AGENT 86

After golf last weekend the vette developed an off beat knock. The drive there was a bit spirited as i was running late, but nothing over 4500 rpm. Today i had time to have a bit of a look and listen. Couldn't really pinpoint the location, but it seemed a little louder on the pass side. Pulled the cover (love the egr delete) and found nothing. Ran it for a while with the cover off and still couldn't pinpoint it.
I'm going to have to bring the stethoscope from work and try again.
I hope it's not the start of a con rod bearing or wrist pin going south as i wasn't planning on any motor work till next winter.
Any thoughts

Redeasysport

Sounds like a plan to me hope it isn't what you think but it is the most likely source.On my car the pass side sounds a little noisier than the drivers but no knock(Knock on wood)yet.

RatC4

Pull plug wires one at a time to see if you can locate which cylinder. That should also indicate rod or small end trouble if the noise goes away without combustion pressure.

AGENT 86

Good thought, i'll try that tomorrow. It's not a loud knock but it's there

MilehighZ51

When you say "off beat knock", do you mean it is not synchronous with engine speed? Does your '86 have pre-catalytic converters, and are they old...?

Don't jump to conclusions yet. I had an '86 which developed a knock which I feared was a rod bearing. Turned out to be a bad pre-cat.

AGENT 86

No cats
It sounds like its comming from the rod area and is kind of off beat compared to rockers and injectors ticking. When i rev it the knock increases and when i let off, the knock decreases faster than the sound of the rpms. Almost like it floats when revved and settles down quickly under no load.

mseven

86,
I hate to say it but it sounds like a rod bearing, did it get louder under load ?
Sorry to hear your havin some probs ..... I think you said you pulled valve cover, checked rockers, collapsed lifter, etc.?? , keep us posted Mick

rick lambert

sorry, but it does sound like a rod knock, however I would double check the valve train-has your oil pressure changed at all?
You might even want to drain the oil and see if any metal particals
appear-if not I might be inclined to go to the next heavier oil-just to see if it makes a difference.

AGENT 86

It's hard to tell if it gets louder under load due to exhaust and other engine noises. It's not to the point where it's obvious rod knock yet but it's there and bugging me.

AGENT 86

No change in pressure yet. Iv'e ruled out valve train. If a lifter colapsed it would inturn cause a rocker to make a lot of noise. The roller rockers are quiet and doing their job.
Draing some oil may shed some light.

Brimis

I agree with MilehighZ51, I had a horrendous noise which turned out to be the timing chain.

77vetteuk

I had (may still have) a similar problem on my '91 L98.
I get an off beat knock like you are describing coming from the lower end off my engine if i take the car on a long run,usually starts after about an hour?
But only on a long run.
This car is my daily driver and ive never had this problem going to and from work every day,BUT now and again when sat at red lights etc the idle would drop right down-almost stall-then recover,when the revs got really low i got the same noise?(only happend on about 3 occasions though)
Last friday i had to go on a long run-got the "noise" on the way home but it did die on me a couple of times.next morning i couldnt start it without the engine dieing on me-no fault codes??
I changed the aic valve for a new one-havent had the problem since going to and from work,not been on a long run yet though.
The old aic valve was well sh**ted up,have give it a blast with carb cleaner in the past for quick fix.
why does a low idle cause this noise?? ony 63,000 miles on the clock and oil changed every 3 months

MilehighZ51

Is the car an automatic? I know a guy with a cracked flex plate in his '84 and it sounds similar to a rod knock.

Caboboy

It does sound like a rod from your description........maybe a bit heavier weight oil could hold it at bay?

The good news is it's almost time for the poor man's carport this year, and it sounds like you planned to do it anyway after next season..........

JrRifleCoach

Our Exploder was diagnosed with a loose flex plate that turned out to be a loose wrist pin that tore up the cylinder wall.

Well, weren't you thinking about a 383 anyways?

Red Tornado

i thought that bad rod bearings normally are accompanied by a marked decrease in oil pressure. a loose wrist pin is beginning to sound like a possibility.

damn, i hate to hear any news like this dan, let's hope this turns out to be a benign situation.

AGENT 86

I'm going to keep driving it till it blows up
I'm leaning towards 406-434.
Hey Tim, how about shootin me some info on your badazz combo

AGENT 86

It's not a real loud knock yet so the gap may not be big enough for substantial pressure loss. Time will tell
Time for a second mortgage

RatC4

Don't let it self destruct. Right now it's got a lot of good parts so it's worth something. Let's pretend a rod lets go, now you have mostly jumk that can't be used to offset some of the expense of a new engine. Oh yeah, I've heard that cam bearings going bad can knock.

Great-White

you might try the routing of the plug wires. if you have a leak in the cables you could be getting crossfire.