Originally Posted by
crank_addict
For the bottom line of cranks, I find these Shimano steel/aluminum interesting. Amazing when one thinks about it. The steel stampings and ramps, the perfect cut notches and then how they fasten it all together. Considered low end of course but the assembly weight isn't too far from full alloy triples.
This was on a 1993 Schwinn ATB I recently picked up from Goodwill ($6.99 - for the entire bike).
The crank arms are "Melt Forged" which is a Jinglish euphemism for pressure cast!
Molten aluminum is injected under high pressure into a precision steel mold. The arms on these kinds of low end cranks are at least 20% larger than true forged aluminum cranks to compensate for the difference in strength between cast and forged parts.
The chainring spider is swagged onto the crank arm with a substantial amount of material on those Shimano triples.
That was a short coming with the early Japanese cast aluminum cranks like the first generation Sugino Maxi and SR "Melt Forged" models.
They were fashioned after swagged steel cranks and the makers didn't allow for enough metal to form a strong joint with aluminum. The wasn't much of a sporting bike tradition in Japan and those components were made for the western market.
1st generation Sugino Maxi cranks
Later style Sugino Maxi with more substantial swagging
SR "MELT FORGED"
The average Japanese person weighs considerably less than the average westerner. The first time a 200 Lb. masher got on a bike with those type of cranks, they frequently spun the spider in the swagging.
Around 1973 Gitane started using Sugino Maxi cranks on their Interclub amateur racing model. We had a bunch of them awaiting warranty replacement cranks from Sugino. It took 6 month to a year to get the re-engineered Sugino Maxi replacements.
Same thing happened with Japanese bikes that came with the early SR cranks.
That's why I've always considered cast aluminum cranks with swagged CR spiders low quality...
TA cottered steel crank
verktyg
Chas.