Piston and rod weights

[daren007]

Can someone please tell me the weights of stock model B rods and pistons from the factory.


Thanks.

[Jim Brierley]

Don't know but if you want to know for balance reasons, just make them all the same. 4 cyl. engines don't need balancing as an assembly.

[Railcarmover]

Got a good gram scale at the local 'smoke ' shop...weighed the pistons with rods,pins and rings as an assembly.Stock A parts and they were pretty damn close.

[Kurt in NJ]

I looked at B rods, NOS, one group(4) is in the 750-758, another group(3) 770-775
pistons, no rings,pins 560-570 ---original NOS centerlock
piston pin centerlock, 125

[daren007]

Thanks. I want to compare with aftermarket parts. Daren

[BILL WILLIAMSON]

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[Jim Brierley]

Please report your findings. B rods are light and strong, don't use castelated nuts.

[hardtimes]

Originally Posted by daren007

Thanks. I want to compare with aftermarket parts. Daren

Hey daren,
Not long ago, I started to look at the same comparison. Got side tracked right away, as 'life got in the way'. I'd like to know of your findings also, if you can carry thru with your study.


BTW...a long ways back, one member here, a very detail type guy (engine ear), commented in a thread , which was concerning similar/same subject, i.e.- various wts of rods / pistons , etc...
I can't locate that thread, as I can't locate computer skills...maybe someone/you can resurrect it and include it in your study ?

[daren007]

I talked to Antique Engine Rebuilding today. I was told their rods weigh 256-270 grams without inserts. The inserts weigh 76-80 grams. This leaves quite a spread from stock rods at 750-775. Can someone tell me the weight aftermarket pistons .100 over.

[old-ford]

Jim: what sort of nuts do you recommend? Why not use castelated nuts?

[BRENT in 10-uh-C]

Originally Posted by daren007

I talked to Antique Engine Rebuilding today. I was told their rods weigh 256-270 grams without inserts. The inserts weigh 76-80 grams. This leaves quite a spread from stock rods at 750-775. Can someone tell me the weight aftermarket pistons .100 over.

I do not have the factory print for a B rod however I know it is specified on the original A-6200 print that the Std. rods are to be 525 grams with +/-1 gram variance. If I am understanding this correctly, you are saying the 'B' rod is 50% heavier than what an 'A' rod is??


Also, I do not have an AAR 'B' insert connecting rod to weigh at the shop however from my memory their 'A' rods typically come in a little over 700 grams without any shells. I cannot imagine their 'B' rods would be 500 grams lighter than their 'A' rods but I am not going to argue against Ryan or Rich, and so if they say they are 270 grams, then they would know.


As far as piston weight, the pistons that come from most vendors will generally come in around the 580 - 595 gram range, and their wrist pin typically adds another 200 grams. Stock pins as I recall were about half that weight. Rich has a new piston out that you might want to check-out as it is supposed to be lighter than his old SBC pistons. I would ask Rich about his new pistons and find out the weight on those as I suspect they are about the best bang available for the money.

[daren007]

where I am going with this is I am on the understanding the crankshaft counterweights should be equal to the reciprocating mass. If the aftermarket piston, Rod, rings and pin are lighter then NOS what affect does that have on the crankshaft balance.

[Gastrap]

My AER A insert rods were all right at 750 grams without inserts, and their pistons in +.080 with pins were also right at 750 each.

[Dave in MN]

Daren,
I question the info given to you by AER. I have a new set of AER Model B rods on the shelf. These rods are designed for pistons with 1" wrist pins. (Not AER's rod that works with a Chevy 283 style piston.) The rod weights without the inserts are:
763.8 grams (g), 762.9g, 764.4g and 763.3g. These rods have not been fine-tuned yet. Note they vary as much as 1.5 grams. They are as shipped from AER as a matched set. When I set them up, they are weight adjusted to within .7 gram of each other.

The AER Model B inserts in .030" undersize...Yup...weighed all 4 (2 pc per given weight): 76.3g, 76.4g, 76.3g and 76.3g.

Antique Auto Parts pistons: .100" oversize:
piston#1- 593.4g, pin 201.5g, clips 3.1g Total weight 798.0 grams
piston#2- Total weight 801.9 grams (I did not take the time to weigh all four)
I adjust pistons to within .7 gram also.

