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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old November 11th, 2017, 10:22 PM
beerman beerman is offline
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Default V6 GMC Balancing

Was surf the ole web and stumbled across this

http://www.rebuiltautoengines.com/gmc-articles.html

about halfway down the page there is some info on balancing our motors which maybe helpful for guys cobbling together motors at least its worth memorizing for the part numbers



Balance & Assembly Data On
GM (GMC) 5.0, 5.8 & 6.6L (305, 351 & 401 CID) V-6 Engines

The following information was compiled to eliminate torsional engine vibration due to mismatching of parts or the use of pistons not balanced to the proper weight.

Although all three engines have used two or three different pistons, only the popular ones have been listed and can be used as listed in sets since the basic difference is in compression ratio, and the weights have remained constant.

Design characteristics make it possible to assemble with any crankshaft, connecting rod and pin combination in any given engine; however, vibration problems can arise since there are weight variations in the rods, pins and pistons. For this reason, the correct combination of rods, pins, pistons and crankshaft is a must.

Note that there are fourteen different crankshafts, three different connecting rods, and two different pins used in the 5.0, 5.8 & 6.6L (305, 351 & 401 CID) engines.

The 5.0L (305 CID) engine uses five of these crankshafts, two of the connecting rods, one of the pins and one piston.

The 5.8L (351 CID) engine uses seven of the crankshafts, all three of the connecting rods, both pins and three pistons. The three pistons used in this engine are all the same weight and compression ratio, and therefore, can be interchanged in less than set quantities as long as the correct pins are used.

The 6.6L (401 CID) engine uses three of the crankshafts, two of the connecting rods, one pin and one piston.

Note that the 2366209 crankshaft used in both the 5.8L (351 CID) and the 6.6L (401 CID) engine. This is accomplished by using the P4563 pin in the 5.8L (351 CID) engine which offsets the heavier piston weight of the 6.6L (401 CID). This is the only crankshaft that is interchangeable.

The next pages list the various combinations that can be used for each of the engines. Following are lists of the various pistons, pins and connecting rods and their weight specifications along with the balance formula for the V-6 engines.

Only Zollner piston and piston pin numbers and piston weights are listed in this bulletin since that company is the original piston supplier for the engines listed.

GM (GMC) 5.0L (305 CID) Engine

Crankshaft Con Rod Con Rod Piston # Piston Pin #
Forging # Part # Forging # Zollner Zollner
----------------------------------------------------------

2367417 2389553 2389554 4564 P-4564
2454191 2389553 2389554 4564 P-4564
8874436 2389553 2389554 4564 P-4564
2475795 2477175 2470891 4564 P-4564
65828 2477175 2470891 4564 P-4564


GM (GMC) V-6 5.8L (351 CID)

Crankshaft Con Rod Con Rod Piston # Piston Pin #
Forging # Part # Forging # Zollner Zollner
----------------------------------------------------------

2366209 2389553 2389554 4563-6* P-4563
2454192 2389553 2389554 4563-12** P-4564
8875589 2389553 2389554 4594 P-4564
2475793 2477175 2470891 4594 P-4564
2475793 2477425 2474281 4594 P-4564
651826 2477175 2470891 4594 P-4564
651827 2477175 2470891 4594 P-4564

* Piston # 4594 can be used in place of Piston # 4563-6 if used
with pin # P-4563

** Piston # 4594 can be used in place of Piston # 4563-12


GM (GMC) V-6 6.6L (401 CID)

Crankshaft Con Rod Con Rod Piston # Piston Pin #
Forging # Part # Forging # Zollner Zollner
----------------------------------------------------------

2366209 2389553 2389554 4565 P-4564
2475794 2477425 2474281 4565 P-4564
652794 2477425 2474281 4565 P-4564


Piston # Piston Piston Pin # Pin
Zollner Weights Zollner Weights
-------------------------------------------------------

4564 1128 g +/- 2 P-4564 318 g
4563-6 1380 g +/- 2 P-4563 516 g
4563-12 1380 g +/- 2 P-4564 318 g
4594 1380 g +/- 2 P-4564 318 g
4565 1560 g +/- 2 P-4564 318 g

* All oversize pistons are balanced to this standard weight and
weigh the same as a standard size piston.


