Head bolt torque, take a good look at this - Steel Soldiers::Military Vehicles Supersite

70deuce · 06-04-2008, 21:43

Look what ONE improperly torqued head bolt can do. One head bolt on cylinder #6 on my Cummins 250 (M81

was very loose. I found this out by first a tell tale sign of moisture dripping out of the engine breather tube, then oil in the water and water in the oil. Measured the temp on each exhaust runner with an infra-red thermometer and sure enough #6 was 120 degress cooler than the others. Come to find out it was a dead cylinder. The one loose head bolt has allowed water and oil to mix with each other. When that head was removed I had been sitting on the fender with both feet pushing against a ¾” drive socket wrench to get the head bolts loose. The culprit bolt was loose enough to get it to turn with hand pressure. Does not appear to be any damage to the engine. This truck has 53,000 miles on an original engine. Must not have been torqued correctly at assembly. A metal straight edge check for a warped head came up negative. The cylinder looks good also. #6 cylinder is on the left in the pics. Oil pressure never dropped. Check out the combustion area on the head and the completely gummed up injector, You can see a nice burn pattern on its neighbor #5 though it looks like one orifice on that injector may be plugged. A screw driver points to the loose head bolt opening. A puddle of raw diesel was on top of #6 piston. Also check out the pic of the culprit bolt and properly torqued bolt. Note the loose one was oil wet. All the rest of the bolts on #6 were completely dry. The weird part was that the M818 this engine is in ran pretty good despite running on 5 cylinders. Did red (52 mph) line fine but it sure didn’t like the 38 foot van trailer behind it on hills. It looks like a new head gasket and the proper torque may give me back the 855 CI I’m supposed to have.

Gamagoat1 · 06-04-2008, 22:44

You can see by the black track, on the head gasket by the loose bolt, where the compression was leaking past the fire ring and into the bolt cavity. Along with water, fuel and oil.
The dark area going across the fire ring, water passage left of the loose bolt is where the water was coming from, at low compression (intake) it would let water into the cylinder area and at high compression (power) it would blow into the water passage. Bet ya had bubbles in the surge tank when running.

Sure glad you found it before it hurt ya.

Crash_AF · 06-05-2008, 02:10

Glad you figured it out. Makes me want to hit all of my head bolts with a torque wrench.

Later,
Joe

WillWagner · 06-05-2008, 08:22

That is a late sty;e head gasket...thet were released in around 1993. Someone has been into it. Be extremely carful when you clean the block. The liner has a fire ring, it is the only thing that seals the compression. Use a wire brush and brake clean. DO NOT use an orbital buffer, if it hits the fire ring, you just turned a very easy job into a bit more time consuming one.

70deuce · 06-05-2008, 20:48

Thanks a bunch for the heads up on that one. Won't be using anything mechanical to clean that area up. Will be ordering parts soon and will post more pic on reassembly.

Phil

70deuce · 06-05-2008, 20:48

Thanks a bunch for the heads up on that one. Won't be using anything mechanical to clean that area up. Will be ordering parts soon and will post more pic on reassembly.

Phil