Bottom end knock when cold

[Tinkering]

I recently bought a 1996 Ranger with about 185,000 miles on it. It ran and shifted great for a couple of weeks. Then the transmission started acting up. It was like the clutch wasn't engaging. Since it gave me no warning and I had noticed an oil leak that appeared to be the front main seal, I assumed the rear main had leaked on the clutch. I decided to replace both seals.

Well, since I was in there, I decided to replace the timing belt, water pump, timing belt tensioner, camshaft seal, clutch, pilot bearing and slave cylinder as well. When I got it back together and cranked it up, it sounded kind of rough. However, it gradually got a bit better and I drove it around the block. By the time I got back home I couldn't hear the knock anymore. I cranked it up this morning and there was a knock coming from the bottom end of the truck. I drove it around the block again and it stopped by the time I made it home. It drives good. It's not missing or shuddering. It just seems to have a bottom end knock when cold.

Any ideas what the cause may be? It definitely wasn't making that sound prior to the work I did on it.

 

[cstarbard]

I don't have an answer for you but I hope someone else does; I have a 1996 2.3 as well and I also developed strange intermittent knock after doing the timing belt. I've been chasing it for months and it sounds very low as well, I hear it most noticeably underneath the motor. Sometimes it's not there, and sometimes it is quite loud

My truck also ran pretty rough right after doing the timing belt as well, but within 30 seconds ran great. Did you disconnect the crank position sensor at any point? I had to for some reason and I thought that the maybe this affected the ecu but I wouldn't know

 

[Tinkering]

Additional info: I just started it up again and the sound was a bit more faint. I noticed that it would go away when I pressed the clutch pedal and would return when I released it (transmission in neutral). Maybe it's in the transmission instead?

 

[tomw]

If the sound changes when the clutch pedal is pressed, it may be the thrust bearing on the crankshaft is involved. When you push the pedal, the throwout bearing is pushed against the clutch fingers by the slave cylinder. The crankshaft must absorb that force, while still rotating. The thrust bearing surface is on the side of one of the main bearings. You may be applying more force to the pedal than before, depending on the pressure plate you chose and installed. I do not know beans about the available pressure plates, but it may be some that are more 'heavy duty' may require more force to disengage.
I would verify that the noise is related to clutch release pressure, i.e., comes and goes with pedal push.
tom

 

[Tinkering]

cstarbard - I did not disconnect the crank position sensor during my repairs.

Tom - Thanks for the input! Others that I have consulted regarding this issue have made the same suggestion. I hesitate to think it is the throw out bearing since the one that is in it now is brand new. Also, it's more a a ticking/tapping and not so much a scrubbing/screeching sound. However, it seems that the slave cylinder/throw out bearing on these Rangers are a bit notorious for failing.

 

[tomw]

A term used in the past was "collapsed piston" which would cause more noise when cold than when hot. The skirt(lower) area of the piston has thrust against one wall(more than the other) when it is on compression stroke, and then slightly more on the other wall on firing stroke. If the skirt is smaller in diameter(collapsed) it may clunk/knock when cold until the piston expands as it heats up and closes the dimension so it is less noticeable.
A test(I think) is to disconnect the spritzer or the sparker, so there is no/less load on the piston. It would not eliminate compression load.
tom

 

[icetherice]

Ahh piston slap. I've been wondering if this is the problem with my engine. It sounds pretty loud when it's cold so I just let it warm up before really getting on it.

 

[tomw]

I think it develops when an engine is started, and then driven as if it was all warmed up right now. IOW, no warm-up time given before being thrashed. Maybe not.
tom