Top End Knock

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ViPER1313

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Alright, I have a serious problem with what I assume are the internals of my rear cylinder head that seems to be temperature related.

* After a hard drive last week (car was full to the brim of oil, never overheated) I came to an idle back at my house and experienced a STRONG knock from the top end of the motor at idle.

*Revving the motor would make the noise disappear completely, and it would not immediately return (very random). Seemed to only happen at idle.

*No oil light was present at any time (sensor works perfectly, 20k miles old)

After the car cooled down, the car returned to normal. Ran fine, accelerated fine, no knock for the duration of this week (short drives too and from school).

*Today, as I was driving normally (80 degrees outside) with the car at full operating temp, the knock came back, accompanied with stuttering from the motor (like it was running on 5 cylinders.) The noise seemed to be coming from the top rear (beneath the secondary solenoid.) Still no oil light, but definite and noticeable intermittent loss of power. Power loss and knock were felt especially while accelerating.

I had the car towed back to my house, so now I need some opinions (my thought processes below):

-Sticky Injector - To me the knock sounds way to loud to be this. It would explain the heat related issue and power loss though.

-Stuck Valve - Could / would the problem appear and disappear as it has been and be temperature related? How can and should I check for this?

-Spun Rod Bearing - Bearings replaced at 130k miles (164k now), 3k mile oil changes, car was full of oil while running hard. I find this hard to believe, because to my knowledge rod knock doesn't go away once it starts, and the oil light should be on.

-Ejected valve shim - This would be obvious when I tear into the top end, but it wouldn't be something that started and went away again? (would it??)

-Secondarys knocking - I have heard about this happening before, but once again I don't think they could be as loud as this noise was.......

-Failed Chain Tensioner - I don't think this would explain the intermittent losses of power, although it would cause a temperature related knock.
 
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ViPER1313

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No one??

Alright, so far I know (all had to be checked cold):

-All cylinders have good compression
-All injectors seem to be firing fine
-Butterflies all have screws intact - seem not to be clacking when opened and closed by hand
-All plugs looked good when removed
-No signs of scorching on the intake valves
 
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TimboSHO

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I have this on my 91 as well, but there is very low compression in one cylinder. Mine is also all of the time, it doesn't get worse hot, and it doesn't go away cold. How did you check for scorched valves? My knocking noise seems to be coming from about the same spot though, so I'm interested in what you find.
 

ViPER1313

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Only checked on intake side for messed up valves.

I have the rear valve cover off right now - nothing jumped out at me as being messed up (no shavings, no ejected shims, no damage to cams that I can see). I'm about to drain the oil (look for shavings in case it is a rod bearing) and check the valve clearances to see if any are completely out of whack.
 

ViPER1313

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I am really at a loss here - what should I do next???? I really need to get this car back on the road ASAP.

Update:

-All valve clearances are within spec. One set of cam lobes on the rear head is showing a little bit of polished copper on the tip of the lobe, although the shim to cam clearance is within spec and the shim does not appear to be damaged / worn (is this normal wear??)
-No metal shavings in the oil from what I can see (sending a sample to Blackstone for evaluation)
-No metal shavings on what I could see of the oil pickup tube screen through the oil drainplug

Engine appears to be as clean as possible - no sludge or deposits anywhere.
 
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SHOBlu

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Mebbe a piston slapping or a loose wrist pin.. :shrug: Those two things will make it knock. Also check your cam chain tension - that will make noise as well. I don't know what else it could be without hearing it myself.
 

ViPER1313

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reportch8.png


Any new ideas? I'm about to put new injectors in it and button the top end back up. I will check the timing belt as well.
 

ViPER1313

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Why would a timing belt tensioner cause a knock that is intermittent and temperature dependent accompanied by performance loss? I thought when the tensioner went bad the belt would skip a tooth / teeth and then the engine would stop running all together or poorly all the time.
 

FREAK_SHO

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Belt is just loose. The tensioer is most likely ok. The belt is just slapping around inside the Timing Cover.
 

ViPER1313

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Haven't had a chance to work on it - tomorrow I'm going to tear the top timing cover off and check the timing belt. If that seems OK, I'm going to install the new set of injectors I bought and replace the butterfly valves while I'm at it (I have a spare set and have heard they can cause a knocking sound / loss of power.) Should have an update by tomorrow night.

I hope I fix this tomorrow, I'm sick of driving my brothers 97' GL (my old car.) I miss SHO POWA!
 
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ViPER1313

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UPDATE:

Not: Injectors, Butterflies

Assuming timing belt tensioner at this point - read below, I really want peoples opinions on this:

Loosened the top timing cover so I could see the belt (didn't remove it completely due to interferences with battery / accessory belt.)

The belt had a few chunks of rubber missing from the smooth side of the belt in one section. Depending on the position of the engine, the piece of belt between the top 2 timing gears was either taught or could be moved ~1in either up or down when pushed on. (is this normal??)

When I started the motor up, the knock was still there. I revved it to 4k RPM, noise disappeared - came back 10 seconds later. Engine would stumble and miss whenever the knocking was occurring. I also noticed smoke near the rear cam seal - smelled like burnt rubber. Went to bed for the night.

When I started it again this morning, it knocked 2 or 3 times and then was smooth - left it running for about 1 minute before I had to leave.
 

Jonny Cash

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First off, get a new belt, then check the tensioner and make sure its still good. The belt may of even skipped a tooth from the belt being so loose, and you putting initial load on it. While your there, might as well change out the leaky camseal, and check the other ones too.
 

LeddZepp8687

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Off Road SHO said:
It's your timing belt. Put on a new one and tension it properly.

Tom

Dont be so sure. I though so too and I spent good money on a new hydraulic unit only to still deal with the knocking sound. Only thing I can think of is that it is the tensioner for the CHAIN on the rear head. Im not even gonna try and replace it. Ill just drop a cammed low comp 3.2 in.
 

93rev2sev

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If the belt looks cooked(sounds like it from your description), pop a new one on there and let us know.

You should not be able to twist the belt more than about 50 degrees between the cam gears. Moving it up and down an inch...thats bad...no matter what the position of the engine....thats what the tensioner is for.

The amount of slack on the belt between the cams should not change as the engine rotates.
 
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ViPER1313

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As my friend pointed out: why didn't you just tighten the belt :nut: . I' probably going home later this week - I'm going to tear the top cover off to get a good visual on how the belt is actually acting and see if I can tighten it up. If that fixes the knock I will order a new tensioner and belt + all the other stuff for a front 60k while I'm at it.
 

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