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engind knock question

J

jeepintexas

NAXJA Forum User
Location
Texas
hey guys, is there anyway i can diagnose an engine knock? my boss believes that it is a pushrod. i was looking around and found them for $3 each.

he says its as easy as taking off the valve cover and moving the rocker arms over. is that really all there is to it? these motors are 12 or 18 valved? should i go ahead and replace all the pushrods or just the one thats bent?
 
2 Valves per cylinder: 12v
Do all of them at once.
Mine knocks from the top end, and Ive put close to 800 miles on it since we bought it. If it makes it through winter Im gonna be replacing pushrods and lifters and pry the cam.
 
haha sorry for the crappy spelling an d punctuation. its kindj hard to proofread your posts when youre doing it from your mobile. sounds like its a serious situation. if my pushrods are knocking is it something dire? im running valveoline dino 10-30 and one quart of lucas right now. the knock doesnt sound very severe, but id like to get it fixed
 
Sounds more like piston slap. These are notorious motors for that. Its normal. Unless you spun the motor up hard I find it hard to believe you have a bent pushrod. Take the valvecover off and pull all 12 pushrods, clean them up, and roll each one on a smooth flat surface to check for straightness. I also blow compressed air through them to make sure there's no blockage. I would at least test that first but its more than likely piston slap.
 
Last edited:
mrtosh said:
Sounds more like piston slap. These are notorious motors for that. Its normal. Unless you spun the motor up hard I find it hard to believe you have a bent pushrod. Take the valvecover off and pull all 12 pushrods, clean them up, and roll each one on a smooth flat surface to check for straightness. I also blow compressed air through them to make sure there's no blockage. I would at least test that first but its more than likely piston slap.
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x2, I usually use the glass top on my desk or the one on the coffee table (when the Wife isn't looking) for rolling pushrods.
 
is chromoly the way to go on pushrods? a buddy of mine who likes to build engines told me this is the way to go. i wanted to verify it with the experts.
 
hardened pushrods are the way to go in high performance high revving motors, preferably w/hardened springs. It's good to have some "give" so if you did happen to overrev the motor it would just bend the pushrod and not damage the valves or springs.
 
jeepintexas said:
is chromoly the way to go on pushrods? a buddy of mine who likes to build engines told me this is the way to go. i wanted to verify it with the experts.
Click to expand...

have you verfied its a pushrod?? seems hard to believe thats the problem when there are other possiblilties that are very common with the 4.0.

and why does the sound go away if its a pushrod? if you dont think its piston slap or rod knock, how about a lazy lifter because of the cold thick oil?
 
89xj said:
have you verfied its a pushrod?? seems hard to believe thats the problem when there are other possiblilties that are very common with the 4.0.

and why does the sound go away if its a pushrod? if you dont think its piston slap or rod knock, how about a lazy lifter because of the cold thick oil?
Click to expand...
Agreed. Why don't you first verify the pushrods are bent by doing what myself and others have posted on here. It'll take from taking the valve cover off to wrapping up about an hour to inspect all the PR's. Unless you like wasting money:dunno:.
 
X2 - rule #1 - Don't assusme that your boss knows anything worthwhile.

It is unlikely that a noise from a pushrod would go away once it warmed up. Does a pushrod make a different noise than a bad lifter? Most likely it is a pistion slap issue that goes away once the piston expands from the heat of running.
 
These motors are generally pretty loud to begin with. Sometimes piston slap will still be present when warm. Nature of the beast on the 4.0.
 
Well I began practicing taking apart a motor that I have. As I loosened up the rockers the bridge that holds the two rockers bent. I used a 3/8 drive and a deepsocket, should I have used an impact wrench or ratchet? Are there any special methods to remove the bridges? I was thinking of possibly replacing the pushrods, fulcrums, and rockers with the stuff off the practice motor. That practice engine had a very clean valvetrain. The pushrods are nice and clean, the rockers and fulcrums are also very clean with no unusual wear. Do you guys think reusing these will be okay? I'd like to fix this knock. I just don't want to risk this motor messing up just because I didnt do anything about the knock.

The only things i'm worried about is the reinstallation and setting the #1 cyl to TDC. I understand that the rockers go torqued at 19 lbs/ft. I've been reading about how to do this but im still kind of lost. I think I read somewhere that I need a feeler gauge for some measurements. Reading that kind of scared me away. I dont really see myself to be this mechanically inclined.
 
I have a similar knock on my 91 jeep with about 200xxx miles. its only evident on a cold dry start up. When i rev it high i can hear it slap/knock. Someone told me to check my flex plate bolts but im not sure where those are located. im new to jeeps and there parts.
 
flex plate bolts go through the flex plate into the crankshaft on the engine, and through the flex plate into the torque converter too though I've always called those torque converter bolts. They're, well, uh, "fun" to get to.
 
jeepintexas said:
Well I began practicing taking apart a motor that I have. As I loosened up the rockers the bridge that holds the two rockers bent. I used a 3/8 drive and a deepsocket, should I have used an impact wrench or ratchet? Are there any special methods to remove the bridges? I was thinking of possibly replacing the pushrods, fulcrums, and rockers with the stuff off the practice motor. That practice engine had a very clean valvetrain. The pushrods are nice and clean, the rockers and fulcrums are also very clean with no unusual wear. Do you guys think reusing these will be okay? I'd like to fix this knock. I just don't want to risk this motor messing up just because I didnt do anything about the knock.

The only things i'm worried about is the reinstallation and setting the #1 cyl to TDC. I understand that the rockers go torqued at 19 lbs/ft. I've been reading about how to do this but im still kind of lost. I think I read somewhere that I need a feeler gauge for some measurements. Reading that kind of scared me away. I dont really see myself to be this mechanically inclined.
Click to expand...

As you've noticed the valves don't open at the same time. If you remove the rockers while one is open and one is closed, it'll bend the bridge. At least it's not an old AMC V-8, those bridges were cast aluminum and would break. So here's what you do, look and see by the nearby ports which is intake and which is exhaust. Roll the motor over clockwise by hand, watch the intake valve open and then close. Neither valve will move for a little bit after the intake closes- this is coming up on compression stroke. On the number one cylinder (front) when the piston tops out on compression stroke the marks will align from the crank damper to the timing cover. This is #1 TDC when the distributor is aligned. There is another, false #1 TDC when the marks will line up but you're on the exhaust stroke, not compression. Watching the valves move is key.
 
kastein said:
flex plate bolts go through the flex plate into the crankshaft on the engine, and through the flex plate into the torque converter too though I've always called those torque converter bolts. They're, well, uh, "fun" to get to.
Click to expand...


i see, so they are what hold the torque converter to the ummm automatic flywheel :p ????

im used to 5 speeds and hondas so yeah, sorry for the wrong terminology.
 
boostamante said:
i see, so they are what hold the torque converter to the ummm automatic flywheel :p ????

im used to 5 speeds and hondas so yeah, sorry for the wrong terminology.
Click to expand...
I'm probably using the wrong terminology too, I just know that they're hiding up in there between the engine and tranny and are a pain to get to :roll:
 
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