The Stovebolt Site Forums The Shop Area Engine Shop 1951, 216 main bearing cap bolts, size & torque

I asked the AI: "This question is about the main bearing cap bolts on a 1951 3600 truck with the original 216 engine. 3 caps each have two of the 9/16" bolts described above. The 4th cap at the flywheel end of the crank has 4 of the .5" bolts described above. On The 9/16" bolts the FSM calls for 100 to 110 ft lbs wet, I'm trying to match that on the 4th cap with a very close clamping load. What should the .5" bolts be torqued to wet with 30w oil."

The AI said: "If your goal is to match the structural clamping force across all four main caps on your 216 engine, you have an advantage here: the factory

engineers already accounted for this calculation when they designed the 4th cap.The Factory Service Manual (FSM) specifies 100 to 110 ft-lbs for the main

bolts, but the correct factory specification for the four smaller bolts on that rear flywheel cap is 65 to 75 ft-lbs

(wet with engine oil). Do not try to force a single bolt to match the tension of a single bolt. The load distribution

across the caps explains why you should stick to the factory specs. Total Clamp Load vs. Individual Bolt Load on Caps (Caps 1, 2,

and 3): These use two bolts per cap. Torqued to 105 ft-lbs wet, each bolt creates roughly 15,000 lbs of tension. Combined, each of these caps exerts

30,000 lbs of total downward force onto the crankshaft journals.The Rear Cap (Cap 4) Because this cap has to deal with the heavy

leverage of the spinning flywheel, GM designers used four bolts instead of two to distribute the stresses more evenly across the block casting. The Math

Behind the 4-Bolt Cap. If you torque the four rear cap bolts to a safe, factory-approved 70 ft-lbs (wet with 30-weight oil), the physics

balance out: One bolt at 70 ft-lbs wet creates 11,200 lbs of clamping tension.Because you have four bolts holding that single cap, you

multiply that force, 11,200 lbs times 4 bolts = 44,800 lbs of total clamp load. By dropping the torque to the correct 65–75 ft-lbs

range for the hardware, the 4th cap safely secures the rear journal with more structural clamping power than the 2-bolt caps (44,800

lbs vs. 30,000 lbs)."

Well, take it or leave it. I'll let the engineers make the call. I'm likely going with 70 (or was it 80) ft. lbs. wet.

RonR