Chain Tensioner and Cam Tower Reseal... maybe

The cam tower leak is a well documented issue. From what I understand, it's due simply to "the robot" applying too little sealant in the back bottom corner of the cam tower when assembling the motor. Some leak, some weep, some spray oil, some don't do anything. Mine has been weeping for quite some time - not enough to cause an appreciable loss of oil between oil changes, or really even to leak on to the exhaust, but if run hard for several hours towing, I will get the faintest smell of oil. So it wasn't strictly necessary but since I had the motor half way torn down, I figured I'd give it a go. Eventually they can leak to the point that they drop oil on to the exhaust. In my case, I'm guessing that would have been several years down the road, if at all.

Judging by what I found, I deemed to leak to be caused by too little sealant in the corner, along with some rougher machining marks. Just a weep, though.

The cam chain tensioner on the driver's side is also a well document possible issue. There is some speculation as to why the tensioner fails, but the general consensus is that the oil passage in the tensioner gets gummed up, or the heat causes a minor tweak to the body and it sticks. In severe cases, the chain rattles raucously at idle and low load with quite a clackity clatter. The biggest (but least possible) concern is that the tensioner fails to the point that timing can skip. I don't recall ever reading about this happening, but there was maybe one case where it was insinuated. My dealer told me that it could happen... But that was a year after they quoted me $2400 to fix it but told me not to worry about it, then decided they wanted to charge me an absurd amount of money a year later when I asked about it again. Doom and gloom tactics, telling me the motor was going to implode. HOGWASH.

In my case, the tensioner only made noise (or rather, the tensioner failed to provide adequate tension on the timing chain, causing the chain to make noise) about 5 minutes in to a warm up cycle, for only a few minutes. I didn't rattle when cold, it didn't rattle when arm, just in the middle. Because I'm a glutton for punishment, I decided to tackle the job while waiting for the supercharger to be rebuilt.

Is it preventable? Well, judging by the varnish buildup (or lack there-of) on the innards of my motor, I'd say my maintenance schedule has been more than adequate. I think that NOT following the Toyota recommended 10k OCI for the first 30 or 40k miles COULD have prevented it, but I can't say that it caused it either. I will say that the 10k OCI is also HOGWASH except in very rare circumstances. After having the dealer service it for the first two years, I started whittling down the OCI to where I was comfortable with it, doing all of the maintenance myself rom thereon out. Eventually, I sent out some oil samples to Blackstone, which validated my truncated OCI schedule.

But the jury is still out on the tensioner. It may fail, it may not, but good maintenance can only help the situation, IMO. The nice thing is, it will most likely give you PLENTY of heads up before failing to the point that it becomes a real issue. The cam tower leak is well known but there isn't much in the way of preventative maintenance for it. I'd just wipe it down from time to time until it starts pouring oil on to the exhaust - which it may never do.

 

I didn't have much time to work on the truck this weekend, but got a few things swapped out last night and started prepping the front cover to go back on. I pulled the alternator and dropped it off at a local shop to have it rebuilt; it still work fine but has 230k miles on it and I figured it would be great to do 'while I'm in there'. I think I'll pull the starter and give the same treatment 'while I'm in there'. I'm hoping it's easier to get to with so much pulled form the motor already, and I'll be swapping in some @Bonzen Solid Offroad motor mounts 'while I'm in there'.

I changed out the drivers side and passenger side chain tensioners, along with the timing chain guides 'while I was in there'. I purchased more parts than I would probably need because if I didn't have them on-hand, I'm sure I would need them. The chain guides look virtually new. You can barely feel a groove from the link marks with a finger nail. Lots of folks have said that they are find and shouldn't need to be replaced - to which I concur.




The passenger side tensioner also looked to be in great shape.

The driver side tensioner - the one that is problematic - looked a little rough, which was interesting to me. There is a two-piece gasket on the backside of the tensioner with a pocket for oil (I don't know why exactly it is designed that way, but it is...); when I peeled it open, there was some very fine metal debris in the bottom right corner of the metal side of the gasket. The gunk is similar to what you find on a differential plug magnet or transmission magnet - very fine metal particles. The fact that they collect in that corner perhaps means that corner may be indicative of an inherent flow problem with the gasket design? I'd be open to some thoughts on the matter. The tensioner itself also appeared to have much more gunk and wear than the rest of the motor innards that appeared nearly spotless.







