I have a smokey Mitsi Legnum VR-4 (not actually that smokey since I added Nulon Smoke Stop additive). The mechanic reckons it is the valve stem seals and has proposed a topend rebuild of the engine, but what exactly gets 'rebuilt' with this procedure as I am not entirely sure and Googling it gives conflicting answers.
Thanks!
esprit,
Jan 20, 10:19am
Generally head off, valves out, head decoked, valve seats reground and lapped, head skim if jecessary, rebuilt with new seals and gaskets
phillip.weston,
Jan 20, 12:11pm
I would be careful rebuilding the top end of that engine without touching the bottom end. I would also rule out the turbos first given they are a common leaking point first, before delving into the top end of the engine.
The reason I say don't skip the bottom end, is often when you do a top end build the cylinder heads get skimmed to make them straight and true again, but this has a habit of increasing the compression ratio and a sudden change to a semi-tired bottom end can cause a disastrous failure.
Case in point was a Galant VX-R I picked up from the previous owner who had overheated the engine, a mechanic performed a total top end rebuild including new heads being skimmed, new gaskets, head bolts, valve stem seals, valve stems, valve grind etc to the tune of some $2800. The very next week the bottom end let go - one piston shattered causing the rod to go flinging and then break in half, another rod bent and then got stuck between the crank cradle and the engine block. The 6A12 and 6A13 have a fairly weak bottom end compared to the older 6G7x or even the 4G series of engines.
From memory you said that engine had previously overheated and had a head gaskets replacement already? I'm surprised they didn't do the valve stem seals or check the guides while it was apart. You can actually change the valve stem seals without removing the cylinder heads, and that's probably something I would do if it does turn out to be the valve stem seals leaking. At the milage your engine has covered, I highly doubt the valve guides themselves are worn out.
At the age of your Legnum too, you might just be better off finding a replacement lower kms engine and have that fitted - would save you money and you wouldn't be touching your existing possible dubious engine.
phillip.weston,
Jan 20, 12:29pm
Oh and because everyone loves carnage pics, here's what greeted me when I pulled the sump on that 6A12 MIVEC-MD in that Galant VX-R I had:
phillip w . looks like the mouse fell off the treadmill at big rpm. cool pics,also agree wholeheartedly with your comments for OP
robotnik,
Jul 30, 3:48pm
Thanks for the advice. I will make sure I know what the problem is, including looking at the turbos, before doing anything major.
It did occur to me that a new engine might be in order, because the old one may have been damaged when it overheated years ago. Of course finding a good replacement engine that doesn't have a whole set of new problems could be an issue - no-one re-manufactures 6A13s and warranties them like they do on small block Chevies or whatever, obviously.
Last time when the heads were off was several years ago when the car had very low mileage, so the valve stem seals and guides were probably OK then.
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