8V71TI Fuel Injector question

[dar636]

The engines on my boat were derated by use of "N70" injectors according to the sales and survey info. This results in a top RPM of 1800, and 14 (not planning) to 18 knots on plane depending on weight and bottom condition. I rarely run above hull speed, 1200-1300 RPM gives me 10 kts consistently.

The engines are original, total times are approx 3500 hrs and they run well.

What injectors were original equipment?
I'd prefer to have full available power, all things being equal - I'd like to be able to decide if it is worth the cost to revert back to original injectors.

Not may hurricanes to outrun here in the PNW, I hope everyone is faring well in the SE. Thx in advance...

 

[kelpy]

You will have to look at the equipment tag on the rocker cover or take the engine serial number to DD to get the original injector part number.

In any event, do your best to return the engine to its "as built"configuration. Attempting to get better fuel economy by using smaller injectors on a DD is as fruitless as trying to raise or lower operating temperatures by changing thermostats or putting props on that do not match the engine power curve. It just doesn't work that way. The engineers who designed the engine configurations knew what they were doing.

 

[Photolomy]

On my 1978 8v71TI they are N90, but as kelpy said, you should get it for your engine specially. Also note the WOT (no load) figure at the bottom right of the plate.

 

[nautibake]

View attachment 34345

On my 1978 8v71TI they are N90, but as kelpy said, you should get it for your engine specially. Also note the WOT (no load) figure at the bottom right of the plate.

Mine are also N90

 

[dar636]

I've got polished aluminum valve covers and blower intake. No decal on either engine that I can find. Would a DD dealer be able to get info from my model and SN's?

ENGINE MODEL: PORT: 70823300
STBD: 70827300
ENGINE SERIAL: PORT: 8VA327812
STBD: 8VA328353

 

[Photolomy]

I would start with the big parts distributors first. DieselPro and PowerlineComponents. And then, I guess MTU. Even with the parts book (the plate on the valve cover) it is hard to find those numbers online. I guess the engines are just that old and before the age of internet. In the day though, they seemed to really have their act together.

 

[KPTIM]

The local Detroit Diesel service group here was able to get me a copy of the original factory build sheet for mine.

Western Branch Diesel

You just have to have a motivated parts person to get it from the factory.

 

[kelpy]

I've got polished aluminum valve covers and blower intake. No decal on either engine that I can find. Would a DD dealer be able to get info from my model and SN's?

ENGINE MODEL: PORT: 70823300
STBD: 70827300
ENGINE SERIAL: PORT: 8VA327812
STBD: 8VA328353


View attachment 34366

Yes. Give Western Branch or RPM Diesel a call and they will be able to tell you over the phone.

And congratulations to you for keeping your machinery spaces looking that nice.

 

[dar636]

Thanks for the leads and comments, I'll let you know what I find.

 

[dar636]

I had a set of N90 injectors built up and finished the installation Saturday, and had a short sea-trial, then a longer one today. I was seeing a WOT underway of 2100 and she did plane out showing 17.5kts with nearly full tanks and a dirty bottom I'm sure. I didn't really expect to pull 2300 WOT considering the engines age, etc - but I was not happy to find that the engines ran differently at lower power settings where we usually run.

What I didn't explore yesterday were all the various RPM settings and with the Admiral onboard today so I could walkaround I noticed several 'harmonics' that I didn't have before. Doors buzzing, stateroom ceiling panels shaking loose, vibrations felt etc.

More of the story. The installation went easily until I got to the last head and I could not remove one injector. It was so tight I thought I would rip out the copper sleeve and so I removed that head and had it O/H'd. These engines are approx 3800 hrs, and the head I removed looked like it was original confirming as I believe these engines have not been rebuilt. The cylinder bores all looked good on that head and all on both engines tested with good compression. All cylinders were firing before the injector change and these engines did run smoothly.

Are there fine rack adjustments to smooth out operations or did I just fix what wasn't broke?

 

[kelpy]

The valves and injectors should be adjusted and the racks set. Check and adjust high idle speed when done. Then go on your sea trial.

 

[Captain Ralph]

Bottom line, Were the injectors popped and matched before installation. New, rebuilt or from Mars, This has to be done to ensure no bugs are installed.

The racks must be re-tuned. You can not throw a new set of injectors in and expect them to be in tune.

Were the valves adjusted? Your pulling more power now, the equipment needs all the help it can get.

Air box check valves been serviced? Are they closing past fast idle?

What is your high idle (not loaded WOT)?

All fresh fuel filters?

 

[Scott Free 41]

I have a stuck motor. can barely turn with breaker bar on crank nut. Boat set a while after a coupe days out. ran fine. do I have water intrusion somewhere? Its in fresh water. Can I pull injectors and scope the cylinders?