Knock, knock....who's frustrated?

jflynn13

Registered User
I have a knocking issue that I need help with. I will provide as much detail as possible.

It is a 90 XR7 that is mostly stock except the air silencer has been removed and the previous owner changed the SC pulley to a smaller one (not sure of the size)

Symptoms
it not really a tapping sound, more like the "knuckles on a wood door" sound
Knock is loudest when car is cold and goes away as the car warms up.
it is louder when car is driven before reaching operating temp.
there is a mild loss of power and gas mileage.
the knock is rapid, rhythmic and in time with RPMs

What I know
The snout seal is starting to leak just a bit but I maintain the oil until I can change it.
The oil was just changed
No codes are reported in memory or after clearing memory
replaced the water pump and power steering pump about two weeks ago. the sound was there already.

Any help or suggestions would be greatly appreciated

James
 
My first hought is "piston slap", as that usually occurs only on a cold engine.

Don't take mine as the final word, though

Cheers
Doug Dwyer
 
That could certainly be something bad, like major engine problem. However, it might be something in the valvetrain too, which would be much less serious. Get an "engine stethoscope" and hold it to the valve covers on each side. If the noise is coming from there, it will be really obvious. You could have a stuck lifter, or possibly a broken rocker arm bolt. That happened to me once - it sounded awful and had a bad misfire.
 
does the knocking happen under load, no load, or anytime it's running?

It is noticeable when idling and louder when under load. When the car reaches normal operating temp the noise is gone.

I hear it mostly between 1300 and 2200 rpm, load or no load until it warms up

I think the next knock I will hear is the howitzer I am going to shoot the car with...:D
 
It could quite possibly be lifter noise. That could cause the same condition you are hearing. If you had a bearing problem, it would get worse as the engine oil warmed up. Sounds like oil is not getting up to your drivetrain sufficent enough until the oil warms and moves easier. Could be a number of different things though. If you use 10w30, try using 5w30 mobile 1 and see if there is a change.
 
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Hmm, not too sure on this one but id keep a close eye on your oil condition,
It could very well be a bearing going out! But as some others stated it could very well be lifter/valvetrain noise. Either way it isnt good.
Get it looked at.

Although the piston to wrist pin tolerance is slopy on these cars it may be piston slap while its cold
 
Narrow it down. Get a engine stethoscope and narrow it down to the top or bottom end or blower.

Or a small tin can and a screw driver.....

Ive used my longest screwdriver and tin can as an ear piece.......I wouldnt do it in front of people....With the clutter of the SC....Might try using multiple extentions and a can.......

What snout seal is starting to leak..Charger starting to self destruct.....Auto or stick....Torque convertor bolts loose...Exhaust leak or vibration....NY weather is cold now..Heats up and silences tiny leak....Dunno
 
I believe your SC rotors are worn

Remove the SC belt from the idler shaft pulley and SC snout and start it. Does it still knock? If so then it is not the SC. If the knock goes away then your SC rotors are hitting and you will need to replace your SC. The problem with SC rotors hitting is that generates metal shavings. So I would do this real soon. When the SC is cold the rotor tolerances are larger causing them to slap. When the rotors get hot the tolerances become tighter and the slap decreases.

Ed
 
the car is an Automatic. All fluid levels are within spec (type and levels)

I used the old rod to the ear trick on the valve covers and did not hear any tapping or knocking.

The SC does have the normal chatter but doesn't sound like an issue. As for the seal on the front of the snout, I find some drops of oil on the snout behind the pulley. I hope to get to it this weekend.

The knock sound like it is coming from the driver side and seems to from the lower portion of the engine. I checked and nothing is rattling underneath.

One thing I have noticed is the car takes pretty long time to warm up and the temp rarely get above 1/4 on the dash gauge.

The knock goes away almost completely after it is warm.

It has been in the mid 40's during the day and low 30's at night here on the eastern end of Long Island. It was not doing this during the dead of winter
 
Knock, Knock...who's there? BOOM you engine just blew up.

I had to drive it for a short trip and it did not make it. I guess I won't have to worry about the knock anymore.
 
i retract my BOOM

It was not quite as bad as it seemed. Here is what happened as far as I can tell.

The fan motor cooked. The seats for the small magnets inside the motor cooked and crumbled, frying the fan motor.

This in turn shorted out the fusable link, then the coolant temp sensor and then the Air Charge temp sensor.

This caused a nickel sized hole in the lower radiator hose. Coolant runs out surprisingly fast with a hole that large.:eek:

The Highly Accurate temp gauge on the dash only got to the MP of TEMP when it made a very unfriendly, loud knocking sound and died.

I drained all the fluids. Coolant (what was left) and oil were clear. I refilled all fluids replaced the unhappy parts and rand it for about 100 miles or so. Drained everything again and all was clear.

It runs well but there is a precipitable ticking from under the driver side valve covers.

Thought I would update with my findings. Any thoughts?
 
Sounds like a bad rod bearing to me from your description of the noise and circumstances. That tick, tick, ticking will soon turn into a clank, clank, clanking and will trash the crank if it is.
 
So the knock turned into a tick after all that?..VERRYYY STTRANNGGEEEEEEEEEEE

strange is one word for it. I have had a few other words so far and none of the were very nice. I am hoping to pick up another 90 XR7 within the next month. I will then disassemble the current car with a large smile on my face.:D

I can't wait to see what damage has been done to the internals.

Just curious, does my guess work at what happened seem logical?

I forgot to mention that the ticking/tapping goes away as the car warms up. The only way to hear it once it reaches operating temp is with stethoscope (ok, not really a stethoscope, just a metal rod).
 
When the oil thins a bit from heating it lubes the damaged bearings better. Mine lasted 2 miles like that but a friends lasted for a year.
 
strange is one word for it.

Is it at crank speed or cam speed?

Does it go away when you put a load on the engine or is it constant?

Do women, children and small animals run away from your car when you stop at a light?
 
It is at cam speed and between 1000 and 2000 RPM until it warms up, then it goes almost completely away.
 
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