bill buttermore

Hi all,

Just bought a '94 4Runner, 3VZE, 5-speed, 172K, thinking it needed a new timing belt. The previous owner started it (before I could stop him, and before I knew the 3VZE was a non-interference engine) to show me what it sounded like. The engine started right up, but sounded really bad, just like what it might sound like if it had slipped a few teeth on one or both of the cam gears. The sound seemed to be coming from the plenum and was kind of like a backfire - loud rattle- thwocka thwocka thwocka sound. I am familiar with the sounds of bad main and rod bearings, and bad harmonic balancers, and it was not like either. He said it happened all at once, i.e., the engine lost power and became noisy, so we both figured it had jumped time.

I bought it and took it home. I removed enough of the front of the engine to determine that the timing belt is fine and the timing marks are correct. I'm thinking - now what? Maybe it dropped a valve? So, I removed the spark plugs, all of which were wet with oil/gasoline and pretty nasty looking with small chunks of carbon between the insulator and the shell. Pulled the EFI fuse and ran a compression check - got 120-150 in the cold (20F) on a cold engine.

Now, I wondered if it was maybe a broken shim or camshaft. So, I removed one (so far) of the valve covers and the cam and buckets look great. Very little wear on the lobes or shims.

I searched the forums here and wonder if the reed valve could make such a horrible noise that you think the engine should not be run? Does a leaking reed valve sound that bad? Does anyone have any idea what else might be making this sound?

Thanks for any help.

yotaman85

do a tune up and see if you are not getting enough spark then check more major parts

bill buttermore

Thanks for the reply.

Well, seeing as I have the thing all torn down now, if it is something mechanical, I'd like to fix it before it goes back together.

toytech76

Ive seen those drop valve seats making them very noisy. If you can find someone with a boroscope, see if you can look into the cylinders with the valves open to see if a seat has dropped

bill buttermore

If it dropped a valve seat, wouldn't the compression on that cylinder be really low? BTW, while running the compression check, the engine sounded pretty normal - no clunks or bangs. I have heard of mechanics using borescopes, sounds pretty neat. I wonder what they cost?

If it dropped a seat, could I tell by checking the clearance between the shim and the lobe? Seems like it would be.....tight?

Thanks for the reply

toytech76

Actually the last one I fixed, ran ok and compression was decent but was noisy as hell. I boroscoped it and I confirmed my suspicion of a dropped seat. I also checked clearances and it was normal. I'm not saying that is what it is, but its a big possibility. Ive also seem a spun rod bearing that doubled under the other bearing which made the piston height taller which made it contact the cyl head so, like I said..its just hard to tell without hearing it

bill buttermore

Thanks. Well, I don't know anyone who would loan one and a new borescope even from Harbor Freight is about $275, so, it looks like the least expensive approach will be to pull the cylinder heads and check them out in person. That thwocka thwocka sounded a lot like the resonance you would get from striking a piston.

So, does the seat drop completely out of the head and just hang onto the valve, or does it more typically just slip down a little causing the valve to strike the piston? In your case, was the head salvageable?

toytech76

It usually drops completely out and rests on the valve when it opens. The valve didnt hit the piston at all, it was all clatter from the seat banging around. The head was not salvagable because it had damaged it and we didnt want the liability of putting another seat in and having it drop as well. If it is making that much noise, typically it is causing damage

bill buttermore

Thanks for the reply. I'll post some pix when I get it torn down to let you all know what I find. It will probably be a couple of days.

toytech76

I will be interested to find out!

bill buttermore

Mystery solved. This is between #5 and #6. Do you think this could be causing that funny noise? The crank seals looked new, as if someone had recently replaced them. Now I am wondering if I should have the block and main bearing carriers alignment checked. This is the first one of these I have seen. Ouch!

I am also curious to see how things look up on top. I will have the heads off tomorrow.

SEAIRESCUE

Be sure and give to your local %!*+& dealer.

One of the dozen reasons why I hate the 3VZ. Poster child for how not to design an engine.

Flame on.....

keithguts

Dude, that does not look good to me, but I don't think that is making the noise your hearing. It might not be, but I had the same problem with that type of noise, and it turned out to be 2 bad injectors. Just my 2 cents.

bill buttermore

Keith, I was just kidding when I said I wondered if the crack was causing the sound. I am certain that the crankshaft is responsible for the horrible noise. The crack in the picture doesn't tell the whole story; the crankshaft is broken in two pieces in such a way that it comes apart and goes back together on each revolution. I am amazed that the engine ran at all.

nate V

thats looking like your prob
im sure thats not all the damage that was done to your engine. Any idea what caused the crack?

toytech76

wow! Ive never seen a crank crack like that before unless it was severly abused. Im sure you dont abuse yours. Im wondering if its flexing enough to let your pistons hit the heads

bill buttermore

nate: I am not absolutely sure yet (will know when I get it all torn down), but I suspect that the crank is a replacement, maybe part of an aftermarket kit. I say that because I have not yet located the stamps for the journal bearings and rod bearings that I have seen on other Toyotas I have rebuilt.

toytech: That crack goes all the way through the crank so that #5 and #6 are no longer connected. The only reason it still rotates (sort of) as a unit is that the irregular shape of the break does not allow complete separation of the pieces. The broken surfaces come apart and go back together during each revolution, and were the source of my truly horrible engine noise. I just hope the break did not allow enough movement for significant damage. I will find out tomorrow when I pull the heads, and examine the bore, pistons, and rods. #6 is likely to be the worst, as the break allowed that portion of the crank more vertical movement than the part connected to #5. The previous owner said this occurred at highway speed while cruising. Just a horrible noise and loss of power. He did not mention anything about having the engine worked on, and he had owned the truck for several years. But, that crank (at least on cursory examination) does not look like a Toyota product to me, and it is clear that the motor has been rebuilt sometime in the past. So, my first guess is that it is an aftermarket crank of inferior quality.

toytech76

Inferior is an understatement! Sounds like a full eng rebuild is in order

mr_schuster

Wow, that sucks.

Looks as if someone has already been in the motor. The rods bolts and nuts have that pretty red nail polish on them and turned 90 degrees.

As far as a cracked crank in that spot, I would be suspicious of the thrust bearings.

bill buttermore

The cylinder heads look fine. No evidence of valves striking the pistons, the bores show the cross hatching clearly from the last rebuild. The piston tops are covered with carbon. The exhaust valve margins look nice and thick. I only had time to remove the rod journal from #6 today- the bearing showed some grooving but the journal on the broken crank looked very good. I think the engine must have been running well until it wasn't running at all.

I'll try to post some pix tomorrow.