When I left off with the last post I had torn the little Detroit down and discovered 2 different liners installed in the engine.  Both of these liners were of oval port style but the ports were different heights.  One liner was an early small oval port (.703 tall) and the second was a later small oval port (.810 tall) according to my inline 71 manual.  Both pistons were of the non fire ring style and the rings, compression as well as oil control, were very worn.  It is really no wonder this engine didn’t start very well.  At some point this engine must have had an “oopsie” because the #2 rod is a replacement as well as the #2 injector rocker.  The crank has also been turned .010 under on the rods at least (I did not pull a main).  The rod bearings are fairly new and don’t exhibit any wear.


Since I am putting late long port (1.050) N liners in this engine I was concerned with air box to port shrouding.  This engine block S/N is 2A18830 which would make it an earlier engine, somewhere around 1949 or 1950 without looking at a serial number chart.  When measuring the air box opening I was surprised to discover that the casting measured just a touch over 1 inch in height the entire circumference on both holes.   Both holes were round and consistent according to the bore gauge and both were stamped #1 on the deck.  At this point I came into some luck was very fortunate to acquire two new standard OD tall port N liners and 18.7:1 fire ring pistons.  These are factory Detroit Diesel  and were still NIB packed in cosmoline and included the rings, wrist pins and pin retainers.


The counter bores in my block (a low block btw) measure right at .248 with my depth mic and my liner lips measure .250 so no shimming was required.  After checking ring gap and side clearance I assembled everything and staggered per manual, oil the pistons & rings lightly and loaded them into the liners from the bottom.  Everything slid easily into each bore as they should with only a bit of drag.


Once I had the rod caps on and torqued the situation became interesting.  The pistons were above the liner @ TDC and were partially shrouding the bottom radius of the ports @ BDC.  Investigation and question asking time.  The low block is 1/16 inch lower than the high blocks that the tall port N liners and pistons are meant for.  In a low block the liner sits in the C-bore and proud of the deck.  On a high block engine the C-bore is deeper and a spacer ring is used to set liner height.  This was done to eliminate the requirement for a shim type head gasket used on the low block engines.  High block engines used a compression ring and o-rings to seal the deck to head.  According to the depth mic my pistons were .040 above the deck (.038 above liner).  The head gasket when compressed is roughly 1/16 (.063).  Thus,  I have a quench distance of .025 inches  (.063 – .038).


Apprehensive I moved forward and inspected the cylinder head and valves.  Everything was nice a tidy in the head and someone had installed valve seats to recess the valves so they are no more than .006 above the gasket surface of the head.  This is required to run N liners on a 2 valve head to avoid “contact” with the piston.  Finally last night I put the cylinder head back on and broke out my big torque wrench.  190 ft – lb later and I was ready to spin the engine over BY HAND.  Without injectors installed I could turn the engine over without difficulty by the fan and everything cleared in a cold state.


Tonight I should have it buttoned up, oiled and  the fuel system bled and we’ll see if she will come to life.

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