Volvo RWD Forum

Not just Volvo. Has anyone experienced carbon buildup on any car that made the car sound like it has a Rod knock?
Does anyone think that Carbon breaking loose off a Piston can cause a Valve to bend?
My daughters Blazer (4.3 V6) went from running beautifully to this harsh Knock in a blink of an eye. At that time it runs very rough like it's down a cylinder. But then noise goes away, Roughness disappears and all is good. I have let it idle for an hour that way and out of nowhere the hard knock comes back. I will do a compression check but the symtoms have me Buffaloed.
Seems like a stuck Valve or lifter but the Knock really sounds like Lower End... but then all goes away except for a new slight tap sound (hence my bent valve question). Then the hard knock comes back at anytime. The Blazer Websites are useless.. No 'real' engine knowledge on those sites.

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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

I was a Chevy service adviser in a past life. While you are in there replace the oil cooler lines as they leak with regularity and when they finally let loose its catastrophic. My parts guy here at Stanley has one where they let loose on the highway. He heard a knock similar to what you are hearing now....it never went away and is still there today. Also check the clutch for the cooling fan as it too fails with regularity and is bitch to get out.

Funny you mention that. I noticed 'wet' lines going to the remote oil filter and I literally was going to change them on a Saturday... My daughter came home with this issue on the Friday before.
Thanks for the Heads up
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

Unless there is something DRASTICALLY wrong with the engine management system, you should NOT have any substantial carbon buildup. That is an old-car symptom.
Even if you did it could not be enough to do anything to the valves except possibly stick one open a bit. But I really doubt it.
Regular oil changes? Fairly clean oil? Using oil too long causes it to lose its cleaning properties and it entrains carbon, combustion products, moisture, etc and will lead to acid formation, accelerated wear and gummed up lifters.
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George Downs, Bartlesville, Heart of the USA!

She ( daughter) bought this car 9 months ago. I did an oil change then, oil was fairly clean, and I did one about 1200 miles ago. When I got teh Valve cover loose and looked under there, the Head was Very clean...no buildup at all. 105K miles.
If a valve was stuck open, I don't know if this is an intereference engine, and if it wasn't, wouldn't the piston whacking the valve sure as heck close it?
Friday I will put a wrench on the Crank and see how much play there is in the Timing chain.. I will also do a compression check and possibly dump the oil through a paint filter to see what I can fish out ( hopefully nothing).
Thanks
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

If it is that clean I would not expect a valve to be stuck open.
You can get an idea of carbon by pulling a spark plug and looking at the end of the threaded part.
If it is not carboned up the rest of the combustion chamber would not be either.
This just does NOT sound like a carbon buildup problem to me at all.
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George Downs, Bartlesville, Heart of the USA!

When this first happened, I pulled the plugs to see what they looked like. Of course the car drove about 300 feet after this happened. The plugs were really nice looking.
Crap! I really don't know where to go from here. I'm learning that this engine has a Shaft balancer. Never heard of this before. It appears that it is a long shaft that runs across the top of the Block just under the Intake Manifold. It is Run off the Timing Belt. Maybe that looseded up and is smacking around under there when it feels like it.
This is the other problem. I really do not know this engine. Even though it's literally a 350 V8 cut to 6 cylinders, it's not the old school Small blocks that I have been elbow deep in years ago.
Compression check, stethoscope probing, screen oil, Timing Lash check, check the Flex Plate Bolts on the torque convertor then probably pull the Intake off. Just too many harnesses in teh way... I hate that
it's odd, for sure. I usually have a direction to go but this is odd.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

Have you put a code scanner on it to see if there are any diagnostic codes? I just got done with a round of frustration on a 4.3L Vortec in my wife's AstroVan. In my case, the codes found didn't really point to the real problem anyway, it took some careful parts replacement (one thing at a time) to figure out what the problem was. Fortunately I hit the problem on the second part I replaced.

