Chrysler/Mitsubishi 3.0L/2.5L v6 6G73 Head R&R

DannyH said:

1996 Chrysler Sebring LXi with 145k miles started blowing out and consuming coolant. Shops want $3k to preserve the $1.5k trade-in value (!). I can rebuild a small-block Chevy to the tightest factory specs without getting out of bed but this motor is new to me. I have the shop manuals (Chrysler, Mitsu, and Chiltons) but all three avoid what apparently are very important considerations. If you've done this engine enough times to know the answer, here is where I'm hung-up.

1. To get the heads milled to the correct "RA" value, you must know the gasket material. "Composite" is different than "Graphite-coated", which is different than metal-layered. Fel Pro must consider the 9037PT material more secret than the Coke formula as this information has been impossible to discover. My shop manuals are silent on this point. Are you specifying a specific range for the RA value when you have the heads for this engine done?

2. The heads use "Torque-To-Yield" (TTY) head bolts. Across the Web, this supposedly tells us two things: 1) Consider the head bolts as single-use and replace them. 2) Look for a torque spec that says to torque to a specific value then go back around and rotate the bolts a specific number of degrees. Again, my shop manuals are silent on this. All three say 80 ft/lbs and let it go at that. Am I missing something???

3. I was schooled to install fasteners with the mating parts (bolt-nut or capscrew-tapped hole) were both clean, dry, and free of lubricant. I'm reading the bolts and washers need to be coated with 30w oil on assembly. Here again, the manuals are silent.

The Fel Pro gasket set has no instruction sheet of any kind for anything in the kit.

If you have hands-on experience with the engine, what can you advise me?

Thanks

Click to expand...

1: nearly all your head gaskets are Multi-Layer Steel nowadays, and the Cylinder Head Grinding Limit for the 2.5L V6 (i'm getting this figure from the 1999 Cirrus/Stratus/Breeze Sedan Factory Service manual, which pretty much has the same V6 as your Sebring) is a maximum of 0.2mm (0.008") (it goes on to Caution you that it is a combined total dimension of stock removal from the cylinder head if any, and the block deck surface is 0.2mm [0.0079"])

2: (again, I'm referring to the 1999 Sedan Factory Service manual for this advice.) the FSM makes no mention for TTY Bolts on the V6 (its a 3 step process in a sequence ending up at 80 Ft.-Lbs.), but on the 4 cylinder Engines, the FSM has you inspect the Head Bolts for Necking (since the Tightening Sequence on the 4 Cylinder Engines is a FOUR Step Sequence, and the 4th step is an additional 1/4 Turn.)

3: again, the FSM makes no mention of having to oil the head bolts on the V6, but it DOES have you oil the head bolts on the 4 Cylinder Engines.

The car is a one-owner, special-order with "Built especially for __________" on the window sticker. Condition is nearly showroom with top-drawer maintenance every step of the way. At 160hp it is underpowered but double-wishbone suspension and discs at all four corners make it a solid--if underappreciated--performer. I am trying to do this By the Book + 18-years field experience of others to arrive at a journeyman-level Job Well Done.

#1: "Milling" should have read "resurfacing". Flat within 0.002 in all directions. "Resurface Head to ____RA" value still unknown.

For those wondering what "RA" is, after the head or block is milled or surfaced, it is placed in a machine that runs an indexing pin across it, reading out the average roughness. The lower the number, the higher the shine. The head and block material and the gasket construction determine the desired value range. For example, the same gasket on an iron/iron engine may have a range of 60-120 but on an aluminum/iron engine 20-60. The engine manufacturer is at the table but it is the gasket manufacturer holding the trump card determining the value to give to the machine shop. Fel Pro is not forthcoming on a range of values for their 9037PT head gasket.

#2: Four circuits around the head, ending at 80ft/lb. "Tighten an additional _____ angle" still unknown. Fel Pro is not forthcoming on a value for their 9037PT head gasket.

#3: Use 30wt motor oil, not assembly lube or anything else, on the head bolts and washers. The washers are cupped: install inverted-cup.

Fluids drained, waiting for teardown, but not willing to go further without the critical values.

BTW, I was at a dismantler on Saturday. Two rows of cars and trucks waiting to be processed in. Some in better shape than others but only two were crashes. The remaining ones had powertrain or other issues making them too expensive to repair in a commerial garage. It is sad to see this.

Thanks

It sounds like a sweet ride. Is this the 2.5L (6G73) coupe?
The 3.0L (6G72) has some reassembly and head differences compared to the 2.5L (6G73) and although is the in same Cyclone family, it should be kept separate service procedure-wise. http://en.wikipedia.org/wiki/Mitsubishi_6G7_engine
If there is an 800 # tech support line on the reassembly instructions, I would call and ask.
It seems like the included instruction sheet is very general in scope as not all head bolts require an additional yield angle and they don't differentiate between iron or aluminum and some head bolts should go in oiled/some not. Don't try to follow them to the letter.
Since you aren't exactly using OEM parts, the service manual may not apply to all reassembly procedures either. Are these the Fel-Pro Blue line of head gaskets?
The Roloc yellow disc should swirl the proper finish on the mating surfaces for MLS gaskets, but I don't know the composition of the Fel-Pro gaskets and this would be another question for Tech Support.

VICTORY!

After downloading a ton of information and ordering the Chrysler, Haynes, and Mitsubishi manuals, I still did not have the answers I needed to reassemble the motor. On a lark, I subscribed to "All Data". Halfway down the deck of Technical Service Bulletins, I come across this: "The head gasket was changed in 1998 to a metal-layer gasket. The pistons were changed to accommodate the new gasket. 1995-1997 engines used a composite gasket. A composite gasket MUST be used or severe engine damage will result."

I came across the Fel Pro technical support line 800.325.8886. Called and got the remaining answers.

1. 9037PT is a PermaTorque gasket, which is a composite-type gasket. A composite gasket in a bi-metal engine is quite happy with an RA of 30-60.

2. Torque-to-Yield fasteners often have a "Torque-to" value then a "Rotate additional degrees" value. In this installation (6G73), the bolts are not rotated beyond the torque value (80 ft-lbs).

An Additional Note: Remove the fasteners in 20-lb increments following the fastening pattern in reverse order. Do this wrong and you warp the heads on removal. Replace the bolts in 20-lb increments following the fastening pattern.

LESSON LEARNED: Spend the $26 and subscribe to "All Data" for your vehicle and get the authoritative word. It will save you from buying $200 worth of 18 year old manuals that have none of the latest information.