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MBP Retainer- 7mm Design Change Info

A slight change in the design of the MBP retainers has taken place over the last few months. All 7 mm MBP retainers now sold are of the new configuration.

A chart attached shows the stock half ring design, the old 7 mm MBP configuration, and the new MBP configuration. Note the angled section on the outside of the retainer has been removed in the newest configuration.

The reason for this design change was due to a problem that developed during the heat treat process. The part is first machined as a continuous ring of material, then put through a heat treat cycle to bring the hardness up, after which the part is cut in half via an EDM process. During the heat treat cycle, stresses were induced. After the part was cut in half via EDM, sometimes the part would deform slightly. This would cause the retainer to fit tight when assembled with the closing shim onto the valve stem. What made the problem difficult to deal with was the fact that not all parts would deform the same amount. Some would fit tight, and some would not.

To assure proper fit of the retainers, they were sent to electropolish where a specific amount of material was removed, depending on how tight fit was. The process of determining the amount of material to remove was laborious and time consuming.

It was noted that the 8 mm MBP retainers did not have nearly the problem with warpage as the 7 mm retainers. So it was simple to try and make the 7 mm retainers similar in design to the 8 mm retainers and see if the warpage problem could be solved.

The design was changed to the newest configuration as seen in the comparison drawing. Sure enough, the warpage was drastically reduced. No electropolish of the parts is necessary for proper fit. The fit of the parts are much more uniform than ever before.

Will the new design affect the function of the MBP retainer? After a CAD analysis of the of the MBP retainer-valve stem-closer shim assembly, it was determined that the angled section on the outside of the retainer did not have any function. The conical surface did not contact any surface of the closer shim whatsoever. So removing it will have no affect on the function of the part.

What makes the MBP retainer a better option compared to stock half ring?

Stock Half Ring
Material- Spring Steel
Hardness Rc-46
Stiffness compared to MBP retainer- 1/4 the stiffness
Ends are mechanically cut with sharp edges and burrs.

MBP retainer
Material- Tool Steel
Hardness Rc-62
Stiffness compared to stock Half ring-4 times stiffer
Ends are cut with wire EDM resulting in nice sharp, normal, cuts.

In real time use the MBP retainers do not deform over time, thus increasing valve adjustment intervals.



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