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Problem solved, the hard and Expensive way..


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Part of  my  last years'  demise  of  mental health,   was  sorting out the problems   I  was  blessed  with  when  I  purchased  an ag tractor with  a  903 vt   Cummins  engine.

Some of you may remember my posts  about  it   scuffing  cylinders..  and  the  ensuing   in-frame  rebuilds.     I was  getting about    200-300  hours   max   service  on a  rebuild.   Not good.

I've  hunted down   mechanics  from coast to coast,  to  pick their brains.    At least  the  ones  that  were still alive!     

I COULD NOT  FIND  ONE   that   ever  heard of  a  constant  problem of  scuffed  pistons   Shoot,  it was a task to just get them  to understand it  was NOT  an injector:  the  tops  plus the ring-lands  were  absolutely perfect.


So,  last year,  I snagged  a spare engine  out of  retirement,  and built a  stand  to  do an  out of frame  rebuild.

My scuffing  was  confined to the  back  1 or 2  pistons,   either bank  was  prone.


So..   here we go! 

Typical   running conditions  just prior to  'melt down'... were    

Et;   1000-1100.

coolant   varied  between   165 and   185,   but  was   quite  'active'..   varying  up and down  between the  two.   I  figured it was  the  'cummins  way'..  quite common   even in  our  pickups.

So  took the bare block into the  shop to be  boiled,  measured,   and  checked for  square, flat,  and  any  corrosion issues.   

Meanwhile,   I went  overboard and  sent the brand new pistons  off to be  coated,   tops and  skirts.      I  was swinging at the fence  here to  eliminate  excess heat  traversing  down the skirt.    Cost;   50 bucks a  piston.       *pistons  over  5 inches  get  a   surcharge.... mine are  5.5 inch     Fantastic  turn-around...   less than a week  to   St. Louis  Mo. 


Even though the  injectors  were  fairly  new,   I  swapped them out for  fresh ones.   These are  PT  style injectors,   they   have a  3rd  pushrod  off the camshaft that  'fires'  them.

I thought I  had an  'aha'  moment when I  noticed    some  oil pooled in the  intake manifold.... possible  turbo  seal  puking  too much oil into the engine -  more heat??     That thought  was  short lived,   the seals  apparently melted down  when the  last engine  failure  caused me to  shut down without  proper cooling period.

New  turbo  installed.

this is  where  things  started to  fall in place!  

WATER PUMP!    I  never removed the old  pump from  engine #1 (original  engine w/problems)    I just    rebuilt the  pump  from  the  spare engine..   Nice kit  from   Interstate-Mcbee.     rebuilt pumps  are non existent,  so  doing it myself  is  the only option.       I even found  the depth seating tool for the  seal on ebay..   took about  an hour of  press work,  but  I got what I needed.

This application   swings a   huge cooling  fan,   almost  33 inches  in diameter,  and  weighs  almost  50 lbs.  JUST THE FAN.   Imagine the  HP  to swing it!    No wonder  cummins   runs  3  robust   v-belts  to drive it.       there is   the  crank pulley,   fan hub,  and  finally the WP  is driven on the slack side of the  rotation..

the wp is very very  similar to our  trucks,   they  are  inside the  block.     My flow is  divided  so half the flow is  directed through the  oil cooler,  then  that flow is  sent to the rear of the block to  take care of the  right bank.   The other half of flow  has  a cross over to take care of the left bank.  ( I checked for  blockages).    Outlet is  taken care of with  2 separate  thermostats,   identical  designs of  what is in our pickups.  (the old engine  had only 1 sensor,  off of  1  bank)

This time,  I  loaded up the  injection pump,  and had it   checked out.     This PT system is   basically a  very simple   low pressure pump...  which supplies  between 100 and  approximately  280 lbs  of  fuel to the  'rails'  internal the heads.    100+/-   would be idle speed,     280  is   full fuel. 

I never made it home from the shop!  I got a call from the pump man  saying  'I think I found your problem'...  hmmmm

turns out  PO  had the pump turned up to  460 HP.     I still had problems  with that however!     still no  tell tale signs  of  piston top degradation,  and/or  huge  exhaust  temps!!

So,  since this  engine  series  didn't    have multiple  piston, cam or injector  combinations  to achieve   various  HP levels, (which is typical of the 855 series)   I was skeptical.. 

Don't forget,  these  HP levels  are  CONTINUOUS  duty ratings..  not   5 second  'bursts'  sitting on a dynamometer

We went ahead and  set it  for   360,  which is  smack in the middle for  the range it was   TIMED for.  I't's a fairly intense  procedure to change the  timing on  these, flywheel housing, flywheel,  rear cover comes off,   cam gear comes off,   new offset key is  installed..  you better have ate your Wheaties  that morning! That is almost 500 lbs of  iron to be  R and R'd!!  


Remember that  rebuilt kit for the WP??   it  came   with a new  cast iron impellor..  

This is  where  it all comes  to the final   'gosh dang'...  moment!

Last  hour of   final assembly,  I needed  a  couple bolts  to put  some bracket  on the  WP.  So I went to the  original engine  and  'robbed'  some  from it.     So I figured to  totally remove the  wp  completely  just for giggles..       The  PLASTIC  impellor  was  chewed down..   

Yah,  I was getting just enough  flow to  keep  some water  flowing,  but not near enough to   circulate it  throughout the entire block.      the  really hot water never  made it  past the  sensor  to  signal  'hey dummy,  you are overheating'...  It just stayed    back there  and  swelled up my pistons.

which  explains  the extreme  swings  in temp.

Now,  I have 2  temp gauges,  one for each head.   and  running full tilt,  I see  2 degrees max variance between the 2,  and  rock solid  185-190.      


I've already  surpassed  any previous  hours  on  rebuilds...by a factor of  2 so far!     

As  far as  the  'de tuning'..   I see  zero  differences  in the setup.   the workload (size of  plow)    I am putting to the tractor apparently  never needed  the  extra fuel,  so   the  360 level is   adequate.      I'd like to tap into the   fuel line to the heads  to monitor pressure,  just to see where I'm at  in various   conditions..      

One  thing I am seeing is  a possible   slight  increase in   exhaust temp...  probably due to  the coated pistons  which reflect more heat up, rather than  letting it  soak into the skirts/rings/ cylinder walls..   25 degrees  is   kinda a rough  guess..  but still well  within  my  'safe zone'. 

Point of this whole post is,  

Check the simple stuff...  a  200 dollar  wp   ended up curing a  problem that  cost me  almost  $15k  spread out over  5 years. 

ONWARD to the next 'project'!!



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