ntoracn

Howdy Folks.
I need some help on finding a loud tapping/light knocking sound coming from my newly purchased 1998 4Runner for my soon to be, first time driver, son. A little back ground on me, I am a former automotive tech with lots of skill's (or so I thought), lots of tools and a shop at my house.
I bought this REALLY clean 1998 4Runner with 178,000 miles cheap from a used car lot becuse of this engine noise. The car runs great with good power, no mis fires and it did NOT overheat on the 30 mile drive home. I have no service history on the vehicle other than a sticker under the hood indicating that the timing belt was changed about 6 months and 5,000 miles ago and a super clean motor on the inside, more on that later.
The noise doesn't start until the engine has been running for a few minutes. The noise is a very loud ticking, nearly on the verg of being a knocking sound. It sounds like its coming from towards the rear of the engine about in the middle or a little towars the drivers side. It sounds like its coming from above the rods and below the valve train. I Know, its weird. The noise completely goes away at 1,000 rpms if I put it in gear and load the engine. In neutral if I raise the rpm's the noise is still there, but a lot less.
In the last two days of owning this thing, this is what I've done thus far, in this order.
1. I pulled the oil pan, screen and windage tray. All 6 rod bearings were tight in every direction. I pulled one rod cap and both the bearing and journal looked great. The crank thrust looked good. No obvious signs of problems. There were only 6 flakes of metal in the bottom of the pan and no sluge or signs of abuse or neglect.
2. I inspected 360 degrees of the flex plate and seen no visable signs of cracking, from what I could see.
3. I pulled both valve covers and measured the valve clearance on all 24 valves. All valves were within spec. All cam lobes looked great as did all gears. No obvious signs of problems.
4. I made sure the timing belt was timed correctly.
5. I changed the oil and filter to 10W-30. I cut the filter open and found another 6 flakes of metal in the filter media.
6. I put the engine back together.
The only thing left to inspect is the pistons, wrist pins, small end of the rod and rings. I know this series of engine can be a little noisey, this single tick is more than that.
Does anyone have any ideas on what to check before I pull the thing out and blast it apart?
Is there any guru's that you know of on this series motor whom I could ask their opinion?
I could get a used engine and install it, but this engine (and vehicle) is SOOOO clean inside and out and well taken care of that I hate to replace it. If used is the way to got, where is the best place to buiy used?
Thank You in advance for your help
Randy
ntoracn@yahoo.com

02SE

It's hard to say without hearing the noise. Here's a couple of ideas anyway.

An exhaust manifold leak can make a ticking sound. Or maybe a serious buildup of carbon on a piston(s).

ntoracn

Thanks 02SE for the info. Keep it coming!

DrummerDaveB

Based on 02SE's response, could it be possible that one piston is preigniting, causing a loud spark knock?
Maybe suck a can of Seafoam through it and see if it goes away?

Oh, and do a compression & leak down test on each cylinder. See if one is any different.

ntoracn

Thanks DrummerDaveB, a compression test showed good numbers.

rworegon

Cracked exhaust manifold? Bad exhaust manifold to block gasket? Bad gasket in crossover to manifold connection or crossover to exhaist pipe? Something like a support bracket just loose and vibrating at certain RPM's? Any chance it's really coming from the front like the alternator bearing, water pump, etc?

vital22re

iTrader: (2)

I've seen a couple flex plates on 4runners with the 3.4 that have sheared all the way around the 6 flex plate bolts.

stir_fry_boy

I had this problem with my 02' Sport. I talked with my friend who is a Toyota Master Tech at the dealer for 10 years. He said he has seen this and it was that the belts were too tight. Mine was lightly knocking after the dealer did my timing belt / wp. I loosened up my belts and it worked, my engine purrs like a kitten now. Better loose than tighter on the belts. I adjusted them until they stopped squeeling. The p/s belt was the most tight I think for some reason. I also have crappy Goodyear Gatorback belts. My friend said he has seen dealers replace the 5vz engine because of knocking when all it could have been was the belts were too tight.

ntoracn

I will look into this, Thank You.

ntoracn

I was thinking the same thing but what I can see of the flex plate from the inspection cover is no cracks. Whats funny is the noise does go away when in gear and i bring the rpms up to 1,000. I'm gonna have to unbolt the torque converter and run the motor and see if the noise stops.

Thanks for the help!

sabre

I think mine does the same. Usually first thing in the morning and once I get half way down the driveway it stops. Doesn't happen everyday either.

stir_fry_boy

Mine was knocking when the engine was hot only. Not cold. When it ticks when cold, could be your valve lashes sticking or dirty. In which case you can run 1 qt of ATF through the engine for about 20 min driving around and then draining it. When it is hot, it definitely could be the belts. When belts get hot they expand putting an extra strain on the internal components of the engine such as bearings. Which in my case, is what I think was happening. I also noticed a quieter engine after I did a direct injection of SeaFoam through the PCV vacuum hose into the intake (about 8 oz).

ntoracn

Yeah, mine only makes noise when its warmed up and below 1,000 RPM's

stir_fry_boy

Yep, same with mine. Soon as I loosened my belts it was way less and the seafoam treatment (directly injected) definitely took care of the rest of the ticking and knocking.

ntoracn

Here is a video of my noise.

http://www.youtube.com/watch?v=mVQtguJvbsQ

stir_fry_boy

Yours is way worse than mine. At idle, mine wasn't too bad but when I put the truck in gear and held my foot on the brake with no gas it got a little louder. Mine was the loudest around 600 RPM. Have you tried using a stethoscope to see if you can pinpoint where the noise is coming from exactly? Have you loosened your belts and tightened them a little bit each time until they don't squeal? This could also be a leaking exhaust manifold gasket. My Toyota friend said he has seen that cause these engines to tick / knock.

DrummerDaveB

I love the ending. haha.

Nice vid. Hope somebody can help figure it out, but for now, bump!

stir_fry_boy

Haven't heard if my suggestions worked or not?

vital22re

iTrader: (2)

piston slap? loud valve?

250000_yota

I'd dig a little deeper into the bottom end. Since you've pulled it part way apart and checked bearings, I'd say it might be piston slap also.