[Jim Moshier]

I'm take apart 1971 400 engine that was came out of a Formula that was rebuilt 5 years ago and it was supposed to have been machined .030 and balanced with RAIV cam clone. I took the oil pan off and all the rod caps have a number stamped into the rod cap,(So I'm assuming the engine has been balanced) there is numbering stamped 1-8 on each cap in order. When you assembly the engine that has been balanced should the rods be in order with the stamped number in order 12345678 or do you follow the firing order and put that numbered rod/piston into the corresponding cylinder and then when you pull the oil pan you would see 21436587 stamped on the rod caps.

Jim

[screamingchief]

Originally Posted by Jim Moshier

When you assembly the engine that has been balanced should the rods be in order with the stamped number in order 12345678 or do you follow the firing order and put that numbered rod/piston into the corresponding cylinder and then when you pull the oil pan you would see 21436587 stamped on the rod caps

I wish there was a standard process for that,but honestly it's likely gonna depend on the guy that did that work in the first place.

Logic would suggest using the firing order as the primary determining factor,and thus doing it that second (21436587) way would be the most dependable way,despite that passenger side offset throwing off the order of the numbers.

But not everyone follows the same logic...

I'm sure some guys would just figure it's a whole lot easier to keep everything down there in the same 12345678 order despite how the cylinders are laid out via the firing order.



Bret P.

[jamaca85]

i had mine balanced, the guy marked the rods per cylinder they went to... 1 for 1 2 for 2 etc..

[Murf'sDad]

I've always marked the rod for the cylinder it was in, knowing the Pontiac is different from the Chebby.

Stewart

[Mr. P-Body]

There is no bearing (pardon the pun) on "balance" as to which rod/piston goes in which hole. The numbers are generally for reference only. In an engine that's been run, at least for any amount of time, it's always a good idea to install them back where they came from. If it's a "new" engine using modern parts, chances are it won't matter WHICH hole they go in.

In olden times, when pistons were still being "hand made" (a human running the lathe or mill), we "fit" pistons individually. We still measure them, but we've found with LASER measuring and CNC manufacturing, pistons seldom vary, at least in "sets". ALWAYS check them, though.

FWIW

Jim

[Murf'sDad]

Originally Posted by Mr. P-Body

In olden times, when pistons were still being "hand made" (a human running the lathe or mill), we "fit" pistons individually. We still measure them, but we've found with LASER measuring and CNC manufacturing, pistons seldom vary, at least in "sets". ALWAYS check them, though.

FWIW

Jim

This is exactly what my machinist told me when he did my work. He said he doesn't measure and fit each piston unless he is specifically requested to by the client, and it costs a lot more.

Stewart

[Jim Moshier]

Originally Posted by Mr. P-Body

The numbers are generally for reference only. In an engine that's been run, at least for any amount of time, it's always a good idea to install them back where they came from. If it's a "new" engine using modern parts, chances are it won't matter WHICH hole they go in.
Jim

Jim, I would think that if it was reference only then you have have to look for the rod and see which way to install the chamfer on the big end of the rod, Chamfer opposite toward the crank or facing each other. The machine shop that did the machining/balancing wasn't the ones who assembled the engine. The machine shop is good/OK but is a chevy oriented shop and when I inquired about the orientation of the rods when they do a balance job all I got was blank stares. Just thought I would ask thanks for the input.

Jim

[PONTIAC DUDE]

As long as the bottom half of the rod is number the same as the top half of the rod and the bearing tangs are facing in the right direction. That's all I worry about. Sometimes depending on the build you might end up changing rod locations to get the proper side clearance without going thru a lot of extra work.

I brought this up in another post awhile back. I have gotten people in my shop looking for say....... a #2 rod for that particular cylinder for their Cheby or Ford. Or quote; don't take the bolt out of the end of the head so i know which side it goes on.

BTW:" Rod only orientation has nothing to do with balancing.

[HWYSTR455]

I had a set of rods once that were stamped with symbols and not numbers, like *, $, !, and so forth. I asked a machinist friend what the logic was there, and together we pondered. We back-tracked it by thinking of basics, like what are the key factors. (cap-to-rod, chamfer, and if assembled with piston, pin offset, etc). We decided that the logic was most likely to keep the caps arranged with the associated rod, nothing more.

I've also had rods in the same engine that have several same numbers, like when a rod doesn't pass inspection, you grab another.

Balancing, a piston/rod/pin/ring/keepers/bearing assembly can vary slightly, depending on the desired tolerance (or the machinist's attention span!). In that circumstance, you may want to pair up certain assemblies, or install them opposing, again, depending on the assembler's retentiveness. (is that even a word!?!) Rods are balanced for total weight, big end and small end. Pistons for total weight. As long are all within the +/- tolerance, then as stated before, shouldn't matter where they go.

On an engine that gets disassembled on a schedule, a builder may chose or want to number them for their' own convenience, to speed re-assembly, especially when doing late-nighters assisted with that typical after dinner beverage! Or to sort through a pile of parts in the pan after the fact!

.

