Came across this picture of a cracked Imprezza crankshaft.
it looks like it's been worked upon and this has led to the cracking
On a different note, how do they machine the various bearing surfaces? Do they turn it at different centre points? (3 in this case)
cheers, clive
That's exactly how it's done!
The message from "Clive George" contains these words:
Yup.
The message from " dojj" contains these words:
Thing is - being a flat-four, it's not got the need for quite such strong webs as an inline 'cos they're closer together and haven't got the same bending stresses. Even so, it's hard to see good grain flow during forging with what are effectivly right-angled turns.
Monstous amounts of boost due to 'home-tuning' courtesy of a "Wunda-Chip" and then missing a gear?
JB
Are there any issues with it being out of balance when doing the big end bearings? (three things come to mind here - 1) hold it jolly tight, 2) turn it slowly or 3) hang a balance weight off the other side. I'd guess at 1) and 2) being done in practice - but am I right? Or indeed, is there a clever
4)? )cheers, clive
The message from "Clive George" contains these words:
Yes, but they use extremely powerful lathes with massive bearings and very heavy bases!
The message from "JB" contains these words:
Well, that goes without saying!
Doesn't seem a problem - the chucks are just set to revolve around an axis that is not the middle of the chuck (IYSWIM). It's not turning that fast (100rpm -ish IIRC) - the thing that is doing the work is the grinding wheel, the crank is just turning to give access to the entire journal.
Thanks for that Simon and Guy.
cheers, clive
The machines doing the rough turning will have fixed counterbalances for the offset journals, as will those doing the grinding. I've seen crank turning m/c's at Ford. The speed they work at is quite amazing. Minutes to turn a forging into a rough turned crankshaft, almost ready for grinding. Mike.
& you don't spin it that fast, the rough turnings more akin to a broaching operation & the grinding wheels what's spinning fast for the finishing operation.
Looking at the casting and machining marks, I'm not surprised it cracked, it must be a mss of stress points
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