Rod knocking sound?

[dburton97128]

Hi,

 

I have a 95 Lagacy L wagon that has had a sound exactly like a rod knocking. I've been driving it for the last year anyway since my experience is they sometimes go a long time with a knocking rod and not die completely.

 

For the last few weeks it has stopped knocking! (I did hear it just a little again today.)

 

I've had cars with the loose rods and with sluggish lifters so I know what rod knock sounds like as well as valve rattle. This sure sounded exactly like a rod knock. RPM and load dependent starting at about 2750 rpm and above, and especially prevalent as the throttle is backed off.

 

I can't image how a knocking rod could heal itself and stop knocking.

 

Valve noise I have experience with tends to last a few seconds at start up or longer if the lifters don't pump up readily. Once they are tight they don't usually start again as RPMs increase. I do hear the valves knock at startup , but it stops after a second or so as expected.

 

What could this be if not a rod knocking? How could it be a rod knocking if it went away? Any other ideas?

 

Thanks.

[markjw]

I bought an nice Outback last year with a "rod knock". Turned out to be a failing timing cog. Initially diagnosed by a local repair shop with supposedly seasoned mechanics. Maybe they were seasoned. Just dis-honest hoping to make a killing off the guy I bought it from. Either way, chk that your timing components are Ok.

[coolskaterkid]

My 93 legacy has been making the same sound yours does, atleast it matches what you described for the last 40k miles. I think it may just be piston slap, that sounds like a rod knock. Or its just got really hardy rod bearings. I plan to keep driving till it quits so i guess ill find out what the noise was when it bites the dust

[dburton97128]

My 93 legacy has been making the same sound yours does, atleast it matches what you described for the last 40k miles. I think it may just be piston slap, that sounds like a rod knock. Or its just got really hardy rod bearings. I plan to keep driving till it quits so i guess ill find out what the noise was when it bites the dust

 

Let us know what it was when it finally does. Thx.

[dburton97128]

I bought an nice Outback last year with a "rod knock". Turned out to be a failing timing cog. Initially diagnosed by a local repair shop with supposedly seasoned mechanics. Maybe they were seasoned. Just dis-honest hoping to make a killing off the guy I bought it from. Either way, chk that your timing components are Ok.

 

Is this observable with the covers off as when you change a timing belt? Thx.

[Fairtax4me]

It's something external. Rod knock would have left you on the side of the road with a hole in the top of the engine by now.

Also rod knock would be present at all RPMs.

Possibly the tensioner for the timing belt, or a cracked flex plate if it has an automagic transmission.

 

You'll have to remove the timing cover to get a good look at the tensioner and other timing components.

 

Really no good way to check the flex plate without removing the engine.

[idosubaru]

i'd check timing components. tensioner could be flopping around under load.....

[987687]

I had rod knock once. It turned out to be the timing belt idler on the passenger side of the engine. It looked fine with the engine running. But if I grabbed it, with the timing belt still on, I could move it in and out and feel general looseness in the idler. I just replaced it with a spare one from my parts pile, and it was better. No more rod knock.

[ivans imports]

coged idler or water pump or loose crank bolt

[dburton97128]

Well, I took it apart. I ran it with the timing covers off and don't see any obvious timing related issues, though I can still hear the knock around 3000 rpm. It sounds like it comes from the block behind the drivers side timing pulley. No pulley or tensioner bolts were loose, though the tensioner bolts were not very tight.

 

Free spinning the pulleys and water pump did not show any obvious issues, though the pulley bearings seem like they've nearly used up their supply of lubricant and probably should be replaced (~180k mi).

 

This is a 5spd car, not auto.

 

Does it still sound like a timing belt related problem?

 

Thanks.

[Fairtax4me]

Does it sound like this?

[dburton97128]

No, I'd say that's a ticking. I hear the valves for a second or so at startup. It sounds more like a 'knocking' and it occurs around 3000 rpm, especially under light load.

Edited February 3, 2013 by dburton97128
sp

[dburton97128]

Mine sounds more like this:

 

 

Doesn't explain why it would go away for a while though. Maybe I should put my timing belt back on and break out the camcorder.

