Mirage 3A92 Engine repair in process. (Problem: low compression)

Hi, early in marsh I took my wife's 2018 Mirage (55000km) to the dealership because of an engine noise that would not go away after the engine had warmed up. They charged me 400$ to do a compression test and tell me that Mitsubishi would not repair it on warranty because the oil change had some time been done 2000 km to late....

After some phone call leading to dead-end, I decided to repair the engine myself as the dealership would charge 3000+$ and I estimated the repair to 400$

Now the engine is out of the car and opened up. The 3 piston have damage to the skirt on one side and the wrist pin are not turning freely in the piston. The cylinder wall have the same kind of damage as the piston.

I would not find any oversized piston for the 3a92 so I ordered a piston set from rockauto for a toyota 1nz. Same bore, same pin, similar valve relief, the compression distance is a little longer. That I will adjust when the block come back from the machinist.

The crankshaft look like new, all the bearing have minimal to no wear at all.

The machinist said that by the look off the piston, the damage would be due to overheating or to excess gasoline.

The engine would flood 3-4 time during the winter and we would have to start it with full throttle. It would smoke black and smell like snowmobile and then run fine. We have never experience overheating with the car.

Maybe the engine would run lean and overheat the piston after the over-fueling event like the 2014-2015 were doing...

I will post picture of everything soon, do you guys have pics request or dimension you would like to have before I put it back together?

Sorry for my English, I live in Quebec, Canada and do not type in English normally.

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The sound was similar but not as loud. It was getting louder quickly so I towed it from the dealership to my friend's garage. The idle started to get rough when we drove it inside.

The connecting rod is 133mm c-c, small end is 18mm bore and 17.8mm wide, big end is 43mm bore and 17.8mm wide, crank pin is 40mm in diameter, rod bearing is 13.5mm wide.

The main bearing housing are 50mm, crankshaft main are 46mm and the bearing are 16mm wide.

No hole in the connecting rod for piston oiling, only 2 little groove on the side of the big end.

I cant find the bearing online but again the bearing have the same dimension then the one on a Toyota 1NZ exept that our bearing dont have locating tab punched in them so there is that.
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The engine from the Toyota echo and yaris. A 1.5 4 cylinder that have much in common with our engine, from the oil pump to the valvetrain everything look similar as if when they designed our engine they started on the basis of the toyota.

Maybe it have someting to do with the Aisin logo on our timing covert, Aisin being owned 51% by toyota.

The parts are not a direct fit, adjustment are required for them to work.

Man, lately it seems like an epidemic of engine issues in cold weather climates with these engines?

Dave, sorry to hear about that, and thanks for posting pix. Presumably you have the FSM?

My 2014 has about 100 000km (60 000m) on it and thankfully no such problems at all.

I wonder if the "Eco-Mod" that further reduces enrichment was beneficial for preventing that sort of thing? It doesn't make it start or run harder, just reduces enrichment during start and warm-up.
See:
https://mirageforum.com/forum/showth...ment-when-cold

Btw, the SMART engines were designed in the joint Daimler/Mitsubishi Kölleda facility as was the engine of our cars and of other European Mitsubishi Colt. There are quite a few similarities in that design, and I would expect a few interchangable parts.
Meanwhile Kölleda is 100% Daimler-owned, and today they make and design allmost all Mercedes Benz passenger car engines.

Hey Dave, just wondering, do you keep your car in a heated garage, or use a block heater to aid in cold starts??? Thanks...

I dont have a heated garage, the car stay outside, unpluged all year long. In winter temperature go to -30 celcius.

I was just thinking about this thread the other day when I was looking at Mirage oil analysis reports. Mirages seem to have a certain aluminum content in the oil. I'm not sure it's an alarming amount, but it's there. Maybe related to piston skirt wear?!? :confused: