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Old 05-19-2007, 08:22 AM
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sorry for how long this is but it's most of the info I've found. you can even search on google too.

melling had problems with pumps in solid mount motor mounts & in performance applications. melling has a pump for performance applications. do a search on this site and maybe a search on
too. or call melling. becarefull till you know your melling oil pumps now.

good info w/pics

More Info: Here's the reply that I got from Melling:

Thank you for input ,we value our customers opinion.

Melling’s design of GM’s Small Block Chevy oil pump was updated in 2004, see attached bulletin. At that time changes were made to the standard volume, M-55 & M155, and the high volume, M-55HV & M155HV, pumps. The changes improved many aspects of the pumps as compared to the original GM pump. To respond to customers requests one of the areas that improved was the hot idle performance of the pump. Durability was improved by eliminating a possible failure mode as noted in the bulletin. Casting improvements allowed the wall thickness of the housing around the gears to be reduced to reduce weight. Additional support rips were added to the neck area on the high volume pump casting. For stock replacement applications the changes will only increase customer satisfaction with our products.

For performance applications Melling recommends an M-Select oil pump be used, especially in solid motor mount applications. Melling has available a full line of SB Chevy performance oil pumps. Not only does the M-Select line of SB Chevy performance pumps utilize the previous casting design but are available with design features to further increase performance and durability. In addition the M-Select pumps are CNC machined to exacting tolerances and surface finishes. The M-Select line was created to provide engine builders a cheap insurance policy to improve one of the most overlooked critical components in a performance engine build, the oil pump.

Melling is a world class designer and manufacturer of Original Equipment, Replacement, and Performance oil pumps. The changes implemented on the stock replacement GM SB oil pumps improved performance, durability, weight and cost. With the recent dramatic increases in raw material costs these changes have helped to reduce the cost increase that is passed onto our loyal customers.

I have attached the warning sheet (pdf) that is included in each Melling boxed oil pump. Some of our private labeled oil pump customers do not to have the warning sheet included in the packaging.

Thank You,

George Richmond


more info


In 2004 Melling Engine Parts will be releasing updated versions of the M-55 and M155 oil pumps. The new M-55 and M155 will have a new look due to a new housing and cover casting. The housing will now have a drilled outlet hole much in the same manner as the original GM pump. As compared to the original GM design the outlet hole has been re-positioned to improve the alignment with the bearing cap to improve oil flow up to the main oil gallery.

The cover design has also experienced a change. The relief valve bore is now machined as a blind hole with a step near the end for the relief valve to seat against. Leakage around the relief valve will be greatly reduced since the valve seats on the end of the valve bore. This will help to improve low rpm performance. This change eliminates the need for the press-fit plug and possible failure mode concerning the press-fit on the plug.

The changes to the relief valve are minor. The end configuration has been changed to match the chamfer on the valve bore. A 90-degree edge has been added to help clean foreign material off the valve bore wall.

The groove pin has been changed from a 3/32” diameter tapered pin to a 1/8” diameter straight pin. This change is to increase the strength of the drill to reduce tool breakage. Pin orientation will no longer be an assembly issue by removing the taper from the pin.

“Quality in all we do”

Melling Engine Parts has an oil pump for almost every application. Whether you need a stock
replacement pump, or one of our M-Select Performance pumps, we build quality into every one.
Special attention to performance and durability has been given to all of the new line of M-Select
Performance oil pumps. Take a look at what the leading manufacturer of oil pumps can do for your
performance lubrication needs. All pumps are tested for pressure and volume and hand turned before being bagged and boxed. The informational charts on the following pages will assist you making the correct choice for the MSelct
oil pump that best suits your needs. In Melling’s continuous drive to improve the quality and customer satisfaction of our products a series of design changes were recently made to the body casting used to manufacture the M-55 and the M155 family of oil pumps. Melling supplies these pumps to the Original Equipment market, as well as the aftermarket. The major design change was a weight reduction in the body casting. The lightening of the casting as and the drilling of the outlet hole resulted in a change in the appearance of the Melling pump. Melling will continue to use the old casting design for the pumps manufactured for our M-Select performance line of products. We highly recommend all performance engine builders choose one of our M-Selct oil pumps.

M-55HV 10550
“Very Important”

Casting Changes to the Small Block Chevy Oil Pumps Location of weight reduction done per General Motors request

this is a warning in some pumps
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