Digging through the parts to put together a mild late 650 Triumph engine-1969. Will be used for daily rider, rare hot rodding, Will probably drop compression down to about 8.5 : 1.
I have this option for my crank, I like it because it's the heavier one, I don't like what the photos show, one side has got some serious pitting- it looks like metal fatigue. This is the only spot on the crank that has this pitting, the rest looks nice. Is this one gonna grenade on me with heat, use and time? (pretty sure I know the answer, confirmation would be greatly appreciated.) Thanks! Joe
That's from the making of the crank in my opinion. Use in a road bike for 'normal duty' and with the regular rev limit (or less). All too often owners 'forgot' that these motors had a recommended max rpm. Is was common to see them revved till the rate of acceleration slowed, then change gear!
It's been like that since it was forged,and it was like that when it was new. It's in a low-stress area.Any force on the counter-weight is almost purely centrifugal,and not much force is transmitted through these minor flaws.
If it was like that between the crankpin and mainshaft,or between the 2 crankpins,it might deserve some attention with grinding and polishing.
T140E, It is pretty apparent that this flaw was there from casting, I am a bit surprised anyone would say to use it. My initial thought was specifically a fear of metal crystalization: this is 50 years old, has been through heat and usage, and I have seen first hand...er, umm..wrecked... first hand the effects of crystalization as in losing the rear wheel when the axle snapped in a van (twice, by the way, two different vans!...) Although it is highly unlikely that a chunk will come flying off at speed, as this portion would be under centrifical force and not a so to speak load bearing force, when I looked at the cases it would go into later this afternoon, the nicely bored cylinders and pistons to go with it, all the time I will put into assembly, then held this crank in my hand and looked at it from multiple angles, it's pretty apparent to me now that for my own peace of mind, a different crank is in order. All it would take is for a tiny section to flake or break off; and I could kiss my effort and engine goodbye. I can always keep it handy for the day that I do blow up an engine playing road warrior, (and since that will be in a post apocalypstic world, we'll all be using cranks like this when we can find 'em!)
If you ground that back and welded it to replace the metal ground off,you'd be replacing about 1/4 ounce of steel.
The centrifugal force trying to pull that 1/4 ounce of steel off the counterweight would be around 15 lbs at 4000 rpm,60 lbs at 8000 rpm. The tensile strength of the weld would be around 15 tons;more than strong enough.