Crossflow Connecting Rod Orientation

**Gordon02** · 07-23-2020, 11:07 PM

I have torn down what I thought was an original V4 115hp that had never been opened, but something I found during clean-up says otherwise. Unless the factory made this mistake - which I doubt. I bring this up because I would have thought the needle bearings and wrist pins would have been burnt/discolored - they were not. The high-ring piston in the #1 hole is what killed this engine and why it's owner said it has lost power. The entire top ring was spit out the exhaust ports. There was no damage to the head which was another surprise.

Two of the four connecting rods were installed with this oil hole down. Page 5-23 of the factory shop manual states clearly that all rods shall have their oil holes facing "Up". The #1 piston like this old-style one lost it's entire top ring and land, so I know it killed the engine first. Was a rod bearing next? Gordon

**H2OPERF** · 07-24-2020, 08:15 AM

I have seen them in that way before with no issues, it may have even been done intensionally if the bottom side silver plating is missing. Personally i think it was a mistake to put it there in the highest loaded area of the bearing surface.

**keefallan** · 07-24-2020, 04:02 PM

The two issues may not be related. The high ring lands are known to blow out/break because of the closeness to the combustion areas. Combine that with really bad gas(like today's gas).............KABOOM!! I have always installed my rods like the manual states........facing up towards the flywheel. I can see why they make that statement. Oil collects on the rod as its spinning and drains into to oil hole and feeds the needles. If it was facing down, that would not be possible. But that is just my .02 cents. It makes sense......pun intended, but I dont really know. I mean the rod is identical either up or down, so why face it up? That's what I speculate............gravity oil feed to the bearings as oil is spraying under the pistons while the motor runs.

Can anyone verify this for me?

This is just me speaking my thoughts out loud. Please no one crucify me for it.

**H2OPERF** · 07-24-2020, 06:09 PM

Ok what about a jetski or dirt bike with a vertical cylinder and the holes on the side or up top...the big ends usually have the opening in the back or sides on pressed cranks. They most likely are relying on some residual oil to run up there since that is probably the hottest bearing and it will tend to dry out on shut down from the piston heat. jmho...

**racer** · 07-24-2020, 06:30 PM

Check the marks at the big end seen the oil hole at wrist pin opposite of big end

**keefallan** · 07-24-2020, 06:32 PM

I have never looked into any other 2 stroke but the crossflow. I take that back. I tore down an eagle motor once, but I didnt give it any attention because I was breaking it down for parts for others. I wasnt rebuilding it or anything else.

That is why I asked for someone to verify my speculation. It is just that, a speculation, looking for an answer. It was me looking at it from a logical standpoint and trying to figure it out......nothing more

Gotta go look at a rod after reading Racer's comment.

**H2OPERF** · 07-24-2020, 08:24 PM

Dude im just wild ass guessing too, Just saying i have seen that hole in almost every location around the small end along with two holes to none, the early skinny v6 merc rods have none so who knows but as said i doubt if it will really kill a motor since i've seen quite a few in down... maybe on the early 125 with small pins that failed anyway. Brp had a patent to sorta positive oil the big end with a lip on the crank cheek to catch oil and direct it to the beaing thru a passage like a 4 stroke not sure if it made it into anything , racer you know?

**FMP** · 07-25-2020, 02:01 PM

Put 4 new Wisecos in it, finish diamond hone to 1/2 thousand more if you're really going to twist it for miles and tune away, plenty of heat cycles in first 10 hrs. JMO
Always warm it plenty with a few minutes 1500rpm away from the dock before the hammer.

**perfmarine1** · 07-27-2020, 03:34 PM

They should go up, have never seen them down and have tore down 100's of crossflows. Check the dots on the big end of rod and cap,if I remember right they go up as well. I think that is what Racer is saying,but not positive.

**racer** · 07-27-2020, 04:52 PM

I have seen a few rods that the big end marks are up yet the hole is down.

**Gordon02** · 07-27-2020, 10:50 PM

Thanks Guys, I'll assemble mine with the oil holes up. Where do I take the weight off to balance the rods? 2 of the 4 are 1/2 ounce (20 grams) different. None of the new pistons are more than 2 grams, so matching the heaviest piston to the lightest rod won't get me there. While I have then off, now would be the time to get them to weigh the same.

**keefallan** · 07-29-2020, 03:52 AM

Mr Stoker is the man to answer that one. I know there are others as well. But I have never heard anyone talk it. I would like to know the answer to that question as well for my next build.

Gordon, were you able to weight the ends(to find out the weight at the ends of the rods) or just the rods in general? I know removing weight from the proper end is the best. I dont have that fixture however.

**H2OPERF** · 07-29-2020, 08:38 AM

I didn't think there was any question of which way the rods are supposed to go, the book shows the proper orientation, I thought from the original question that he was concerned that the rods/bearings were damaged from being in upside down due to lack of oil at the pin and or if the motor was going to fail early...

**Gordon02** · 07-29-2020, 10:13 AM

H2O - you are correct. I never questioned how they should go, only if anyone else had seen them installed from the factory that way. This engine had no signs of having been opened before. I knew too that the oil at the small end would have nothing to do with the piston top getting hot enough from fuel/air ratio to let a ring fold over.....but if I throw stones at any reply, I can't play with the others. I appreciate all inputs and don't mind wading through those not relating or what I wanted to hear to get to those that are. Gordon

**keefallan** · 07-29-2020, 04:48 PM

WOW!! H20 you da man for picking up on the core question............you get a raise!!! I missed that completely. Gordon, its okay to restate what you were really asking

. I not dat bright sometimes!! Gordon, you have loose needles and cages right? Just buy new needles. They are cheap. The cages are fine(or should be fine). If you dont have serious marks on the crank journals(or scoring), the crank should be fine too. If in doubt..........mic it out...........hey I made a funny!!

The rods should be fine as well, just check for bluing and scoring.