OK, got this ol' gal running after she sat for 40 years, engine was stuck and did the diesel fuel pickle treatment and got'er broke loose and running.
Block is cracked and seeps a minute amount of water externally but no biggie, the truck is just a toy- for now.
Cylinders #4 and #5 are dead holes, you can hear it in the video
Cylinders #4 and #5 are neighbors, both with exactly 50 psi.... Hmm, sounds like a blown head gasket.
I put cylinder #5 on power stroke and blow air into the plug hole, air comes out cylinder #4 plug hole, Hmmm must be a head gasket or burnt valve.
I pull the head and the valves "look" OK, I havent pulled them yet but I can usually spot an obvious burnt valve pretty easy just by looking.
The head gasket is intact, now Im stumped, but when I put a straight edge on the block (crossways) Ive got a very loose .005 and .006 clearance, head is the same way, this makes about .010 to .012 warpage total, obviously they got the ol' gal hot.
The block and piston tops are very clean so Im guessing the gasket has been replaced by someone that didnt check the warpage of the head surfaces.
Upon further examination I can see carbon on both sides of the head gasket (between cylinders #4 and #5.)
Since I dont know where to look for block and head warpage limits on the 270 Im wondering if someone has a ball-park figure for spec.s?
Shouldnt it be around .001 to .002 between the cylinders when holding a straight edge crossways over the block or cylinder head?
Ill probably throw in a set of rings and have the head milled and maybe do the JB-Weld on the block until I find a better engine, who knows? all fun and good.
(Dont scrap it, JB-Weld'er!)
By the way, I know about the different dome-top and flat-top pistons that the old Jimmys used but does the 248 and 270 use the same head with respect to the dome or flat pistons?
Face of cylinder head Max allowable warpage per ft of length .008 Max surface grind from orig surface to correct warpage .020 Min distance from face to flat surface at combustion chamber .707
from GMC Maint Manual 47-54 Models 100-400 p 221 and 222.
"Nothing astonishes men so much as common sense and plain dealing." - Ralph Waldo Emerson