[Mr. P-Body]

Jim,

Yup. ALWAYS "look" at the rods for orientation. But as Ken said, rod "orientation" has nothing to do with balancing. The rods are weighed and "matched" before the pistons are installed.

As for "factory markings", Pontiac didn't mark their rods with 1-8. They DID mark the cap and rod with similar markings to make sure they stayed in "pairs". Some were letters, others numbers and still others, "symbols". Chevrolet rods (in a "virgin" engine) have no marks on the rods. That may have changesd in recent years, but all the small blocks AND big blocks produced through '87 or so, that I've torn down, had no marks. unless someone had already been "in there".

The scariest one I've seen (and all too common) is the filing of "notches" on the rod's beam for ID. Surely a "shadetree" method, it actually puts a major stress riser on the most important part of the rod. I know of at least two small blocks that the rod broke right at one of the notches.

You may have noticed letters "stamped" on the deck and in the tops of the factory pistons in Pontiacs. These are "clearance codes" to determine the best locations for the varied bore sizes. Common practice in olden times.

FWIW

Jim

[Ken K]

You can buy one of these scales. They are pretty accurate. Weigh all the pistons and rods. Don't mix up the rod caps. Keep them in the order you took it apart.

[Tom Vaught]

Originally Posted by Mr. P-Body

Jim,

The scariest one I've seen (and all too common) is the filing of "notches" on the rod's beam for ID. Surely a "shadetree" method, it actually puts a major stress riser on the most important part of the rod. I know of at least two small blocks that the rod broke right at one of the notches. Jim

I am not a big fan of "stamping" hardened parts (like connecting rods and their caps), the notching deal is even worse. Basically you are creating a problem in your engine! (:>( In simple terms, Good rods are HARD. To make a mark you have to hit the stamp pretty hard. You ever think that by hitting the "y" of the connecting rod or cap you might be making the shape go out of round? Course the rod is attached to the crank with the bearing supporting the part you are smacking BUT you are still deforming metal to make the stamp impression.

Some info below:

"Before reworking an OEM connecting rod, be sure the caps and rods are matched numbered and marked. (SEE BELOW COMMENT) (Likewise pistons are matched with their pins) Disassembly of the rod can cause mistaken cap substitution. NEVER USE A METAL STAMP TO IDENTIFY CAPS AND RODS. It will only CREATE A STRESS FLAW where fatigue cracking could occur. Each big end diameter is matched bored/honed and it is critical that the matching caps stay with its matching rod. Notice the front and back position differences of the rod and cap."

Some Carrillo Wisdom (by Jack Sparks)

"This is a reconditioned Formula Atlantic Carrillo rod. Nevertheless it is the ‘mother’ of all connecting rods. Notice the special 12 point 3/8 inch Carrillo specified SPS fasteners rated for 260KSI ultimate tensile and the small dimple where the rod was hardness check after the shot peening process. As a note, new rods will have a matching alphanumeric stamping on the side to identify them during manufacturing. Reconditioned (used) will many times have this ground off. This Carrillo design is symmetrical. However, the cap of the connecting rod must be placed relative to its original manufactured position. The bearing tangs inside the cap would be on the same side of the connecting rod when assembled. It IS SUGGESTED THAT before the parts are disassembled AN ELECTRIC PENCIL OR SIMILAR DEVICE BE USED to IDENTIFY AND NUMBER EACH CONNECTING ROD AND CAP. This is non-evasive and assures that the correct caps and rods are assembled properly. Each set of new rods includes Federal Mogul’s Felpro Moly base assembly lube to insure the proper ‘stretch’ during assembly."

Using a stamp on a connecting rod/cap is as bad as filing notches in the parts, IMO.

Tom Vaught

[Mr. P-Body]

Tom,

I agree. We use an engraving tool when marking is necessary. It barely scratches the surface and there's no "impact". There are some "permanent" marking pens that also will leave the ID on them, except through the harsher cleaning processes.

FWIW

Jim

[PONTIAC DUDE]

When we mark we use an electric engraver. Sorta sounds like the wife's vibrator and adjustable. Bwahahahahahahahahaha

If your reading................ Just kidding dear. I'm her vibrator.

I know I'm in trouble. LOL.

[Probird]

I always use a black marker. It stays on there long enough to put it back together.

[lust4speed]

Originally Posted by Tom Vaught

...Some Carrillo Wisdom (by Jack Sparks)..." As a note, new rods will have a matching alphanumeric stamping on the side to identify them during manufacturing... It IS SUGGESTED THAT before the parts are disassembled AN ELECTRIC PENCIL OR SIMILAR DEVICE BE USED to IDENTIFY AND NUMBER EACH CONNECTING ROD AND CAP. This is non-evasive and assures that the correct caps and rods are assembled properly..."

Seems to be some inconsistencies in Carrillo's advice. Didn't they just state that they stamp theirs rods? Or am I missing something?

While I understand stress risers, they would seem unlikely at the thick area rods are usually numbered. This area is about the only place on the rod that remains in constant compression. Also, stamping rods on an engine that is being torn down seems like the best time for stamping since the babbit material would be taking the strike load, the bearings will be disposed of, and the rod re-sized before they are placed back in service.