GM (GMC) GM (GMC) Pin End Crank End
Rod Rod Of Rod Of Rod
Part # Forge # Weights Weights
-----------------------------------------------------------

2389553 2389554 380 g +/- 2.5 966 g +/- 2.5
2477175 2470891 410 g +/- 2.5 1145 g +/- 2.5
2477425 2474281 390 g +/- 2.5 1155 g +/- 2.5


GM (GMC) V-6 Balancing Formula


The bobweight formula is 50% of the reciprocating weight and 100%
of the rotating weight of each piston-rod assembly. Determine the
bobweight (6 required) as follows:

Reciprocating Grams

Piston
Ring Set
Pin
Pin End Of Crod
Lock

Total Divide Total by 2 =


Rotating Grams

Crank End Of Rod
Bearings
Oil Estimate

Total


Bobweight Total
(50% of Reciprocating + 100% Rotating)


The 478 diesel uses the same crankshaft as does the 478 gas
engine. You must mount the flywheel and the dampener on the
crankshaft for balancing the diesel engine. The flywheel and the
dampener are counterweighted to offset the additional piston and
rod weight. Use exactly the same formula as above.

The AERA Technical Committee










Balancing On
GM (GMC) V6 Engines

Much confusion exists on the proper bobweight formula for balancing the GM (GMC) V6 engines. For this reason balancing requests for these engines have been turned down or a marginal job performed.

During the Open Forum at the St. Louis Convention, questions were asked concerning balancing the subject engines. At that time no atisfactory answer was given. The following information is now available.

The bobweight formula is 50% of reciprocating weight and 100% of the rotating weight of each piston-rod assembly. Determine the bobweight (6 required) as follows:

Reciprocating Grams

Piston _____
Ring Set _____
Pin _____
Pin End Of Con Rod _____
Lock _____
Total _____ Total divided by 2 = _____

Reciprocating

Crank End Of Rod _____
Bearings _____
Oil Estimate _____
Total _____ _____

Bobweight Total ( 50% Reciprocating + 100 Rotating) _____

Naturally, all piston-rod assemblies are matched in weight.

Approximate bobweight amounts are as follows:

5.0L (305 CID) Gas 2222 grams
5.8L (351 CID) Gas 2355 grams
6.6L (401 CID) Gas 2454 grams
7.8L (478 CID) Gas 2482 grams
7.8L (478 CID) Diesel 3041 grams

The 7.8L (478 CID) diesel uses the same crankshaft as does the 478 gas, however, you must mount the flywheel and dampener on the crankshaft for balancing. The flywheel and dampener are counterweighted to offset the additional piston-rod weight. Use exactly the same formula as above.

The AERA Technical Committee
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  #2  
Old November 14th, 2017, 07:27 AM
BobBray BobBray is offline
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Default Re: V6 GMC Balancing

I always wondered why some use solid wrist pins and some use hollow. I figure it is for balance. Interesting how the smaller V-6's don't have vibration dampers.
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  #3  
Old November 14th, 2017, 10:12 PM
bigblockv6 bigblockv6 is online now
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Default Re: V6 GMC Balancing

The reason for the solid wrist pins is some 351 engines used the forged steel crankshaft from the 401 so to make up for the weight difference of the smaller and lighter 351 pistons solid wrist pins were used. As far as vibration dampners really out of the gas V6 engines only the 478's had them, the 379 and 432 just had eccentric external weight balancers since they basically used a 478 type crankshaft. The 401's basically used the same setup as the 305 and 351 just a flanged hub for the pulley to bolt on to. Here's a pic of both types of wrist pins
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  #4  
Old November 15th, 2017, 10:53 PM
James James is offline
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Default Re: V6 GMC Balancing

I had came across that page about 3.5 years ago and made a copy of it. I had forgotten about it until now. It has a lot of info on that page.
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  #5  
Old November 22nd, 2017, 12:11 PM
POWERSTROKE POWERSTROKE is offline
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Default Re: V6 GMC Balancing

