Need help on balancing stage 2 motor all machine work in done except for balancing the rotating mass like crank,rods pistons,pins,flywheel and balancer.The machine shop had trouble balancing the crankshaft because there was alot of material meaning metal removed that i had to weld back on the bob weights.The crank i have is LA billet 3.590 billet crank,carrillo 6.5 on center rods wide journal 741 grams,CP pistons with pins,total seal rings,JW wheel and BMS steel balancer with sensor rings.The problem was that the crank had about six 1 inch dia. by 3/4 deep holes drilled with one mallory slug and the machine shop said it was almost impossible to balance the crank without filling back the drilled holes.Has anyone had this problem before and how many slugs of mallory will it take to balance my crank with the parts i have thanks.
Stage 2 build
- Thread starter Noe
- Start date
turbodave231
Moderator
- Joined
- May 24, 2001
Something to think about:
What balance factor are you using? 50%?? If you use a 36.6% factor the bob weights will be less and you will able to get away with adding less mallory.
Is this a pure race car or a street/strip car? the 36.6% balance factor works best with rubber (not solid) engine mounts.
What balance factor are you using? 50%?? If you use a 36.6% factor the bob weights will be less and you will able to get away with adding less mallory.
Is this a pure race car or a street/strip car? the 36.6% balance factor works best with rubber (not solid) engine mounts.
turbodave231
Moderator
- Joined
- May 24, 2001
You can use any balance factor from 36.6 to 50%. The factory used 36.6% to help keep vibration to a minimum.
Using 36.6% keeps the primary imbalance in the horizontal plane (rubber mounts can absorb this type of shake). As you move toward 50%, the primary imbalance moves to the vertical plane and rubber mounts are less effective to dampen the vibration.
If you are going to use HR mounts and a rubber trans mount, you can still use the 36.6% balance factor, but the stiffer mounts may transmit more vibration.
Dave
Using 36.6% keeps the primary imbalance in the horizontal plane (rubber mounts can absorb this type of shake). As you move toward 50%, the primary imbalance moves to the vertical plane and rubber mounts are less effective to dampen the vibration.
If you are going to use HR mounts and a rubber trans mount, you can still use the 36.6% balance factor, but the stiffer mounts may transmit more vibration.
Dave
As it pertains to driver feel as long as OEM mounts are used. It does not make 'engine vibration' minimum.
turbodave231
Moderator
- Joined
- May 24, 2001
Don,
You're right. The engine will always vibrate. The balance factor only shifts the vector of the vibration. With engines balanced at 36.6% , The theory is that the majority of the energy will be absorbed in the engine mount (stocker) and not transmitted to the frame. HR mounts have a much higher durameter rubber (poly) and will transmit more vibration into the frame.
Some people don't like the vibration characteristics of the standard HR mounts. I believe Paul recently came out with a softer version to help this problem.
At 50% balance factor, the engine mounts do little to decouple the vertical vibrational forces.
I've balanced engines both ways. I haven't run into any durability problems with even fire V6's balanced at either factor, Have you?
You're right. The engine will always vibrate. The balance factor only shifts the vector of the vibration. With engines balanced at 36.6% , The theory is that the majority of the energy will be absorbed in the engine mount (stocker) and not transmitted to the frame. HR mounts have a much higher durameter rubber (poly) and will transmit more vibration into the frame.
Some people don't like the vibration characteristics of the standard HR mounts. I believe Paul recently came out with a softer version to help this problem.
At 50% balance factor, the engine mounts do little to decouple the vertical vibrational forces.
I've balanced engines both ways. I haven't run into any durability problems with even fire V6's balanced at either factor, Have you?
No I haven't. You explained it perfectly.
Im no expert ,but I believe your choice of balance factor is more RPM related than type of motor mounts. An engine that sees under say 5000 Rpm should be near the 36% because that is where it is the happiest. An all out race engine seeing higher say 8000+ RPM needs to be happiest at higher RPM and so it needs to balanced at closer to 50%. If you plan to turn high RPM and use solid or poly mounts then you have to live with the vibration at low RPM.
Am I on target here??? Mike
Am I on target here??? Mike
GARY HARVEY
Member
- Joined
- Aug 17, 2001
BMS V6 Balance percentage #'s
I'm with you Mike.
My S2 came from Jimmy Spencer's operation and was done at 50% per BMS data.
Some were even balanced at higher percentages (I've been told).
Tim Cole was with GM/BMS before he moved to Comp Cams,
Maybe [if] he would add something to this discussion?
I'm with you Mike.
My S2 came from Jimmy Spencer's operation and was done at 50% per BMS data.
Some were even balanced at higher percentages (I've been told).
Tim Cole was with GM/BMS before he moved to Comp Cams,
Maybe [if] he would add something to this discussion?
Similar threads
