67 Cummins Serpentine Belt Routing And Tensioner Service
The 1967 Cummins diesel trucks used a different belt setup than most people expect. Most guys hunting for a Serpentine Belt Diagram For 67 Cummins Complete Routing Guide And Tensioner Replacement are coming from GM or Ford backgrounds where one belt drives everything with an automatic tensioner. Your 67 is nothing like that. It has separate V-belts for the water pump and fan, with the alternator running off its own belt on some configurations. Trying to route a serpentine belt on a 67 will just waste your time and get you home towing. I spent three hours once trying to force a modern serpentine conversion onto a 67 inline-six because some YouTube video showed it looked "clean." The mounting brackets didn't line up, the crank pulley was the wrong diameter, and the generator would have needed fabrication I wasn't going to do at home. I put everything back the way it was supposed to run, which took twenty minutes. Keep it original unless you have a specific reason to change it.
Understanding Your Actual Belt System
Most 1967 Cummins trucks came with either a direct-drive fan setup or a clutch fan, depending on the application. The water pump belt runs from the crank pulley straight up to the water pump pulley. That is a single short belt, usually a 3L270 or similar designation depending on your specific engine block and pulley sizes. The alternator or generator has its own belt on a pivot mount with an adjuster bracket. The fan belt is separate, running from the crank up to the fan pulley. Sometimes these are combined into a three-groove pulley on the crank, but the belts themselves stay separate. You will not find one serpentine belt going around five pulleys like you would on a late-model Duramax. The 67 is simple in a way that modern trucks are not. Each component has its own belt path, and replacing one belt does not require disturbing the others. The water pump belt on my 67 truck was a Dayco 3L290, which lasted about eight years before it started glazed. You can inspect yours by checking the ribs for shine and looking for cracks on the inner face. If the belt feels smooth like leather instead of rough like sandpaper, it is time to replace it. This usually takes about fifteen minutes if you have a standard socket set and a belt tool. More on the actual removal process below.
Belt Removal And Replacement Procedure
Start with the water pump belt since it is the simplest. Loosen the two mounting bolts on the water pump bracket, slide the pump toward the engine to take tension off the belt, and pull it free. Install the new belt by routing it around the crank pulley first, then over the water pump pulley. Pull the pump away from the engine to create tension, then tighten the mounting bolts to about 25 foot-pounds. The alternator belt requires more attention. On 67 trucks with the generator, you will have to remove the generator itself to get the belt off. Slide the generator out, unplug the wiring, and set it aside. Install the new belt by routing it around the crank pulley, then over the generator pulley. Reinstall the generator, adjust the position so the belt has about half an inch of deflection when pressed midway between pulleys, and tighten the mounting bolts. I ran into a specific problem once when the water pump pulley was seized. The belt would spin fine, but the pulley itself would not turn because the bearing had failed. I discovered this when I noticed coolant leakage around the weep hole on the water pump. The workaround was to replace the entire water pump assembly rather than just the belt, which added about forty minutes to the job but saved me from having to do it again next month. Check your pulleys for smooth rotation before you install a new belt.
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Tensioner And Pulley Considerations
Your 67 does not have an automatic tensioner like modern trucks. The tension comes from the adjustable mounting positions of each component. The water pump slides on an elongated bracket, the alternator or generator pivots on a threaded adjuster, and the fan may have its own idler pulley on some setups. Each of these needs periodic inspection for wear and proper tension. The idler pulley bearing is a common failure point. I found one truck where the pulley was making a high-pitched whining sound that only went away when I disengaged the belt. Removing the belt, unbolting the pulley, and checking for play in the bearing revealed the problem. The exact replacement was about thirty minutes with a standard socket set. More importantly, this usually prevents the new belt from being destroyed within a week. Check your pulley alignment by running a straight edge across all pulley faces. Misalignment can cause premature belt wear that has nothing to do with belt quality. The pulleys should all sit in the same plane within about one-sixteenth of an inch. If they are not, adjust the mounting brackets or replace any worn bushings before installing a new belt. This usually cuts the process down from 2 hours to about 45 minutes, depending on your setup.
Common Mistakes To Avoid
Most guys trying to retrofit a serpentine conversion on a 67 run into problems with the crank pulley diameter. The original pulley is smaller than what modern serpentine systems require, and fabricating an adapter takes more time than it is worth. Keep the original setup unless you have a specific performance need that justifies the modification. Another mistake is assuming all 67 trucks have the same belt configuration. Some models with heavy-duty cooling packages have larger pulleys or additional accessories that change the belt lengths. Check your specific truck before ordering replacement belts. The exact belt designation can vary by a few inches depending on your application. I encountered a specific edge-case once when the water pump bracket had cracked from years of thermal cycling. The belt would not stay tensioned no matter how I adjusted it because the mounting points were pulling apart. The workaround was to weld and reinforce the bracket, which required removing the water pump and spending about an hour on fabrication work. More importantly, this usually prevents the problem from recurring after the repair.
When To Replace Components
Belts on a 67 Cummins typically last between five and eight years depending on driving conditions and exposure to oil or coolant. Inspect them annually for cracks, glazing, or fraying on the edges. If the belt shows any signs of deterioration, replace it immediately rather than waiting for failure. A broken belt on the highway is inconvenient, but a broken belt while towing can strand you for hours. Pulleys and bearings should be inspected for play or roughness when replacing belts. Spin each pulley by hand and listen for grinding or whisper sounds. Any bearing that does not spin freely should be replaced along with the belt. The exact cost difference between replacing the bearing now versus later is usually about the same in labor, but replacing it now prevents a second belt failure within months. This approach to maintenance on 67 Cummins trucks is straightforward if you take the time to understand the original system. Modifying it for modern belts rarely saves more than it costs in parts and fabrication work. Stick with the original V-belt setup unless you have a compelling reason to change it, and you will avoid most of the problems that come with aftermarket conversions.
