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Correct. They have perfect primary balance but generate a rocking couple that shakes like an orbital sander. Heavy cranks mean more flywheel interia but I suspect that the extra mass also tends to dampen some of the rocking couple.

GT750 really shake their mirrors and any fairings or long fiberglass parts tend to shake like a scared teenager.
 

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Speaking about learning...
I was told by a crankshaft company you couldn't really balance a triples crankshaft.
I tried looking into it and got into info that was quickly over my head.
Seems as though for an inline 3 the pistons are balanced internally? but the engine has a marked rocking moment.
If thats the case, why the heavy cranks?
Did you specify 2-stroke or 4-stroke crank balancing when you posed the question?

If his crank has twisted it needs to be balanced. Put straight again and welded in place to keep it there possibly,
If not what are they charging you for?

Triples have the same heft of crankshaft as anything else, the power delivery is completely unique
:/ closer to a six cylinder or a 9 cylinder or a 12 cylinder... for obvious reasons.
 

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Yeah, I was referring to my plain bearing 4 stroke crank. My bad.
I was sending my crank to be checked. And inquired about lightening and balancing. Ive had inline 4 cranks lightened and polished and balanced by this company in the past. They took off an impressive amount of material without compromising functionality of the counterweight. It was on a zx-11. Something they have had years and years of development on.
Anyway, this company basically told me the triple Crank cant/doesnt need balancing and the mass should stay on it unlike my other bikes.
 

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No worries. I fixated on the thread theme and didn't ask.

I need to think about that, but I think they are assuming that the crank webs are all the same so don't need to be balanced. If there's much of a mass difference say between cylinders 1 and 2, then it will be out of balance regardless of the theoretical perfection. When they put a crank on a balancing machine and attach weights for the rods, they should still see out of balance forces that they can minimize.

There's a guy in the UK, Chris Applebee that can correct an out of balance GT or H1/2 etc crank, so that capability must also be available in the US. Have you tried Falicon or Bill Bune?
 

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The way I see it, if it was important you could put an automatic balancer on it.
... obviously it's not that important because nobody does.
 

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No one designed motors in 1971 with balancer shafts. Singles and twins were typically balanced to a certain % of reciprocating mass and triples were assumed to be fine, even though eveyryone knew they weren't. BUT a triple tyically didn't shake as much as a single or twin, so they were considered to be acceptable by the market.
 

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....My uncle has one with a Sheene, Dunstall fairing kit. They were called kettles over here as they regularly boiled water if ridden hard or even tuned. He bought a TR engine to go in it but after pulling it apart it got left on the shelf, think he's now sold the TR engine and other race bits but it still isn't together as he has too many projects, mosty old brit bikes.

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Dunstall kettles are not exactly common in the UK and are as rare as hens teeth in the US. There are a couple of guys in the Kettle Club with Dunstall 750s. I love the look and I even remember visiting Paul Dunstall's small shop many decades ago when I was very young. What's not to love, but boy are they heavy and awkward. Probably OK for young strong men, but young is not an adjective that is commonly used in my case and with two destroyed shoulders, heavy bikes are not in my future which is why I'm selling my Dunstall GT750.

I wonder what happened to the original poster?
 
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