Noisy New Water Pump

[Bruce A]

I have just installed an MMI water pump with the sealed bearings and I hear a tapping (or maybe it is a slapping) sound coming from the vicinity of the water pump at an idle. When RPM is increased to about 800 the sound diminishes and goes away completely at 1000 RPM. This noise was not present with the old Sherwood pump.

The new pump moves a lot more water than the old pump so I am wondering if this may account for the noise. Is it possible that the load on the pump shaft to accessory drive coupling is variable or pulsating at low RPM's (due to impeller surge) but then this load smooths out when the RPM's increase and the flow is more consistent?? Could this pulsating at low RPM's cause the tapping/rattling noise? Has anyone experienced anything like this?? I am also wondering if it is OK to run the engine under this condition since it is hardly ever at an idle?

Thanks for any help or comments.

Bruce

[Don Moyer]

Bruce,

I may be in the best position to respond to this question. We have had one other case of a tapping/clicking type noise showing up after installing an MMI Flange pump. We and the customer pulled our hair out for several weeks, checking everything we could think of in terms of any anomaly within the pump, and nothing we ever did seemed to scratch the itch. The noise abated and went away within a few hours, presumably as the new pump wore in a bit (bearings, new impeller, etc.).

Our conclusion was that the slightly higher performance and new stiffness of the MMI pump imposed a slightly higher loading on the idler gear and spindle, which in turn caused it (the idler gear) to make its sometimes characteristic ticking sound. I'm attaching a Q&A we prepared some time ago on the subject of ticking sounds. The idler gear issue is discussed in paragraph 2.

In summary, I believe you're perfectly safe to use the engine while observing (or listening) for the sound to diminish. You might also bump your idle RPM up a bit to a more normal 800 RPM (at least until the noise abates).

Don

[Bruce A]

Don,

Thanks very much for the response. It most likely is the idler gear as you have suggested. Is the idler gear part of the accessory drive or is it located and supported in the engine block? Hopefully the noise will abate with some use. Also, I will increase idle to 800 RPM.

Thanks again,

Bruce

[Don Moyer]

Bruce,

The idler gear is mounted on a spindle that presses into the rear face of the block. The gear is a rather crude gear with diagonal teeth which continually causes the gear to press against a hardened steel flat washer (officially called a thrust washer) between the retaining nut and the gear when under load. At low RPM there is very little side load on the gear and it will sometimes chatter a bit as it runs and make a clicking sound.

If you have an MMI Service and Overhaul Manual, you can see a picture of the idler gear on page 5-1, Fig. 1. The idler gear is not labeled, but it is the gear between the small crankshaft gear and the accessory drive gear.

According to Universal tech folks whom I spoke to years ago, they intentionally established a quite wide clearance between the steel spindle and the brass-bushed idler gear. This wide clearance (I could never find an official specification, but I'm guessing .004 to .005") allowed for a lot of oil (which is fed under pressure through an oil hole in the spindle) to find its way to the outer diameter of the idler gear and be flung into the small collection basin cast into the face of the accessory drive, to lubricate the bearings in the drive. I know, this seems to be rather hokey engineering, but it has worked for all these many years. And, although we find the idler gears very sloppy on almost every engine we rebuild, we have never heard of one actually failing in some way so as to cause an engine failure.

Don

[Bruce A]

Don,

I wanted to let you know that the clicking noise associated with the new MMI water pump that I installed several months ago has diminished to the point where I no longer notice it---the click/clack maybe gone completely or maybe I have adjusted to any remaining sounds. The pump has about 7-8 hours of operation since installed so it probably just had to be broken-in a bit to reduce load on the accessory drive gearing (if that was where the noise originated).

Thanks again for your help,

Bruce

[msauntry]

Don,
Thinks like oil catch basins make me wonder if there are risks involved with running the engine while heeled over. Could something get starved of oil?

For engines mounted on a 14 degree aft slope, should we calibrate our dipsticks to account for more oil aft? I'd imagine it would read higher than a level engine. Any thoughts on this?

Thanks,
Micah

[Don Moyer]

Micah,

The dip stick measures the oil level very close to the lowest part of the oil pan, which is also where the pick up screen is located for the oil pump. In other words, you're really measuring the oil level over the oil pump pick-up, so there is no need to compensate for the slope of the engine. In terms of cavitating during heeling, you would think there would be an upper limit, but I've seen quite a few days where healing to 45 degrees occurred and I never noted any decrease in oil pressure.

In early model engines, the dip sticks were actually marked with four small hash marks corresponding to certain slope angles, but in the later model engines (which are most of the 40,000 engines built throughout the 1970's) they discontinued this practice and put a simple "Full" and "Add" mark on the dip stick and ignored the slope angle. In case you have an early model engine, it turns out that the uppermost of these four marks corresponds to the full mark on the late model dip sticks.

The reversing gear is pressure fed by the engine oil pump, so as long as you have normal pressure, the reversing gear is happy. The only other oil sump is in the bottom of the accessory drive and although the accessory drive has other problems that are related to slant of the engine (see our tech note on that subject at moyermarine.com), it is not particularly affected by heeling.

Don

[msauntry]

A great explanation... Thanks, Don! These engineers were a pretty savy bunch.