When everything is taken into consideration, all my assemblies (piston, pin, clips, rod and inserts) are no more than 1.4 grams different...usually within 1 gram by combining light rod to heavy piston.

Weight adjusting is a tedious process. It typically takes two hours to adjust the rods and pistons to within .7 gram. The rods typically require the most time because light and heavy ends need to match from one rod to the next.
Good Day!

[MikeK]

Originally Posted by daren007

where I am going with this is I am on the understanding the crankshaft counterweights should be equal to the reciprocating mass. If the aftermarket piston, Rod, rings and pin are lighter then NOS what affect does that have on the crankshaft balance.

Single plane crankshafts, such as the model A, are dynamically independent of piston and rod mass. Unlike multi plane cranks, such as V8 cranks, they do not need 'bob weight' corrections during balancing.

If you change piston/rod mass and big/little end distribution on a V8 (multi-plane) crank you need to re-balance the crank with a corrected bob weight mass.

On an A crank the dynamic balance will be unaffected with piston/rod changes provided the new set is weight matched in total and in rod big/little end distribution.

[hardtimes]

Originally Posted by old-ford

Jim: what sort of nuts do you recommend? Why not use castelated nuts?

Do you have Jim Bs book (first one) ?
He gives the recommended nut part # and maker.
They are ARP, but I don't have the number at hand just now. They are what I've used also. Jim recommended them, because they have MORE threads engaged on stud than stock and are harder than ...hadies ? No lock washer either, as I remember and no cotter pin either.

[Kevin in NJ]

The key is balance.

Ford made the A rods (according to the print) +-1 grams at each end of a specified weight.

My reading about the factory line says that the piston/rod combo was sorted into 4 bins. Any 4 from the same bin would be within 4 grams of each other.

It really does not matter so much how much they weigh as long as they are same weight. You need to have a set up that allows repeatable weighing of each end of the rods. I have made up some weighing rigs, but I do not get the repeatability I would want to trust my measurements. I need a better scale. Kind of hard to find a kilo scale that does .1 gram that is economical. FWIW, I was use a small scale from harbor freight, the pocket kind. My triple beam was not accurate enough.

[daren007]

I understand the make all parts weigh the same thing what I do not understand is why have counterweights. I thought the counterweights were to off set the piston/rod mass. I would think the amount of counterweight for the crank was determined by the amount of piston/rod weight. If that applies then wouldn't you want to keep the piston/rod weights close to factory specs. If not what is the point of a counterweighted crank.

[Dave in MN]

Daren,

Your comment: "I thought the counterweights were to off set the piston/rod mass. I would think the amount of counterweight for the crank was determined by the amount of piston/rod weight. If that applies then wouldn't you want to keep the piston/rod weights close to factory specs."
In reality, the amount of counterweight on a Model B crankshaft (second design) with integral counterweights may not have been optimum. I think it may have been light but it was as much as Ford engineers could achieve given the clearances needed to grind the main journals and have the counterweight clear the camshaft.
To your concern: The addition of weight in the correct location to help offset the weight of the piston and rod will lessen the stress placed on the main bearings....even if it is not quite enough to fully offset the full force.
Hope my explanation helps ease your concerns.

When Ford remanufactured B crankshafts, they installed the heavier counterweights (third design) on original un-weighted crankshafts. I am not sure of the dates Ford started adding the removable weights to original crankshafts that I call the "third design" so let's not debate which is second and third...
JMO: When I study the mass of the removable counterweights included on the third design crankshaft, I would estimate that the effective weight (forces created), due to where the mass is positioned, is about 1.5 times the effective weight included on the solid counterweighted B crankshaft.

Working with the later designed crankshafts:
The heavier counterweights need to be repositioned or removed to regrind the main journals. I currently have three of these third design crankshafts and will be moving the counterweights to make the mains accessible for grinding. I plan to use this later design crankshaft in an upcoming "strong" touring engine build as I believe it is the best design for an application where the engine continuously rev's a bit higher. There is a reason Ford engineers designed these later weights to be heavier and I plan to follow their lead.
Good Day!

I will add some photos when I get back to my shop.

[daren007]

Now it's making more sense. Thanks.


Daren