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Thread: AM General 6.5

  1. #1

    Default AM General 6.5

    Long story short, 18 months ago I bought a AM General 6.5 N.A. Of course it shows up the day after I have surgery. Finally got the chance to open this thing up, I had heard all the stories that the military doesn't have a swapout program and when they remove engines they are toast. Took the heads off no sign of valve damage or head cracking, the cups weren't even cracked. The cylinders still had the cross hatching in them and no lip at top of cylinder. Rolled motor over and after having to cut the super rubber they use for gaskets loose finally got oil pan off. The bottom end was just as clean as the top, I could run my finger on the inside of this motor and no black residue. The motor turns over nicely without any binding feeling. No signs of water in crankcase or oil in water. My question is should I totally tear this engine down and have it magnafluxed and rebuild or change out mains and button it back up? I wish my old motor was this clean. MFG date is April 2004, 506 in valley and on flywheel end of block. I was told, but did not hear it, that it was running when removed from humvee, still had fuel in lines, pump and injectors.
    1994 C3500, vin "F". PMD w/heatsync, mech. waste gate, 4" exhaust, cold air intake. 165,000 miles

  2. #2
    Join Date
    Feb 2007
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    Baja California Sur Mexico
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    It sounds like it has recently been rebuilt. Check really well the heads and rear cylinders for cracks, then put it back together. Cracks kill these engines, I'm building a new one from a Brazilian block and new heads, the old block and heads were cracked.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban "F" VIN #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, Positrac 3.73 diff, 17 mpg highway.
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, 21 years.

  3. #3

    Default

    I had the block upside down to inspect lower end and when I turned it back over noticed oil seeping around the rings on #7. The top of the piston didn't appear to have any indications of oil burning. The motor bars over pretty smooth but tight, maybe that cylinder just hadn't seated yet? Do you recommend replacing the rod and main bearings just to be sure and get a look at the crank in case there was bearing damage? I guess I don't trust the "engine replacement program" idea. lol Tomorrow I will post pictures of this engine.
    1994 C3500, vin "F". PMD w/heatsync, mech. waste gate, 4" exhaust, cold air intake. 165,000 miles

  4. #4
    Join Date
    Feb 2007
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    Baja California Sur Mexico
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    Cylinder 7 is the one that cracked in my engine, it and 8 heat up the most. Any signs of bore scoring on 7? I would pull that piston to check for broken rings, and the state of the bearing will tell you if they are new or worn. If you replace the mains, get new bolts, they are stretched like the head bolts.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban "F" VIN #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, Positrac 3.73 diff, 17 mpg highway.
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, 21 years.

  5. #5

    Default

    I was wondering about the main bolts. I didn't get a chance to check things out yesterday. As soon as I can I will get the pictures posted for you to look at. I was told that the engine will run fine with NA mains in it, but since I want to know condition of crank need to pull anyway. What's taking so long is I'm missing half my tools, moving into new shop I built, so half in old shop and half in new. Did get it open, crank/rod journals look great and bearings not bad either. Mains are STD. size with what looks like a date stamped on them as 08 03, rods are STD. also with 12 03 stamped on them. I have included pictures with this post. So far it is looking like a fairly new motor.engine 018.jpgengine 020.jpgengine 024.jpgengine 025.jpgengine 027.jpg
    Last edited by agb1758c; 07-24-2017 at 01:46 PM.
    1994 C3500, vin "F". PMD w/heatsync, mech. waste gate, 4" exhaust, cold air intake. 165,000 miles

  6. #6
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    The bearings look good. There is a red light shining on them that makes it look like the lead has gone in parts and the copper is showing. Check the "corrosion" area around the inlet valve at the top of the picture for a crack and pitting of the head. The bore has honing marks, was it rebored? Pistons stamped oversize?
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban "F" VIN #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, Positrac 3.73 diff, 17 mpg highway.
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, 21 years.

  7. #7

    Default

    Looks like everything will go back in like it came out. The red on the bearings was the reflection from my shop. The uppers will be going back in as .013 undersized, lowers standard, rods standard and the bore and pistons are standard also. No ridge or taper in cylinders. Glad I had these forums to learn from, ended up going through Peninsular Diesel for matching my mains, actually inexpensive being able to get the uppers and lowers 2 different sizes. Never realized that each 6.5 was actually hand fitted for exact clearances. Now back to waiting for parts.
    1994 C3500, vin "F". PMD w/heatsync, mech. waste gate, 4" exhaust, cold air intake. 165,000 miles

  8. #8
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    All looks good, I just put STD bearings in recommended but you were lucky to find the .013 undersize. but mine is a bastard engine.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban "F" VIN #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, Positrac 3.73 diff, 17 mpg highway.
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, 21 years.

  9. #9

    Default

    I think I may have found a problem today. If you look at the picture of the crank rod journal, you can see some slight grooving. After cleaning up the crankshaft, what I thought was oil streaks actually turned out to be real fine grooves. They are deep enough that your fingernail will hang up slightly when run across. Thinking may need to check out the crank in my old motor. I had good oil pressure, replaced balancer before it became a problem and it has about 185k on it. See how the journals measure out for wear.
    1994 C3500, vin "F". PMD w/heatsync, mech. waste gate, 4" exhaust, cold air intake. 165,000 miles

  10. #10
    Join Date
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    That scoring won't cause a problem, but if the other crank is better, you should use it. The engine out and in process is a pain, where are the easy 60's cars, I could have a 4 cylinder ford motor out in 45 minutes.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban "F" VIN #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, Positrac 3.73 diff, 17 mpg highway.
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, 21 years.

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