1956 – 1961 Melling M-51
Oil Pump Overhauling
Poly 277, 301, 303, 313, 318, 326
This article covers overhauling/rebuilding including disassembly, cleaning, repair, inspection, blueprinting, and reassembling of the factory oil pump 1618949 Melling M-51 used on 1956 – 1961 poly 277, 301, 303, 313, 318, 326. The pump is vastly different than the Melling M-72 used on 1962 – 1967 A-blocks and LA engines and don’t interchange. See the specifications page for a list of the pump specifications included in the figures below. I include a YouTube video of the process at the bottom from my channel @poly318.
An issue for those with 1956 – 1961 A-blocks, new aftermarket M-51 pumps are extremely expensive compared to M-72 pumps. I’ll be the first to argue for buying a new pump if an M-51 cost $50 like the M-72 at the time of writing this article, but at current M-51 prices nearing $300, overhauling a used pump is an economical and perfectly acceptable option when the pump core is usable. For problematic cores, there comes a point where purchasing a new pump is the logical route. Factory 1618949 and Melling M-51 pumps in suitable condition may be overhauled for the cost of time and $4 in sealing rings.
One area worth discussing is the expectations of an overhaul. When comparing this article to the one for blueprinting, porting, and upgrading a new M-72 oil pump to high pressure, the overhauled pump at the end of the article has noticeable nicks, pitting, scratches, staining, and other blemishes. Some of these like pitting and nicks were present from the factory, while others are from normal wear in a 60+ year-old workhorse with unknown oil-maintenance history. The goal of an overhaul is to repair what can be reused within tolerance and replace what cannot. The overhauled pump will never be brand new but will be safely usable for many tens of thousands of miles to come. Since the majority of 1956 – 1961 A-blocks are now used not for commuting but for leisure, a properly overhauled pump will likely outlive the owner. New Melling and M-51 oil pumps are available through can be purchased through most retailers including Summit Racing, JEGS, Rock Auto, Napa Auto Parts, and other retailers.
As part of my larger technical article on performance oiling system modification, I also cover converting the trustworthy Melling M72 used on 1962 – 1967 A and LA engines to a high-pressure pump, performing porting work, and blueprinting the unit to improve the oiling system over the factory’s design.