Crankshaft balancing

[ihaveanaccount]

Hello,

I am trying to save a buck on crankshaft balancing and would like some opinions about what I'm doing.

I modified the crankshaft of a GM I4 to change the signal at the crankshaft position (ckp) sensor. This change added a small amount of metal to one side of the crankshaft at the ckp gear. I estimate the weight around 5 grams. Can I offset this by adding ~5 grams to the flywheel at the same distance from centerline? The flywheel is ~3 inches from the ckp gear.

I want to know if anyone thinks this will add vibration, or I should be adding 5 grams every 90 degrees of crank, etc. I am a noobie in the engine building world, so all info is appreciated.

Jim

 

[GregLocock]

Sounds reasonable. I'd actually weight the thing on lab scales, and compensate for all the metal you remove or add.

I'm struggling to remember what a crankshaft balancing tolerance is, 7 g cm rings a bell.

I wouldn't fret too much about the 3 inch distance, that seems OK.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[larrycoyle]

Since a I4 does not balance with a bobweight like a v-8 or v-6 you need to understand that if you change the weight of the back counterweight you really need to do something to the front. Since balancing one of these cranks is a no-brainer why don't you call around and just ask someone in your area how much to just spin your crank. Have you already balanced the pistons and rods?

Larry Coyle
Cylinder Head Engineering

Larry Coyle
Cylinder Head Engineering, LLC

http://www.cylinderheadengineering.com

 

[ivymike]

um, balanced the pistons?

 

[patprimmer]

Well adjusted them to equal weight I think he means. This is generally refereed to by performance engine builders as balancing.

Regards

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