Author Topic: MCI7 8v71 stranded grey smoke increasing with accelleration (injector issue?)  (Read 34264 times)

Offline Geoff

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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
Geoff
'82 RTS AZ

Offline luvrbus

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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
Life is short drink the good wine first

Offline Geoff

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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
Geoff
'82 RTS AZ

Offline luvrbus

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They won't go 500 lbs at 2500ft I know that much lol
Life is short drink the good wine first

Offline Dlsnow

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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
1972 MCI7 8v71 converted - 1kw solar on roof

Offline B_K

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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.
;D  BK  ;D

Offline Dlsnow

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Well BK if all goes well i will use the money i saved for a cylinderkit and pickup an EZ-UP
1972 MCI7 8v71 converted - 1kw solar on roof

Offline luvrbus

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You have been quite for a few days any updates ?
Life is short drink the good wine first

Offline Geoff

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

--Geoff
Geoff
'82 RTS AZ

Offline luvrbus

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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
Life is short drink the good wine first

Offline Dlsnow

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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
1972 MCI7 8v71 converted - 1kw solar on roof

Offline luvrbus

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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
Life is short drink the good wine first

Offline Dlsnow

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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
1972 MCI7 8v71 converted - 1kw solar on roof

Offline eagle19952

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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.... ;D
Donald PH
1978 Model 05 Eagle w/Torsilastic Suspension,8V71 N, DD, Allison on 24.5's 12kw Kubota.

Offline B_K

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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.... ;D



You would be correct!
Quote from: eagle19952
I am guesssing it takes about 7000 posts before you become visable here.... ;D

How would I know, I only have 40 posts here    ;)
;D  BK  ;D