PDA

View Full Version : Engine knock that goes away?


bfarroo
03-07-2009, 08:40 PM
The engine in my shadow knocks pretty loud on startup. It sounds like it's coming from the head. It will instantly go away after a few minutes of idle. Any ideas? Possible lifter problem? I may pull the valve cover and see if there's anything out of the ordinary. I seemed to notice it after the last oil change also. The oil is quakerstate 10w30 synthetic with a puralator premium filter. The oil pressure is good as far as the gauge reading. I'll be looking into it more in the next week, I just haven't had much time lately so I figured I'd get some suggestions before tearing into it.
turbovanmanČ
03-07-2009, 09:44 PM
Probably piston slap.

Got a vid?
86turboz
03-07-2009, 09:46 PM
It could also be an exhaust leak that goes away when the engine gets hot and everything expands and the leak seals up...that is what I am leaning towards since they are more common.
butchsuppe
03-08-2009, 02:47 AM
Just a crazy idea but check to see if the check valve in the fitting the oil filter screws on to is stuck open. I once found a bad fitting but was lucky enough to catch it before I put it on the motor.
bfarroo
03-08-2009, 11:14 AM
It's not like the noise slowly goes away as the motor warms up it will be rattling and then just quit instantly.
blk86trbo
03-08-2009, 11:21 AM
If that's the case I would say it's probably a lifter.
BadAssPerformance
03-08-2009, 11:23 AM
+1 on lifter or piston slap...
bfarroo
03-08-2009, 01:38 PM
The motor was rebuilt last season and I only have about 250 miles on it. Granted they are all miles with the go pedal to the floor at 17psi. I'm going to muster up some energy in a bit here and pull it in to check it out. If it is a lifter how would I go about determining which it is and how do I fix it?
BadAssPerformance
03-08-2009, 01:40 PM
One way to spot check is to pull the valvecover off and see if any rockers are loose with the cam rotated so it is not engaging them when you check for looseness.
bfarroo
03-08-2009, 01:59 PM
I'll take a look, if that's the case can I replace that one lifter?
BadAssPerformance
03-08-2009, 03:56 PM
yes..
dds78910
03-08-2009, 06:01 PM
Probably piston slap.

Got a vid?

+1 on the piston slap.
86turboz
03-08-2009, 10:24 PM
My expedition does this and I am almost certain that what you are describing is some form of exhaust leak. Check your spark plugs to make sure one hasnt come a little loose. That is the biggest problems with the Triton V-8....they have 3 threads on the thread that holds the plug in and when you replace them, if you dont have them torqued perfectly 1 of 2 things happens....1... you strip the thread and it makes that sound it the plug finally blows completely out....2....the plug is loose and makes that sound until the plug finally blows out...... which, I need to go ahead and re-check mine soon before that happens....I really dont feel llike pulling the head on an expedition....pain in the @$$....

Exhaust leaks can be weird .... they dont neccessarily have to gradually go away...

Although everything that has already been said is very possible, I personally believe that the bad lifter wouldnt have trouble only on cold start.... I guess it could be possible that it just isnt pumping up right because the oil is thin on cold start, but you can check that by runningn it with straight 40 weight.......other than that I dont think that their would be any other reasons the lifter would be noisy at cold start, but if you dont have pt lifters now would be the time to get a cheap set, if you are going to pull the valve cover anyways.

Piston slap from being worn and oblonged usually is followed with excessive oil burning especially at cold start.

I say check the spark plugs and look for signs of other exhaust leaks if that is not the case.

Good Luck
dds78910
03-09-2009, 10:46 AM
My 8v Spirit did the same thing in the mornings then went away when it warmed up. When I tore the engine apart I saw that all of the pistons on the back side of the skirt had been hitting the cylinder wall. The walls were ok you could still see the grooves but the back of the pistons had taken some abuse. So I'm still going with piston slap.
86turboz
03-09-2009, 01:41 PM
My 8v Spirit did the same thing in the mornings then went away when it warmed up. When I tore the engine apart I saw that all of the pistons on the back side of the skirt had been hitting the cylinder wall. The walls were ok you could still see the grooves but the back of the pistons had taken some abuse. So I'm still going with piston slap.

Did you have JE's? I know they are pretty bad about egging out.
bfarroo
03-12-2009, 08:32 PM
Pulled the valve cover and found one suspect lifter. I have another head here that was originally on the car when I bought it. It has a 91 date cast on the front of it. Is there any difference in lifters throughout the years? The motor in the car is a TII out of a 88 Z. I'm swapping in the lifter now so hopefully it's ok. We'll see if it fixes the rattle.
bfarroo
03-12-2009, 09:04 PM
I replaced the lifter and still had the noise. I ended up checking what I was going to check in the first place and forgot which ended up being the sound I was hearing. Anyone want to guess what it was? After replacing the lifter the valve train noise that it had before is gone so I guess it wasn't for nothing.
86turboz
03-12-2009, 09:34 PM
Still either an exhaust leak or piston slap... unless the machine shop you took it to, when you had it rebuilt, honed it a little too much...I doubt it is piston slap. I am still leaning towards exhaust leak.
bfarroo
03-12-2009, 09:42 PM
Nope, Much more simple than that.
turzbo
03-12-2009, 10:17 PM
something to do with timeing?
Turbodave
03-12-2009, 10:48 PM
loose power steering pump bracket?
dds78910
03-12-2009, 11:54 PM
Did you have JE's? I know they are pretty bad about egging out.

Nope, just stock pistons with 155,000 miles on the clock.
86turboz
03-13-2009, 01:40 AM
Nope, just stock pistons with 155,000 miles on the clock.

Wow, you dont hear of that very often with steel pistons. Usually, the rings are shot before that happens.
turbovanmanČ
03-13-2009, 05:04 AM
Nope, Much more simple than that.


You changed the oil and it started, so I'll lean towards crappy oil, loose oil filter or low oil level.
86turboz
03-13-2009, 11:58 AM
So what was the problem?
bfarroo
03-13-2009, 05:50 PM
Ended up being the dust shield between the engine and trans. I don't understand why it would go away when the engine warmed up. It must have expanded enough when it warmed to pull away from the TC bolts.
blk86trbo
03-13-2009, 06:58 PM
Those shields can be annoying, although...I have bought a few cars cheap because of a supposed "rod knock" that ended up being that tin piece rubbing!

Glad to hear you figured it out!
86turboz
03-13-2009, 09:08 PM
Wow...glad to hear it was something so simple...although, it still doesnt make sense...lol. Maybe it was the high cold start idle that made it rattle?
bfarroo
03-14-2009, 12:46 PM
I don't know, The only thing I can guess is the block grows ever so slightly and pulls the cover away from the bolt just enough to stop the interference. Either way I'm happy it was something simple. I wish I would have checked it before changing the lifter.