Piston and rod weights

[Honda Rush]

I thought i would ask the following as it is new ground for me
The engine in question is a Honda F20C ex S2000 It is a mix of internals from two seperate engines of the same type but different years, Both of which had suffered failures hence the mix of parts.
I have just weighed the rods two from one engine and two from another and they came out at 641/641/642/643 grms the pins 102/102/107/107grms and the pistons from different batches numbers again at 348/352/353/350 grms So the question is should i mix the items to get as near to equal weights as possible which is 1096/1097/1097/1098 grms
Or remove weight from rods and pistons to get the weights equal of individual items ? As i would think the pins would be rather hard to hold without marking them in a lathe. The engine will spend most of its time at the high end of 8k rpm in a sprint car. So balance of components is paramount

Edited by Honda Rush on Monday 11th February 19:19

[jimbob82]

if you can do it I would balance everything individually, match the rods to the lightest one you have then do same with the pistons

thats what i'd do

[stevesingo]

Honda Rush said:

I thought i would ask the following as it is new ground for me
The engine in question is a Honda F20C ex S2000 It is a mix of internals from two seperate engines of the same type but different years, Both of which had suffered failures hence the mix of parts.
I have just weighed the rods two from one engine and two from another and they came out at 641/641/642/643 grms the pins 102/102/107/107grms and the pistons from different batches numbers again at 348/352/353/350 grms So the question is should i mix the items to get as near to equal weights as possible which is 1096/1097/1097/1098 grms
Or remove weight from rods and pistons to get the weights equal of individual items ? As i would think the pins would be rather hard to hold without marking them in a lathe. The engine will spend most of its time at the high end of 8k rpm in a sprint car. So balance of components is paramount

Edited by Honda Rush on Monday 11th February 19:19

Pistons and pins are fully reciprocating, that is they only go up and down. In such a case they should be matched only for mass. So jiggle the pins and pistons around to match them up.

348+107=455
350+107=457
352+102=454
353+102=455

+/-3gram.

given that steel is 7.8g/cm3 to even things up you would need to remove 0.38cm3 material from the pins.

Rods are both reciprocating and rotating. The big end rotates around the crank axis and the little end goes up and down. Due to this the rods should be balanced both total mass and end to end as the rod effectively pivots around it's centre as it goes through the rods range of movement.

AS you are not looking at a huge difference with the rods +/- 2g I would not bother.

Steve

[The Black Flash]

Or if you're feeling flush, get down to vibration free,And they'll do it to a fraction of a gram...

[Evoluzione]

You won't have any problem holding the pins in a lathe - they're harder than Hells doorstep. If you are worried then use soft jaws or put something (copper strip) in between the two.
You'll have more trouble finding something to actually touch them enough to remove any metal!

[84Dave]

And most importantly, balance the clutch/flywheel assembly, minus the clutch disc. I've found terrible clutch/flywheel balance on those particular engines. How to perform the balance? Balance the crankshaft by itself. Then bolt the flywheel & pressure- plate to the crank. For any imbalance found, drill weight out of the flywheel. Then, before you remove the clutch assembly from the crank, use red nail polish & swipe a solid mark across the flywheel & pressure-plate. Then disassemble. In that manner, you can then bolt the clutch assembly to any balanced crank simply by lining up the red nail polish marks. Why balance the clutch assembly without the disc? The major mass of the disc is near the middle of the clutch assembly,and it can be a major problem getting the disc absolutely centered within the clutch assembly for the balance process. -84Dave-

[dandare]

Shouldn't the crankshaft counterweights be matched to the piston-rod assemblies, or am I getting confused?

[Honda Rush]

Thank you all for your advice so far, The flywheel is a TTV 5.5" super lightweight unit which is as purchased no clutch as yet. I do have access to more pins so will have a look and weigh a few more before and machining

[PaulKemp]

Pins can have material ground from the inside as long as you spread the removal around and along the internal surface
The rod little ends can have material removed from any obvious lumps or by thinning the external circumference