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3.0 V6 / Caravan Valve Stem Seal / Timing Belt Installation Notes

by Ellsworth Chou

If your Chrysler, Plymouth, or Dodge product has a 3.0 liter Mitsubishi V-6, and smokes at idle or startup but not while cruising, you may be able to fix it yourself for under $200.

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Table of Contents

The Story

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Mitsubishi V6 cross section

About this Document

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Reference Materials

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Special Tools I Used for the Job

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Parts Required

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  1. Checking for Fallen Guides
    • Of all the references I used, only Keith Vickers' Web account suggested the possibility that in some cases, the valve guides themselves may have slipped down into the head. In these cases, the seals bottom on the head rather than seating on the guides. Apparently this condition necessitates removal of the head. Keith Vickers suggested inspecting all the guides before beginning the operation, because it'd be pointless to continue in this condition. The front head is fairly easy to inspect: just pull the hose off the PCV valve, pull the plug wires from the harness and loosen the valve cover's two 12mm bolts. Removing the rear valve cover requires removal of the alternator, and it's awkward to work in the back of the engine compartment over the manifold/intake plenum. Thankfully, our valve guides seemed perfectly normal.
    • Once you've determined that your valve guides haven't slipped down into your head(s,) you can begin the operation.
  2. Preparing for Cylinder Head Access
    • Pull the air conditioner belt andthe serpentine belt.
    • Pull the air cleaner assembly. It's attached to the rear head with two bolts through steel straps.
    • Pull the alternator. I suppose you could actually leave it connected to its harness and rest it out of the way near the brake master cylinder. I completely disconnected it. It's held in place by a pivot bolt and nut which is very visible, and another anchor bolt toward the firewall end of the alternator, head towards the passenger front wheel. I did not remove the alternator bracket - it didn't create an interference problem that I noticed.
  3. Removing Intake Plenum and Manifold
    • I'd say that it's necessary to remove the intake plenum and manifold. Even if you found a really short spring compressor which fit between the intake valves and the intake runners, the ease of access to the rear head without the intake parts is worth the effort. Furthermore, the sludge I found in our EGR plumbing was also inside the intake plenum where the EGR pipe hooked in, so it'd be easier to clean that out off-vehicle. Here's what I recall of removing the intake:
      • This necessitated the removal of several vacuum hoses. I didn't have to label anything. Sizes of hoses and unique angles were adequate. I also had to pull several sensor connectors - no problems there. Throttle and cruise control cables had to come off the throttle body bellcrank. Then I removed the throttle cable bracket from the intake plenum. At the driver's end, toward the rear of the plenum, the EGR pipe is a 5/8" O.D. steel pipe which connects to a flange at the plenum and another flange at the EGR valve itself. The plenum came off with a little sideward tap from a hammer and a block of wood. Now the plenum came free of the car.
    • Before pulling the intake manifold off, I pulled the injector harness connector at the rear of the intake manifold. I chose not to disconnect the fuel lines from the injector rails, or to remove the rails or injectors from the manifold. This spared me from depressurizing the fuel system. After removing the nuts and bolts from the manifold, I tapped downward on the top surfaces of the manifold with a rubber mallet. The manifold came free with a couple of taps. The manifold-to-head gasket did tear in a couple of places, but I'd planned on buying a new gasket anyway. (Don't expect to find a manifold-to-intake plenum gasket at a non-factory place. I didn't actually try, but I wouldn't count on it. Ours survived intact.) I gently folded the manifold on its three fuel system hoses backward so that it rested upside down on a pad over the passenger fender.
  4. Removing Valve Covers and Rocker Assemblies
    • Now that the intake's out of the way, you can pull the valve cover(s) (if you didn't already have them off for the guide inspection.)
      • *NOTE: Remember to stuff rags into the oil return passages cast into the heads, to prevent small parts from dropping through during the following operations.
      • *NOTE: When removing the rocker shaft assemblies, it is likely that one or more of the hydraulic lash adjusters will fall out of the rocker arms. These 7/16" diameter, 3/4" long steel lozenges are recessed into the valve end of the rocker arms, and are only retained by oil viscosity. When they fall, the adjusters are easily retrieved from beneath the cam (the typical place they'll fall) or other cavity with a magnetic parts retriever. Upon reinstallation, dip them into grease to stick them in the rockers during handling. Keith Vickers' Web account suggests securing the adjusters to the rocker arms with wire twist ties. Would've been a pretty good idea, if I'd remembered.
    • Getting the rocker shaft assemblies on and off was a pain. Because some of the valves and rockers are open and thus under compression, the rocker shaft assemblybolts must be removed a quarter turn at a time. Each of the eight bolts takes many of these quarter turns to remove. Because of my own errors (detailed later) I ended up removing and installing the rocker assemblies some five times (twice in front, thrice on the rear head.) I made the mistake of following a manual's instructions and removed all the bolts before removing the cam assembly. Mistake. The bolts should stay in the assembly during removal, temporary storage, and installation. Otherwise, the springs between the rocker arms will push the cam bearing bosses and rocker arms off the rocker shafts. You'll be faced with many separate pieces, which the factory manual points out must be reassembled in the same order.
    • Place the removed rocker assemblies on a clean surface (a sheet of newspaper will soak up some of the oil which will drain from the assembly.) If you can set them on their sides, you might avoid having either the bolts or adjuster fall out. It proved useful to go ahead and stick the adjusters in the rockers with grease to keep them in place while they're set aside.
    • Carefully remove the two rearmost bolts (furthest from the pulley) and the associated cam bearing cap from the rocker assembly. The endmost springs and rocker arms will threaten to spring off, so be advised. Now reinstall the cap on the head. Without it, the free end of the cam can be levered into the air when the engine is turned, possibly slipping off the pulley and resulting in loss of crank-to-cam synchronization. I should know - this happened to me! (more about that later)
  5. Compressing/Removing the Valve Springs
    • I did the front valve stem seals first, because they were easier, and I hoped to learn some technique before proceeding to the awkward rear head.
      • I'd intended to use a technique for holding the valves in place I read in the Haynes manual - stuffing the cylinder with nylon rope instead of using compressed air. If I could have done that, it would've saved me some grief - more about that later. As it turned out, I couldn't get access to the spark plug holes to stuff the rope. Because of a sheet metal heat shield between the exhaust manifold and the spark plugs, I couldn't get my fingers within 4 inches of a plug hole. Pushing a rope across a four inch gap to stuff a cylinder is less than practical. So I went with the traditional method of using compressed air.
      • (*NOTE: because of the 4 inch access problem, you'll want to use a spark plug/air compressor device that uses a piece of flexible hose. It'd be really difficult to use some of the spark plug/air adapters which are solid metal)
    • The preferred technique for pressurizing the cylinders is this:
