What rods do I have P/N 1339643B

[70sWagoneers]

Hello, I bought a set of straight 8 rods from a chap who said they were from a 248ci with insert style bearings. Well, my machinist says the bearing housing is much too large. So can anyone tell me what rods I have? The casting number is A1339643B. 

 

He says he can machine my babbitt rods out to accept insert bearing so that is probably how Im going.

[herm111]

On ‎8‎/‎4‎/‎2016 at 11:15 AM, 70sWagoneers said:

Hello, I bought a set of straight 8 rods from a chap who said they were from a 248ci with insert style bearings. Well, my machinist says the bearing housing is much too large. So can anyone tell me what rods I have? The casting number is A1339643B. 

 

He says he can machine my babbitt rods out to accept insert bearing so that is probably how Im going.

I looked in every spec. book I have, and that number is not in any of mine. They must not have made many.

 

Thanks,

 

Herm.

[NTX5467]

It might take a Sealed Power or Perfect Circle engine parts book to find that casting number.  Sometimes, casting numbers are very similar to the actual GM part number, varying by a few digits up or down from the casting number, BUT not always.  The actual engine (replacement/machine shop) parts book I'm referring to would have the casting numbers as I believe they sold reconditioned connecting rods, for which knowing the original casting number (as with replacement pistons) would be needed.

 

Typically, as long as the connecting rod is of the correct (center to center) length, has the same diameter and width for the crankshaft bearing/journal interface, plus the correct diameter/width of the piston pin interface, then they'll physically fit the application.  The OTHER consideration is the weight of the piston they were intended for.  THAT weight determines how much material is removed from the "balance pad" on the connecting rod cap.  Having a set of "factory balance" rods usually means the balance pad is not quite as tall as a "replacement" connecting rod, by observation.

 

The same casting number of connecting rod can go with different "bore" sizes of pistons, for different displacement engines, with the same crankshaft "stroke" and "deck height".  When the particular piston is "weight matched" for the particular pistons, THAT generates a particular (OEM manufacturer) part number for the connecting rod casting, which then makes it "application specific" such that "factory balance" occurs.  Connecting rods, as pistons, are usually weighed in "grams", although a sensitive electronic postal scale can be converted from "ounces" to "grams" mathematically.  The casting number would dictate the basic size/height of the balance pad, with the machining-down of the balance pad would be the "fine tuning" to the particular matching piston weight for the particular application (and related weight specification for a "standard size" piston use).

 

It is ALSO very critical to make sure the connecting rod end caps are MATCHED to the rods they "came with" from the factory.  NO mix or match!  One reason that engine rebuilders (professional and otherwise) are supposed to put "an identification mark" on the rod cap and rod so they remain "matched set" items.  Otherwise, you'll be using somebright light and a magnifying glass to match the hone marks on the inner surface of the cap and rod!   The alternative to this is to have the rods "re-sized" by a competent engine machinist, re-honing the surfaces to the correct inner diameter and roundness specs.  If its a "Babbitt rod" motor, IF the caps have been "filed", that can be another issue to check on.

 

End result is that the rods will need to be checked for weight and such to see if they match the exact desired end application.  That's before getting them "reconditioned" at the competent machine shop.  Many sellers might know the engine size, but possibly not the exact model year of the engine.  Luckily, there were many years of the same-spec engines built, over the years, BUT if the particular model year might have been when a "new and improved" piston might have been around, probably need to do some checking before the connecting rods are used.

 

As with many "swap meet" engine parts of this nature, the default mode would need to be that "they'll fit", but purchased as "core parts" for reconditioning rather than something that is "assembly ready with a little clean-up".  Some times, things work "as desired", some times not quite.  One reason I'd like to see "piston and rod" assemblies, still together from removal, at the swap meet.  Then you can roughly-measure the bore diameter and see if the pistons match what's in your engine (either by vertical dimensions or by the shape of the piston crown, or both).  You might not need the used pistons, but they are there for additional verification.  Later, with appropriate cleaning, they cam become interesting paper weights and such.

 

I hope what you ended up with  is the "as desired" situation!  This might be more information than you desired, but I wanted to illustrate how the same casting number can be used in several applications.

 

NTX5467

[Guest VegasClassicParts]

I realize this is an old post but I just came across NOS connecting rods in our parts hoard with the same casting number.  These are Buick part #1393912, which are for 1950-1953 Buick Series 40 (Special) and Series 50 (Super) with Aluminum Pistons. 

