Connecting Rod Bearings on 2 Cylinder Diesel Engine

[taylors1243]

I am having alot of failures on Onan engines Model# DN2M-1 engines. I have been unable to get a drawing of the connecting rod bearings (onan part number 186-6081).

I basically need to find out if the upper half bearing has an oil hole and grove in it. The ones I have are flat on both sides and that doesn’t make a lot of sense to me. I have wear showing at less than 40 hours with little or no load and catastrophic engine failure at 70 hours or before with them loaded. I have been unable to tear apart a fully failed engine but I did tear one apart that is vibrating like crazy - and that is what I found - no oil hole or groove in the connecting rod big end bearing.

Can anyone shed some light on this for me - please!

Thanks!

 

[chief]

I am not familiar with Onan engines. But the normal oil supply to a big end (con rod) bearing is supplied via the main bearings to the crankshaft. Then a hole in the crank pin to a groove and hole in the con rod shell bearing. The supply to the small end (piston bearing) is then supplied via the conn rod and possibly piston cooling internal spray.
Would appear that the conn rod shells are either incorrect parts or the bottom half of the shell is inserted in the top half and blanking the oil supply.

Offshore Engineering&Design

 

[Tmoose]

I'd blame the rod bearing inserts last.

What oil are you using?

http://www.qclubricants.com/mill2104.htm

I'd test a used oil sample for coolant and fuel dilution and contamination.

The very hard working con rods are usually just about the last stop on the pressurized oil delivery circuit.

http://www.aa1car.com/library/oil_system.jpg

Insufficient oil delivery tends to kill the rod bearings long before the main bearings. Sometimes some of the cylinders are enough further from the oil pump that they are the canaries in the coal mine when lubrication is marginal.

If new bearing inserts are installed in a rod whose bore was distorted by a previous incident they will die. Similarly if the rod journal ovality, taper, size OR finish are beyond limits then new inserts will die, sometimes in minutes.

Limits for heavy duty applications are often less than 0.0002 inch taper, 0.0005 inch out of round, and within 0.001 inch of size, for journal and housing. Journal finish should be better than 10 rms and polished in the "correct" direction.

Diesel engines require careful control of dimensions of items related to compression ratio and piston-to-head clearance.
Rod length, piston height, block and head machining will often require selecting a particular head gasket thickness to create the correct piston-to-head clearance. If the piston hits the head the rod bearing load is enormous.