Cummins 4bt/6bt Sherwood M71 raw water pump

[dvarholy]

This pump is commonly used on the lower HP versions of the B series Cummins. I have used these for years with no trouble and also rebuilt a few. A few minor issues are, first, the minor and major rebuild kits do not include the engine oil seal. NAPA part number 6904 will work. Automotive oil seals such as this one use a thin steel tension spring that will rust away after a few years storage in a marine environment. I noticed my spare seal was ruined while inspecting the spare engine parts. Consider packing any spare oil seals with grease and storing in a Zip-Lock bag to prevent failure. Of less concern are the two size 6202 ball bearings also used to rebuild the pump. These are available from McMaster-Carr as part number 6153K56, but regular steel bearings are fine if they are also packed in grease.

Daniel

 

[bshanafelt]

Hi Daniel,

I have searched the web and youtube to find some rebuilding advice for the M71 without success

I usually get around 800=1000hrs out of these pumps before I get some leaks/seal failures
, so my procedure is to just swap in a new one.

I have a ton of seals and bearing that I have collected over the years and would be happy to try a rebuild, but again don't find any instructions.

i assume some type of press is required for disassembly?

thanks

 

[Greg QS]

I had the 6cta for years. The pumps were a problem. I replaced mine with a smx unit. Never leaked in 10 years. Yes 10 If leaking just replace with these you will be happy.

https://www.sbmar.com/product-category/engine-components/seawater-pumps/

 

[dvarholy]

My two pumps were still original when the boat was purchased 5 years ago. Engines were about 2,000 hours then. Bought two new pumps and rebuilt the better of the originals as a spare. I regularly rebuild mechanical seal pumps as part of my employment. The stainless shielded ball bearings will not easily corrode and run cooler than sealed bearings. Insist on a good brand such as Timken, NTN, or Koyo. No special tools are needed to rebuild these small pumps.