One forum I frequent has an abundance of stupid questions, and unfortunately, many many stupid answers, and in the last week I answered a question about engine balancing that I know went WAY over the original poster's head. That article is as good of explaination of engine balancing as any I have read in 45 years. C.J. Baker wrote a great technical article for Hot Rod magazine back in the early 1970's explaining engine balancing and how to make sure you get what you are paying for.
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  #6  
Old November 23rd, 2017, 02:53 PM
George Bongert George Bongert is offline
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Default Re: V6 GMC Balancing

Quote:
Originally Posted by POWERSTROKE View Post
One forum I frequent has an abundance of stupid questions, and unfortunately, many many stupid answers, and in the last week I answered a question about engine balancing that I know went WAY over the original poster's head. That article is as good of explaination of engine balancing as any I have read in 45 years. C.J. Baker wrote a great technical article for Hot Rod magazine back in the early 1970's explaining engine balancing and how to make sure you get what you are paying for.
Happy Thanksgiving to Powerstroke, and all Club Members!

Not to correct you Powerstroke, but way back in 1970 when I was in Technical School Studying Automotive Technology, one of my fellow students asked of our instructor what he (the student) though was a "stupid question," to which the instructor replied: "There is no such thing as a stupid question, only a stupid answer." I've always remembered that quote, and used it many times over the years when someone said that they had a stupid question to ask of me. I'm glad that you were able to provide useful information to the followers of the other forum that you frequent. Have a great Thanksgiving Holiday!!
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Old January 15th, 2018, 03:04 PM
Motiv8 Motiv8 is offline
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Default Re: V6 GMC Balancing

Gentlemen, Never rely on printed weight listings for certain cast or part #s.They are often wrong. Most all those Jimmys are externally "balanced". Not. Really counterweighted.
The moment of truth is when you present your eng parts to the balance shop. The camshafts and "so called" balance shafts must also be part of the balance attempt. The engine isn't truly balanced, and the term "balance" is misleading. David
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Old January 16th, 2018, 12:38 PM
massey478 massey478 is offline
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Default Re: V6 GMC Balancing

Thank you for the excellent parts interchange information. These are details I as a mechanic who worked on these motors in a truck shop from 1966 to 1972 then to the present on my own equipment and trucks did not have because all parts for the engine being worked on were kept together so no mix and match was necessary. As a point of interest, the county highway had a truck that had the V-12 in it. It had so much power they would get to plowing snow at 30+ MPH. One time on a gravel road the plow dug in, the truck vaulted over it, breaking the crankshaft.
I replied here because It seems out of place to me with all of my past experience with these motors and most all others in that time frame that now it seems everyone wants to pin a liter designation on motors that never had it in their time period. Liters mean almost nothing to me with that experience and the designation is not precise enough to separate some close cubic inch displacement motors of that time period. It is good though as was done here that if one wants to assign a liter number to a motor that also designated is the cubic inch displacement. Thanks for that!
As a side note I have collected many of these motors including V-12. I have 30+ of them here of all displacements. I also converted a Payloader to 305 power and a Massey Ferguson 1100 to a 478. I used them on this kind of equipment because of their low end torque. I find that using MSD 6 or 6AL boxes on them is a big advantage. Keep up the good work all!
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Old January 17th, 2018, 12:49 AM
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Default Re: V6 GMC Balancing

Quote:
Originally Posted by massey478 View Post
I have collected many of these motors including V-12. I have 30+ of them here of all displacements. I also converted a Payloader to 305 power and a Massey Ferguson 1100 to a 478. I used them on this kind of equipment because of their low end torque. I find that using MSD 6 or 6AL boxes on them is a big advantage. Keep up the good work all!
Good to see you finally back on the forum again, Marti! We've missed your expertise.
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1962 K1000 Suburban 401M & SM420
1965 2500 Suburban 351C & SM420 with Watson overdrive
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Old February 27th, 2018, 09:27 PM
LEWISMATKIN LEWISMATKIN is online now
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Default Re: V6 GMC Balancing

MASSEY478, this is Lewis Matkin. I agree totally with your quote on the cid/liter conversion for these and other engines of this era. Having worked in the automotive/h-d aftermarket for 44+ years, I find it humerous when others want to "metricize" these engines.

cordially,
Lewis Ellis Matkin, Jr.
Ridge Manor, Florida
1965 1002 305E V-6
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