'91 Montero refresh

In all reality I will probably put this engine back together exactly as it was with the new heads, but while it's torn apart is there anything wise to delete or modify on the 6G72 for more reliable running/better response/power? 

dannyp84 said:

In all reality I will probably put this engine back together exactly as it was with the new heads, but while it's torn apart is there anything wise to delete or modify on the 6G72 for more reliable running/better response/power? 

Not really beside fixing the valve stem seals and then replacing the cat if it's been in an oil burner the last 15 years. I replaced mine in my 89 and the old one was terrible 

Don't know if you have discussed this yet, but replace the hydraulic lifters with the updated ones while you have it apart. Can't recall the part number or which vehicle they came out of but it was inexpensive to do 10 years ago.

In reply to captainawesome :

I have replaced the lifters on one bank so far a couple years ago but they're still noisy, were the updated ones from a different vehicle?

In reply to dannyp84 :

I believe so. They have a different hole size if I remember correctly. 

And both heads are off! I left the plugs in so I could see which cylinders were burning oil the most, looks like just the middle one on the passenger side bank was doing the worst of it.. I didn't know how to get the cam gears off without spinning the cams so I just jammed a wrench under the lobes since the new heads have new cams and rockers anyway. The new heads arrived today and they're so clean it's a shame to put them on this crusty motor.. photos of the heads and cylinders:

Miscellaneous notes:

I've never timed a distributor before so I'll have to look up how to reinstall that properly.

the exhaust manifold looks especially crusty on that 2nd cylinder which is the one I think was burning the most oil, I wonder if part of my power loss is a clogged cat. It does not appear that any headers are available in the US for the montero and I'm skeptical that they'd make any additional power anyway, especially with all other components being stock. I will consider a replacement converter though. 

Part of me wishes I had just paid a trusted local mechanic to do this, but I know he wouldn't have time to run everything through a parts washer and I'm tired of how greasy this thing is so I'll take the time to clean most of it. This time I'll also figure out how to properly install the valve cover gaskets without getting leaks there.
 

Another part of me wonders how well the 5 cylinder Atlas motor from the 1st gen Colorado might've fit in here.. that engine makes more peak torque at a lower rpm and 5 cylinders almost always sound better than any V6.. but that's a can of worms I'm probably not prepared to open..

How clean does the mating surface need to be on the block to accept the new head gasket and head? I went over it with a razor blade and a green scotch pad but it still doesn't look shiny and new.. I assume a wire wheel on a drill is too abrasive but I could go get one that's made of plastic or something? 

400 grit emery cloth and carb cleaner. 

Minor/major setback update: Yesterday I was convinced I had the block surface clean enough to accept the new gaskets and heads, but to be sure, I had a my friend from the champcar team who is a mechanical engineer come and have a look at the engine. In about 5 min he noticed dents and dings in the old cylinder head, which corresponded with damage on the #2 piston. Upon inspection of that cylinder, we found 4 grooves worn in the cylinder probably a couple thousandths deep. Something got in there and went for a ride. His opinion was that if those gouges aren't honed out, the engine will at best continue to burn oil at excessive rates. Also, hopefully it wasn't a piece of one of the rings. Right now my thought is to return the cylinder heads which were $600, and just buy a reman engine for $1500, but I'm open to other ideas. I have no experience honing or assembling a short block and the local machine shops are backed up for months when I last checked. I'll also take a quick look around for a healthy used engine, but that seems unlikely. Sometimes the bear eats you..

If there's a silver lining, it's that the Montero being down has been a good excuse to drive the RX7 more, it's a real joy on the secondary roads to and from work..

Also if anyone has a 6G72 in running condition, I'm interested.

Substantial Update:

A friend of mine found a new old stock short block for sale on marketplace, so last Friday I drove to Chicago and picked that up:

For an extra $100 he also included this blown up engine which I thought was worth it just to have spare accessories for everything:

also pictured is the non cracked radiator he threw in with the deal.

So now with my reman heads on the new short block I'll essentially have a zero mile engine which really should outlast the truck since these things don't make enough compression to wear themselves out..

I need to research best practices for installing the little dowels in the block that locate the head, and then get started on assembly. This project went sideways quickly I guess with the bad cylinder bore on the old engine, but I still felt like putting up the $900 for a new short block was a smarter and less hassle option to sourcing a used motor somewhere even if the used stuff is a lot cheaper. I'm going to order a gasket kit this week and see what I can get done within my comfort zone/skill level. I don't want to rush the assembly and I have knowledgeable friends to call if I'm not certain of something. 
I would've hoped that a garage full of engine stuff like this would've all been for a rotary build, but that will just have to wait till the Montero is buttoned up and getting me through the snowy months. 

I covered the 6G72 rebuild in my Raider build thread in some amount of detail, as I recall. Not that it's anything too difficult, honestly. But could be a useful reference for you if you didn't already see it. Incidentally, mine runs perfectly and doesn't burn (or lose) any oil at all after a good amount of hard driving and wheeling. 