      • rotate the engine by hand to TDC for the current cylinder; this will require either using a probe in spark plug hole or using the distributor position (provided the distributor hasn't been removed; now rotate the engine slightly past TDC, so that it's on the downward part of a stroke; then secure the ratchet on the crank so that it prevents rotation of the engine in the forward direction (clockwise as viewed from the pulley end); if the ratchet handle is long enough, you can rest/clamp it on the passenger-side halfshaft
      • *NOTE: the reason for doing this step is to provide some insurance that the valve won't drop completely into the head in case of accident or malpractice - I don't actually know that it'll keep the valve from falling past the end of the guide - the consequence of that occurring is removal of the cylinder head; which would be BAD
    • Here's where a semi-disaster occurred:
      • I thought I realized at this point why one account I'd read didn't worry about keeping the engine from turning when pressurizing the cylinders: since the rockers are removed from the head, it wouldn't seem to matter whether the engine was at TDC for that cylinder or not. The valves will always be closed, in any crank position.
      • However, I'd completely missed the argument that keeping the current piston near TDC might save a valve from falling through, so I chose to let the engine turn. I was very lucky that I dropped no valves. You probably shouldn't take the same risk.
      • The bigger problem was the unsupported cam problem, mentioned at the end of "Removing Valve Covers and Rocker Assemblies," above: the cam bearing caps are part of the rocker shaft assemblies recently removed. When the rocker shaft assemblies are out of a head, the cams are merely resting on the lower bearing surfaces and a seal around the shaft between the cam pulleys and the inside of the head. Every time I connected the compressor air supply to the spark plug adapter (without concerning myself with the current cylinder's position,) the engine would spin a partial turn until that piston was at BDC. A couple of times, the non-pulley end of the cam violently lurched two or three inches up off the head, levering itself on the front seal. This was really distressing. On the front head, I was so disturbed by this that I removed the top cam bearing cap from the end of the rocker shaft assembly(this was before I figured out that I could leave all the bolts in the rocker assembly) and bolted it in place at the rear end of the cam. (In fact, Keith Vickers did suggest this very procedure, which I'd forgotten by time I was working on the engine. Just goes to show that I shouldn't trust my memory. Perhaps yours serves you better.) Later, I would attribute losing a couple of teeth's worth of cam timing to these incidents. I would eventually reset the cam/crank timing by manually tilting up the rear end of the cam and slipping the belt off the pulley. I don't know what kind of damage these abuses did to the front cam seals.
        • Do this at your own risk: If you're willing to forgo the insurance of leaving the piston at TDC to keep a valve from dropping, or just believe that having the cylinder at TDC wouldn't help anyway, here's a method that would save you from locating TDC and restraining the crank's turning for every cylinder. If you could put a socket and breaker bar on the crank pulley bolt and clamp the breaker bar to something (the halfshaft is convenient in the Caravan) to prevent its turning in either direction, that would work. You would want to wedge something between the inner fender and the breaker bar to make sure it didn't slip off the bolt head. It's critical that you prevent rotation in either direction, since any given piston might be either before or after TDC, and you couldn't predict the direction of rotation.
          • *CAUTION: If the engine does move under 100+psi of air pressure while there is a tool connected to the crank, you could injure yourself or damage part of the vehicle.
        • You could leave this rig in place for the duration of the valve stem seal work, as there's no reason to rotate the engine during the procedure (if you're not trying to catch falling valves.)
        • If you have a manual transmission, you can avoid all these engine-securing procedures, and simply leave the vehicle in gear and set wheel chocks and parking brake.
  6. Compressing Valve Springs and Replacing Seals
    • The K/D compressor worked well. I could only grab a little less than two thirds of the spring, which was a little disappointing at first. Compressing two-thirds of a spring left a little more than 1/4" of clearance. But it proved adequate, requiring a "special technique." Almost none of the top spring retainers released easily from the valve stem keepers. I tried banging on the spring compressor with my hand - this worked on the first intake valve. But the exhaust valve was really stubborn. I could bang so hard that it'd pop the exhaust valve open, even against 100psi from the compressor. The system I eventually worked out was this: stuff a little piece of rag or paper towel on top of the top of the valve, between the arms of the compressor, to catch any keepers that might shoot out when they release (one of mine did, in fact, do this - leading to a prolonged search about the engine compartment - the towel trick was developed at this point.) Then I'd place a small drift somewhere on the top of the retainer and tap lightly with a hammer. Eventually the spring assembly would drop to the head, and I'd remove the keepers with a magnet. Now I could slip the spring off the valve.
      • *CAUTION: It's critical at this point that you not lose air pressure from the compressor. Likewise, a hard enough tap on the top of the valve stem might pop it loose, even with air pressure. If you drop the valve into the head, and you haven't left the piston at TDC, it'd be really ugly. Again, I don't know that a piston at TDC would catch the valve high enough to leave the stem accessible. Nor do I know if a valve could be recovered without removing the head.
      • The Haynes manual suggests at this point that you slip a rubber band around the valve stem (small nylon wire tires fit well into the keeper grooves,) so that you can de-pressurize the cylinder and check the valve by hand for straightness and guide condition. If you aren't going to check these, you can just leave the air compressor connected and go on to installing the new seals.
    • The old valve stem seals I removed with a pair of slip-joint pliers. They require a little effort to remove. Be careful: it's easy to slip off, and potentially nick a valve stem. Go slowly and twist the seal back and forth around the guide, with constant upward tension. The seals often release suddenly, so keep your face clear of the pliers (especially while you're bent over the engine working on the rear head.) Now choose a tool to help tap down the new seals. I used a 1/4" drive 1/2" deep socket. It should fit around the narrow part of the stem seal without touching the top of the soft seal, and evenly contact the top of the metal shell. It's important not to damage the narrow part of the seal or its little spring.
      • *CAUTION! It is CRUCIAL that the socket (or whatever tool you use) not touch the top of the valve stem. Test fit your proposed tool on the new seal and on the bare valve stem and guide. You'll be tapping on this with a hammer - if the socket came into contact with the top of the valve stem during the tapping, you might tap the valve into the head, despite the compressed air. That would be BAD.
    • To install the new seal, oil the stems with fresh engine oil, and slide the seal down until it contacts the guide.
      • (One account I read said that the new seals should come with some kind of installation sleeve that slips over the grooves in the valve stem, to prevent damage to the new seals. I received no such sleeves, and only noticed this in print after the job was done [notice a trend here?] For what it's worth, most manuals merely mention oiling the stem before installing the new seal.)
    • Press down as much as you can with your fingers. Now slip the socket carefully over the valve stem until it rests on the seal. Tap on the socket with a rubber mallet until the seal bottoms on the guide.
  7. Valve Spring Reassembly
    • Put a glob of white grease on the keepers during reassembly to stick them in place on the valve stem during reassembly. Use a magnetic retriever whenever possible to keep from dropping parts. Make sure the keepers seat when you uncompress the springs.
  8. Final Reassembly

