I am in the process of rebuilding a small diesel in a piece of equipment. As I am going through the process of measuring everything up, and testing oil clearances, I have started to think about oil viscosity.
Correct me if I am wrong, but my basic understanding of selecting oil viscosity has to do with trying to hit a particular oil pressure specification at a certain RPM and temperature. Which really boils down to proper lubrication of the crank bearings. So if the clearance in the crank bearings increase, I may need to think about going up a little in viscosity.
For example, after measuring the crank journals, I am on the lower end of the factory spec, but they are in good shape, so there is no need to grind the crank and go to an oversize bearing. We will simply polish the crank and use stock size bearings. That's great from a cost perspective, but the oil clearance will be on the upper size of the spec... so I am wondering about bumping up in viscosity.
My second question for all you engine rebuilding Gurus is unrelated to oil...
The engine is a Shibaura N844LT (also Perkins 404 and Cat 3024). Measuring the cylinder bore diameters. The factory spec is 84mm - 84.019mm and the "repair" value is 84.2mm. After carefully measuring the bore diameters, along the crank and perpendicular to the crank (top, mid, bottom). The generalization is that the cylinders are .001-.002" oversize inline with the crank and .002 - .0025" oversize across the block perpendicular. (That is .0025-.0508mm) so I fall outside of factory specs, but inside of the repair value. Do I hone it..which I have to assume will take at least another .001" off, or do I have it bored .020" by the machine shop? My concern with machining it, is who is to say the machine shop will get it perfect, and the obvious additional cost.
Correct me if I am wrong, but my basic understanding of selecting oil viscosity has to do with trying to hit a particular oil pressure specification at a certain RPM and temperature. Which really boils down to proper lubrication of the crank bearings. So if the clearance in the crank bearings increase, I may need to think about going up a little in viscosity.
For example, after measuring the crank journals, I am on the lower end of the factory spec, but they are in good shape, so there is no need to grind the crank and go to an oversize bearing. We will simply polish the crank and use stock size bearings. That's great from a cost perspective, but the oil clearance will be on the upper size of the spec... so I am wondering about bumping up in viscosity.
My second question for all you engine rebuilding Gurus is unrelated to oil...
The engine is a Shibaura N844LT (also Perkins 404 and Cat 3024). Measuring the cylinder bore diameters. The factory spec is 84mm - 84.019mm and the "repair" value is 84.2mm. After carefully measuring the bore diameters, along the crank and perpendicular to the crank (top, mid, bottom). The generalization is that the cylinders are .001-.002" oversize inline with the crank and .002 - .0025" oversize across the block perpendicular. (That is .0025-.0508mm) so I fall outside of factory specs, but inside of the repair value. Do I hone it..which I have to assume will take at least another .001" off, or do I have it bored .020" by the machine shop? My concern with machining it, is who is to say the machine shop will get it perfect, and the obvious additional cost.