In reply to irish44j (Forum Supporter) :

I will have to look up your thread as that will be really helpful! My old motor leaked oil badly from the valve cover and burned roughly half a quart in one tank of gas so I'll be ecstatic to have an engine that holds its fluids in. Your truck being the SWB I imagine it gets out of its own way with a little more pep than mine. 

dannyp84 said:

In reply to irish44j (Forum Supporter) :

I will have to look up your thread as that will be really helpful! My old motor leaked oil badly from the valve cover and burned roughly half a quart in one tank of gas so I'll be ecstatic to have an engine that holds its fluids in. Your truck being the SWB I imagine it gets out of its own way with a little more pep than mine. 

Here's a link. It's a kind of long thread but may have other stuff of interest to you as well: 

https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/rad-rally-dodge-raider-akamonteroakapajero-build/160959/page1/

Yeah, it gets up and goes pretty decent, especially with a 5-speed manual. It's on 31s. Even tows ok :)

So since my last update, I've fitted the reman heads onto the new short block, and pulled my original block out of the truck. Over the weekend I put a new rear main seal on the new engine, and I've been cleaning and prepping the oil pump and oil pan for installation. The Haynes manual merely says to pack the oil pump with petroleum jelly to prime it, do I not need to crank over the motor without starting to get oil through the whole system ? And on the 6G72, how is oil fed to the cylinder heads? 
Irish, I'm going to go back to your thread to see if you said anything about priming the system, also how to set the distributor in its housing with the right timing. Photo updates, some dirtier than others:

Truthfully, I haven't moved very quickly on this project because it feels overwhelming and a bit over my head, replacing the heads was one thing, but going with the new short block created a lot of extra careful steps I hadn't considered.. but my goal is to work on at least one thing every evening, no matter how minor, so that every day the project progresses.
 

I cracked the first timing sprocket on the crank trying to remove it, so the one pictured above is from the blown engine. I also stripped a screw on the oil pump housing, then learned to be more patient with the oil pump on the blown engine, which came apart nicely. So this far, the extra blown engine has paid for itself due to my inexperience and haste to get something done. It seems that patience is important with this kind of project, but I do miss driving this thing..
 

More filth ^
 

and cleaned up and packed with jelly as per the Haynes manual:

My vague recollection is that I actually poured oil down The oil filter housing so it would fill the system and then I maybe cranked it just with the starter to try to prime it. But I honestly could be mixing any of those stages up with one of my BMW engines or the Porsche engine lol. I used assembly lube on everything and put some marvel mystery oil in the cylinders so I may have just did a partial prime cranked it and checked to see if I was getting oul  pressure on the gauge while cranking (which it did). After that I just started it up. 

Edit: thinking back I'm pretty sure I actually started the engine with no oil in it initially because I forgot I had no oil in it! In any case it did not seem to have hurt anything It runs fine.

In any case I'm pretty sure I documented it in the thread so if I did anything weird I'm sure I put it there :)

In reply to irish44j (Forum Supporter) :

I liked your trick with using compressed air to get oil flowing through the system, I got the oil pump on last night as well as the front main seal and the pick up tube, tonight is the oil pan..

dannyp84 said:

In reply to irish44j (Forum Supporter) :

I liked your trick with using compressed air to get oil flowing through the system, I got the oil pump on last night as well as the front main seal and the pick up tube, tonight is the oil pan..

lol, I honestly don't remember doing that. Guess that's why I document everything :)

Small update: Last week I was pleased to get the oil pan on and tightened down nicely, then Saturday morning I went into the garage with the intention of bolting up the motor mounts and dipstick. It was only then that I found that the new short block was never drilled for the dipstick tube, it has the boss for it but no hole :/  So now the pan has to come off, and I need to drill a fairly substantial hole through an iron block. So my Saturday plans turned into me walking out of the garage in frustration after about 15 min of trying to think of a way around this. I imagine I'll need to use something for cutting oil, and that the drill bits need to be a bit better than your standard fare from tractor supply? I have some maintenance to do on the IS300 this week before I get back to the Montero, but I'd like to at least get back to where I was Saturday, but with a functioning oil tube..

Yep...good cutting oil, good bits (maybe a couple), slow speed and back the bit out and clean it regularly.

So just as I was about to drill for the dipstick tube, my neighbor noticed that the new short block has a hole for the tube, just on the opposite side of the block. I had to create a small window in the motor mount bracket to make that hole work, but otherwise it doesn't look like it'll foul on anything on that side of the engine. Otherwise, the oil pan and pump are in place, water pump is installed, crank sprocket is on, I need to tighten the camshaft sprockets but the haynes manual says to stick a screwdriver into one of the sprocket holes to secure it while tightening.. As far as I can tell though, there's no where for the screwdriver to land that will keep it secure, so I need to find a different way to keep the cam from spinning. Once that's done, the engine can be timed and I can bolt on the remaining accessory stuff. Hopefully we get a warm day next week and I can power wash the engine bay (mostly the crossmember) and get rid of years of oil leak filth..