The tensioner shaft also had some obvious wear marks and a barely perceptible wobble to it. It would also rotate about 10 degrees.



After that, I started to clean the gasket surfaces for the front cover but needed to get a pork butt on the smoker before I went to bed, so called it early.

 

Got a few things done this evening. I cleaned up the front engine cover and mounting surface. Then I got brave and pulled the pins on the chain tensioners, threw the balancer and crank bolt on, and pulled the spark plugs. Then I grabbed a wrench and slowly turned the motor over...



No bad noises, no binding, compression shooting out the spark plug holes. Hopefully that means timing is good to go!


I went to the hardware store and grabbed a couple of M8x1.25 x 60mm bolts, then cut the heads off of them so that I could use them as guide studs to replace the front cover without smearing the sealant.

But first, I decided to take a closer look at the valley plate (might have the part name wrong, but it's the plate that sits in the valley that helps direct coolant through the block). I have suspected a minor leak for a while, but I had a couple of hoses leaking on the coolant crossover after the SC install, so I wasn't 100% sure that the coolant I found in the valley was from the leaking plate.



But I guess I might as well reseal it 'while I'm in there'... Now I'm 100% sure the coolant I found in the coolant was from the leaking plate. So I pulled the PCV plenum or whatever it's called out of the valley, fought with the AIP valves a little (really just one bolt on the passenger side that is obstructed by the head unless you make a little extra room with and advantage multiplier. Got the valley plate out, cleaned up the sealing surfaces, and resealed it with more seal packing. There are two studs that help keep the plate centered so you can get a good drop on to the sealing.












Got the AIP system and PCV systems put back together, and had to call it quits for the night. Hopefully I didn't booger up the AIP system or Hewitt may be getting my attention in the near future.




Hopefully that means next go round I'll inventory gaskets for the front cover and valve covers, then hopefully be able to re seal the front cover, reinstall valve covers, and then put the front of the motor back together. I still have three more things to do 'while I'm in there' but I don't think they will take too long: new Solid Off-road Engine mounts (I've swapped engine mounts before, and it should be even easier with how much is already torn down), inspect the wiring harness that got hot and install a thermal sleeve (I purchased a Design Engineering thermal wrap), and figure out how to secure the passenger side header heat shield in a better fashion as it appears to have worked loose (I removed it a while back and didn't get it 100% secured).

 

It’s starting to resemble a motor again..

 

Great plan to align the timing cover with some "cheap tools"

 

Question about the PCV system. That looks like a substantial air/oil separator tank. Have you replaced the PCV valve itself or did you let it ride? Seems like a lot of newer vehicles don’t have a mechanical PCV valve, and more or less employ a fixed orifice adapter on a separator of some type

 

Thanks. They worked great. I was worried about moving an o ring or seal, as well as smearing the sealant. The dowels allowed me to slide it back in to the motor cleanly and straight on. I did test fit it a few times before applying sealant and needed to clock the oil pump that rides in the cover around the crank snout. I fiddled with it while cleaning things up so figured I would get it dialed before hitting the go button.

The black plastic reservoir (for lack of better term) in the valley is the stock PCV system. It plugs in to a port in the back of the valley underneath the AIP valves that I believe goes to the block. I have a catch can that intercepts that garbage from getting regurgitated by the motor after the PCV.

 

Specifically referring to the “PCV valve” component of the assembly circle in red. Have you cleaned or replaced that part? Is it a mechanical check valve style or fixed orifice?

 

Gotcha. Yes, it's a serviceable part that I've replaced recently but may was well add it to the list 'while I'm in there' since I've got one on the shelf. I believe it's a mechanical check valve type since it rattles around if you shake it. I know that it's designed to vent pressure from the black reservoir out, but prevents pressure from going back through the PCV into the black reservoir. You can blow through a new one from the black end, but not from the green end.

 

perfect. Thanks!

 

It appears to me that the black bladder is similar to a catch can that is designed to trap most of the oil vapor and drain back into the block, correct?

 

It would appear so, though I’m not up to speed on the PCV system workings on these trucks.