What to Look For in 6.7 Cummins Pushrods
TL;DR: A 6.7 Cummins pushrod is a hardened steel tube with a formed end at each side, and in a healthy engine it is one of the last parts you should ever have to think about. When one comes out bent, the pushrod is the symptom rather than the disease - something stopped a valve from moving, or the valvetrain was asked to control more spring pressure and more rpm than the stock rod was designed for. Buy on construction and correct length rather than on finish, replace in sets rather than one at a time, and find out what bent the last one before the engine turns over again. Otherwise you will be back under the valve cover with a new set of scrap.
What a pushrod actually does on a 6.7
The 6.7-litre Cummins, in trucks from the 2007.5 model year onward, is an overhead-valve inline six with the camshaft in the block. That layout is worth stating plainly, because it is what makes the pushrod a load-bearing part rather than an incidental one. The cam lobe lifts the tappet, the tappet lifts the pushrod, the pushrod pushes the rocker, and the rocker presses on the valve bridge that opens a pair of valves. Every bit of the force needed to compress the valve springs and accelerate the valve mass travels through that thin steel tube, twice per crankshaft revolution per cylinder, for the life of the engine.
Two things follow from that. First, the pushrod is a column in compression, and columns fail by buckling - which is why a failure shows up as a bend rather than a clean break. Second, the pushrod is the cheapest and most easily replaced link in the chain, and it is also the softest. When something in the valvetrain goes wrong, the pushrod is usually where the damage lands, and that is not an accident. It is a great deal easier to fit a new set of pushrods than a new cylinder head.
The 6.7 also runs adjustable valve lash, with a screw and lock nut in each rocker, which means lash is a maintenance item rather than something a hydraulic lifter takes care of on its own. Set lash in the sequence and to the value in the factory service manual for your engine and model year - the procedure is engine-position specific and it is not a place for a rule of thumb. Anything you buy in pushrods has to work inside that adjustment range, which is one of the reasons length matters so much.
Why 6.7 Cummins pushrods bend in the first place
Before shopping, diagnose. A bent pushrod on a 6.7 usually traces back to one of a handful of causes, and each one has a different fix:
- A valve that stopped moving freely. Carbon and soot on a valve stem, or a guide that has gone tight, can hold a valve open or slow its return. The rocker keeps arriving on schedule, the valve does not, and the pushrod absorbs the difference.
- Valve float or over-rev. A downshift at speed, or a build with more rpm than the stock spring package can control, lets a valve hang open into the closing ramp. The valve gets slapped back, and the pushrod buckles.
- Hydraulic lock. A leaking injector, coolant intrusion or water ingestion puts an incompressible column of liquid over the piston. The engine tries to compress it, and the valvetrain and connecting rods absorb the result. If this is the cause, the pushrods are the smallest part of your problem - inspect the rods and the head before spending anything else.
- A failed tappet or a damaged cam lobe. The rod loses proper support at its lower end and hammers itself out of true.
- Incorrect lash. Set too tight, a valve is held off its seat; set too loose, the rod takes an impact load every cycle instead of a smooth push.
The inspection is the same regardless of cause. With the rocker assembly off, roll each pushrod on a surface you know to be flat - a machinist's plate, a table saw wing, a piece of thick float glass - and look for daylight under the middle. Then check both ends for galling, flat spots, a hollowed or mushroomed contact face, and any discoloration that says the end ran dry. Compare a suspect rod against one you are confident in, and inspect the matching rocker arms and lifters while you are in there. A worn rocker socket will destroy a new pushrod end quickly.
The buying criteria that actually matter
Once you know why the old set failed, these are the things worth checking on a new one.
| What to check | Why it matters | How to verify |
|---|---|---|
| Correct length for your engine | Length decides where the adjuster sits in its range and how the rocker geometry lands over the bridge | Confirm the current part number and length against the manufacturer catalogue for your exact engine and model year |
| End style at each end | The rod has to seat properly in both the tappet and the rocker socket | Match the design of the rods you removed; do not assume both ends are identical |
| Intake versus exhaust position | Some engines use different rods in the two positions, some do not | Check the catalogue before ordering, and keep removed rods in cylinder order on a labelled rack |
| Material and heat treat | Determines how much column load the rod carries before it buckles | Stock-specification steel for a stock truck; chromoly-grade alloy for a build with heavier springs |
| Wall thickness and diameter | The single biggest driver of buckling resistance | Heavier-wall rods are the standard answer for higher spring pressure and higher rpm |
| Straightness on arrival | A rod that arrives out of true is already a fatigue problem | Roll-test new rods on a flat surface before installation, every time |
| Oil passage design | Some rods are drilled for oil transfer, some are solid | Match what came out, and confirm against the catalogue rather than by eye |
| Sold as a set | Mixed old and new rods age unevenly and can hide a second bent rod | Buy a full set unless you are replacing one rod on a low-mile engine with a known one-off cause |
Two practical notes on that table. Wall thickness is where the real difference between a stock-replacement rod and a heavy-duty rod lives - a thicker tube of the same outside diameter resists buckling substantially better, which is why upgraded rods are the usual pairing with a stiffer spring package. And straightness is worth checking on parts fresh out of the box. It costs two minutes and it has saved a lot of people a second teardown.
