Packard Forum Index » Pre-War (1899-1942)

Reply to post 26,
All eng configurations have a different procedure. I'm assuming you're talking a 90 deg V8. That eng crank is not balanced separately. Actually no crank is ever balanced on knife edges. That is the wackiest idea that's ever been floated. A separate story.
A V8 is extremely sensitive to changes in rod or piston asmy wt. A (bob) weight is clamped on each V8 journal to represent a % of the component's wt. The oil in the crank's rod jrnl is also factored. A natural resonance peak is read on the crank w/ the bob wts attached, then spun. Each end of the crank will have a different plane of imbalance. It might look fine on knife edges but create thousands of lbs of imbalance force when running. The corrections are made on the counterwts. Sometimes removing wt if new parts are lighter or Mallory if they're heavier. Hope this is helpful. I'll answer about externally bal'd engs another time. David

Well the trend now is toward very short skirt short compression height pistons lighter then stock with long strokes and increased rod lenghts. I would want to keep piston weight down so as not to have to ad weight. The mallory added to the sides of the counterbalances have less effect thus requiring multiple slugs. A slug on the face will put the increase out further from centerline but I have seen them fly off and exit the block so it was customary to set them just below the face and run a weld bead around the lip to secure.

Look at the 55/56 parts catalouge.

SAME crank number for ALL 56. i.e. 374 and 352 cid. I doubt that the 374 and 352 pistons weigh the same. Never weighed them tho.

Parts cat. does call out different cranks for jr 55 and Sr. 55 320 v 352. But that difference could very well have nothing to do with ant weight difference in the pistons.

I think neither PackardV8 nor Motiv8 are contributing anything positive to this discussion.

Motiv8 says Packard motors are no good and that he knows better than them how to build motors. I don't think he has any engineering background because if he did he would demonstrate the balancing formulas for an engine and then show mathematically why they should be ignored.

PackardV8 insists that motor rebuilding is a basement operation which denigrates people who have the qualifications to speak knowledgably on the subject.

While I don't think that Packards are the best thing that every rolled down the highway, I have driven low mileage examples and found them to be impressive performers. Back in the 60's and 70's they drove better than many a brand new car.

However, wear and tear has taken a toll on the machinery and it exhibits the faults of being worn out. Thus, enthusiasts have to make due with suboptimal results.

People familiar with my advice know that I try not to be condescending because the intention here is to help people with their cars. If it's mathematics and technical discussions you want that can be done somewhere else. I can fill the trunk of my car with authoritative journals and I can spread them out on a table and you can declare they mean nothing. But this discussion not the appropriate place for such.

To aid in the point I am trying to impress consider the following balancing formula:

Rotating Weight
* Big end of rod (including fastening hardware)
* Bearing
* Oil (normally estimated at four grams)

Reciprocating Weight
* Piston
* Wristpin
* Pin locks (if used)
* Small end of rod
* Piston rings

Bob weight = Rotating Weight + (Reciprocating Weight x .50)

The bob weight is a model weight bolted to the crank to simulate the operation of the motor. Suppose the Packard company was using a different formula based on the results of trials at the proving ground? Suppose after running a Packard 8 25,000 miles at full throttle they found the motor would benefit from a proprietary formula? If you don't have the required specifications then even the best attempts at rebuilding will yield sub-optimal results.

To claim their motors are junk based on results gathered from using the wrong specifications is non-sense.

No. My only claim is to make no attempt, nor is there any reason to make any attempt to change or modify factory balance of any bit, piece ,part nor of the the engine as an entire assembled unit.

In t he case of the Packard V8 engine it is the I'changeability of the crank betwee the 374 and the 352 that pretty much dispells the smoke and mirrors of any piston/rod weight variation claims.

ok. so the factory came up with a reasonable design and balance for the crank. THEREFORE, make no attempts to change it!!

So much talk or claims of any "REbalancing" is simply much to do about nothing.