Connecting rods installed backwards?

[wakepics]

I'm rebuilding my 1992 xri 200 serial 0D122896 after #6 failure. I'm currently redoing the connecting rods and needle bearings, and noticed that all my starboard connecting rods are assembled with the part number down, instead of up as described in the service manual. I didn't think this motor had been taken apart before, but i also wouldnt think it would come from the factory this way. What issues would having the rods backwards cause? Obviously I'm going to redo it as per manual, but I'm more curious if this would have shown up in any symptoms I noticed before the failure.

[wakepics]

Another question. When installing the needle bearings I'm using 2-4-c as instructed in the Merc manual. I've seen some opinions suggesting that using grease, particularly grease with teflon, isn't the best and it's a better idea to stick with 2 stroke oil. Do I have anything to be concerned about, or just keep following the manufacturer's instructions?

[OldTimer57]

I can't imagine that mattering. More important is to re-install 'em just like they were. Same positions. Same orientation. Ditto for the pistons assuming you have separated the rods from the pistons. I've rebuilt a 2.5 several times, I always used an oil can with 2-cycle oil in it. Oiled each bearing before installing, then flooded them again before buttoning up the block. Much more important to get the rod caps on right and torqued correctly with that oddball socket you need. They need to fit completely flush as you install on the crank, using the pencil trick to make sure there is no tiny misalignment (which will eat a caged bearing quickly). I have also used other types of lube (there are specific lubes for such things in the category of "assembly grease" but I had zero problems with using plain TC-W3.

As far as numbers up vs down, I honestly can't say I have ever noticed, and I rebuilt my old 2.5 racing motor multiple times. I just always numbered everything and put 'em back in the same orientation / hole as I removed them from. Pistons you would certainly not want to rotate unless the top is perfectly flat and the piston is 100% symmetric. Not sure about your specific motor. It is a cousin of my old 2.5 motor but not exactly the same motor due to porting, power band, etc. The old 2.5 motors would fly, but they did tend to go through rings compared to the more traditional motors like yours. Take your time, with the service manual close by, and it will go back together and run like a champ.

[Merc2.4]

On a 2.5 it doesn't matter which way the part number goes , if ur picky bout ur mota like I am , u will pick a way ,up or down , I did mine all up ,can b all down , or mixed up, now omc has a oiling hole in small end and they have to b installed a certain way but for ur mota ur ok

[wakepics]

I'm not trying to question anyone but when the service manual says in bold letting "IMPORTANT: Position connecting rod part number facing toward the flywheel" I feel like there's a reason for it?

[OldTimer57]

He said his came from the factory with half up and half down. Which suggests it doesn't matter. Sort of like the 4.0 Toyota Tacoma motor that came from the factory with one brand of spark plugs on the left head, a different brand on the right, all cross-referenced to the same thing. No rhyme or reason sometimes. If you are really curious, you could find a connecting rod and look at it carefully for any sort of asymmetry. IE an off-center hole, a notch somewhere, etc. Always best to re-install things in the same hole they came from, oriented exactly the same way. Once something "wears in" a bit there is no good reason to reverse it and make it wear much faster.

[lpugh]

When I see Important in a factory service, I would follow those instructions

What is important is rod alignment, inspect both ends for a offset. It is important that when installed that the upper end is about center on the wrist pin as well as the rod not be forced to either side on either end.
Source:http://www.biggerhammer.net/mercury/

Connecting RodsTwo different methods of aligning the connecting rod to the piston and/or the crankshaft are possible. These two methods of alignment must not be intermixed in any engine.

1. Bottom aligned, early style. The connecting rod bottem end is guided by the inside surfaces of the crankshaft and the top end is able to move horizontally on the piston wrist pin. Top end washers which are stepped on one side are used with this rod.
2. Top aligned, later style. The connecting rod top end is guided by the inside surfaces of the piston and the bottom end is able to move horizontally on the crankshaft. Top end washers which are flat on both sides are used for this rod.

IMPORTANT: A different type top end washer is used for each type of connecting rod and cannot be mixed between the connecting rod types.

a	Bottom Aligned Rod - .812 in. (20.59mm)
b	Washer - stepped one side (stepped down side against connecting rod)
c	Top Aligned Rod - .712 in. (18.08mm)
d	Washer (flat on both sides)

[OldTimer57]

I would completely agree. Hence my statement about "no asymmetry". If there is an asymmetry anywhere, then this is important. If there is none, it's irrelevant. IE you can check part of the offset issue by laying a rod on a piece of glass, holding the crankshaft end against the glass, and measure the clearance between the other end and the glass. Flip it over and repeat. That will tell you if there is asymmetry directly in the rod. Then you have to check both journals to see if there is any machined asymmetry (ie deeper chamfer or something).

I'd hope that anybody this deep into a motor would have enough experience to get all of this stuff right. This is not always tenths of inches. It is sometimes thousandths or less. And they are critical thousandths... Same sort of issue on piston skirts where there is a heavier load side and a lighter load side, caused by how the pistons try to "rock" when pressing down on the rod/crank to turn it under load.

Been many years, but I recall measuring all of this stuff when building a 9-10K 2.5 racing motor, striving for 6 exactly identical rods, pistons, etc... The idea of "blueprinting". My memory might well be off, but I don't recall any asymmetry on the 2.5 motor. Since I don't have any old parts any longer, no way I can confirm or disprove that so I will leave that to those that actually get their grubby little hands on the actual parts. :)

[TrackerPro16]

Never follow what the manual says. Ever.
Just kidding. Follow the manual. It could be it was not put together correctly at the factory. JUST because you do not see a reason ‘why’ does not mean there is not one. Even if you measured it out. The only way to be sure would be to talk to the designers and ask them. I would ask if this is a factory manual? Not an off shoot?

[EuropeanAM]

Follow the manual's recommendations. Have seen them both up AND down (but all the same within the powerhead). Never seen one "mixed".

Pay careful attention to locations of pistons.

I don't like 2-4-C for needle bearing assembly. Two stroke oil works well- if you want something with a little more "stick" use a bearing assembly lube (years ago we used petroleum jelly exclusively with good results). Main thing is something FUEL SOLUBLE.

[wakepics]

Yes, factory service manual. Pistons are all going back in their original holes, as are connecting rods (aside from #6 which is all new). Thanks for the discussion everyone!

[wakepics]

A follow up question. I installed the crank and pistons last night. I hand tightened the conn rods, didn't torque them down, but there's a lot of play side to side on the bottom end. How much is normal? I know this is a top guided motor, so I assume some play is normal, just don't want to close it all up and find out they should be tight.