Conrods

[flabum]

Ok OMC guru's.

On a crossflow con rod at the big end, do the sides (not the needle bearig surface) have any type of babbet material where it contacts the crank?


The reason I ask is because I began cleaning my parts for a rebuild and noticed what looked like galled aluminum on the sides of the big end on the rods. A couple of the rods were spotty and a couple had full coverage. I was able to remove this material using a razor blade. I was thinking this was aluminum from the pistons and had been galled onto the rods, but if it is actual bearing material applied at the factory, I will need new rods.

 

[rolmops]

Re: Conrods

I found the same material on a 9.9 and a 50 horse and at the same place.I left it on thinking that is material that is used for the exact balancing of the rod.the engines run fine with the material on .

 

[72SideWinderSS]

Re: Conrods

More than likely, the rods have came in contact with the the crankcase.
Look at the case where the rods run and see if they have been in contact with the case.

 

[Lakester]

Re: Conrods

Ok OMC guru's.

On a crossflow con rod at the big end, do the sides (not the needle bearig surface) have any type of babbet material where it contacts the crank?

hello,

not to say i have seen all possible engine designs, but i have never seen a connecting rod with any sort of bearing surface to the crank throw journal side...

in general, on engines with pressure oil systems the mains and rod have oil discharge ports. if u have never seen or read about what goes on in a crankcase, it is an absolute tornado/sunami of an oil explosion. vilolent at least. this is what keeps the crank in suspension in the mains, and the rods around the crank. the oil's path of route is out the sides of the rod. so since by physics a liquid cannot be compressed, the parts never touch, ie, the big end of the rod never touched the crank and so the engine's parts just live happy and float along. idle to WOT.

the same happens in a 2 stroke. albiet somewhat diiffernet. please correct me if i am wrong...

outboards use rollers on rod to crank. unlike the soft bearing insert of a conventional pressure oil engine, like a sbc, the hardened rollers make contact with the crank's surface. the oil in the fuel, however adds a cooling effect to maintain the bearing/journal's hardness, plus lubes the rollers. and the rod's big end has an oil cushion constantly bathing it and since the two faces of rod end and crank journal cannot compress the hig volume of liquid oil present, they do not touch.

other than valve seats, the only place metal to metal rubbing/touching really is present is on the rings to bore, and they are scraping oil off the bore walls, so they are constantly bathed in oil. since the alum piston and steel cylinder are dissimilar metals, given the oil on bore wall... they live together quite well in that the piston does not wear down. well, it wears some but it is of no consequence until way up into service miles or hours.

well, that's how i understand it.

regards,
lakester

 

[Dhadley]

Re: Conrods

Those rods are what's called "bottom guided" meaning they are held in position by the rod being between the counterweights on the crank. If that material is coming off, by the book it should be replaced. In the real world it will be fine.

We have sanded that material off and in other cases just left it alone. It'll be fine.

 

[flabum]

Re: Conrods

Thanks for the replies. I'll put these rods back in. I did clean them then surfaced them on glass with 320 paper. I have a spare crank if this doesn't work LOL.