Blueprint 103 - Connecting Rods
Connecting rods are the crux of the engine. They're responsible for carrying the force of the explosions that occur in the combustion chamber and using it to turn the crankshaft. Oil clearance specifications of the "big end" and "small end" are crucial to maintaining consistent oil pressure. In this video we take 3 measurements: Rod Gap Rod Journal (also called Crank Pin) Diameters "Big End" Bore diameter Using the Journal diameters and the "Big End" Bores, you can calculate your oil clearances of each bearing. The process is illustrated here. Anyone rebuilding an engine who doesn't know its history should check all of these clearances whether or not they're re-using the rods. If the crank, bearings or connecting rods are going to be replaced, it's imperative that you measure the new parts as well to ensure they're in spec.
Shortblock Tech Measuring Crankshaft End Play
Crankshaft endplay is critical to ensure proper positioning of the crankshaft. Its a pretty easy measurement to take as you assemble or disassemble the your motor. To elaborate on the clutch pressures and the forces they exert, here is a written version for your viewing pleasure. We did disable the clutch start switch to greatly decrease the load on startup and im sure this aided in minimal thrust wear. The reason this is important is because, there is little or no oil to protect the thrust bearing at startup. Another contributing factor is the increased pressure that is applied by aftermarket clutches. According to Road Race Engineering, a stock clutch replacement measured 380 lbs at install height and 420 lbs when engaged. An ACT 2600 measures 530 lbs installed and 710 when engaged. Their is no measurement for the ACT 2900 but from the above specs, the install pressure of the 2600 (530 lbs) exceeds the engaged pressure of the used stock clutch (420lbs) by 110 lbs. If you compare the engaged pressures of both clutches, the ACT applies 290 lbs more pressure when engaged. Do you see why the clutch start switch could cause and issue? All the more reason to unhook it and preserve those clearances. Happy Boosting
Measuring Crankshaft Bearing Clearance - DIY
A quick demonstration how to measure a crank journal with a micrometer and measure a bearing with a bore gauge to determine clearance.
Blueprint 105 - Main Bearing Oil Clearances
In this episode we measure the bores for the crankshaft and calculate the oil clearances based off of information gathered in the previous video. If you subtract the diameter of the crankshaft from the bore diameter, you end up with your oil clearances. If this were an assembly with new parts, I would have also paid close attention to bearing measurements 45° off-centerline just to make sure the bearings aren't pinched. I would also have double-checked the clearances using Plastigage. But what I'm doing here is just getting baselines prior to machining. If you're doing a dry assembly like this, DO NOT ROTATE THE CRANKSHAFT. Without oil, there is nothing preventing it from being damaged.