I'm back again. I mentioned this in my last thread, but it would appear that my Duster's reasonably new slant six has decided to fry the #5 wrist pin, or so I think. The engine only knocks intermittently, and if you take out the #5 plug it stops. Also of note is the 40psi of oil pressure at low idle while warm. Are these engines known for wrist pin failures, or am I just extremely unlucky? Previous engine was pulled due to a bad wrist pin on #3. The last engine had about 170k miles on it and had clearly been abused, so I expected something to let go, but this one is practically new with very good oil pressure and factory compression. It just doesn't make any sense.

I'm not aware of any particular wrist pin problems. However I have seen many slants with a problem on number 5 rod bearing. When I first started "playing" with slants, I lost a couple of #5 bearings. A friend of mine just lost #5 bearing earlier this year.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Rod bearing is a far more likely failure than wrist pin. I wouldn't assume the rod bearings are good just because you have good oil pressure; the rod bearings are the very last item in the oil flow path, so 1 of 6 being loose might not have a measurable effect on the upstream pressure.

The good news? #5 is toward the back, so a very careful and enterprising individual might be able to remove the oil pan and replace the bearing without pulling the engine.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

How would I go about that? the pan has a very large crossmember right in front of the "hump", and there's engine mounts and frame to either side. This is a 1975 car, so that probably affects what I can and can't do with the engine in the car.

You often have to unbolt the motor mounts, drop the center link, and raise the engine a bit to pull the oil plan. That is required on my '66, and I suspect the procedure on later A-bodies is similar - somewhat awkward to pull the pan without pulling the engine, but possible.

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Matt Cramer
1966 Dodge Dart turbo / EFI project

If you want to do the job right, pull the engine and do a full disassembly. Measure everything, figure out what if any machine work needs to be done, and build it back up in a considered manner with plenty of advice from this board.

If you're short on money, or time, or space to have a disassembled engine spread out across your garage, and you just want the car back on the road in a manner that will probably work, then follow my stupid advice.
1. Unbolt motor mounts from K-member, jack up the engine, set engine back down with blocks of wood under the mounts to give you clearance.
2. Remove all oil pan bolts and wiggle oil pan out. If necessary for clearance, drop the center link. You probably just need to disconnect from the pitman arm and idler arm.
3. Rotate engine by hand until #5 rod journal is pointing straight down. Scribe or center punch some marks on the bottom of the rod cap to tell you which direction it goes back on.
4. Unbolt #5 rod cap nuts. Don't lose them. It's probably a good practice to keep track of which one goes on which side, but I doubt it really matters.
5. Remove rod cap. If rod cap can't be pulled free, tap it on both sides with a rubber/plastic hammer. (Don't pry it loose or hit it with a steel anything.)
6. Remove both halves of the rod bearing. You'll probably have to push up on the rod and get it clear of the journal. Don't damage the rod, rod bolts, or journal! Try not to push the rod bolts out of the rod; if they slide out, you'll need to make sure they are properly seated before you torque the cap back down.
7. Examine the rod bearing! If the babbit is just wiped, you're probably good to slap a new one in there. If it spun in the rod or is heavily shredded, your rod is probably damaged and you'll need to further disassemble the engine to replace it.
8. Examine the journal! Light circumferential marks are okay as long as the surface is smooth to the touch. Gouging or scoring means your crankshaft is hosed and needs to be reground.
9. Examine the connecting rod and cap! If the inner surface is mangled at all, or if you see heat checking, see above about your rod being damaged. If the notch for the bearing locking tab is gouged out at all (in which case the bearing halves were probably not perfectly lined up with the rod and cap when disassembled) then you're also pretty much out of luck.
10. Install new upper bearing, making sure to line up the upper oiling hole with the hole in the side of the rod, and the locking tab is in the notch on the side. You may need to rotate the crank a bit to give you space to work. Coat the inner surface with cheap assembly lube from the parts store.
11. Pull the rod with upper bearing back down over the rod journal, making sure not to (A) dislodge the bearing or (B) gouge the crank journal surface with the rod bolts.
12. Install new lower bearing in rod cap, with the locking tab in the notch. Coat the inside with assembly lube.
13. Install rod cap, making sure it's oriented the same direction it came off. If you forgot to make marks earlier, both bearing locking tabs should end up on the same side.
14. Install nuts and torque to 45 ft-lbs (for forged crank). I generally avoid using loc-tite on the inside of an engine*.
15. Spin crank by hand to make sure everything rotates smoothly. If you can no longer spin the crank, you probably put the rod cap on backwards.
16. Reassembly is the reverse of removal. Don't forget to refill your oil



*Unless, for example, the bearing spun slightly in the rod and you just need to get home for Christmas, or just want to make a few more laps at the Lemons race on Sunday afternoon, or you are that broke and desperate and willing to drive the car like a little old lady henceforth just to get to work. In which case, apply a very thin layer of red loctite to the OUTSIDE of the new bearing shell before installation, keeping in mind that any excess pressed out when you tighten the rod bolts is going into your crankcase. You can also sand the mating surface of the rod cap in a vague attempt to increase clamping force on the bearing shell and discourage future spun bearings.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Very Lemony Frank. Me likes it!

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Rob

I’m Mater
The Kentucky Poser

I already have one disassembled slant six in the garage, the original engine that came with the car. It was taken out by the aforementioned #3 wrist pin. I'm just hoping this engine lasts long enough that I can get my other car running, and then when I get a few days off I can replace the #5 and #6 rod bearings (I'm not taking any chances here). Frankly I'm getting a little tired of doing major engine work on this thing, if V8s weren't so expensive I'd have bought one already.

As an update, the #6 rod has joined in on the fun and is happily beating away at the crank. While I'd love to stop driving the car, I can't. It's got 15-40 Delo for oil and I'm not sure what else can be done to prolong its suffering.