Tacoma: intermittent engine knock/rattle

[sdold]

Hi Folks! This is my first post here. I really like the forum, I know I'm going to be wasting a lot of time at work reading this site :-)

I have a 1999 Tacoma 4WD, 4-cyl, 2.7 with 160,000 miles that's got me worried. This might be unrelated, but at about 140K miles, it started making a vague intermittent knocking sound like a hydraulic lifter that wasn't staying full. As a fun experiment, I decided to let it go and never have it looked at. This was about 9 months ago, and the problem seemed to have gone away.

Until today

Today, while driving about 25 mph, the engine suddenly started making loud rattling/knocking sounds, and after a few seconds, the noise went away and the engine ran fine. Later in the day I parked for awhile and then started it up, and it did it again. This time I threw the hood open in time to take a good listen. It sounded like something inside the crankcase, around the middle of the engine, on the left (driver's) side, like something hard hitting the side of the case with each revolution of the crankshaft. After a half minute or so it went away and has been running OK for the rest of today, about another 50 miles.

Oil level was fine, temp was fine. I could make it come/go with engine speed changes while parked (working the throttle cable).

Is there anything that could hit the side (or an internal part) of the case? Like crankshaft counterweights or anything similar? I've never heard an engine make this sound without self-destructing shortly afterward. But it's running fine...for now.

Steve

[yoder-bug]

sounds like u have spun a bearing. my toyota did that too for about 25 k and the one day it just all of a sudden it just went i knew what is was from past experiences ( kinda got a patern here huh). it all depends tho cause in my opnion a rattle and a knock are 2 totally different things but from what u r saying i gather its a knock more than anything. my advice pull th oil pan and see how the conecting rds feel if they are sloppy or if they are firm if they are firm well theres somethig else wrong but kinda sounds like a bearing to me

[Bill C.]

Here's something you may consider, I hope it's the same for you.

My '93 has ~182k miles and it recently did the same thing. It really sounded horrible. I had it towed to a friends shop and put it on a lift. The sound was loud, but it was very hard to pin down to a location(WTF??). It would come and go, and finally after about 3 hours of fiddling with it, I noticed alot of rust around a bolt head that fastened the p/s pump or alternator to the truck. Got a flashlight and saw that the bolt was loose. After tightening it up, we started the truck and the noise was gone!! All it was, was a brace hitting against the boss on the block.

[sdold]

Thanks, guys, I'll look into those two possibilities. Yonder Bug, I've had that happen to me in a Triumph TR-7 (big surprise there, huh?) and that sound was more dull than this is, it sounds like it's either right at the surface of the case, or like Bill says, on the outside. I'll check the accessories tomorrow.