hey guys, my Blazer has this knocking sound its kind of deep and rapid with the rotation of the crank, I cant figure out what it is! my transmission went out in december so i havent driven it in awhile. I took it to a local shop to get the fluid changed but it did no good, so I asked the mechanic anyway what the sound could be but he said it didnt sound like rod-knock. here is the video, any ideas to what it could be would be appreciated! thanks!

http://www.youtube.com/watch?v=ZxNpSJH2Dlw

 

Sounds like the fan blade hitting something..I was going to say the flywheel bolts hitting the cover, but I see it doesn't have a cover,,still could be a flywheel bolt hitting something tho..
I bought a car once for a real cheap price because someone told the lady it was a rod knocking, it was a flywheel bold hitting the cover which was missing all but one bolt and was hanging down. Sounded just about like yours.

 

I checked all the bolts on the flywheel and they are tight as can be. but the sound is definitely coming from the lower end of the motor. i also dont think a rod knocking could last over the 3,000 miles that ive driven it in total? it would be so nice to have a hoist..

 

Take a piece of rubber hose, about like a garden hose. I use a washing machine filler hose, with the fittings cut off. Put one end up to your ear, move the other end around where you think the noise is coming from, you should be able to pinpoint it.

 

i took a screwdriver and put it on the oil pan to determine if the noise was coming from there, but it wasnt. im almost positive now that its coming from possibly the torque convertor? i checked all the bolts to the flywheel, they were tight. i cant see up on top of the bell housing to check if theres something caught in there either, without taking the transmission out. guess ill have to find out once i replace it soon.

 

sounds like a lifter. funny same exact thing happened to me today, my truck started running like crap then died. i was able to get it started again and limped it into a near by parking lot and shut it off. then tried starting it again and it took forever to get it to start. it sputterd and ran really rough then started a knock in the back of the engine. so i tried to drive it up to our family mechamic which was a couple blocks away and on the way there the knock started going away and the engine started running smoother then ran like new. so your truck sounded exactly like mine did. it was still knocking a little bit when i got there and the mechanic told me its my lifter and the cause of it is probably too light of oil. he said you dont really want anything under 10w30 as cars get older. and the reason for my truck running like crap then running fine is probably a bad fuel pump. so my question is what oil do you have in there? and when you change it use either 10w30 or 15w30 and my mechanic told me you would be surprised at what that will do.

 

Did you inspect the flywheel itself when you checked the bolts? They are known to crack around the bolt holes and it causes a noise that sounds like a rod knock.

 

Now that I think of it.. It could be something in my trany as well. This all happend right after I yanked my buddy out of a ditch. I had to pull pretty hard and on the last tug I think the tranny slipped into nutral because my rpms hit 3500 and I'm pretty sure my tires weren't spinning. That worries me a little.

 

I just got a 1995 blazer last night. I got it knowing it had a knock. It sounds exactily like yours. I drove mine about 45 miles home and the knock was getting louder. As I drove it home, the oil pressure would fluctuate from 0 to 20 psi and when it had 20 psi the knock would fad away. I am thinking that it is the oil pump not pushing oil into the engine. Maybe this has helped at all? I hope it gave you another thing to think about. Please update, I am curious how your findings go.

 

did you check the heat sheild on the catylitic converter? on my 95 mine was coming off and making a rattle knock noise, unforunately my engine was knocking too, if its engine knock try using 40-50 weight oil(cause its ganna go sooner or later unless its fixed or replaced) untill winter time, cause when it gets cold that heavy oil will stress the flexplate teeth when you start it and end up breaking off/grinding down, i to say i know this from exsperience when mine was knocking, you dont know by chance if the high pressure oil line ever blew do you? cause mine did and when it was replaced, wa-la i had spun a bearing when it happen, but check the heat shield on the cat(its like a peice of sheet metal, no REAL purpose, took mine off never had a problem) btw, randy rules! been my favorite sence i 1st discoverd who he was as a kid, im assumming you play guitar too?

im sorry, after watching the video when my computer finially loaded it, that deffinatly does not sound like a heat sheild, sorry bro, and yes a knock can last 3000miles, mine last 2500 with LOTS of red lining and off road abuse before it went(not a good idea to do though)