1. Home
  2. Mitsubishi Cars and Trucks
  3. Well, it wasn't a broken ring...

Well, it wasn't a broken ring...

The head off and the pistons are out of the 4G63 in my Summit GTX. No broken rings surprisingly. One piston is very carboned up, another less so, and the other two are normal. Obviously the problem had been coming for a while, and I had noticed the unexpected high oil consumption, esspec under boost.

Measuring with a simple protractor gauge shows none of the bores are obviously oval. There are expected vertical scuff marks on the all cylinders, but the cross hatching is still visible. I'll get a bore guage into it tomorrow and see how much wear is present.

Piston-wall gap is the correct .020". The ring lands on the worst pistons are not obviously non-parallel, but the #1 and #2 ring vertical clearances seem not the same. The spec is approx .001 to .003, and .004" max: I'll check with a feeler gauge tomorrow.

With any luck, the bores are OK and a light hone is only required. Hence the problem is the old pistons. Given the amount of smoke it was blowing failure was pretty severe, so ring clearance is more important on the turbo engine.

Reply to
Stewart DIBBS
Loading thread data ...

Yes, yes, absolutely a Typo, and relying on memory (always a bad thing) quoting from the manual. In fact the piston to cylinder clearance spec is .0012 - .0020. I was visualizing the gap at the top of the piston to the wall, which IS about 020.

After all, this is a 4G63. In my youth in Australia, we'd say the Holden (GM) 308 V8s would themselves wear out into 309s ...

Stewart DIBBS

formatting link

Reply to
Stewart DIBBS

"Piston-wall gap is the correct .020"."

Is this a typo Stewart?

Reply to
simpleton

The bore seems to be fine. The gauge STILL didn't arrive today, but indirect measurements (ring gap and skirt clearance) have no indication of excessive bore wear top or bottom. No head, valve or valve stem problems.

The current thinking (based on experiences with a Renault 5 Turbo) is

- rings were not sealing as well as they could be, allowing excessive oil blow by. This was seen in the exhaust under boost (at night). Used about

1.5L / month for the last 4 months: irritating but accceptable.

- The excess unburned oil accumulated in the (original) rear muffler

- When the ECU fried itself it went into "limp" mode before it failed entirely. This caused excess fuel into #2 cyl that washed off the carbon, as seen. Unburned fuel in the muffer disolves the oil. Engine was running rough.

- When the new ECU was installed, the engine runs smooth and clean for about

30 seconds, until the oil in the muffler heats up enough to start smoking.

So ... tomorrow we remove the rear muffer and see if there's copious quantities of oil in it. If so, there's the smoking gun...It needs a rerouted system anyway for the awd conversion.

I'll get a new set of pistons and rings, give the bores a light hone and put it all back together.

Does anyone know of non-turbo rings are the same as turbo rings? The ones we pulled out were supposed to be for a turbo.

Reply to
Stewart DIBBS

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.