Just had a look see inside a 2002, ZR2 Tracker with a 2.5L and 150K on it whose owner was complaining of "a noise in the engine".  If these pics don't convince someone to stay on top of their oil changes.... nothing will.  The last pic is/was the oil pic up in the sump of the pan.  Was almost completely closed with crusty oil build up.  The sludge on the rockers, in the pan, on the front timing chain assembly was about 1/4" thick and looked as if it had been baked on at high temperatures.  It wasn't putty like... you could scrape/flake it off and I am sure the entire lube system is populated with pieces of this crap floating around.  And STILL this little engine was running well... except for the chain noise in the front.  Amazing.

Sheesh! Looks like they were using grease instead of oil!

Change the oil much? Id say not.

Obviously this engine hasn't seen routine maintenance forever.  I am also curious what kind of oil they ran in it when it did get changed too.  I cleaned the oil pick-up screen on it today.  The bottom and lower sides were totally plugged... as in solid.  It was only sucking oil through the top sides of the pick-up screen.  It is amazing the lifters were still gliding around smoothly and the journals in the cam caps were clean and lubed.  There aren't any bearings in the cam journals.  They are simply machine fitted with oil holes and oil reliefs in them.  These things are fitted together like a sewing machine.  The first pic below is the pick-up after a little cleaning and the second is right before it was re-installed.  The last pic is of the sump of the tensioner that sets under the passenger side cam chain... nasty stuff through the block.

It appears the owner brought it in 'just in time' (before complete failure) although the longevity of this engine has to be greatly compromised now.  This thing is going to require an oil change every 1000 miles for several thousand miles and even then I'm thinking there is a good chance the pick-up may become plugged again because of all of the debris within the system.  A $1500+/- repair and greatly degraded engine longevity... all for the want of $600 worth (30 changes |removethispart|@ $20) of oil changes.

Don got the engine back together with new chains, tensioners, guides and oil pump plus alot of cleaning and it idles like a sewing machine.  Unbelievably smooth for all the massive build-up throughout the block.  The longevity of this engine has to have been severely compromised with the apparent failure to maintain oil changes but it is running great for now.

Update... the 2.5 is running great... but the owner is now having to add a quart of oil every week.  Probably the valve stem seals are shot.  Would have, could have installed these when the engine was taken down the first time for the front cam gear, timing chains, tensioners and chain guide replcement, but the owner 'wanted to limit the repair cost'.  

Well, to replace the valve stem seals now will require taking the engine down like before (minus the cost of new gears, chains, tensioners and guides) because you have to remove the cams to access the valves.  Not much savings on the repair cost.  Wow.

Nprecon,

What had to be done to take the engine down to clean it up like you did.  Can this be done without removing the engine?  Could you remove the oil pan without pulling the engine?  I probably need to do this same thing to mine.

Thanks,
Brad

My friend Don was the mechanic who did the lion's share of the work on this Tracker. Long story short:  yes it can be done without pulling the engine.

The qualifiers I would give is Don had the Tracker on his hydraulic lift which makes accessing the under carriage much easier.  

You have to drop the front diff, which can be accomplished by removing the three bolts on the driver's side of the housing on the CV shaft, then remove the four bolts on the front drive shaft (be sure to secure the shaft up or it will pull out of the front transfer case and you'll bleed gear oil all over the floor), then remove the bolts securing the third to the cross member... then wrestle (literally) it out and hope the c-clip holding the passenger side CV in the carrier releases easily. Having a yoke on hand to pry the CV out of the housing would be a big plus.  Some come out easily and others need to be convinced with some hammer taps.  If you get a stiff one, be sure to continually rotate the CV shaft between taps so the c-clip will center itself up and come out easier.  Once you get the passenger side CV shaft to release and pull out of the housing, visually inspect the end of the CV shaft to ensure the c-clip is still on the end of the shaft.  If it is not... then you get to split the third from the housing and look for it.  You don't want this little piece of metal in there chewing up your ring and pinion gears.  Did I mention having a buddy there to lend an extra set of hands would REALLY come in handy during this part?

You should also consider removing the four bolts holding the rack and pinion to the front crossmember and allowing it to sag down to give you more working room. I've said it before, but sitting behind a computer and typing gives zero appreciation of just how tight everything is stuffed up under these little trucks.

Then remove the oil pan.  It is a two piece design.  The "sump" portion is aluminum and is bolted to the steel part of the pan.  After removing the sump, you have to reach up and remove the oil pick-up tube and screen retaining bolts.  Note the difference in length for reassembly.   Once these parts are removed you can take the other bolts out of the metal pan and turn it around until you can work it out of the opening created by the diff removal and the sagging front R&P.  REMEMBER what position it is in when you remove it.  Make sure you remove and replace the o-ring collar on the pick-up tube. It may stick up in the bottom of the oil pump.  If you replace the oil pump at the same time, fill the new pump with some oil as you turn it a few times so it is saturated with oil and begins pumping quickly.   Assembly is the reverse of the above.  When you pull the metal pan out you will see there are about 7 bolts holding the metal baffle in.  Remove these 7 bolts to remove the baffle and clean the pan completely and properly.

The radiator will need to come out as well.  You need the working space on the front to wrench and be able to see the casting, gear, and chain markers.

On the top side, everything comes off to include the injectors, fuel rails, intake and valve covers.  Same with the front cover. All the bolt ons; alt, power steering pump, compressor.   Unbolt the compressor from the block and just lay it over to the side of the frame.  Don't discharge it.  Be sure to clean off the front timing chain cover with a good degreaser so you can see what you are doing.  There is a bolt in the lower middle which you won't see if it is caked with oil and road dirt.  

Oh yeah, the water pump.  It sits right in the middle of the timing cover.  Yours may not be leaking now, but I'm telling you, you may as well replace it and hope like hell the new one is not a defect because you essentially have to remove all of the above (minus the pan and diff) to get at it.  So while you are in there, think hard about replacing it at the same time.

Before you start pulling off gears and chains, inspect the chains and see how they are lined up.  Put a socket on the crankshaft and turn it around a few times with a breaker bar so you are familiar with the alignment and what it looks like before you attempt to replicate it with no references.  There are several markings on the cast of the block (some are difficult to see) and the gears which all need to be aligned properly.  Think about it:  you have four cams (2 on each head) that have to be synched properly.

Remember the valve stem seals.

You will also have to remove the cam shaft caps on the passenger side in order to replace the tensioner that sits under the cam shafts on the front of the passenger side head.  If you wipe down the cam journals and the cam shafts be sure to coat all of them again with clean oil before re-assembly.

Clean all the gasket surfaces well, don't scratch them, apply some RV sealer to them, allow the RV to air cure a couple minutes, then snug the bolts down to almost tight, then wait 20-30 minutes and run back across them and torque each of them to specifications and you should be good.

Oh, and another observation, the torque requirement on the crankshaft was only half of what the 2 liter engine calls for.  I thought that was a bit strange.  These little engines are built like sewing machines.  Impressive.  Hope these thoughts help you make the decision.