Changed out rod bearings, 3k rpm knock!

[TRSCobra]

Because this forum wouldn't be complete without yet another rod bearing thread...

My motor has 148k on it. At 147,000 I did the rod bearings (they weren't bad) as preventative maint. I had the new bearings coated with dry film lubricant. I've noticed lately that I'm getting a faint knock at around 3000 rpm when I'm at moderate throttle. It's non-existant under deceleration.

Does this sound like rod bearings???

If it is, my car's got a date with the junk yard.

I've sunk enough money into this thing.

 

[SeanMc]

Could be the timing belt tensioner. Does it go away at a higher rpm?

 

[laxmax327]

i highly doubt its your bearings. allthough i cant really suggest anything else w/o actually hearing it myself. i think you would have had to do something really dumb to already toast your new bearings. but if it somehow is them, pease, i hope your kidding about the junkyard. i could understand getting rid of it, but dont just junk it.

 

[yozsi]

originally i thought i had knock. turned out to be resonation out the exhaust.

 

[Ishodu]

Denotation maybe? Try a higher octane see what happens. Run codes and see if knock sensor is working ok.

 

[BeautifulDisasterSho]

Could your vavle lash be out of specification? Cams also get louder with rpm.

 

[SHOtimer]

If your timing chain tensioners haven't ever been cleaned, they could be the issue.

Doug

 

[jedhead]

I am with IDSHOU. I would try some octane booster. When my engine pings it at around 3000rpm with part throttle.

Bob

 

[TRSCobra]

Its definately not detonation. I run 93 and only 93 octane. Both cam chain tensioners have been completely cleaned out. (they're from a 93 3.2 motor) It seems to go awat at about 4000ish rpm, but thats when the engine gets alot louder anyway, so the intake/exhaust noise could be drowning it out.

This thing leaks or burn oil like crazy. Around 1 quart every 200 miles. I never see smoke, never see puddles. Every seal and gasket besides the head and exhaust manifold gaskets have been replaced. I have seen the check oil light twice. And i drive this car hard. Could it be possible that it was low on oil and I hit 7k rpm, maybe wiped out the rod bearings??? The oil pressure light never came on, and I never drove it more than 10 feet with the check oil light on... The rod bearing caps were torqued properly... WTF!!!

I'll drive the car until the noise gets worse. If it does, I'll look for a 3.2 swap maybe.

I'm just sick of working on this car.

 

[jedhead]

I still get light pinging with 91 and octane booster when my EGR is acting up. I would run a compression test for you oil comsumption. The SHO uses very low tension rings and carbon deposits on rings can allow oil to get by the rings. If the wet compression is much higher than dry then the problems is with the rings. If they are close to the same, then the problem is most likely the valve guides. When you did the rod bearing did you use plasticgauges to make sure that you don't have out of round rod ends or clearance problems? My SHO has gone through about a quart of oil every 1000-1500 miles since I bought it with 17K miles.

Bob

 

[NotSoSlowSHO]

Lots of oil burning will also effectively reduce the octane of gasoline.

1 qt every 200 miles or hirrid. Make sure your PCV system is working properly. Recently my SHO was using nearly as much oil, and it turned out to be a plugged PCV line. So it was force-feeding itself oil.... thru the intake

 

[TRSCobra]

Lots of oil burning will also effectively reduce the octane of gasoline.

1 qt every 200 miles or hirrid. Make sure your PCV system is working properly. Recently my SHO was using nearly as much oil, and it turned out to be a plugged PCV line. So it was force-feeding itself oil.... thru the intake

I'll check that pcv line, but the weird thing is that I've never once seen or smelled smoke.

EDIT: I didn't plastigage the rod bearings because they weren't bad to begin with, I just replaced them because the engine was out. They're very easy to do when the engine's on a stand!

 

[Mac]

Is it better to use the dry lubricant when you install rod bearings, or engine assy ****?

 

[SHOWYA]

You should try different weight oil. It could help. Or maybe switch to a syntetic.

 

[shojuan]

Is it better to use the dry lubricant when you install rod bearings, or engine assy ****?

Even with a dry film coating you would want to use some sort of assembly ****.

Personally, I wouldn't get regular bearings coated. Just more steps that could go wrong. Clevite has some new lubricant film coated bearings but right now the offerings are slim. Next time around if they are available for the SHO I would give them a try. Until then I would stick with unmolested regular ol' clevite 77's.

I suggest trying a treatment or two of Auto-RX. My 89's motor runs smooth and absent of those annoying and concerning little noises. In the past I've had the occasional noise that raised the ears. The car's 3.0, with 200,000 miles is spotless inside on the places that get lots of oil flow, everywhere else is only a light caramel color that wipes off with a rag. There were some small chunks of carbon in the oil pan, evidence of what has been cleaned out from the rings. My old bearings were in pretty good shape. Only a bit of copper on the top ones. I used the Auto-RX about 40,000 miles ago and I used it again and a rinse phase just before dropping the pan. For good measure I did an oil change with some chevron 5W/30 that was on sale a couple hundred miles before dropping the pan. I'd rather do the job with clean oil everywhere rather than dirty stuff. Anyways, plenty of evidence that carbon was cleaned out and the motor was purring right up to the moment it went on jackstands. Like I said the bearings were in good shape, so any worries about the larger carbon particles damaging the bearings are unfounded. The filter gets what the screen doesn't. And the oil pumps gears are harder than the little chunks o' coal.

 

[NotSoSlowSHO]

I'll check that pcv line, but the weird thing is that I've never once seen or smelled smoke.

Be sure to check the PCV ports in the throttle body. Both of mine were plugged.

Also, I never saw or smelled smoke, unless the car sat for more than a day or two. Then it blew a bit of smoke on startup.

Since finding the plugged PCV line and ports, Ive also performed the PCV "mod" that eliminates the valve cover to throttle body line. My SHO's oil consumption has gone down to about 1 qt every 2k miles.

 

[TRSCobra]

The bearings were DFL'ed, but I also used assembly ****.

Could someone explain this PCV "mod" for me?

 

[jedhead]

I put together many small block chevys and other engines by myself and with family. We used STP Oil treatment as assembly ****.

Bob

 

[LookAtThatSHO]

Just curious, how many quarts low would the SHO engine need to be before the check oil light is triggerred? After I do an oil change, my check oil light is triggerred after about 1,000 miles. I always make sure to have oil in the trunk, and I pull over immediately to refill with a quart when the light does come on.

TRSCobra, my problem is different then yours, because I can actually see smoke coming out of the exhaust when flooring it up to 7K in 2nd gear. Would this be a sign of the piston rings gone bad or having carbon deposits? My SHO never 'leaks' oil either, I think it's just burning it more than it should...

PCV Mod?

 

[RAYJAY]

I put together many small block chevys and other engines by myself and with family. We used STP Oil treatment as assembly ****.


Bob

Old time assembly **** use it on mine also

you can also try rislone to to clean out the carbon on the rings

Jeff