Connecting rod number order

I believe the engine I'm playing with is an 88 It's definitely a Renix.
When I pulled the connecting rods I wrote down the order from front to back
4-3-5-1-2-6 . I could of sworn I verified this multiple times but I may of been high.

I know for a fact one was in the middle so that throws out the firing order.
So what is the point of this sequence?
*Waits for the all knowing 5-90*

If I remember correctly they are stamped, 1-6 front to rear on the cap. Though I do remember one motor with two number "3's". I imagine the direction the number is facing is also relevant, but I always notched one side so I wouldn't install anything bassacwords.

The number should read from the passenger side left to right So I suppose I should flip that order around .
Or atleast that's how my engine was.
two 3's? did it have vibe issues? lol

I'm not reusing these rods so I don't really care just interested in expanding my knowledge.

Don't forget to plastigage the fit for the new ones.

So your saying mine was disasembled before and they reassembled out of order?

Edit: Or your not anymore? lol


Also On a side note my Main caps were in numerical order from front to back.

MpSlayer said:

So your saying mine was disasembled before and they reassembled out of order?

Edit: Or your not anymore? lol

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It's been five or six years since the last time I was in the bottom of 4.0 (the specifics are a little fuzzy). So maybe 5-90 is the man for answers. Though it has been running fine since then, so I must have done something right.

I thought that you had marked the rods yourself in a weird order. They should always be 1-6 front to rear. Reading the other posts that were written while I was writing, I realized that there must have already been numbers stamped in the bottom. Now it seems like, yeah, it had been reassembled wrong, or maybe even a factory FU.

8Mud said:

It's been five or six years since the last time I was in the bottom of 4.0 (the specifics are a little fuzzy). So maybe 5-90 is the man for answers. Though it has been running fine since then, so I must have done something right.

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Thanks 8mud I was replying to winterbeater. I have no doubt in your numbers. Though hearing two 3's spikes my interest even more.

winterbeater said:

I thought that you had marked the rods yourself in a weird order. They should always be 1-6 front to rear. Reading the other posts that were written while I was writing, I realized that there must have already been numbers stamped in the bottom. Now it seems like, yeah, it had been reassembled wrong, or maybe even a factory FU.

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I know I said I may of been high but I was kidding Lol.

I'm curious there has to be a method to the factories madness. Maybe weight differences in the numbers? instead of making everything uhh "Match Grade" Use slight varients in weight to help balance the crank? I don't know what else could possibly make the number worth marking if they wern't in any specific order.

Of course I'm sure it will turn out to be somthing simple and I'm way off. Or mine and 8muds were assembled wrong at one time

I don't have anything clever to say for this bump

The order of the rods matters less than the orientation of the caps on the bodies - DO NOT screw that up!

If the rods are all weight-balanced within a couple of grammes (since we're running at low revs, no need to be terribly picky. Although I am anyhow...:lecture you'll be fine.

BUT, if you lose track of the cap orientation, you are going to have to get the caps and ends re-honed to each other so the bore will be nice and round. What is done is that about .005-.010" is chewed off of the parting lines from the cap (not the rod - that would change its effective length,) and the cap is reinstalled. It is then marked for orientation (usually using some idiot-proof mark!) and the big end is re-honed round.

Not much material needs to be removed, but you have to remove just a touch so that you can get it realigned properly.

If the whole set is taken in, the numbers are usually ground off, the caps re-matched, and then the rod balance pads are ground down to match weights (at least on the total rod weight and the "big end" weights. The small end weight is less critical, since all it does is go up and down. The small end balance pad is typically used for final weight-matching, while the big end balance pad is used to match the big ends of the rods.)

So it's supposed to be 1-6 front to back?

I kept the order I have no use for it since i'm running 4.2 rods but I kept them lol.

I was just wondering what the numbers mean.

One of the first 4.0's I ever opened up the bottom on (a long time ago). I started my standard procedure of stamping a dot into the left side of the cap (same thing I do for a piston pump or whatever). One dot for one, two dots for two, until I ended up with a circle of six dots on six. About half way through the job (oil dripping in my eyes), I noticed the number on the cap, then thought, well I'm wasting my time, then saw the same number on the next cap (think it was three) and then thought, I'm not wasting my time after all.
Not sure about the 4.0 though in most all motors, the connecting rod is cast and honed in one piece, the end cap sawed off. I've actually been able to match the caps with the rods using a magnifying glass, metal dye and matching up the saw marks, good eyes and a little luck. Maybe not necessary but who knows if they were sawed off in exactly the same spot or not, if the honing process was absolutely true or not, 0.008 doesn't leave you a lot of margin for error? The guy who made that rookie mistake thanked me profusely. Though the book does say you can mismatch the bearings to get the desired clearance, so the hone may have a slight allowable error margin.
I never really worried much about the balance in most motors. Tried to find out if they were internally balanced or externally balanced, kept the proper flywheel or torque converter with the externally balanced motors. A torque converter full (of half a dozen quarts of oil) has to have more affect on balance than does a couple of grams on a connecting rod.
Best basic tip I can give you is, too tight will kill a motor quick (heat expansion and friction), to loose my be noisy but will usually outlast too tight. Plasti gage is pretty good stuff, take your time, do it twice, top of the bearing and bottom of the bearing. Clean the oil off first, oil melts plasti gage.

Maybe but I wouldnt want to risk anything not matching in weight on anything spinning 5000 rpm

MpSlayer said:

Maybe but I wouldnt want to risk anything not matching in weight on anything spinning 5000 rpm

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If the bearings get too loose they stop being mostly a rotary hammer and more just a hammer. Worse things than a little metal in the wrong spot.
Just to switch to theory and maybe start an argument, but acceleration and even gravity changes the relative weight of a piston almost continuously. I doubt the fuel charge in any given cylinder is equal. the burn constant or even the air charge the same.
If your six shakes like a four, it's may have balance problems LOL
Mostly the direction in any car or truck is figured, as you are sitting in the drivers seat. Unless some brainiac decided to undo a century of tradition for some reason.

8Mud said:

Mostly the direction in any car or truck is figured, as you are sitting in the drivers seat. Unless some brainiac decided to undo a century of tradition for some reason.

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I don't know where that came from... :thumbup:

Fuel/air would be the only one I could see that create a variaton depending on the fluidness of the intake.

Gravity how ever would vary the weight but in an even manner. not like haveing your 5th rod with a major difference then your first.
I'm no physicist so I would just prefer to have things match up then take a shot in the dark.