Currently giving an old alternator the once over and found that it's missing the woodruff key which helps lock the pully to the shaft. 7Zap says it's to 4x5 (for Bosch) which is all straight forward enough. The VW part number is N0127082 and they seem readily available, however being a tight arse I thought I'd look elsewhere and sure enough 4x5 is a common enough size. For the price of 1x 'genuine' VW key, I can get 20 non-VW's ones. It also turns out VW doesn't limit 4x5 to the alternator, for example the crankshaft key is the same part number / size, so be handy having the (effectively free) spares. And to the question... woodruff keys don't seem to be advertised with a spec. though there is the occasional reference to them being 'standard steel' and/or DIN 6888 for some of them, which is meaningless to me. If it had been like bolts where tensile strength is rated as 8.8, 10.9, 12.9 etc. I could understand. Do woodruff keys have strengths depending on application and is any one knowledgable enough / qualified to comment?
Standard steel refers to the material (usually tool steel or stainless of specified grade) din refers to an industry standard. I will check on Monday re the tensile strength, launched these as a product at the machine parts firm I work at so had to do a lot of research, can't remember right now but I do have the info at work.
Just remembered, my work publishes breaking strain as this is a common measurement of strength for them. Have a look https://www.wdscomponents.com/en-gb/woodruff-keys
That's spot on, very useful thanks... It's possible then that keys aren't as a rule graded in the same way bolts are for example, and for most uses merely to confirm that they conform to DIN 6888 is sufficient proof of strength / quality? Would explain why 99% of key descriptions make no particular mention of 'strength', they're all going to be the same as long as they're made to that DIN standard. Did find an advert on a classic Merc. Benz. part site that lists the woodruff for one of their crankshafts and it specifically gives it's strength as being to DIN 6888... a lone example, but maybe goes a little way to confirming if keys are made to DIN 6888 they are at least strong enough to handle those sort of loads. https://www.niemoeller.de/en/190SL/190SL/B040/3/c03016-woodruff-key-5x7-5-din-6888 Wasn't particularly looking, but found what appears to be a copy of the original certificate issued for the DIN 6888 standard (from 1956) and it references the tensile strength as being 60kg/mm2 and material as ST60 steel - that last one might be the older equivalent of modern day C45 perhaps? All answers my question in a roundabout way - as long as the key is confirmed as being made of C45 steel (or it's equvalent) and to DIN 6888 it'll be fit for (my) purpose.
Suppose like anything nowadays there's cheapie ones that can be inadvertently bought if you didn't realise their importance or intentionally sold as DIN standard when they're not (or am I just being cynical). Might be small, but I'd imagine the consequences could be big if it failed!
All the instances I've seen with Woodruff Keys is they are there to initially locate the pulley/ sprocket. The actual torque of the fastener secures the pulley/ sprocket in running order. I would hazard a guess the Woodruff Key in the Alternator Pulley is to enable initial torquing of the pulley retaining fastener (by locking the pulley).
It's an odd one and as I don't know much about these things it's all open to correction as I'm just speculating. The seat for the woodruff on this alternator means the large fan affair and the next biggest washer are actually sited beyond it, so ultimately it's the torque alone holding them in place, the key plays no part. It's only as you add the rest of the parts do they begin to coincide with the keys position and it dictates how they must be positioned. In my case with the missing key, it did make me think about what the key was actually there to do as it not being present didn't appear to have had any impact on the alternators running, not what VW intended presumably, but as long as the torque was sufficient to keep the parts secure in one place, it worked. If the key / slots for it had never been included you could probably spin any of the parts around by 180 degrees before tightening and it'd not matter, they're all the same profile throughout their 360 degrees regardless of orientation. If any had a distinct top or bottom for example, it would've definitely mattered, but they don't Could it be the keys (in this case at any rate) have several roles? Like you say it helps the initial positioning so nothing twists / moves or gets damaged as you apply potentially large amounts of torque to secure them. Maybe it also acts as a fail safe in case the fastener loosens, it would prevent the pulley from spinning freely for a time at least? If so that'd possibly need a certain predetermined strength to ensure it held things adequately, hence the DIN standard? If it was soley to initially position parts maybe a lesser quality / strength of key could do that adequately (which is maybe the case in other less critical applications)?
To support your point, I forgot to fit the woodruff to mine and ran it for 6 months with no issue. It wasn't until I took it off clean it up that I noticed! Pinched one from work and fitted it just because once I knew it was missing, I couldn't un-know
