GEN1 LWB 6G72 12V Engine Refresh

[chadzeilenga]

Hi All,
Some of you have read up on my recent HG issues. For those that did not, the 3.0L engine in my 89 LWB overheated while on the highway. I have done an initial analysis and torn the engine down to the short block. I found presence of coolant in the #3 cyl. There was rust on the cyl wall and accumulated on the valves. Below are some pictures of what I found:


You can the the rust on the cylinder wall and exhaust manifold from the water getting in.


Corresponding cylinder head


The stem of the intake valve has rust on it. Since I took this apart a few days after I overheated, I'd assume this corrosion pre-dates my immediate issue. Would the other source be a crack in the head?


Never the less, the cylinders look pretty good for a 200k mi engine. There is not even any ridging at the top and factory pistons appear to be installed, so I'd assume it hasn't been rebuilt.

Based on the above, my compression is 120psi and that I'm so close to replacing some of these wearable items on a 200k mi engine, I'm thinking of refreshing the bottom end while I'm going through the HG repairs. Below is my initial plan that I've assembled after reading various posts here and at 4x4. Would like to get input from other more Sr. members who have gone down this path:

• DIY Verify Cylinder Head Condition
  • Warpage (<0.019”) & Cracks
  • Thickness - Height > min thickness per FSM
  • New Valve Seals
  • 3mm VLAs
  • Cam Seals
• Remove engine block - Take to machine shop
  • Disassemble, Clean & Inspect
  • Ball Hone Cyl, New Bearings & Rings
  • Rebuild Oil Pump
  • Water Pump/Timing – Aisin Kit
• Crank Seals - OEM
• Motor Mounts - OEM
• Injector cleaning

Aside from the above I have a list of a few items to get at my local yard and also planning to replace as much of the wearable items my budget will allow:

• TB Coolant Hose – MD140937 & MD138049 & Clamps (4) MS660242
• Supply Fuel Line O-ring
• Fuel Supply & Return lines
• Injector harness - Existing damaged
• Brake Booster Vac Line - Damage
• Exhaust studs & Nuts MD108396, MD000569, MD041192
• Distributor Cap O-ring – MD611460
• Thermostat – MD997221
• Rad Cap - OEM
• Exhaust heat shields MD141465 & MD141464
• Water Inlet Pipe O-ring – MD330763
• Distributor Cable - MD611921 - Is this serviceable? Mine has some damage to sheathing, but I can't see on distributor how it connects.
• Distributor Shaft O-ring – MD611463
• Rear main seal – MD101915
• Front Main Seal – MD068855
• Cam Seal – MD008762
• Rocker Cover Hose – MD139348 & MD136258
• Fuel Pressure Regulator
• Silicone Vacuum line

Junk Yard Parts

• AC Compressor bolt
• LH Timing Cover
• Valve cover harness nut
• Oil fill neck hose
• Upper Intake Brackets
• Lower manifold
• Water Inlet Pipe – MD132760

Do any of you more experienced members have suggestions on my plan above or any other suggestions while I am in here?

 

[Toasty]

Seems like you're on the right track dude.

 

[chadzeilenga]

Spent some time on the heads tonight.

I checked flatness on the heads and got <0.002” in all directions on both heads. Not sure how this is possible since I was in full on overheat. During disassembly there were 2 head bolts which were loose. PO probably reused the bolts.

I also measured the thickness and was only able get a measurement with my calipers on the exhaust side. The the thickness ranged from 3.304”-3.302”, which is 0.006”-0.008” below the MIN FSM value.

Does anyone have any experience exceeding the FSM limit?


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[Toasty]

Both of those finds are probably what caused your issues in the first place. You can get a thick head gasket but really you should just buy heads. We had a 3.5 head get machined too far and it caused overheating issues.

 

[chadzeilenga]

Thanks for the feedback Toasty. There is a set at local U-Pull that are waiting to be pulled, they are just an unknown condition, but at a minimum, likely not decked below the minimum spec. I can go through and take care of the valve seals and VLA's on them if they measure OK.

