Author Topic: Internally or Externally balanced engine?  (Read 229 times)

1975W87

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Internally or Externally balanced engine?
« on: April 16, 2018, 11:10:12 AM »
I installed a Tremec 6 speed in my 75 T/A now I have a vibration when in neutral. I called American Power Train spoke to Marty he asked if my engine was internally or externally balanced. I do not know. how can I verify this.


Thanks in advance!

nas t eh

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Re: Internally or Externally balanced engine?
« Reply #1 on: April 16, 2018, 12:47:10 PM »
Origional, stock 400-455 are external balanced, most non stock rebuilds with new light pistons and forged rods are internal balanced. I don’t recall if you had your motor done but if you did you could ask the builder
current
73 T/A 4speed
past birds
75 T/A 455 4speed
75 T/A 400 4speed

1975W87

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Re: Internally or Externally balanced engine?
« Reply #2 on: April 16, 2018, 07:26:20 PM »
Thanks,  nas t eh  when I bought the car the engine was already built  so I don,t know what was done internally.  but I will attach a photo of the flex plate I took off the car looks like 8 holes were drilled into it possibly to make it a neutral balance.

20180416_091315 by Victor Grigolo, on Flickr
20180416_091326 by Victor Grigolo, on Flickr

DeVilliers

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Re: Internally or Externally balanced engine?
« Reply #3 on: April 17, 2018, 02:23:08 AM »
I'm no expert, but recently had my rebuilt motor balanced.
The process was two part. The crank and all the pistons were balanced (internal), then the flex plate and harmonic balancer up fort was also balanced at the same time with the crank, which is probably seen as external.
I do not think when balancing an engine, one should just do internal or external, but rather do both.
1979 Trans Am

nas t eh

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Re: Internally or Externally balanced engine?
« Reply #4 on: April 17, 2018, 08:37:11 PM »
I'm no expert, but recently had my rebuilt motor balanced.
The process was two part. The crank and all the pistons were balanced (internal), then the flex plate and harmonic balancer up fort was also balanced at the same time with the crank, which is probably seen as external.
I do not think when balancing an engine, one should just do internal or external, but rather do both.

Internal balanced in this case means that the motor does not need the flywheel/ flexplate and vibration dampener to balance the motor. Stock Pontiacs have weight on the flywheel or flexplate because the crank does not have big enough counterweight for the heavy piston/rod combination. If you use light aftermarket pistons and rods you can zero balance a Pontiac internally. You can do it to a stock Pontiac too, but you have to add weight to the crank.

His flexplate looks like it had the external weight removed. I would think it is an internally balanced motor and the new flywheel he bought needs to be zero balanced on its own.
current
73 T/A 4speed
past birds
75 T/A 455 4speed
75 T/A 400 4speed

Re: Internally or Externally balanced engine?
« Reply #4 on: April 17, 2018, 08:37:11 PM »

1975W87

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Re: Internally or Externally balanced engine?
« Reply #5 on: April 18, 2018, 05:36:46 AM »
nas t eh  you are correct. After a bit of detective work I was able to connect with the owner previous to the guy I bought the car from. I was able to speak to him his name is Roberet. I'm glad I was able to talk with him, I originally thought he only put a cam, and intake on the engine. turns out it was bored .30 over  new pistons some head work and it WAS internally balanced. This was done in 1997-98. The work was done at Speed Performance in Wauconda IL.  I looked up shop number called and they are still in business. I spoke Mike he remembers building the engine and confirmed he did "zero balance" the flex plate.  I am going to the shop this morning and bringing the flex plate and flywheel and will have them balance the flywheel. Mystery Solved!!

Re: Internally or Externally balanced engine?
« Reply #5 on: April 18, 2018, 05:36:46 AM »
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