Help with MCI8 / 6v92T

Bdelahunty · July 19, 2015, 11:20:04 AM

I have an 1978 MCI 8 Crusader, Allison automatic, that I've repowered with a 6v92 turbo. The original 8v71 was blown when I bought the bus. Radiators have been upgraded/enlarged, added louvered vents to back doors, blowers and housings are from a 1985 with a 6v92T.

The engine runs well. It had minimum white smoke at start up for less than a minute, then no smoke at all unless you were heavy on the pedal under a load. Adjusted the injectors and now the start up white smoke lasts for at least 5 minutes.
Everything runs fine except the bus has no power to maintain speed on any sort of interstate grade.
I'm suspicious of two things, first the rear end gearing . Can anyone tell me what gearing would be correct for this setup and how to identify what's in it now?
Second the injectors. What are the correct injectors and how do you identify which ones you have.
The truck is at my shop where we service our fleet of diesel delivery trucks. Mostly cummins so this our first experience with a 2 stroke diesel.
Thanks

bevans6 · July 19, 2015, 11:57:51 AM

white smoke and no power are both indicators of lack of air, so look for low boost things like cracked exhaust manifolds, air cleaner issue, etc. If you ran the rack and reset the injector timing, did you set them to the right spec for that particular engine? Did you check to make sure you have the rack on both sides set to go full with the speed lever at full? Did you reset the fuel delay to the correct setting, same with the starting aid? What injectors do you have - 6v92 came in a lot of buses set at around 270 hp, but you can get a nice 350 hp.

Dave5Cs · July 19, 2015, 12:31:14 PM

Is there still the metal plate attached to the valve cover or the driver side? All engine info should be printed on that plate to include which injectors are in the engine and which timing it was set to ( A,B etc), unless it has been removed.

bevans6 · July 19, 2015, 01:29:36 PM

Or someone modified the engine by changing the injectors...

Brian

Scott & Heather · July 19, 2015, 01:45:38 PM

Curious to know what you did to "adjust" the injectors that caused the white smoke...I'm learning about my own 6v92Turbo so I'm interested

Bdelahunty · July 19, 2015, 03:27:53 PM

Boost pressure is 13.5 psi on the interstate under load. New turbo. Plates on valve covers are missing. Block has rebuild tag from detroit diesel. Tried getting info from them, no luck. I agree white smoke could mean lack of air or poor atomization, ie bad injector(s).

Will the injectors be marked as to size if I pull one out?
As for injector timing, just adjusted the rods to be snug per a video we found on you tube.

Haven't been able to find any other tech info for other tuneup adjustments.

Iceni John · July 19, 2015, 04:11:47 PM

Quote from: Bdelahunty on July 19, 2015, 03:27:53 PM
Boost pressure is 13.5 psi on the interstate under load. New turbo.

That seems low. I get up to 26 PSI on my 277HP Californicated engine, but usually about 10 to 12 just cruising at steady speed. Is your turbo boost gauge accurate? Is your air filter old or getting blocked? If you have a Filter Minder, what does it show? After I replaced my air filter a few years ago I noticed the turbo was much louder (more whistlery) and the bus had noticeably more power and less smoke on acceleration.

John

eagle19952 · July 19, 2015, 04:22:36 PM

Quote from: Bdelahunty on July 19, 2015, 03:27:53 PM
.

Will the injectors be marked as to size if I pull one out?

You can see the tag on them without removing them...

As for injector timing, just adjusted the rods to be snug per a video we found on you tube.

Uhmmm..find another video...snug is not what it calls for..... the plunger height is critical...u need a pin gage..like this...

Haven't been able to find any other tech info for other tuneup adjustments.

http://busgreasemonkey.com/uploads/FileUpload/b8/c6b33345182ddfb99f558ca4a29209.pdf

bevans6 · July 19, 2015, 04:45:37 PM

One of the biggest problems is finding out what the right thing to do is. It sounds to me like you did a tune-up that wasn't required and screwed it up, so you need to undo what you did. Finding a two stroke guy would be the first choice, reading the book would be the second choice. You need to find out what injectors you have so you can find out what height gauge you need, then you need to get the right gauge, then you need to understand how to adjust the injector height correctly. If you changed the rack adjustment, then you really need to find a two stroke guy. Doing a complete injection setup from the book without a teacher or any experience is certainly possible, because I did it, but it did not take me me a couple of hours, more like a couple of days. Snap-on makes a tool kit that has all the two stroke tune up tools (or most of them, does not have a governor wedge) and there is usually one or two on Ebay.

Brian

Scott & Heather · July 19, 2015, 08:19:04 PM

I was kinda trying to politely figure out if he messed it up. Two stroke diesels don't work by the same playbook as the new high pressure rail diesels in modern trucks. Totally different rules. Definitely advise getting a two stroke mech on this...or if you want to learn, the guys on this forum are a wealth of knowledge. Definitely worth tapping into

Sent from my iPhone using Tapatalk

lostagain · July 19, 2015, 08:57:49 PM

You at least need a service manual for the V92 series Detroit. You can read the chapter on tune up. Then do it yourself. But read the book good until you understand how it all works and how to set it. You can do it if you have some mechanical sense and feel. It is not the space shuttle...

You can figure out the rear end gearing by jacking up one wheel and counting the revolutions compare d to the ones of the drive shaft. Or if you remove the yoke off the differential input shaft, you will see the ratio stamped on the end of the shaft. Or tell us your rpm at 60 mph. 2100 or so=4.11 to 1, 1900 or so=3.73 to 1, 1700 or so=3.36 to 1.

JC

Bdelahunty · July 20, 2015, 07:46:00 AM

Kind of figured we screwed something up when white smoke increased at startup. WIll look for injector ID and have been looking for a local 2 stroke mechanic. Any recommendations in the cincinnati ohio area are welcome.

In lieu of finding someone local, would also appreciate info on where to find a 6v92 service manual.

Thanks again

eagle19952 · July 20, 2015, 07:54:00 AM

Quote from: Bdelahunty on July 20, 2015, 07:46:00 AM
Kind of figured we screwed something up when white smoke increased at startup. WIll look for injector ID and have been looking for a local 2 stroke mechanic. Any recommendations in the cincinnati ohio area are welcome.

In lieu of finding someone local, would also appreciate info on where to find a 6v92 service manual.

Thanks again

Everything you need to know regarding tuning is in the link I provided.....

Bdelahunty · July 20, 2015, 08:29:10 AM

Thank you. Snap on kit found on ebay, should be here in a few days. Will keep you posted.

eagle19952 · July 20, 2015, 09:19:06 AM

Quote from: Bdelahunty on July 20, 2015, 08:29:10 AM
Thank you. Snap on kit found on ebay, should be here in a few days. Will keep you posted.

download the instructions yet... i will remove the link soon....