So our families spare car took a crap. The trans wouldn't down shift so I did a trans flush and put a new filter in her. I go to start it up after some charging issues(wouldn't start) and now it's knocking like crazy! It def. sounds like it's comming from the front bank of the eninge. If I put my hand on the front valve cover I can litterally feel it knocking. Put your hand on the rear bank valve cover and it doens't feel nearly as bad. I'm assumming a compression test would tell me exactly what cylinder is having problems. My question to you folks is what is the main thing that would cause engine knock/engine failure on a GM 3.8ltr? I don't know to much about these pushrod engine except how to tear them apart and put them back together....haven't gotten to good at diagnosing internal engine damage. I just wanna see if it's something worth tearing the heads off over for further inspection? Please help a brotha out. Hate to have the other car break down and be stuck with out a spare car to get around in. Thanks in advance!

 

Its definately worth taking the valve cover off at least. The problem is most likely going to be right there staring you in the face once you do so.

 

so you killed the battery and caused the motor to knock from changing the tranny fluid and filter?



damn dude, thats rough.


is that all you touched?

 

I took the valve cover off and found that the Rocker Arms weren't touching the valve cover. I even held it slight above the head so oil wouldn't splatter and started it. Still knocking like crazy. I'm thinking about pulling the front bank head off and taking a look inside the cylinder walls. I'm trying to weigh the pros and cons on this. The car has 130xxx miles on it. The car ran like a top before hand too. Should we just scrap it for the 250 and get another car or should I delve into a shady area of vehicle maintenance. I've pulled motors completely apart but they were all military vehicles. I know I can do it but is it really going to be worth it. Damn I keep repeating myself. It sounds like a bent rod is slapping the cylinder walls.



^nah I didn't touch a thing....tranny wouldn't down shift so I did a filter/gasket on the trans pan. Then the car wouldn't start or charge. So a week later I plug in the battery and it fires right up with this horrible knock! WTF I'm so stumped!

 

well if its not a rocker arm off or loose or something, and it does have oil pressure. than i have no real idea what could have happen man.


but i'll say this. i've never seen a gm trans be fixed by changing the filter and fluid. i think unless you really want to fix this car up, your better off selling it like it is and picking up a cheap car somewhere. it would suck to fix the knock, then have to rebuild the trans. by then you will be into it for like 2k and could have just picked up a car.


do a compression test on it first. that will atleast tell you if a piston is rattling around in there. you can rent them at autozone for free. just pay the deposit.


its still really really weird to have just set for a while then threw a rod.

 

^yeah a compression test is goign to be my next order of bus. After that I may just yank the heads off to take a peak inside the chamber. How much do you think an obd1 gm 3800 would go for if I decided to swap in another motor

 

I would check the balancer on the crank they are notorious for going bad

 

yeah, look for anything else this could be.


how does it run?



can you drop the oil pan in these cars without pulling the motor? on some cars you can, if so. would be easier to check the bottom end out than bulling a head.

 

I think so. If you drop the pan and pull the head off you can unbolt the caps on the rod and pull the rod and piston out together to check it out right alongside the head. Although if you say the knock is coming from the top of the motor, I.E. the cylinder head, then your problem is in the cylinder head, no?

My only guess might be that there were oiling problems since it sat and then got started. Maybe you spun a rod bearing. In fact, now that I think of it, thats a very good possibility.

 

^I guess I'm just better off scrapping it for the 250 then? The car rarely ever gets driven seeing as I don't have a license so it's really no skin off of my nose. I just want to get to the bottom of it. I love to learn soemthing new everyday. I can feel the knock when I put my hand on the front bank VC but not the rear. After feeling around with it running it feels like most of the knocking is comming from either the #2 or #4 piston. Would dropping the oil pan give me easy enough acess to see if I indeed roasted a rod bearing. I'm about to take it apart just to take it apart to see what I find. I don't work so it'll give me something to do. One last question. Say it is a rod bearing on said piston I don't need to take off the other head to get the troubled piston/rod out right?