Con rod scratches?

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wrecks

wrecks

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The recent discussion of "D" con rods and other posts with con rod questions and pictures got me looking at my own. I noticed these scratches along the edge of the rod. Is this something I should be concerned with?

Timing Side Rod:


Drive Side Rod:
 
Yes, scratches are stress raisers and therefore potential starting points for failures. They need polishing smooth.
 
I cannot claim to be an expert with Norton aluminum rods but 35 years tool and die experience has shown me the danger of stress risers, surface flaws that give a failure a place to start.
 
Heh, reminds me of when I had my first 750 in 1977. Broke a couple of pistons (yeah, you know) and one took a big bite out of a con rod just below the small end. Did not look good. But I was not wealthy so glued on another piston and buttoned it back up, missing chunk and all. Then I tried to vent my anger by redlining it through the gears everywhere, defying it to snap. Got bored of trying after a few weeks and got a replacement con rod.
It was handy having a local racer who had not long switched from racing a Commando, lots of cheap spares.
Oh, to be young again!
Cheers, Martin
 
Some polish it out smooth and then bead blast. Im leary of bead blasting as there may be some bits still in the metal waiting to
come out and start circulating in the oil.
Fear mongering Im sure but....
 
Onder said:
Some polish it out smooth and then bead blast. Im leary of bead blasting as there may be some bits still in the metal waiting to
come out and start circulating in the oil.
Fear mongering Im sure but....
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If new glass beads (not glass abrasive) are used at lower pressure, they peen the surface which improves the metal and does not leave bits behind. I use 45 psi. Using old or the wrong media or using too much pressure could do just as you fear.
 
Not sure why anyone would bead blast this - if you are thinking shot peening - that's a whole different thing, and a good idea.
 
Dutch said:
Not sure why anyone would bead blast this - if you are thinking shot peening - that's a whole different thing, and a good idea.
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"Shot peening" means peening with Glass Beads, Ceramic Balls, Round Metal Ball, etc. Glass Bead is most commonly used for crankshafts and connecting rods.

So, what I described is shot peening and is done like I said by many industries.
 
Yeah, but don’t take alloy rods to an industrial shot peen company... they’re more used to doing steel etc and will peen your alloy rods into oblivion !!
 
That looks to me, like some where along the line, it was subjected to a wire wheel on a bench grinder.
 
concours said:
That looks to me, like some where along the line, it was subjected to a wire wheel on a bench grinder.
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My money is on that damage being caused by spending years rattling around in someone’s parts box...
 
Fast Eddie said:
My money is on that damage being caused by spending years rattling around in someone’s parts box...
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This is the first time the motor has ever been apart. It was my father's bike and he was the original owner. So, no wire wheel, no parts box - is the damage indicative of something else I should be looking for?
 
But even a factory engine was made from stored parts, and if stored incorrectly. Either that or something was bouncing around inside the cases. Either way its needs rubbing down and polishing.
 
kommando said:
But even a factory engine was made from stored parts, and if stored incorrectly. Either that or something was bouncing around inside the cases. Either way its needs rubbing down and polishing.
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As recommended, I plan to see about cleaning it up and buffing out the scratches. I was more worried about something that had been bouncing around inside the cases! That said, I haven't seen other evidence of damage.
 
Yup, in that case, like Kommando says, it’s either been like that since new, or some shrapnel inside the engine has caused it. Did it ever have a seizure or holed piston or similar?

Whatever the cause, the scratches need removing IMHO. IF the rods have possibly suffered trauma in the past, they should be checked for straightness and cracks if you wanna be totally safe.

But if it’s a one owner bike, with a known history, that’s never been raced or blown up, I’d just polish them and re use them.
 
My self I would suspect that it started, as a bad bend of alloys at the factory, just to constant of damage...
No motor would stay together with that much shrapnel floating inside the cases

Me I would replace them
 
I would imagine if there was something inside the cases, the damage would be spread around more.
(IMO) - Sand out the scratches and polish the rods, call it good.
 
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