The 71 series Detroit 2 stroke diesel is a dry liner engine which is 2 cycle. In other words every time the piston goes down it is a power stroke. 71 means 71 cubic inches per cylinder. They came in 2,3,4,6,V6,V8,V12,V16,V24 types.
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These  Happen to be One of My favorite diesel engines
     These engine were produced since the 1930's with various configurations. 2 valve and 4 valve exhaust. Old style comp ratio of 17:1 New N series 18.5:1New Style turbo 17:1. With sleeve ports of .950 to 1.05. These Dimensions as comparable to a intake valve size and they are cut at a angle which imparts a swirl motion  to the incoming air charge.  DO NOT REUSE LINER INSERT RINGS.

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         The single most cause of engine problems with these is the use of multi-grade engine oil. ie,15W40. These engines were designed to operate on straight weight engine oil ONLY30W or 40W as this engine has cast iron full round pistons the running clearances are tight .002 to .003 piston to liner clearance. Plus the inverted scraper type oil rings(4) have a high tension abutment ring which causes a "slicing action" to the oil. Multi grade oil cannot stand up to this type of abusive use.

           Everyone wanted to "In-Frame" overhaul these engines. The parameters for a In-frame overhaul are very tight. The reason is that these engines require a super charger to supply air thru the internal air box, which means this engine has a top and bottom half. These two parts move over time shift front to back, so when a standard or .001 liner is used it cannot conform to the misaligned block. Within  about 20 to 50 hrs the pistons are wiped out. See Photos right (click for larger). What will happen is the pistons will seize in the liner and actually pull the connecting rod apart. Sometimes it will pull the rod pin bolt (x-head rods) out of the piston pin. This will cause the rod still connected to the crankshaft to whip around inside the block and cause serious and fatal block damage (see photo).
All 71 series blocks need to be bored and honed for oversize liners, PERIOD.
 I could write about these engines for weeks and still not cover all the things about these engines. 
The end result is you cannot just throw these engines together.

I get these engines in that have had the pin caps installed with a socket Instead of the
cap upset tool designed for this. I also get them in where the Liner has been installed
in the block and a automotive type piston ring compressor was used to compress the
rings on the piston and then installed piston from the top of the liner. This breaks
all the cast iron oil rings scrapers and causes the piston to seize.

900 HP 12V-71 TTA