I also discovered an interesting bit of information while researching deck heights. The MLS gaskets that our engines were designed for require a significantly better surface finish on both the block and head to be effective. So for anyone who is getting their heads machined and planning to use the OEM gasket, should target a surface finish ~30 Ra where as standard graphite gaskets require 80-110 or so.

Felpro Surface Finish Article

 

[Toasty]

Yeah our V6's are very sensitive to surface finish.

 

[GrantC]

I also discovered an interesting bit of information while researching deck heights. The MLS gaskets that our engines were designed for require a significantly better surface finish on both the block and head to be effective. So for anyone who is getting their heads machined and planning to use the OEM gasket, should target a surface finish ~30 Ra where as standard graphite gaskets require 80-110 or so.

That's interesting. Do you know if that's applicable to Mitsy engines in general, just the V6s, or just the 3.0L?

 

[chadzeilenga]

From what I’ve read it is related to the MLS gasket style as other brands were mentioned in what I had read.

I spoke with a VR4 performance shop today and their suggestion was to run the over-decked heads with thicker MLS gaskets. Does anyone know if the 3.31” minimum thickness for the heads is due to compression ratio issues or with weakening the casting due to thinner wall thickness?


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[GrantC]

I don't know specifically about the 3.0L engine, but historically heads shaved below factory specs sometimes presented piston-to-valve (PTV) clearance problems. Some OHC engines would also have cam problems (perhaps a duration issue related to the change in compression ratio?) It's plausible that there could also be some rigidity issues with some head designs.

I'm a "by the book" kind of person where engines are concerned, so the idea of using thicker gaskets to take up the space from an over-shaved head doesn't fill me with optimism.

 

[chadzeilenga]

I removed the rockers from the heads and confirmed that they are done. Note the cam journals.

I don’t think this VLA is useable

But I’m thankful the PO used OEM seals...

So now it is off to the junk yard to pull the heads



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[chadzeilenga]

In reviewing the FSM tonight on the short block removal, the instruction I'm reading is to pull the block, trans and transfer case as 1-unit. Is that required? I was hoping to leave the trans/t-case in the vehicle while I am rebuilding the engine.

One other obstacle is that in my dumb garage, I am fairly limited on the space in front of the Montero. I won't have the space in-front of the Montero to get a hoist in and lift engine and pull it out. My thoughts were either:
A - Lift it out from the drivers side (I haven't done this before)
B - Roll the vehicle 1/2 way out of the garage so that I have the room in front of the vehicle to maneuver the hoist. The problem with B is that once engine & trans are disconnected, I'll need to support the front of trans while I roll it back in.

Anyone out there had the same issue?

 

[Toasty]

Leave the trans in, it's a cun* getting to the upper back bellhousing bolts but totally doable (get your curse words ready and learn some new ones). A long set of extensions and a nice wobble socket can work and so can a ratchet wrench after you break it free (wear gloves). You can use a ratchet strap around the frame rails to support the bellhousing of the transmission while you have the engine out, i've done this.

 

[chadzeilenga]

Leave the trans in, it's a cun* getting to the upper back bellhousing bolts but totally doable (get your curse words ready and learn some new ones). A long set of extensions and a nice wobble socket can work and so can a ratchet wrench after you break it free (wear gloves). You can use a ratchet strap around the frame rails to support the bellhousing of the transmission while you have the engine out, i've done this.

You mean these bolts...?

Looks like there is a small advantage to having top half of motor apart, probably won’t be as much fun putting in.


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[Toasty]

Those are the ones! They're not actually that badif you have a body lift ?

 

[Montynv]

The first time I had my top end removed and pulled the bottom end out. I left the trans/transfer case in. I used a rod and had ur straddles across the frame to support the trans. The second time I pulled it it was a complete engine, yes it was as easy. But some extensions and universal and all the bolts came out and doable.