Top End Rebuild, Worth It?

[PHeller]

I'm not a Montero owner yet, but I know that these engines go through heads and valve seals quickly compared to most vehicles.

Most reports say that the bottom end of both the 3.5 and 3.8 are stout and should last well into the 200s.

Is it worth getting a spare set of heads, having them rebuilt, and keeping them for a nice warm summer weekend to swap on a 150,000 mile engine?

Or are the rings just as likely to be worn on a higher mileage engine as the valve seals?

 

[jeep-N-montero]

Depends on which engine you are talking about, there a many of us with over 150k miles with the SOHC 3.5 that have zero smoking issues.

 

[PHeller]

I'm not sure there was a 3.5 SOHC, I believe all the US market 2 and 2.5 Gens all had the 3.5 DOHC motor, which are notorious for bad valve seals on engines that have not run synthetics most of their lives.

 

[scrubber3]

I'm not sure there was a 3.5 SOHC, I believe all the US market 2 and 2.5 Gens all had the 3.5 DOHC motor, which are notorious for bad valve seals on engines that have not run synthetics most of their lives.

For the Gen 2, it was only the SR that had the 3.5 dohc. I believe the Gen 2.5 had a 3.5 sohc. The Gen 2 LS had a 3.0 sohc iirc.

Sent from my SAMSUNG-SGH-I337 using Tapatalk

 

[Swank Force One]

Correct. No Gen2.5 had a DOHC motor.

 

[jeep-N-montero]

I'm not sure there was a 3.5 SOHC, I believe all the US market 2 and 2.5 Gens all had the 3.5 DOHC motor, which are notorious for bad valve seals on engines that have not run synthetics most of their lives.

All 97-00 models had the SOHC 3.5 engine and were improved over the DOHC 3.5.

 

[jeep-N-montero]

For the Gen 2, it was only the SR that had the 3.5 dohc. I believe the Gen 2.5 had a 3.5 sohc. The Gen 2 LS had a 3.0 sohc iirc.

Sent from my SAMSUNG-SGH-I337 using Tapatalk

Correct. No Gen2.5 had a DOHC motor.

The 3.5 SOHC started in 97, this is why the 97 SR is kind of a unicorn for some folks due to the gen 2 body but the SOHC engine.

 

[PHeller]

Are you sure you're not thinking of the 24v 3.0L SOHC motor?

What bugs me is that there is no definitive buyers guide about the various combinations of options and models and years. The Wikipedia page blows, as it focuses too heavily on the Pajero and not enough on the North American Montero.

Can anyone spell out the engines available for 1991-1999 and 2000-2006 Montero and the notable problems those engines might have had.

 

[jeep-N-montero]

Are you sure you're not thinking of the 24v 3.0L SOHC motor?

What bugs me is that there is no definitive buyers guide about the various combinations of options and models and years. The Wikipedia page blows, as it focuses too heavily on the Pajero and not enough on the North American Montero.

Can anyone spell out the engines available for 1991-1999 and 2000-2006 Montero and the notable problems those engines might have had.

Here, have a look https://www.google.com/?gws_rd=ssl#q=mitsubishi+3.5+dohc+issues

And in the future please try to actually research something for yourself like a big kid should know how to do, looking at your threads it would appear you tend to ask a lot of repeated questions that have been asked a dozen times and have existing answers.

 

[PHeller]

A quick search of this forum for something as simple as a "Montero Buyers Guide" yields all of 7 whole results. WOW SO MUCH INFORMATION

A quick search of Google for "Montero Engine Changes" yields only discussion about the SR/LS and gearing topics. Nothing about the fact that apparently there was a DOHC and SOHC motor available. The only way I find the various engines is by searching for posts by Toasty on VINs, who actually knows how to explain stuff.

Even in this very thread there seems to be some confusion.

Gen 2 Montero
1992 Montero
LS 3.0L 12V MT JA4GK41S1NJ007034
SR w/ the 3.0L 12V engine AT JA4GK51S0NJ009430

1993 Montero
LS w/ the 3.0L 12V JA4MR41H6PJ002885
Non-SR AT JA4MR31H1PJ000763

1994 Montero
3.0L 12V MT JA4MR41H2RJ008797
3.0L 12V MT JA4MR41H2RJ004202
LS w/ the ???? engine & MT JA4MR41H4RJ002466
SR w/ the 3.5L dohc engine JA4MR51M5RJ008781
SR w/ the 3.5L dohc engine JA4MR51M5RJ004827

