Kubota 3 Cylinder Balance

[rcull]

I have a Kubota D1105 3 cylinder diesel here. The OE pistons were 374 grams, the replacement ones are 417. It makes me wonder about balance.

If I were to balance it, for the bob weights, what percentage of the reciprocating weight would I use? I assume I would still use 100% of the rotating weight.

[NORSK]

You would have to add weight to the counterweights since the new slugs are heavier

[PackardV8]

Wouldn't a 3-cyl follow the rules for a 6-cyl and not require bobweights?

[DaveMcLain]

Wouldn't a 3-cyl follow the rules for a 6-cyl and not require bobweights?

I don't know about that; I looked in the book that came with our balancing machine and in there it mentions a Perkins 3 cylinder gas and diesel. For that engine it says zero % reciprocating and 50% of the rotating weight. I would say the best and easiest way to know would be to just spin the crank in a balancing machine. If it reads really close with no bob weights then you'll know.

[roc]

Wouldn't a 3-cyl follow the rules for a 6-cyl and not require bobweights?

I don't know about that; I looked in the book that came with our balancing machine and in there it mentions a Perkins 3 cylinder gas and diesel. For that engine it says zero % reciprocating and 50% of the rotating weight. I would say the best and easiest way to know would be to just spin the crank in a balancing machine. If it reads really close with no bob weights then you'll know.

I'm with Jack.

[Scotty]

Yes dave is correct with the percentage he quoted for a perkins and that they require bob weights i have done 3 cyl suzuki and daihatsu petrol cranks and they both required bob weights to balance the cranks. I cannot remember offhand which engine but one of them required a different percentage on the bobweight to the percentage quoted by dave.

[roc]

Yes dave is correct with the percentage he quoted for a perkins and that they require bob weights i have done 3 cyl suzuki and daihatsu petrol cranks and they both required bob weights to balance the cranks. I cannot remember offhand which engine but one of them required a different percentage on the bobweight to the percentage quoted by dave.

I'm not arguing, but confused why an inline-3 requires bob weights, and 4 and 6-bangers don't.

[modok]

4 qnd 6 cylinder the front half and the rear half are mirror image, so they balance eachother out.

[panic]

Glen has it

[Dave Koehler]

If in doubt, spin it up without BWs to verify. It will need BWs.