1. Incorrect Pushrod Length: This is the most common culprit. If the pushrods are the wrong length, they'll be subjected to excessive stress, leading to breakage. This can happen if:
* Incorrect pushrods were installed: Double-check the length of the installed pushrods against the specifications for your engine. There might be variations between years and even engine revisions.
* Incorrect rocker arm geometry: The rocker arms might not be correctly adjusted, leading to excessive valve lift and putting extra strain on the pushrods. This is often linked to incorrect pushrod length.
* Head gasket issues: A poorly installed head gasket could lead to uneven valve train geometry, indirectly influencing pushrod stress.
2. Valve Train Binding or Interference:
* Improperly installed lifters: Damaged or incorrectly seated hydraulic lifters can bind, leading to pushrod breakage. Make sure they're seated correctly and that there's no debris interfering.
* Bent pushrods: A pre-existing bent pushrod might have been overlooked during the head replacement. Even a slight bend can weaken it enough to break under normal operating conditions.
* Valve spring problems: Broken or weak valve springs can cause excessive valve float or improper valve closure, leading to increased pushrod stress.
* Rocker arm issues: Damaged or improperly installed rocker arms can also bind or put excessive pressure on the pushrods.
3. Engine Issues:
* Camshaft problems: A worn or damaged camshaft lobe can put uneven stress on the lifter and pushrod.
* Pre-existing engine damage: The engine might have had underlying issues (e.g., detonation, excessive valve lash) that were not addressed during the head replacement, leading to pushrod failures.
Troubleshooting Steps:
1. Verify Pushrod Length: This is the absolute first step. Use a reliable source (repair manual, parts catalog) to confirm the correct length for your specific engine. Measure the installed pushrods to ensure they match.
2. Inspect Pushrods Closely: Examine the broken pushrods carefully for signs of bending, fatigue, or manufacturing defects.
3. Check Valve Train Geometry: Inspect the rocker arms, lifters, and camshaft lobes for damage or misalignment. Measure valve lash (if applicable) to ensure it's within specifications.
4. Inspect Lifters: Ensure all lifters are seated correctly and pump up properly. If possible, try to diagnose any issues with lifter operation.
5. Inspect Valve Springs: Check the valve springs for proper tension and any signs of damage or fatigue.
6. Check for Head Gasket Issues: Ensure the head gasket was properly installed and that there are no leaks.
If you've replaced the pushrods multiple times and they keep breaking, it's crucial to carefully examine *all* components of the valve train. It's likely not simply a matter of the pushrods themselves but rather a problem with a related component causing excessive stress. If you're not comfortable performing these inspections, it's best to consult a qualified mechanic.
