MCI7 8v71 stranded grey smoke increasing with accelleration (injector issue?)

[Geoff]

I don't know where this 350# compression came from, but an "N" piston (non-turbo) needs 500 psi compression, that is on startup, and that is the minimum-- 550# for a new or rebuilt engine. 

--Geoff

[luvrbus]

Use the starter they will go 350# then at 900 rpm they should be 500 ,I have friend with N/A 8v71 in a Eagle that Diesel Exchange installed for him the best it would ever do is 450# on any cylinder it was a bear to start in cold weather but ran good with normal power come to find out they used 17:1 pistons

[Geoff]

I got my DD Field Service manual out and looked at compression readings for a V-71 N engine:

Compression is taken with engine running.

Compression at sea level 600 rpm 565 psi for a new engine, Minimum for a used engine is 515 at 600 rpm.

For a turbo engine with the lower compression pistons the readings are 475 and 425, respectively.

I know from personal experience and many compression tests that once you get at or below 500 psi at idle the "N" Detroit engine gets hard to start.

--Geoff

[luvrbus]

They won't go 500 lbs at 2500ft I know that much lol

[Dlsnow]

Well...as usual...life happens...
compression test kit shows up...
pouring rain and I cant work on the bus
Cant wait for this weekend.

FWIW my experience starting is
50 deg or higher and the bus starts right up (3 or 4 seconds on starter) especially if it was run the last day...rough idles for 10 seconds then smooths out
40 and it is usually 3 reps of 6-10 seconds...rough idles for a minute then smooth

PO said he has had only straight 40 for oil and convinced me the same...only straight 40

[B_K]

Dave there is a solution for working on buses outside in the rain, snow, extreme sun/heat.

I use an "EZ Up" Awning. I use it here outside the shop, & I take it with me on road service calls. Just put it up next to the bus where your going to be working and walla you have a "carport" to work under.
They don't cost that much and fold up nicely for storage and can be used for other uses too!
I think that EVERY BUSNUT should have one.
  BK 

[Dlsnow]

Well BK if all goes well i will use the money i saved for a cylinderkit and pickup an EZ-UP

[luvrbus]

You have been quite for a few days any updates ?

[Geoff]

The Harbor Frieght diesel compression tester does not have a dummy injector for a a 2-stroke Detroit.

--Geoff

[luvrbus]

Geoff, I have been wondering how he was going to make it work 

The only thing I like about some 53 series (military) is they have glow plugs and you can remove the glow plugs and use about any type compression gauge

[Dlsnow]

Well - compression seems to check out - the HF kit is the 14 piece one http://www.harborfreight.com/14-piece-diesel-compression-tester-set-46800.html and it does have an adapter that is shaped like a v71 injector - followed BK's advice on WORK FAST (note don't burn the #*&$ out of your arms on the exhaust).

Compression was jumping around 300 - 330 with engine warmish (~160) and at fast idle
but...I found the injector wasnt really seated good - reseated and got a solid 480 - engine was cooling though - thinking cooler engine will get higher compression (is this logical?)
the compression gauge is filled with a thick fluid slowing its descent and letting me get a reading - not as nice as the ones with a "max reading" dial but workable.

I want to test it again as I broke rule 1 - Dont be in a hurry (visiting friends from out of town) and I think I can get the cover off faster now with a 12 point socket (was previously using a wrench - took forever to remove rocker covers).

here is the adapter pic -


So I checked the airboxes - no more parts showing up in there - scoped the cylinder again - still clean

installed new injector and reassembled -
no more smoke and a whole lot more power
hapilly moving down the road to tulsa OK - any busnuts in/around Tulsa?

heres the compression gauge pic

[luvrbus]

Not a bad looking kit for 119 bucks my Kent/Moore was a little more than that, a lot more lol good luck on your travels

[Dlsnow]

one issue I have is the tach reading - I dont have a tachometer
im not sure what my fast idle is set to either
but I assume with the compression reading I have in that hole I dont have valve issues
bus is running remarkably well

I will temp gun the exhaust to see if those readings are the same on each pair of cylinders after my run tomorrow
other than the new injector I didnt adjust the injector rocker as they all checked at 1.460

[eagle19952]

it does have an adapter that is shaped like a v71 injector - followed BK's advice on WORK FAST (note don't burn the #*&$ out of your arms on the exhaust).

THAT WOULD HAVE BEEN CHOPPED LIVER'S <----who would be me>
WORDS OF ENCOURAGEMENT, BK SUGGESTED YOU TO BUY A TENT.


were i you..
1 startup and get engine up to temp...drive it around till 180 deg
2 shutdown
WORK FAST

I am guesssing it takes about 7000 posts before you become visable here....

[B_K]

it does have an adapter that is shaped like a v71 injector - followed BK's advice on WORK FAST (note don't burn the #*&$ out of your arms on the exhaust).

THAT WOULD HAVE BEEN CHOPPED LIVER'S <----who would be me>
WORDS OF ENCOURAGEMENT, BK SUGGESTED YOU TO BUY A TENT.

were i you..
1 startup and get engine up to temp...drive it around till 180 deg
2 shutdown
WORK FAST

I am guesssing it takes about 7000 posts before you become visable here....

You would be correct!

I am guesssing it takes about 7000 posts before you become visable here....

How would I know, I only have 40 posts here   
  BK