Balancing Question
Thread Starter
Registered User
Joined: Sep 2004
Posts: 1,872
From: Lantana, TX
Balancing Question
I have a quick question concerning balancing a rotating assembly. I've never personally done it so I don't know.
Do you weight all the components seperately and then pair them (rod/piston) with each other so that the bobweight is equal or close to it on each throw or do you weight them all and get an average bobweight and then just drill or add heavy metal to balance?
Do you weight all the components seperately and then pair them (rod/piston) with each other so that the bobweight is equal or close to it on each throw or do you weight them all and get an average bobweight and then just drill or add heavy metal to balance?
Registered User
Joined: May 2004
Posts: 2,001
From: Bay Area, CA
The rods and pistons are balanced(ground or drilled) to match the lowest weight in the set - that sets your number to put on the balance card. If you just take averages you are really not balancing anything.
Banned
Joined: Oct 2006
Posts: 4,970
From: Goochland, Va.
I have seen it done many times but noone ever explains anything to me
Thread Starter
Registered User
Joined: Sep 2004
Posts: 1,872
From: Lantana, TX
What exactly are you trying to balance? One cylinder to it's counterpart or just the whole receipocating mass on the crank so it's smooth? Won't doing the former automatically cause the latter? If so then why are people able to use weighted flywheels and balancers?
Registered User
Joined: Mar 2000
Posts: 2,037
From: 51°N 114°W, 3500' elevation
Rods are balanced at each end to match the weight of the lightest one. All the big ends are weighed the same, all the small ends are weighed the same.
All the wrist pins should be matched to the same weight. It's very difficult to change their weights. If close enough but not exact, the pins can be match weighted to the pistons so a specific pin must be used to a specific piston. If the weight difference of the wrist pins is too great, different pins need to be used to get a set close enough to the same if not exact.
Once the rods have been adjusted to the same end weights and the pistons/pins have been adjusted to the same weight, their weight is added to the weight of the rod bearing, rings, rod bolts/nuts and pin locks if used to get a total weight for the bob weights.
It's just about impossible to do a proper backyard balance job. You just don't have the proper balancing jigs and you have no way to spin it up to check the bob weight balance on the crank.
Spending $500 to get your rotating assembly balanced properly is worth it. When I had mine done, the balance sheet showed it was spun up 8 times to get a perfect balance.
All the wrist pins should be matched to the same weight. It's very difficult to change their weights. If close enough but not exact, the pins can be match weighted to the pistons so a specific pin must be used to a specific piston. If the weight difference of the wrist pins is too great, different pins need to be used to get a set close enough to the same if not exact.
Once the rods have been adjusted to the same end weights and the pistons/pins have been adjusted to the same weight, their weight is added to the weight of the rod bearing, rings, rod bolts/nuts and pin locks if used to get a total weight for the bob weights.
It's just about impossible to do a proper backyard balance job. You just don't have the proper balancing jigs and you have no way to spin it up to check the bob weight balance on the crank.
Spending $500 to get your rotating assembly balanced properly is worth it. When I had mine done, the balance sheet showed it was spun up 8 times to get a perfect balance.
Last edited by Stephen 87 IROC; Mar 4, 2008 at 11:16 PM.
Registered User
Joined: May 2004
Posts: 2,001
From: Bay Area, CA
Thread
Thread Starter
Forum
Replies
Last Post
stockssn2o
Parts For Sale
14
May 25, 2015 08:54 AM