Does it make the 'rod knock' sound only while driving, or does it do it while in Park also? Let us know what you find out on this, the answer could help someone else out (not just Chevy owners) with similar symptoms.

billy242
1980 242DL with lots of GT and IPD stuff
2000 AstroVan with 4.3L v6

It does it Under Load or not.
No Check Engine lights. No codes ( which makes it stranger)

It first happened when my daughter was about 300 feet from teh driveway, she basically coasted it to teh Driveway. I went out and restarted the engine and it was Knocking bad and ran like crap(i drove it about 30 feet). After fighting with the passenger side Valve cover that I couldn't get past all the harnesses I ran my fingers under there and it seemed like the Rockers were all in place. At that point I refused to work on a car that I told her not to buy. That night After adding some Marvel Mystery oil down the Intake and letting it sit,It actually started up much quieter. So I'm leaning heavy on Valves or lifters hanging up OR carbon that shifted causing the Piston to hit the Valves. I let teh car run about an hour and out of nowhere it start hammering again, I ran to the car to shut it down but at the same time I was trying to get an ear where it was coming from...definitely the passenger side but not sure how deep. I absolutely dread pulling the Head on this thing. As you know on your van...no room to work. Yours is worse, the engine is sideways.
So now, It's quieter like a valve tap. I actually drove it about 6 miles and it feels good but something isn't as right as it was before this Knock started.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

I know what you mean about not having room to work around the engine. FWIW, the AstroVan is RWD and the motor is not transverse mounted, but that doesn't make it any easier to work on. I end up pulling the passenger seat and the engine cover from inside the van to get at most of the engine as the AC and air intake box take up most of the room that is under the hood. The dash still presents a major obstacle to getting access to the engine in some cases.

Odd that there are no OBD codes. Definitely leads me to think that the problem is mechanical and not computer/sensor related. Not sure that it would be lifters or rocker arms causing it, as they are roller lifters in the 4.3L Vortec engine, and the cam runs at half the speed of the crankshaft. I would look for something external to the engine first, perhaps harmonic balancer or flexplate/flywheel related? Torque converter bolts loose? Perhaps broken motor mount? Timing chain slapping inside the timing cover?

Do you have a mechanic's stethoscope? Might help in pinpointing the source of the noise. Harbor Freight sells them for @ $5, not great quality but good enough to get the job done.

Feel free to contact me off-list if you wish to save bandwidth for Volvo stuff. billmz at cox.net

billy242

Oh, the astrovan is RWD? one of the few Mini vans that are I guess.

I do have a stethoscope and that is Fridays plan alond with a compression check and wrenching the Crank to see how much play is in the Timing Chain.
I was thinking about loose Flex Plate bolts.. there is a trani service sticker in the engine compartment. I assumed the P.O. had a flushing done but maybe he had the Trani out. The thing is, when it was wrapping hard, it felt like I was getting popping through the intake manifold.
I heard that these engines have an issue with a clogged oil passage to the Timing Chain. The Head looked too clean to have Passage clogs and I don't think it would sound as it did from Chain slap. Just popped the hood for a peek again last night... ahhhh, I really really REALLY don't want to disassemble this mess to get the Head off. I had the Head off my sons '70 Plymouth (slant 6)... 40 minutes it was on the workbench.

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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

Howdy,

Check for a bent valve, broken valve spring, bent pushrod, or broken rocker arm. You will probably have to loosen the rocker and spin the pushrods one at a time until you find it. If you find a pushrod bent, inspect it's valve, spring, rocker, and lifter carefully.

I think you will find a bent valve sticking and then eventually freeing itself until it rotates around to the same point again. The valve guides wear oblong so a bent valve will jam in certain orientations. That is the only thing I can think of to explain an intermittent knock.

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Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 53 year old fat man. ;-)

that makes sense.

I wasn't thinking how it could come and go but your comment does make sense.

I've been under there this morning. Compression is even across all 6 cylinders.
But the Engine is running real quiet again.

I wanted to check the Torque converter bolts to see if they loosened and was smacking but this trani has no Dust cover, not sure how they pull the converter off this thing.
I had it running and used a medical stethoscope. Valve cover is quiet, the exhaust manifold ( before it got to hot)is quiet on each port. really weird
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

Hrmm, odd that the sound would come and go. I once had a serpentine belt cause a rod knock type noise, at least that's how I interpreted the noise. There was a six inch section of the belt that was missing all the longitudinal ridges.
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