[Ben Bruce aka First Born]

On 5/25/2017 at 1:17 AM, VegasClassicParts said:

I realize this is an old post but I just came across NOS connecting rods in our parts hoard with the same casting number.  These are Buick part #1393912, which are for 1950-1953 Buick Series 40 (Special) and Series 50 (Super) with Aluminum Pistons. 

 

 Please be aware, this statement is misleading. The 1950 Series 40 had a 248 ci engine. The 1950 series 50 had a 263ci.  The rods for the 263 are about 1/4 inch shorter, I believe.  1951-1953 Series 40 did indeed have the 263. 

 

  All Buick pistons  were Aluminum in this era. Had been for several years.

 

  Ben

Edited May 27, 2017 by Ben Bruce aka First Born
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[NTX5467]

The notation about "aluminum pistons" could have TWO side issues. 

 

One is the weight of the piston, which would relate to the amount of unused metal remaining in the "balance pad" area of the rod.  Second is the possibility that the aluminum pistons could have a different location of the piston pin in the piston, as small as that different dimension might be.

 

In situations where the deck height (distance between the centerline of the crankshaft and the block's "deck surface" (what the head gasket seals against) is the same, the two ways this distance can be compensated for is the (with a longer stroke, if we're going from a shorter stroke to a longer stroke) is generally a shorter connecting rod (generally by the additional length of the stroke) or, again, by a higher piston pin location in the piston (with the same connecting rod center-to-center length).  

 

There is generally a desired area of the piston side where the piston pin location is probably better than others, but in some specialized applications, the piston pin location can migrate upward to behind the piston ring package location.

 

In piston specifications, the "compression distance" relates to the location of the centerline of the piston pin to the deck of the combustion surface of the piston (might be affected by "domes", but in many situations, the displacement of any significant "domes" or "dishes" are stated in "cc", for the computation of the mechanical compression ratio of the engine.

 

Enjoy!

NTX5467

[Guest VegasClassicParts]

Thanks for the comments - For now, I'll just say these are for 1950-1951 only, with Aluminium pistons.  I'll dig out my 1953 parts manual to check the difference between 248 and 263.  See below for info on the use of cast iron pistons in 1951.

PISTONS: 1951 Series 40 & 50 - CAST IRON & ALUMINUM PISTONS (SERIES 40 & 50) PRODUCTION CHANGE & REPLACEMENT CAUTION: Beginning 1951 Series 40 Eng. No. 63319254 Cast Iron Pistons were used in partial or complete production in place of regular aluminum alloy pistons (use of aluminum pistons resumed later in 1951).

 

CONNECTING ROD & BEARINGS: 1951 SERIES 40 & 50 CONNECTING RODS FOR CAST IRON & ALUMINUM PISTONS (SERIES 40 & 50) PRODUCTION CHANGE & REPLACEMENT CAUTION: Special rods and matching bearing caps used with cast Iron pistons due to increased weight of pistons (see PISTONS above). THESE RODS & BEARING CAPS MUST BE USED WITH CAST IRON PISTONS (can also be used with aluminum pistons if necessary).

 

CAUTION: Connecting rods and bearing caps intended for Aluminum Pistons MUST NOT BE USED with Cast Iron pistons.

 

CONNECTING ROD IDENTIFICATION: Cast Iron Piston Type-Part No. 1390669 (Assy. with Bearing Cap). Has two raised dots on rear face of connecting rod web and forging number 1344306 on front face. Bearing cap has two ribs on rear face.  Aluminum Piston Type--Part No. 1393912 (Assy. with Bearing Cap). Has one raised dot on rear face of connecting rod web and forging number 1339643 on front face. Bearing cap marked correspondingly.

[Ben Bruce aka First Born]

Wow! Where does this info come from? Learn some thing new even at my advanced age. 

 

  Ben

[Guest VegasClassicParts]

This info is from the Reed Service Manual

[Guest VegasClassicParts]

Well, I came across one single Cast Iron Type Connecting Rod in our NOS parts hoard.  I am attaching pictures showing they are pretty much identical.  The only difference is the grinding out of the bottom of the Connecting Rods, which is deeper on the Cast Iron Type - I guess this makes sense since the cast iron piston weighs more than the aluminum piston.  The weight difference between the two is the cast iron piston type weighs 0.1 ounce less than the aluminum piston type.  1390669, casting 1344306 (Cast Iron Type) on the Left; 1393912, casting 1339643 (Aluminum Piston Type) on the right.

[70sWagoneers]

Thanks guys! I went ahead and machined my original rods for insert bearings and so haven't check back on this post in a while. This very useful information.

 

Thanks,

James C.

[Bulletbirdman]

I'm 5 or six years late but how much does these rods wiegh?