it varies with size and material of the fastener. In a critical application (take a racing engine connecting rod bolt for example) fastener stretch is routinely measured and recorded. The torque required to get the proper stretch doesn't matter and is not the same for all. (oh yes, they don't use "lock washers" either)

In this case that tiny key is not going to provide a reliable way to transmit all the force, not gonna happen. Do you think a fastener large enough to require 220 lb-ft is necessary just to keep a damper from falling off the end of the shaft?

 

nov0798, remember that the pulley bolt on the engine is a stretch bolt according to MB. This agrees with DCX's statements. Ideally, it should only be used once as the stretch changes on reuse. DCX knows what he's talking about, it is foolish to argue with someone that works with engines every day for a major maker as he does. Do you trust a doctor or some guy that took bio in highschool?

 

its not that I dont beleive what people are saying its just that they are stating that it COULD NEVER BE. to state that something could never be when they are not the ones who designed it is wrong. lets use oil for example here, some people still beleive that you have to change oil every 3000 miles, this is not true anymore as i dont change my oil but once a year. the reason, TECHNOLOGY. so people cannot accept the fact that technology changes and things that used to be are not anymore. dcx, show mw pictures of the engine you speak about. the reason why i am asking is that i have never seen an engine use cam pulleys that do not have a key in them, or some other means to locate them properly. for you to say that no load is placed on the key in anyway or that it is not used to help transfer some rotational force is wrong. show me proof otherwise. you state that you have shown me proof, WHERE? in your words, big deal these are your opinions and have no factual proof to back them.

 

nov0798, you just said it yourself, "or some means to LOCATE them with". The key is used for location not connection. The key aligns and the bolt holds. I'm sure he'd love to show you a picture but he'd loose his job. Also if the bolt is tight enough so the pulley doesn't slip how can the key do anything. There is no force on it, the bolts tension along with the friction between the two surfaces do all the work.

 

At least having a stainless steel hub will allow you to torque the pulley to 220 ft-lbs without any fear of distorting the metal. The problem is how do you get 220 ft-lbs semi-accurately. I've heard using motor oil might only torque it to 3/4th the correct torque and you should use assembly lube to achieve the correct torque. Is their an MB guideline on correct assembly procedures to achieve the correct torque?

 

Hmm, I can believe dynodog, who works for a major manufacturer on prototype engines all the time, or I can believe nov0798 who is a certified motorcycle mechanic and argues with everyone about everything. Gosh, I just can't decide who to believe.

nov0798, dynodog doesn't owe you any proof about anything. I suspect it would be highly frowned upon for him to take pictures of a prototype engine on the dyno at work and post them on the internet just to convince you that what he says is true. Slotted cam gears are used all the time on racing motorcycle engines and they are held in place by clamping force and nothing else. You should know that. If you want to believe what he says, Kleeman says, and basic engineering principles dictate, fine. Otherwise believe whatever you want, but don't suggest that he is lying.

 

Here are the two pages direct from the MBZ WIS system that describe the pulley installation. Note that NOWHERE is it stated that the crank pulley is a stretch bolt and should not be re-used.

 

page two- sorry about the size- just wanted to be sure everyone could see it.

 

All torqued fasteners work on the principle of stretching the bolt- that's how you get a clamp load.



Yeah, if youve got steel on steel that works. I was under the assumption that the ASP pulley had the bolt head clamping onto the aluminum.

Aside from an industrial right angle DC electric torque gun with a built in tranducer and a reaction bar, your best bet is a big long torque wrench and a strong arm. That's a lot of force to apply manually. An impulse gun w/shut off would work...but most folks don't have access to a transducer to calibrate the shut off. And you'd need a right angle impulse gun to get in there....not too many around that are capable of that kind of torque.

Do you have an adjustable 'click out' torque wrench? Those work good.

 

That's great Brandon, it's very informative. I suspected but wasn't sure about the washers being concave. If put on backwards by chance, it would not spread the load of nut across the entire hub and this may cause the hub to fail, specially on an aluminum pulley. If for whatever reason the washers fell off the nut during installation and you didn't notice which way they went, it maybe a good time to check that they are facing the right direction. To me they weren't obviously concave but I wasn't paying attention as the washers never left the bolt during the install.

 

This is what I used and set it to 220, and it is a lot of force to apply manually. But I got it eventually. If I didn't have it up on a lift and able to stand and push with my legs, it would have been even harder.

 

speedfrk, i argue with people because there are so many people here that are experts on everyhthing. Alot of people talk alot of smack, yet never seem to provide any factual data to support thier basis.I asked for a photo of the cam gear that uses no keyway, and is not a press fit. I doubt I will ever see this photo most likely because it does not exist. as for keyways, let me ask you this. If the key is there to only locate an item, then why all the different designs? I mean it seems like a waste of time to engineer all these different types of keys if their only job is to locate two parts. as for the motorcycle slotted cam gears, yes those two parts are held by clamping force, but the force on those parts is not the same. you see the pulley, or cam bolt has to deal with twisting force created by the crank or the cam. the reason for this is because it is at the center. the bolts in which you talk about do not see twisting force, so the above argument does not apply.

http://www.utm.edu/departments/engin...cture%2019.pdf

read this.

 

youll find page 2 useful. youll notice here that they talk about key size and shear strength. now this has nothing to do with our cars, but it is proof of what a key can withstand.

http://www.eeeng.com/html/catalog/PDF/A44_45.pdf

you see the key is there to protect the crankshaft. if you have a failure of one of the parts that are run by the pulley and it locks, the key is made to give under a certain load, to protect the crank. now if we use the other theory that the bolt supplies all the clamping , and driving force then you would not be protecting the crank. now if you use the other theory ,you would have a bolt that would need to break to protect the crank but if this were to happen then you would have a loose pulley on your hands which is dangerous. now lets look back at the original reason for this post and the pulley in question. the key tore the hell out of the pulley because the key was a harder material then the aluminum, yet the bolt stayed in place. now if the key doesnt transmit any power then why did his power steering, and water pump stop working? because the key wasnt driving anything, yet the bolt was still tight. so the theory of the bolt does the driving doesnt hold water.

 

http://www.colorado.edu/MCEN/MCEN302.../26-Shafts.pdf

 

nov0798, you assumption that the bolt would have to break to protect the crank is wrong. The pulley would just slip if the load was greater than the bolts holding force and there was no key. Think about it, what happens if you don't tighten the alternator pulley enough, it slips. You are just showing your inablity to accept and grasp concepts. DCX knows what up, you don't. His paycheck proves that he knows his field, listen to him.