6-71 Foam Air Intake Covers

[Bob Bradley]

Apparently I have once again become a DD mechanic despite having replaced my DD powered 43 with a Cummins powered 45. My kids' boat has a pair of 6-71s that have the old style foam covers on the air intake instead of the Airseps that I am familiar with. I presume that these require regular cleaning or replacement just as the Airsep cones did. What is the best course of action here? Should they be cleaned, and if so how, or should they just be replaced regularly. If dirty, will they have a significant impact on performance like my Airseps did? They're only making 2100 rpm or so, and before opening up the intercoolers or having prop work done, I want to be sure we address the simple stuff.

 

[Captain Ralph]

6-71 air filter? There was a sleeve (course foam) air filter on the air silencer for the old and original 6-71T or TI. It might keep big wasp out (might).
6-71N had no air filter, just the big air silencer.
If your not puking any black smoke, it's not an air filter.
Cleaning the old Detroit required a squirt of liquid detergent, squeeze thru the foam, in a ball. rinsed out well with water, squeezed out and re-mounted.

Without vacuum and pressure gauges, your still guessing about your fuel system.

 

[Bob Bradley]

Thanks, Ralph. I guess I'll have to pick up a couple.

McMaster Carr has a glycerin filled fuel pressure gauge with a 1/4 npt male fitting. I installed one on my old 6v92s. Is that also correct for the 6-71? I'm presuming it goes on the secondary filter housing. What pressure range for the gauges? They have 0-100, 0-160, and 0-200 that seem to be likely ranges.

I've never had occasion to use a vacuum gauge. What type gauge should I be looking for, and how is it attached and used?

 

[Captain Ralph]

Your looking for at least 40 psi of fuel pressure at high RPM. The upper scale may reach 70 psi.

Pending a few model options, There should be a secondary fuel filter past the fuel pump, that allows for a pressure gauge to tap into it's output. Remove a plug from the housing and screw the gauge in. Save the plug and remove the gauge when testing is completed.

The vacuum gauge goes before the fuel pump, after the primary filter(s).
Racor makes one that replaces the T handle on the top of their filter assemblies.
4 to 5 inHg at high RPM is good.
This gauge makes a good tool that can go back in your tool box when testing is done.

Get the gauges with the tell/tale pointer. So you can see the readings without having to be in the engine room during speed testing.

 

[Captain Ralph]

Just woke up with a memory that bit me many many years ago;
Are the throttle control cables really moving the governor arm to full fuel?

Yep, that boat was a recent purchase with 6-71Ns.

Naturally the next question is; Is the governor moving the whole rack to full fuel. I know you replaced one injector on one of the motors, so not sure if you just matched it to the rack or backed all off and started fresh.

 

[Bob Bradley]

Thanks. I'll double check the throttle cables. I did a full valve adjustment, injector timing, and rack set on both engines.

 

[omecojh]

I have the filter part numbers on my boat for the 671 -TI. (Baldwin?)

I'll let you know after I visit the boat this weekend.

 

[Bob Bradley]

Thanks

 

[grey goose]

You might call PC industries at 877 615 7737 , the part number 6422214 may be what you need.
These foam covers also known as Element air silencer tend to degrade and let that failing material get sucked into the engine.