Rod Knock?

[arco777]

I'm looking at picking up a 94 Explorer 4dr tomorrow. 172K miles. It's nice inside and out, just had the tranny rebuilt ($1700 receipt), some options. Factory alloy rims and a great set of AT tires. Very good paint, small dent in tailgate and front bumper, no other damage. I talked the guy down to $425. The catch? He says it's got a knock.

He started it up for a few seconds and it rattled a bit. Not loud but from the Youtube vids I've been watching it sounds like it could be a rod knock. I only heard for a few seconds and until I look at it again tomorrow (hopefully drive it home) I don't know what to make of it. Oil seems good, should be changed soon but no bad smells or looks. He says no CEL.

Questions! Am I looking at a new motor, or possibly just something like lifters? Any chance it could be a seriously sooty MAF, cleaning of which was the miracle cure for my current 94 X? Any other ways of telling what's up with this motor before forking over the cash? Can I drive it home or should/could I tow it home with my Explorer? And finally, is this car a good deal?

EDIT: If as he says there was never a CEL event, why not? Shouldn't the knock sensor trigger one? Could this be an issue of fuel injection timing instead of a bearing going out?

 

[Masterd]

If you could get a sound clip of what youre hearing that would be the best way for us to tell you what the sound is.

 

[arco777]

Re:

I don't think I'll have time or a way to... as I remember it was more like a chittering noise than a knocking, similar to a serpentine belt's noises. Can't get any more specific than that, my short term memory is bad too. I guess I'm asking what is common on these cars, shouldn't be a bearing yet at only 172K miles?

 

[Masterd]

If it doesnt sound like a hammer hitting the engine block...then its likely not a rod knock.

 

[ricco750]

If it doesnt sound like a hammer hitting the engine block...then its likely not a rod knock.

Ditto. A rod knock will really get your attention, as in "bam, bam, bam" per piston stroke. No "chittering" here. Try a can of Engine Restore or comparable additive. This stuff totally silenced my occasional lifter noise.

 

[arco777]

Re:

Thanks, I will keep that in mind when I go pick it up. There was a bit of steam coming off the motor too, I'm thinking head gasket or cracked head. No big deal if the rest of the motor's worth keeping.

 

[Masterd]

The heads on the ohv 4.0's tend to crack if overheated...

 

[Joes4x4Ranger]

For only paying $450 for it as good as it looks it's way worth putting in a reman. engine. They run around 2k, you'd have for all intents and purposes a "new" power train.

 

[arco777]

Cool, thanks! I should be able to drive it home even if there's a rod knock, right? Not thinking my Explorer or the cops will like me towing it.

 

[Masterd]

Driving it if it has a rod knock is only going to make it worse, and you run the risk of throwing a rod.

 

[Willard]

It's likely lifter tap, and is common. Mine has lifter tap until warmed up. It's had it for probably 30,000 miles. Just annoying, that's all. If it runs fine and the noise isn't too loud, I wouldn't worry about it.

 

[arco777]

Re:

I drove it home. Appears to be a rod knock, it's definitely a clattering noise. Lots of exhaust smoke, runs hot, blows smoke through the heater vents when the heater's on.

 

[ricco750]

I drove it home. Appears to be a rod knock, it's definitely a clattering noise. Lots of exhaust smoke, runs hot, blows smoke through the heater vents when the heater's on.

You have more problems than a rod knock.

 

[Masterd]

Its gotta have a cracked head..at least....

 

[arco777]

Re:;

Its gotta have a cracked head..at least....

My current driver X arrived home when I bought it in a cloud of steam, which was a cracked head. This new X arrived in a less dense cloud of smoke. Motor is probably done. Wish it was just the head.

 

[Masterd]

So are you going to drop in a new motor, or sell it off again?

 

[arco777]

Re:

Most likely I'll keep it around, fix it up, put it in storage eventually and go for a new motor when I have spare cash for one. I don't really want to sell it, it looks so good next to my 2-door. Thanks everyone for the help.

 

[Masterd]

I would get some oil pressure numbers from it....and also do a compression test.

The compression test will pinpoint your cracked head / blown head gasket.

 

[seth247]

yeah compression test is the easiest way to check the heads. and cheap too just need the guage.

 

[arco777]

Re:

The motor's dripping a bit of oil on my driveway and there's oily crap on the underside of the transmission... air filter was caked in sludge and needed to be cleaned badly, airbox was sludged too... ack. I don't think this particular motor's worth fixing, I'd sooner grab a lower mileage one out of an X that's being parted out (there are a few locally).

I ended up stealing the nice alloy rims and AT tires for my 2 door and putting the steelwheels with snow tires on the new 4 door. Also took the bugflector, spare tire, K&N filter, and floor mats because the 2 door didn't have them.

New 4 door goes up for sale tonight on a local site. If it sells the money goes into my 2 door in the form of interior detailing, intake, and other little things. If it doesn't sell, I'll keep it and store it, but otherwise I am making a nice profit considering the goodies I got for my 2 door and what I'm selling it for.

Thanks for all the help, guys! I learned a lot. :exp:

EDIT: Compression test... good idea but on my 2 door it was easier just to see which side the jet of steam was coming out of, or look for the clean side of the firewall.