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Most Likely 6V92TA DDEC Failure? JR 12-5-02  
I recently purchased an'87 MCI-9 with a 6V92TA DDEC engine. 176K showing?? Runs great...but what is likely to fail on this type engine?
It came from the New Jersey Transit system. Appears to be well maintained.
Also can the speed be increased thru PCM mods? Top is 63 MPH. I have no clue as to what the RPM or rear drive axle ratios are.
Trying to figure out how to install a tach on the thing. SW makes an electronic drive for a electric tach. Anyone know what NJT's ratios were on this buses? I know zip about a Detroit Diesel. Will learn fast. Thanks, JR
Re: Most Likely 6V92TA DDEC Failure? Joe 12-6-02  
The first thing to wear out on the Detroit Diesel powered transit busses is the main bearings. Bus engines are "lugged" in normal use. "Lugging" a Detroit Diesel wears the main bearing lower halves. NJT drops the main caps and just replaces the lower halves the first time. Normally they should be replaced at 200,000 miles. NJT monitors the engines with oil samples and when copper is detected the bearings are changed. Maybe replace rod and main bearings. Cheap insurance...get an oil sample done.
Next...the usual ratio on the NJT busses was 444. that gives you 63 mph at 2100 rpm. your engine can be safely turned up to 2350 rpm, that will give you about than 70 1/2 mph. 2350 divided by 2100 equals 1.12. That's a 12 percent increase. 63 multiplied by 1.12 gives you 70.56. (Still too slow)
Finally....go to a heavy truck shop and get a tach kit that works off the flywheel. They should be able to get the right info from the engine serial number.
Detroit's like high RPM...Wind that baby up....Happy motoring.....
Re: Most Likely 6V92TA DDEC Failure? paul dumstorf 1-11-03  
If not to late the enexpensive way to get a tachometer on line is to use a alternator tach. Most alternators, (in your case on a 6V92 probally a Delco) have a tap on the back of the alt that reads A/C frequency before generated voltage is changed to D/C. Simply hook up the tach to the tap along with a 12vdc source with a ground.
Re: Most Likely 6V92TA DDEC Failure? Joe 12-7-02  
I have to make a correction....12 percent to the rear will only give you a.0277 increase to the drive wheels. That equals to about 65 mph. I was up all night dealing with a snow storm and wasn't thinking clearly....sorry but you will need to change rear ratios to get a decent higher speed.
Re: Most Likely 6V92TA DDEC Failure? JR 12-8-02  
Joe, you don't live on the east coast do you? Ever consider moving to NC?
You would make an excellent next door neighbor! You got a cell phone? Just joking. My MCI-9 will go flat-out about 70. It does not like grades at all. Runs very smoothly and gets real good fuel milage. Still need that tach. If I go down on the ratios I will also give up what little hill climbing capacity I now have...which ain't much. Reckon NJT detunes these things to prevent major speeding? Once I have an accurate RPM I will be able to make a decision. Probably going to leave it alone. I had someone follow me the other day and found out that my speedometer is way off. Apparently the sender (or whatever drives the speedo) is not correct. I thought it was much slower (55-60). This is all new to me. It will run 65 all day.
I worry more about the trans failing now than the engine. Thanks for the Ratio's and NJT info. I will find a tach soon. Got to get the steering tightened up too. Hope the box is servicable. Saw what those things cost! It sounds like the kingpins are loose. That's within my capabilities to fix. Trying to give these seats away right now. Know anyone that wants some real nice, matched seats, driver and all, for free? They can have mine! If you have any other interesting tidbits about the NJT's I am interested.
Thanks much for your help, JR
Re: Most Likely 6V92TA DDEC Failure? Joe 12-9-02  
Well as a matter of fact, I have a place in NJ and one in FL so I travel the east coast often. A perfectly tuned 6V92 will produce 350 hp. These NJT engines were detuned sometimes as far as 260 hp. The cam setting and injectors make up the difference. Injectors are easy to replace, but cam timing is done with the rear of the engine apart and thats a big job.
Re: Most Likely 6V92TA DDEC Failure? ray 4-26-03  
Saw the reply on most likely failures. jr. had seats for mci 9. i could use them for church bus
Re: Most Likely 6V92TA DDEC Failure? Jim 8-7-03  
Side note: You may be able to "up" to 350 HP, but the cooling system may kill the deal. Don't run that engine over 180, head gaskets will pop.
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