More Info on 7 mm MBP Retainers - Ducati.ms - The Ultimate Ducati Forum
 
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post #1 of 1 (permalink) Old Feb 16th, 2015, 9:57 am Thread Starter
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More Info on 7 mm MBP Retainers

I posted this information on a thread in response to questions about the applicability of the 7 mm retainers. Thought I would post it up on my forum as I think info is useful.

Just to clarify compatibility of shims when MBP Retainers are used in all bikes with 7 mm valve stems:
All 2V bikes after 07' have the 7 mm valve stems. The 7 mm MBP retainers are a direct replacement in the 2V bikes. They work with the stock Ducati closer shims and EMS closer shims and the stock Ducati or EMS opener shims.

With all 4V bikes with 7 mm valve stems (thats all 4V except the "R" bikes and 749S) modified opener shims are needed when the MBP retainers are used. This is required because the MBP retainer extends up past the groove in the valve stem. The bottom of the opener shim needs a counterbore in it to avoid interference.

Concerning the fit of MBP retainers in all 7 mm bikes:
Last year I licensed the design, manufacture, and marketing of the MBP retainer product (both 8 mm and 7 mm) from MBP (Guy Martin). The current batch of MBP retainers in stock have a slight redesign and are made from a different vendor with a different heat treat spec and an added electropolish step. The result is a much more consistent fit of the retainers.

In the past, three factors caused inconsistency in retainer fit. The first was the design. The cross section had a very irregular shape which caused internal stresses to occur during machining and more so during heat treat. This caused the part to warp just slightly. Since the fit of the 7 mm retainers is almost line to line (meaning no clearance) with the groove in the valve stem and closer shim, any minute warpage would cause inteference and make it difficult to assemble and seat the closer shim onto the valve stem. Since the retainers are stiffer and harder than the stock half rings, they dont deform easily and really need to be spot on size wise to fit properly.

Guy and I talked about this issue and I suggested a very slight redesign making the cross section more uniform from top to bottom. The second factor was the heat treat spec. I found a heat treat spec that minimizes dimensional changes. I also found that during the wire EDM process (Retainer is machined as a ring then cut in half with a wire like a cheese cutter), a small burr would form on the ends. This was the third reason. Since the fit needs to be so perfect this little burr was also causing interference fit. I instituted an electropolish process that gets rid of the small burr on the ends.

The result of all these changes is a much more consistent part. Scrap rates have gone down significantly.

I also found that actually two designs of 7 mm MBP Retainer are necessary. The fit of the closer shim and valve stem on the 4V bikes after 07' (the 1098, 1198, Multi 1200, 848, etc) is just slightly tighter than on the earlier 4V bikes. Using the stock half rings you can get away with just one design, since the stock half rings are soft and not as stiff they will simply deform as you force them to fit. Not so with the MBP retainers. The are so stiff and hard that the design that fits the older 4V bikes (Desmoquattro, 999, etc) will not fit the 1098. The difference is very small, only about .001 in. on the diameter, but is necessary to be able to assemble the closer shims.

Long winded response here but it explains why in the past sometimes the MBP retainers were inconsistent in their fits. Now, they fit easily make the installation process go much more smoothly.

The two pics attached show the 2V-7mm assembly and the 4V-7 mm assy.

Mike
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