      I'm going to wimp out and hope that you can figure out most of the reassembly yourself. Here are some notes:

    • Remove the end cam bearing cap from the head and carefully reassemble it with the rest of the rocker shaft assembly. The bolts will hold the endmost rockers, springs and bearing cap in place while you move the assembly back to the head.
    • Put a 3/8" long, 1/16" strip of Permatex High-Temp RTV (oxygen-sensor safe) at the corners where the round seals or bearing caps meet the flat machined surface to which the valve cover seals.
    • Place the rocker shaft assembly on the head, being careful not to knick any cam bearing surfaces. It might take some wiggling to seat the assembly. I felt the gaps between the cam bearing caps and bosses with my fingers to determine whether it was going together symmetrically. Now thread the eight rocker shaft bolts with your fingers until they just contact the cam caps. It's important again to run them down equally to prevent bending or breaking the rocker shafts. It's only important that the bolts progress an even depth into the head, even though the loads on the individual bolts during tightening are very different (because some of the valves will be open.) They'll finally be torqued very lightly, so be gentle with a ratchet as you get close to seating the bolts.
    • Tighten rocker shaft bolts in several steps, to a final torque of 180 inch-pounds. Work from the ends of the shafts toward the middle.


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I'm really not sure now if what I thought went wrong at the end of day two ever went wrong. Here's the week:

Here's why I had to retime the cam:


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Ellsworth Chou's Other (hopefully) Useful Pages

Contact Info

Questions or comments to Ellsworth Chou at [email protected].

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