How much clearance should rod bearings have?
The factory specs include 2.450-inch main bearing journals and 2.100-inch rod journals, which means the target bearing clearance should be about 0.0024-inch (0.0025 is the common spec) on main bearings and 0.0021-inch on the rod bearings.
How are rod and main bearing clearances measured?
Measuring the inside diameter of a main or rod bearing will require a dial bore gauge. The best ones to use are accurate down to 0.0001-inch. With these two tools you can quickly determine the clearances in any engine. Measuring bearing clearance is only valuable if the numbers are accurate so use quality tools.
What will insufficient bearing clearance cause?
Thus, a clearance of 0.002” (0.050mm) can pass almost, twice as much oil as with 0.0015” (0.038mm). So, if the oil pump capacity cannot meet this demand, the pressure will fall. This will result in bearing failure. This illustrates the importance of accuracy in fitted bearings.
What are the bearing clearances for an engine?
Most of these engines are running rod and main bearing clearances of .001? or less, and they are doing it with low viscosity racing oils such as 0W5, 0W30 and 0W50. These racing oils are as thin as water and are highly friction modified.
What are the advantages of looser bearing clearances?
One of the advantages of looser bearing clearances is that it allows more room for “slop,” which is important if the crankshaft isn’t machined to near perfection or there is some misalignment in the main bores. Wider bearing clearances do require a heavier viscosity oil (such as a 20W50 multi-viscosity oil or a straight 30, 40 or 50 oil).
How does inertia affect the bearing clearances?
When the piston reaches top dead center on the exhaust stroke, inertia stretches the rod and elongates the bore on the big end of the rod. This, in turn, deforms the bearings and reduces bearing clearances on the lower rod bearing while increasing it on the upper rod bearing.
What should be the clearance between connecting rods?
Using a feeler gauge, measure the clearance between the connecting rods. Rod side clearance should be 0.0043 to 0.020 inches for stock steel or titanium rods. For aftermarket rods, follow the connecting rod manufacturer’s recommendations.