Gen 3 Montero/Pajero "Thumping" at Start-up

[nnamssorxela]

The Montero has been sitting since monday(?). Today I decided to replace the rear "cam seal" o-ring on the passenger side, as I determined that was the source of the oil leak, not the valve cover gasket. Went to start her up to shuffle some cars in the driveway and I was faced with a HORRIBLE rattling clank (video attached). I immediately turned it off and and removed the belt to see if it was accessory related and unfortunately it wasn't, as the sound persisted without the belt on. This is not the thumping sound originally mentioned in this video, but something else. I could feel the ticking on the top of my intake manifold, and the sound seemed loudest in that area according to my long screw driver. Against my better judgement, I drove it around the block and noticed the sound was a lot quieter. I tried the 15sec rev to 3000rpm trick to adjust the tensioner or whatever it claims to do, and it helped but it was still making a definite hard clicking. Turned it off, and not 5 minutes later started it back up again only to have it be purring like a kitten. Any suggestions?

This is the sound at it's worse...beware!

 

[jhill15]

Mine will make the same sound when its cold outside and has been sitting all night. Its not as loud as yours and goes away after 30 seconds or so, then just like yours the next time I fire it up it purrs like a kitten. I couldn't tell where mine was coming from as it sounds like the entire engine is making that horrible sound. I would love to know what it is though. Mine is in the shop getting much needed catch up maintenance so I will be interested to see if the noise is still there wjen I get it back.

 

[clmrt]

Timing belt issue - tensioner let go, that's what mine sounded like. The belt is still in place but without tension it allows the PS cam to lag in time and your valves are smacking the pistons. Or something.

$$$

 

[nnamssorxela]

Interesting, timing belt was done less than 50k ago IIRC, I'll check the records. I find it weird that the sound goes away. In my experience when timing tensioners just "let go" there is a lot more damage and they don't just fix themselves after a couple minutes. Perhaps this is oil pump related, and the tensioner just isn't getting the pressure it needs at start up?

Any additional insight is appreciated. Not in the mood to rebuild the heads just yet.

 

[clmrt]

Not sure, but I think it's the TB / TBT. I suppose it could have jumped a tooth or two and is keeping better time now? No idea. I do know that sound, in my situation, was due to the tensioner letting go. The mechanic said the noise was from the tensioner idler bouncing around on the shaft but it seems to me like it was in the head. It was consistent, but I didn't drive anywhere with it - towed straight to the dealer, under the knife.

 

[nnamssorxela]

I appreciate your input. Hopefully my tensioner is just low on pressure and rattling (in the way that your mechanic mentioned) heavily before it builds pressure. If my valves and pistons were hitting that hard, it would not be drive-able, or even close to running smooth after the fact. I drove it to work today so when I get hope I'll park it. If my timing belt doesn't jump between now and then, I'll inspect the tensioner sometime next week when I have time.

Fingers crossed.

 

[nnamssorxela]

Thanks for the tips clmrt! Googled it a little more and this is the sound almost exactly, including how it goes away at higher rpms. I don't think that sound was valves hitting piston, but the sound seemed to be coming from the center of the motor under the intake. I also don't think the belt losing tension would allow the pistons and valves to hit unless it skipped a couple teeth.
https://youtu.be/f71QFaq7kKQ

 

[nnamssorxela]

For the one person that might find this thread in a search, a new timing belt tensioner solved my issue! I'm guessing that horrible sound was the tensioner getting slammed around, and the sound was "escaping" through the top of the motor. At any rate, I replaced it and all seems well. In hindsight I should have just done the timing belt itself while I was in there, but I didn't want to waste time and money on a new belt if I have bigger issues.

In addition to the tensioner, my coolant was black, so I pulled the radiator, flushed all that, and did the power steering flush as well. Thing are starting to shape up, can't wait to start modding!

Also for reference, the procedure to change the timing belt is pretty straight forward and easy, and any one with patience and some sort of mechanical aptitude should be able to knock it out with only few specialty tools.