OK, I'm going to put this one on the board...
In the process of de-griping our 155Kmi '94 (4.0, 4wd, AW4), one of our gripes was a scraping noise in the engine/transmission interface. Basically, there's this metallic "chatter" noise at the frequency of crankshaft rotation that manifests itself mostly when idling in park. It's usually minor, and worse if it's facing downhill. If the A/C compressor is running, the noise is really objectionable, and sounds like it's ready to do some damage.
I originally suspected the much-discussed loose torque converter bolt problem in the flexplate, but I pulled the inspection cover and checked, and all 4 bolts are tight. There is no evidence of cracking near the crankshaft flange either. I can't check the crank/flexplate bolts without removing the engine or trans of course, but I can't detect any play in the plate that might indicate a problem there.
Curiously, the dust cover shows old scratches in an arc at the radius of the TC bolts, indicating that at some point in the past, a bolt came out and rattled around in there. The scratches were dirty, that's why I know they're old. My guess is that the flexplate was replaced at that time (it's quite clean, no marks).
I've scoped the noise right at the starter/belhousing point. Put a rebuilt starter in because the bendix looked a little worn, and the bushing at the tip was getting bad (maybe this is why). This helped, but only slightly. With the A/C on, it's still a problem. And the weather is warming up...
I'm stuck now. I don't believe that the flexplate is a problem, but I don't know for sure. Stuff I suspect:
* Crankshaft flange slighty bent from prior loose bolt damage such that it's runout is slightly out of spec, so that the flexplate doesn't rotate in a true plane. I would think this would destroy the tourque converter though.
* From what I've seen, one of the main bearings has a "thrust surface" to keep the crankshaft in position. It could be that this bearing is worn to the point that the crankshaft "floats" forward when the TC isn't loaded, or when the A/C is on and the belt is heavily loaded.
* Starter did not have, nor new unit come with any kind of gasket. Not required anyway, there's no need for a seal. However, I'm thinking about fabbing one to go between the starter and the bellhousing to pick up .010" or so of clearance. This would really just be a workaround for the real problem.
I'm thinking about going ahead and trying a starter shim gasket for now. I'm also thinking about pulling the engine and doing several things (bearing check, new seals, can't get to the oil filter flange bolt for new rings, needs coolant drain anyway, I could see the bolts on the flexplate, etc). I'd prefer to wait until fall for this though, and I'm fantasizing with the idea of bulding up a stroker to go it in anyway, which will take a few months.
Any thoughts? Thanks...
In the process of de-griping our 155Kmi '94 (4.0, 4wd, AW4), one of our gripes was a scraping noise in the engine/transmission interface. Basically, there's this metallic "chatter" noise at the frequency of crankshaft rotation that manifests itself mostly when idling in park. It's usually minor, and worse if it's facing downhill. If the A/C compressor is running, the noise is really objectionable, and sounds like it's ready to do some damage.
I originally suspected the much-discussed loose torque converter bolt problem in the flexplate, but I pulled the inspection cover and checked, and all 4 bolts are tight. There is no evidence of cracking near the crankshaft flange either. I can't check the crank/flexplate bolts without removing the engine or trans of course, but I can't detect any play in the plate that might indicate a problem there.
Curiously, the dust cover shows old scratches in an arc at the radius of the TC bolts, indicating that at some point in the past, a bolt came out and rattled around in there. The scratches were dirty, that's why I know they're old. My guess is that the flexplate was replaced at that time (it's quite clean, no marks).
I've scoped the noise right at the starter/belhousing point. Put a rebuilt starter in because the bendix looked a little worn, and the bushing at the tip was getting bad (maybe this is why). This helped, but only slightly. With the A/C on, it's still a problem. And the weather is warming up...
I'm stuck now. I don't believe that the flexplate is a problem, but I don't know for sure. Stuff I suspect:
* Crankshaft flange slighty bent from prior loose bolt damage such that it's runout is slightly out of spec, so that the flexplate doesn't rotate in a true plane. I would think this would destroy the tourque converter though.
* From what I've seen, one of the main bearings has a "thrust surface" to keep the crankshaft in position. It could be that this bearing is worn to the point that the crankshaft "floats" forward when the TC isn't loaded, or when the A/C is on and the belt is heavily loaded.
* Starter did not have, nor new unit come with any kind of gasket. Not required anyway, there's no need for a seal. However, I'm thinking about fabbing one to go between the starter and the bellhousing to pick up .010" or so of clearance. This would really just be a workaround for the real problem.
I'm thinking about going ahead and trying a starter shim gasket for now. I'm also thinking about pulling the engine and doing several things (bearing check, new seals, can't get to the oil filter flange bolt for new rings, needs coolant drain anyway, I could see the bolts on the flexplate, etc). I'd prefer to wait until fall for this though, and I'm fantasizing with the idea of bulding up a stroker to go it in anyway, which will take a few months.
Any thoughts? Thanks...