1995 Montero
LS w/ the 3.0L sohc engine JA4MR41H9SJ000590
LS w/ the 3.0L sohc engine (Fed) JA4MR41H4SJ007091
SR w/ the 3.5L dohc engine JA4MR51M7SJ008996
SR w/ the 3.5L dohc engine JA4MR51M5SJ017583

1996 Montero
LS w/ the ???? engine ?? JA4MR41H1TJ006398
LS w/ the 3.0L sohc engine AT JA4MR41H9TJ001739
SR w/ the 3.5L dohc engine AT JA4MR51MXTJ000439

1997 Montero
LS w/ the 3.5L sohc engine ?? JA4MR41R3VJ003028
LS w/ the 3.5L sohc engine ?? JA4MR41R0VJ005903
SR w/ the 3.5L sohc engine ?? JA4MR51R8VJ008392

1998 Montero
w/ the 3.5L sohc engine JA4MR41H9SJ000590
w/ the 3.5L sohc engine JA4MR51RXWJ002126

1999 Montero
w/ the 3.5L sohc engine JA4MR51R7XJ007267
w/ the 3.5L sohc engine JA4MR51R8XJ007195 <this one is mine

2000 Montero
???

Gen 3 Montero's
2001 Montero
Ltd w/ the 3.5L engine JA4MW51R71J027180
XLS w/ the 3.5L engine JA4MW31R51J039283

2002 Montero
Ltd w/ the 3.5L engine JA4MW51R12J056143
XLS w/ the 3.5L engine JA4MW31R32J004839

2003 Montero
Ltd w/ the 3.8L engine JA4NW51S03J050164
20th Anniv w/ the 3.8L engine JA4NW61S03J043995
XLS w/ the 3.8L engine JA4NW31SX3J032520

2004 Montero
Ltd w/ the 3.8L engine JA4MW51S54J010692

2005 Montero
Ltd w/ the 3.8L engine JA4MW51S55J003176

2006 Montero
Ltd w/ the 3.8L engine JA4MW51S06J000445
Ltd w/ the 3.8L engine JA4MW51S76J002032

Looks like the go to spot for DOHC cylinder heads is Clearwater Cylinder Heads. Although it looks like 6G75 3.8L available in the 2003+ are SOHC, so at least they aren't quite as complicated. By 2003 the valve seal issue isn't really one, and the top ends are pretty stout, so long as you don't lose the timing belt. Still sounds like they need the timing belt and tensioner replaced every 60,000 miles.

There, I answered all my own questions with no help.

 

[jeep-N-montero]

Now you are getting somewhere, keep up the good work! Try to do the same on GRM.

 

[JohnnyBfromPeoria]

I'm not a Montero owner yet, but I know that these engines go through heads and valve seals quickly compared to most vehicles.

Not really

Most reports say that the bottom end of both the 3.5 and 3.8 are stout and should last well into the 200s.

I'd second that

Is it worth getting a spare set of heads, having them rebuilt, and keeping them for a nice warm summer weekend to swap on a 150,000 mile engine?

Not in my opinion, especially since you're not even a Montero owner yet.

Or are the rings just as likely to be worn on a higher mileage engine as the valve seals?

There's always a compression tester.

John B.

 

[JohnnyBfromPeoria]

All 97-00 models had the SOHC 3.5 engine and were improved over the DOHC 3.5.

Speculative, in regards to the improvement, SIR! I mean, why make things simple and reliable when they can be complex...and wonderful!?

John B.

 

[evomaki]

Rebuilding a top end, when it is not 100% mandatory (blown head gasket, valve issues, etc.) is always the $64 thousand question, and a hard one to answer in a blanket statement. Where do you stop once you go that far? Valve seals leak on my Monteros and that needs to be addressed. Rope trick is pretty cool. There is some video out there of some Montero DIY ************ doing this job in a parking lot with the attitude of no big deal. Some years back that might have been me, but my Monty is not a daily driver, and I'm getting older. I might just take the heads off and send them to the machine shop. Might be cheap insurance to avoid the risk of a keeper dropping into my sump. JohnB. is right. It's got to start with a compression (or leak down) test. I'm going to let that be my guide. Evidence of rings causing a low cylinder or two below some threshold, and it's rope trick for the seals, or just a complete refresh of the engine. I suspect if the rings looking OK, then the heads are off to the machine shop.

 

[BEG]

If you want simple bolt-on and go, I'd order a set of rebuilt heads from Clearwater Cylinder heads. Plenty of members have used them for their Monteros.