Oil Pump Gears (Straight Cut): DSM/EVO

Oil Pump Gears (Straight Cut): DSM/EVO
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The straight cut gears (MD121120 & MD125361) have been discontinued by Mitsu but we still have a small qty on hand.  If the webstore "allows" you to place an order, it means we have the gears in stock.  If not, it means we are out of stock.

These are the two gears that make up the oil pump:  the drive gear (MD121120) and the driven gear (MD125361).

They are the oil pump gears that came stock on the 6-bolt 4G63 engine.  However, they will physically fit and correctly function within the oil pump housing of a 7-bolt 4G63 engine (both DSM & EVO).

These gears are what is referred to as "straight cut".  The alternative to a straight cut gears are "helical cut" .  Straight cut gears are said to be more efficient than helical cut gears because they generate no axial load on the gear.  This lack of axial load means there is no force trying to push the gear against the housing restraining it (the oil pump housing).   The disadvantage is that it makes more noise than an equivalent helical cut gear (generally referred to as "gear whine").  It is generally accepted that the advantage that straight cut oil pump gears have over the helical cut equivalent is only meaningful at very high speeds and loads such as would be found in racing applications.

As it happens, the drive gear (MD121120) we sell is NOT an OEM Mitsu part, but rather it is manufactured in Belgium by a company called Total Source.  (Total Source is a very big name in the materials handling industry worldwide; as is Mitsubishi.  In fact, this is the connection between these two companies.  We suspect that when Mitsubishi discontinued the straight-cut gears, a large market still existed for them so Total Source decided to manufacture them.  We looked into the supply of the Total Source gears and it appears that they have since been discontinued as well.  The supply we ordered appears to have exhausted at least the North American supply (and possibly the worldwide supply)).

We looked at the Total Source gear very closely and took measurements of all important dimensions and it exactly matches the OEM gear.  We found only one noteworthy difference: there is no "timing" dimple present.  (There is a timing dimple present on the OEM gears that allow the drive and driven gears to be easily timed to match the oil pump and rear balance shaft to which they are attached).  Of course, the oil pump and rear balance shaft can still be timed without using marks on the gears, but it is a little more inconvenient.  Also, we suspect anyone intending to run straight-cut oil pump gears has probably already removed (or intends to remove) the balance shafts, and thus the absence of timing marks on the gears is irrelevant. 

The straight-cut oil pump driven gear (MD125361) is a genuine OEM Mitsu part.

NOTE: Photos may show what appears to be imperfections and/or a rough finish. This is a rust preventative coating applied at the factory.  This coating exists on both the OEM Mitsu gear and the Total Source gear.

DSM (1990-99).

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