Piston Balancing

[rgh0]

Bill
A few observations on your sequence

1. In a flat plane crank the rods balance themselves and you dont need to compensate for rod / piston assembly weight in the crank couterweights. The crank counterweights only need balance the journal weight.

2. I normally never use anything on the big end assembly bolts. Most rod makers recommend tightening bolts with a little moly lube or similalr to ensure a consistent tightening torque or use a stretch guage. The torque loading is so high they never come undone without locktight or any locking tabs.

3. Balancing to 1 gram is better than 4 and noticeable. Going to 0.1 gm better again but into the area of diminishing returns - but if you have the scales and time it does not cost you much, for the dynamic balance how accurate depends on the machine used and how much time the machine shop wants to spend and you to pay for

4. My sequence as follows
balance rods assembled with bolts and bearings to minimum end weights.
balance pistons including wrist pins, gapped piston rings and wrist pin circlips to minuimum weight
dynamically balance crank and flywheel and clutch cover separately
assemble and dynamically balance crank , flywheel and clutch cover and match mark assembly

[bill308]

Thanks for the comments Rohan.

If one does not use the crank to support the flywheel and clutch cover for separate dynamic balancing, how is this done by the machine shop, a custom mandrel?

It's also probably a good idea to individually balance the clutch cover retaining hardware prior to balancing the clutch cover. These items are quite a distance from the center of rotation so may have a significant affect on. If all are the same mass and location is uniform, they can be used in any position and the clutch cover can be replaced at any time by just balancing the replacement clutch cover.

Bill

[rgh0]

Yes typically the machine shops will have a range of adapters for balancing individually items such as cranks, flywheels clutch covers. This gets the individual items well balanced but do not accomodate any eccentricity in the assembly of the components so then assemble and balance as a complete unit and match mark.

If the indiviual items are weel balanced and little adjustment needed once assembled due to good concentricity on assembly then you can usually get away with replacing a clutch cover or flywheel without having to pull the crank to rebalance the whoile assembly again.

Yes - I forgot to mention the clutch cover bolts and washers - I weigh those and match to minimum weight - generally with new commercial high tensile bolts and washers the weight variation is zero so no work on them needed.

cheers
Rohan