It seems that MDS is not so much the issue as manufacturer defect that they knew about, excerpting to much forces on parts, and lubrication issues were key, and using heavier weights only made it worse.
Dr. Andy Randolph, technical director at ECR Engines—a NASCAR engine developer based out of Welcome, North Carolina whose lab does lots of failure analyses—gave me his thoughts, too, positing that perhaps there was an issue with oil viscosity. The result would yield the excessive lash that the above R&D engineer told me about:
First, these lifters control lash hydraulically and are designed for 5W20 oil. If the owner uses a heavier oil (for instance a 10W30), this could impede the hydraulic action of the lifters and increase lash between the roller and cam lobe under some operating conditions. This increase in lash will generate impact loading when the lifter contacts the lobe and lead to premature failure of the needle bearings along with the ticking noise that some of the owners report.
Second, the needle bearings are fed oil continuously through the body of the lifter. Once again, if the owner uses a heavier oil then flow to the bearing will be reduced and failure could happen prematurely.
Though not familiar with the Hemi's MDS, Randolph says he doesn't think the cylinder deactivation system is playing a role based on what he's seeing here. In addition, both he and the R&D engineer don't think this failure should lead to bent pushrods, though Randolph did add that it could happen if "the lash increases sufficiently for the pushrod to be displaced from the cup in either the lifter or the rocker arm. Once displaced, the pushrod could easily become overloaded and bend." That's what I think happened, but that's just a guess..
In any case, it's pretty clear that a fault in the lifter's ability to control lash—possibly caused by debris or improper oil viscosity—could theoretically be the cause of these failures.
https://jalopnik.com/chrysler-built-hemi-engines-with-a-major-engineering-de-1842400890
Dr. Andy Randolph, technical director at ECR Engines—a NASCAR engine developer based out of Welcome, North Carolina whose lab does lots of failure analyses—gave me his thoughts, too, positing that perhaps there was an issue with oil viscosity. The result would yield the excessive lash that the above R&D engineer told me about:
First, these lifters control lash hydraulically and are designed for 5W20 oil. If the owner uses a heavier oil (for instance a 10W30), this could impede the hydraulic action of the lifters and increase lash between the roller and cam lobe under some operating conditions. This increase in lash will generate impact loading when the lifter contacts the lobe and lead to premature failure of the needle bearings along with the ticking noise that some of the owners report.
Second, the needle bearings are fed oil continuously through the body of the lifter. Once again, if the owner uses a heavier oil then flow to the bearing will be reduced and failure could happen prematurely.
Though not familiar with the Hemi's MDS, Randolph says he doesn't think the cylinder deactivation system is playing a role based on what he's seeing here. In addition, both he and the R&D engineer don't think this failure should lead to bent pushrods, though Randolph did add that it could happen if "the lash increases sufficiently for the pushrod to be displaced from the cup in either the lifter or the rocker arm. Once displaced, the pushrod could easily become overloaded and bend." That's what I think happened, but that's just a guess..
In any case, it's pretty clear that a fault in the lifter's ability to control lash—possibly caused by debris or improper oil viscosity—could theoretically be the cause of these failures.
https://jalopnik.com/chrysler-built-hemi-engines-with-a-major-engineering-de-1842400890
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