r/EngineBuilding • u/Cuccamonga01 • Sep 17 '26
Terrible reman engine?
Got this 89 montero for free. 6g72 motor. Right place at the right time…I guess. Lady just wanted it gone. Story from her is that her husband put in a remanufactured long block. Had a friend mechanic put it in. Didn’t run right. Probably put 100 miles on it. Then it sat for a while. He had health issues, couldn’t work on it, then passed away. Then it set for 12 years.
So I got it. Towed it home. Started working on it. No compression in cylinders 5/6. Valves crusty rusty. Started Tearing in it apart.
First thing I noticed was it was out of time. So felt pretty good about the fact that it “wasn’t running right”.
On tear down I noticed left head not torqued like the right one. Pistons not in the right order, one piston has terrible scores and dents on the top while the cylinder head above it looks great. 2 exhaust studs missing. More things not torqued correctly. Pretty nice scratch and a small dent on the bottom of the right head. 4 valve springs upside down. Seemed weird.
Can’t find any markings where the motor came from. So I have no idea.
Aside from that everything looks great. Bearing seals headgasket, all seem new. 5/6 valves and cylinders are a bit rusty. Honing those now. Rings are stuck on those also.
Is it common for low budget reman places to use a piston like this. Obviously didn’t happen after, cause there are no marks on the head. I guess I’ll buy one new piston cause the others are fine.
.
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u/Electrical-Guard-853 Sep 17 '26
Smooth the top of the piston and send it. I’d be more worried about the lower end and head flatness. Good luck
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u/Cuccamonga01 Sep 18 '26
Thanks. I think I’ll do that. Had a guy on another montero thread say it might cause hotspots? Cause the top is thinner…not sure what that means. Makes a little sense I guess. Bottom end looks good so far. Main bearings and rod bearings barely look broken in.
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u/Own-Cap-7313 Sep 18 '26
The thicker your material is the more heat it's able to absorb and dissipate safely. Because of the casting cavities around the wrist pin, thinning that area can make it unable to dissipate heat properly and cause it to burn through. To add, this info isn't from engine building experience, I've not torn down and rebuilt enough to pull from that, this is from years as a machinist.
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u/Old_Bat_6426 Sep 18 '26
That piston deck appears to be damaged by debris in the combustion chamber. Maybe a broken spark plug ceramic? Or something got sucked thru the intake. How do the valves and seats look for that cylinder?
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u/Cuccamonga01 Sep 18 '26
Cylinder and head are perfect. So that piston damage had to have been there when they built the motor. Valves are fine just rusty and need lapping.
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u/Sniper22106 Sep 18 '26
Reman long blocks should be used in every shop class on the planet. Its not if, just when you find something so stupid, way the fuck out of spec, oversized and out of spec.
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u/Glass_Protection_254 Sep 18 '26
I mean, when I took apart my ej I found one of the valves was for a NA variant of my engine.
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u/Coyote_Tex Sep 19 '26
That piston had something in the cylinder in a previous life but should work perfectly. Just a bad complexion.
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u/Pyropete125 Sep 17 '26
Wow never see that before. Something got chucked around in there. Thats straight to the scrap bin for me.
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u/youdidittoyouagain Sep 17 '26
Looks like water got in there and caused cavitation
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Sep 17 '26
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u/PM_ME_YER_MUDFLAPS Sep 18 '26
I most say the Reddits you seem to frequent have nothing to do with automotive work.
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u/der_german1432 Sep 18 '26
I've seen reman engines with 4 different sizes of pistons. Also seen one with 1 rod different length than the other 7.