[markjw]

What about the hydraulic tensioner? Does it seem to be in good working order? Do you know a good one from a bad one? I know they dont fail offen but if it wasn't keeping tension on the tensioner cog, I believe you could get a Knock there. But I think you would have seen that when running the engine with the covers off. All the same, check that closely.

[coolskaterkid]

Mine also sounds like the second video, but has newer timing components. Most noise is anywhere above 3k rpms, but under light load it gets a lot louder

[Fairtax4me]

Use a long screwdriver or stethoscope if you have one, poke around the timing parts with the engine running. Obviously you can't touch the moving parts, but you can rest the point on the bolts that hold the idlers on. Listen on the block as well and try to pinpoint the noise.

[dburton97128]

I did a cell phone video. See it here:

 

Timing covers are off, belt and tensioner shown at up to around 3000 rpm.

 

A knocking sound occurs around 3000 rpm with the engine lightly loaded. The knock sounds a little more solid in real life than in this cell phone video.

 

I can't see anything to make me thing it's timing belt/pulley related.

 

It's due for a timing belt change, but I think I'll just put it back together and run it until it dies. I have a 90 engine I can swap in when the time comes.

 

I've been driving this a bout a year now and it hasn't gotten any worse. (I keep the rpm below the knock speed).

 

Is there any chance I could change a rod bushing just by dropping the pan? The rear pan bolts are unaccessable behind the support cross member, but I suppose I could drill some holes just over the bolt heads.

 

What's worth doing here?

 

Thanks

Edited February 4, 2013 by dburton97128
enhanced content

[dburton97128]

I did a cell phone video. See it here:

 

Timing covers are off, belt and tensioner shown at up to around 3000 rpm.

 

A knocking sound occurs around 3000 rpm with the engine lightly loaded. The knock sounds a little more solid in real life than in this cell phone video.

 

I can't see anything to make me thing it's timing belt/pulley related.

 

It's due for a timing belt change, but I think I'll just put it back together and run it until it dies. I have a 90 engine I can swap in when the time comes.

 

I've been driving this a bout a year now and it hasn't gotten any worse. (I keep the rpm below the knock speed).

 

Is there any chance I could change a rod bushing just by dropping the pan? The rear pan bolts are unaccessable behind the support cross member, but I suppose I could drill some holes just over the bolt heads.

 

What's worth doing here?

 

Thanks

Edited February 5, 2013 by Turbone

[Idasho]

Thats not a rod knock.

 

Have you done a compression test? That would rule out valve train problems. But that noise is FAST, so look to valvetrain first.

 

If no problems there, as many have mentioned, look towards the timing tensioner for probable cause.

Edited February 4, 2013 by Idasho

[davebugs]

I don't click on links.

 

But I usually notice rod knock the most by after the engine is warmed up playing with the throttle and listening towards the back of the engine closest to passenger firewall when RPM's are coming down from lets say 2,500-3k.

 

Since you can't put it under load when you're standing in front of it. Thats where I usually notice the noise - AFTER it's warmed up or you could eb hearing piston slap and you may not know the difference.

[86BRATMAN]

Well If you would listen to the sound in the video you would know it is not piston slap. It is indead a knock, I had one do this in a 95 legacy a few years ago. I just ran it till it blew up and had another one handy when it finally decided it had enough.

 

I can't tell by the video, but if your car is a 96 up then to use the 90 engine you'll have to swap to a dual port exhaust manifold and either way use your original intake manifold and sensors.

[ivans imports]

if it was the rod it whould have throw it by now piston slap ? pull off plug wires one at time till you find the hole thats making the noise. If you suspect a rod the oil will have meatal in it same as pan. Probly woth pulling it and taking a look

[86BRATMAN]

I know mine was rod knock, and I drove it hard for 6 months before it just didn't make any power, never threw a rod. Plenty of metal in the oil as well.

[Fairtax4me]

I'm not convinced that is a rod knock. It's not piston slap though.

 

Still think you should poke around with a stethoscope and try to find the source of the noise.

[ivans imports]

I hear the piston hitting the head before i hear the rods on most that are knocking a oil preshure check may help if rod is bad the preshure will drop when it fires on the bad hole the gauge will bounce and not hold steady