Stock replacement or heavy-duty: which one you need
| Stock replacement | Heavy-duty / performance | |
|---|---|---|
| Best for | Stock or lightly tuned trucks, towing, factory power levels | Higher rpm, heavier valve springs, elevated fuelling, competition use |
| Construction | Matches the factory design and material | Alloy steel, heavier wall, often a larger tube diameter |
| Fitment considerations | Direct fit, no other change required | Confirm clearance through the head and at the rocker; usually paired with upgraded springs |
| Usual reason for choosing it | The old rod bent because of a specific, correctable fault | The old rod bent because the valvetrain has outgrown the stock part |
The honest answer for most trucks is the first column. If a single rod bent because a valve was sticking on carbon, then a stock-specification replacement set plus fixing the sticking valve is the complete repair, and a heavier rod would only have masked the problem for a while. The second column earns its money when spring pressure has gone up, which is common alongside a cam change or a serious fuelling package - in that case, plan the valve springs and the rods together rather than one at a time, and match both to the rpm and lift the engine will actually see.
Whichever way you go, budget for the parts you will disturb getting there. The valve cover gasket comes off with the cover, and if the head has to come off to chase a stuck valve or inspect after a hydraulic lock, add the head gasket and head studs to the list along with the relevant items from gaskets and seals. Torque every fastener in the factory sequence to the value in the service manual for your engine.
Installing them without repeating the failure
Keep the removed rods in cylinder order so that a wear pattern tells you which cylinder is misbehaving rather than leaving you guessing. Wipe each new rod clean, roll-test it, and pre-lube both ends before it goes in. Make sure every rod is properly seated in its tappet before the rocker assembly comes down on it - a rod sitting on the edge of a socket rather than in it will bend on the first revolution, and it will look for all the world like the new parts were at fault.
Torque the rocker assembly fasteners in the factory sequence to the manual value, then set valve lash by the published procedure. Turn the engine over by hand through at least two full revolutions before it is asked to start, feeling for anything that binds. Then run it, let it come to temperature, and re-check lash on the schedule the manual gives.
Full-set replacements and the supporting hardware for these engines sit in Cummins 6.7 parts, and the wider Cummins and diesel engine parts ranges cover the rest of the job. Shop labour for a pushrod and lash job on a 6.7 typically lands in the two-to-four hour range if the head stays on the truck, and considerably more than that if the head has to come off. Orders over $70 ship free, and if you are not certain which set matches your engine, email sales@coretransmissionparts.com with the engine serial and model year before ordering.
Frequently Asked Questions
Can a bent 6.7 Cummins pushrod be straightened and reused? No. Bending means the rod has been loaded past its yield point, and its remaining fatigue life is both unknown and short. Straightening puts a part that has already failed back into a high-cycle compression load path. Replace it.
Do I have to replace all the pushrods if only one is bent? Not necessarily, but replacing the set is the safer choice. If the cause was a clear one-off on a single cylinder and every other rod rolls true with clean ends, replacing the one rod is defensible. On a high-mileage engine, or where the cause was rpm or spring related, replace the full set so that every rod shares the same history.
Will a bent pushrod set a check engine light? Often it will. A valve that is not opening properly produces a cylinder-specific power loss or misfire that the ECM can flag, and the truck will usually run rough and down on power. A mechanical tick from under the valve cover alongside a cylinder-specific code should be diagnosed by pulling the cover, not by replacing sensors.
Do heavy-duty pushrods require any other changes? Check clearance through the cylinder head passages and at the rocker, because larger-diameter rods do not drop into every engine without verification. Beyond that, heavier rods are normally chosen alongside upgraded valve springs, and the two should be selected as a package rather than separately.
How do I tell whether a pushrod is worn rather than bent? Look at the ends. A worn rod shows a flattened, hollowed or scuffed contact face, sometimes with heat discoloration, while the tube itself still rolls true. Bending shows up on the roll test. Either condition means replacement, and both point at something else in the valvetrain that needs inspecting.
Should I set valve lash after fitting new pushrods? Always. New rods change the stack height slightly, and lash on a 6.7 is adjustable for exactly this kind of reason. Follow the engine-position sequence and the value published in the factory service manual, then re-check it once the engine has been run and brought up to temperature.
Sources
Written from the overhead-valve, block-camshaft valvetrain architecture of the 6.7-litre Cummins ISB as documented in factory service manual procedures - solid tappets, pushrod-operated rocker arms, valve bridges and screw-and-locknut lash adjustment - together with standard engine-building practice for pushrod inspection, roll testing, column buckling behaviour and valvetrain load management, and the failure modes commonly reported on these engines in service. All lengths, part numbers, torque values and valve lash specifications must be confirmed against the factory service manual for your exact engine and model year, and against the current manufacturer catalogue for the parts being fitted.