I believe cylinder #7 in my 85' 6.9l has a hole in the piston. I will be comfirming this today for sure. It has 0 pounds of compression in this cylinder and a large ammount of blowby from the engine. I do not know of any mechanical failures in the engine "loud Bangs" that could have caused this? So why would cyl. no. 7 burn a hole in the piston? What are your thoughts on this?

 

Your prolly going to have to pull the head off, in order to get a picture of what your dealing with.

Are you the same guy that posted this prob earlier?

If so, did you pull the valve cover and turn the engine by hand, to confirm valve operation?

 

This could be part of the problem....... but untill you get it open were just guessing.

When the CDR valve is not properly serviced, engine oil enters the air intake and is drawn into the engine. The diesel engine will burn this oil as fuel, however, it is heavier and thicker than diesel fuel and, having greater BTU output, causes excessive heat in the cylinder. Due to the intake manifold design, most of the oil will migrate to #7 and #8 cylinders; the last two cylinders in the rear by the firewall. The increased temperature here will cause the cylinder head to lift off the gasket and allow water or oil to leak out the back of the cylinder head where it meets the block.

 

I pulled the valve cover today and all valve train is there and working. Then I pulled the GP and rotated the engine until both valves were closed. Shot compressed air in the GP hole and the air came out the oil filler. I am sure there is a hole burned in the piston now. So oil from the CDR system is most likely the reason why the piston burned down?? I checked the serial Number on the block and the number is really low 6.9D U2U 047914* With a number this low it is a block known for cracking around the engine heater? Is this engine worth fixing?? Is this even the original engine? The truck is a mid year 1985. I would think the serial number would be higher than 47,914 for an 85' motor.

 

Mid 85 was when the block was changed by the block heater.

Look at the block casting numbers.

Block casting........INTERNATIONAL HARVESTER DIESEL ENGINES
6.9L and 7.3L Core Identification

6.9L Old Style Block

Block Casting Number:


On left side of block (beneath oil cooler) 1805440C1
Note: Some 440 blocks are truly new style and must be visually inspected by raised donut around the block heater, frost plug (right rear). Old style below serial number 173828.
Visual Identification: *No counter bored area for block heater
*No defined area on side of block for dip stick
*Thickness of cast iron around block heater 3/8" (.375")
Head Bolts: *7/16, 12 point socket is used to torque head bolts
*Block tapped with 7/16-14 for head bolts

6.9L New Style Block

Block Casting Number: 1807996C1 Note: Some new style blocks have casting
number 440. Above serial number 173828.
Visual Identification: *Has counterbored area for block heater
*Very defined relief area cast in side of block for dip stick tube.
*Thickness of cast iron around block heater 15/32" (.470")
*Latest style (not all new style 6.9) has ribs around head bolts, rear two on left side go from head gasket surface to pan rail - same as 7.3
Head Bolts: *Same as old style 6.9

 

You might have collapsed or busted rings in that cylinder.

A hole in a piston can be caused by dirty injector shooting a stream of fuel at the piston. More common would be foreign material getting into the cylinder. I have seen a valve get hit by a stream of fuel from a partially plugged injector and it took a slice out of the valve that looked like it had been cut with a laser cutter.

 

It would be hard for a fuel stream from the injector to hit the piston on an IDI engine.
I guess it could if the precup was broken, but if that were the case the precup pieces are probably what broke the piston.

There is very little room between the head and the piston top at TDC in an IDI.

 

Yep, you're right Dave. I forget about the head design in these engines. Worn out brains at times.