D24T Ramblings from Badge988

The first non-turbo motors had wall wear problems like no ones business. This was because first they had no real oil cooling and second not enough oil reached the walls due to the tight clearances of the rod and main bearings. Little throw off means little oil and lots of wear. The turbo motors had piston cooling jets located on the left side of the engine that went directly to the oil gallery and they had a sandwich type oil/water cooler that knocked temps down by 40 degrees C.

The second issue was the fact the non turbo motor burned dirty meaning lots of smoke per given mile, this loaded the heck out of the rings and made them stick and the hard carbon was a good abrasive to the walls so it was like running a 1200 grit paper lightly over the walls at all times. No piston cooling to speak of in a diesel makes pistons expand tighter at high temps and this put more pressure against the walls.

The other issue was with the casting itself. The non turbo motors were made of a low nickel iron that was hard and brittle, easily machined but was a poor running surface, the turbo blocks were a high nickel iron that wore better, was harder to machine and heavier by almost 25 pounds. Thread retention was better with the turbo blocks but with the machining issues the threads were thinner and more prone to breaking. A give and take with this but I have only seen 2 issues with this so far.

The other issues were with timing belts and heads themselves. The lower crank pulley is held with a very stout 15MM fine thread bolt that is torqued to a real value of 425 ft/lbs and this is all that holds the lower timing gear to the crank. The key is only to locate the timing sprocket and provides no driving force through the assembly. Timing belts need to be changed at the proper intervals at the very least, 50k miles is a better calender to follow with these. Many times people will take the car for a timing belt and the mechanic will not tighten the lower bolt to the 425 pounds because they dont have the torque wrench available or are just to damn lazy and use a breaker bar until it feels good. Either way you will end up with a slipped timing lower gear with a broken off key and a mashed valve or busted camshaft. I have seen both and Im holding onto a trashed block that has a good crank, this one lost the lower key to a slip and it busted the cam up through the top cover.

Heads... Early models used a 10MM head bolt that was a non torque to yield or TTY bolt, later blocks and all turbo used 11MM TTY bolts that needed to be retorqued in order to maintain good gasket compression for the head. The bolt was torqued to the yield point but retained enough "spring" to follow the head during expansion and would follow it down when cooling to maintain pressure on the gasket to avert surface shear. The heads themselves had no real issues other than surface cracking between valve seat inserts and warping due to mis-torqued bolts. Many an engine has been sent to the grave because some nit-wit mechanic said "your head has all these cracks and its bad. A new one is xxx thousands of dollars" and the owner would say no and junk it. The crack is superficial and extends to a maximum of 0.5 to 1MM deep and has almost 6 more millimeters to go before it hits water. I have yet to see one hit the water table and normally I dress the cracks to a 45 degree rounded radius and blend it down to the level of the valve seats.