To start with some background, I recently got a '91 Stealth for cheap because the previous owner screwed up the DOHC 6g72 inside of it. All he really said was he dropped the clutch one day and from then on it started rattling like hell. I don't recall a distinctive rattle every time I've seen it run (then again I don't think I was listening for it), but it always immediately began to smoke profusely from an unknown area. Exhaust pipes are on tight, so the only other thing I could think of is a blown head gasket.
Anyways, the point of this thread is to clear up some confusion, for me and hopefully others. The previous owner of my Stealth had bought a SOHC 6g72 supposedly from a decommissioned car in Japan, claiming it to have only 30k miles on it. He was planning on swapping the broken DOHC with this SOHC, and so was I, at least as a temporary solution. Problem is, after a looking both engines over for quite a while, I determined the SOHC would simply not fit in the Stealth, because the crankshaft output was on the other side of the engine. Not to mention the mirrored locations of the accessories and engine mounts. After a bit of research, my understanding is that this SOHC is of the Eclipse/Montero variant of the 6g72, while the broken DOHC is of the 3s/Diamante variant. (Please correct me if I'm wrong in this) The question that then comes up is how many similarities do these variants hold? Do they end at the number of pistons, displacement, and 6g72 moniker? Or are there other parts they share like the specific pistons themselves, crankshafts, blocks, etc.?
Now, to go back to my specific case, after some digging into the DOHC, I've found copious amounts of oil and deposits in the intake/plenum and cylinders, as well as chunks of metal inside the intake manifold. The exhaust valve rockers for the cylinder closest to the right headlight (I assume this is #3?) had significantly more play in them than every other set of rockers, and looking down the intake port with the plenum off and intake valve open, I can see one of the exhaust valves stuck open even with the camshaft not putting pressure on it. Using a borescope, I can also see damage on the piston itself from that exhaust valve, so there's definitely something up there.
Now I still don't know exactly what needs to be done to this engine to get it running again, and I have been contemplating if it's more worth my time to find an actual replacement engine. But say I go further into the DOHC and find it needs a complete rebuild, are there parts on the SOHC I mentioned earlier that I can carry over to the DOHC? If they have the same displacement, why would something like the pistons be any different?
And if it is smarter to find a replacement, what's the best way to go around that? I'm not really all that experienced in that realm, but I know some places people get engines are from scrapyards and ebay/Craigslist/marketplace.
UPDATE: My DOHC is toast. Found a hole in the oil pan, which seems to have been caused by the connecting rod getting shot out, because it's not there. Cylinder wall has some nasty gauges, which look too deep to be fixed without shaving out tons of metal and using really over sized pistons. So now I'm looking for a replacement DOHC, otherwise the Stealth is creeping towards the scrapyard. (Or anyone willing to take it)
Would still love someone to explain the difference between the two 6g72 orientations though, I can't be the only one who was scouring the internet looking for a clear answer on that.
Anyways, the point of this thread is to clear up some confusion, for me and hopefully others. The previous owner of my Stealth had bought a SOHC 6g72 supposedly from a decommissioned car in Japan, claiming it to have only 30k miles on it. He was planning on swapping the broken DOHC with this SOHC, and so was I, at least as a temporary solution. Problem is, after a looking both engines over for quite a while, I determined the SOHC would simply not fit in the Stealth, because the crankshaft output was on the other side of the engine. Not to mention the mirrored locations of the accessories and engine mounts. After a bit of research, my understanding is that this SOHC is of the Eclipse/Montero variant of the 6g72, while the broken DOHC is of the 3s/Diamante variant. (Please correct me if I'm wrong in this) The question that then comes up is how many similarities do these variants hold? Do they end at the number of pistons, displacement, and 6g72 moniker? Or are there other parts they share like the specific pistons themselves, crankshafts, blocks, etc.?
Now, to go back to my specific case, after some digging into the DOHC, I've found copious amounts of oil and deposits in the intake/plenum and cylinders, as well as chunks of metal inside the intake manifold. The exhaust valve rockers for the cylinder closest to the right headlight (I assume this is #3?) had significantly more play in them than every other set of rockers, and looking down the intake port with the plenum off and intake valve open, I can see one of the exhaust valves stuck open even with the camshaft not putting pressure on it. Using a borescope, I can also see damage on the piston itself from that exhaust valve, so there's definitely something up there.
Now I still don't know exactly what needs to be done to this engine to get it running again, and I have been contemplating if it's more worth my time to find an actual replacement engine. But say I go further into the DOHC and find it needs a complete rebuild, are there parts on the SOHC I mentioned earlier that I can carry over to the DOHC? If they have the same displacement, why would something like the pistons be any different?
And if it is smarter to find a replacement, what's the best way to go around that? I'm not really all that experienced in that realm, but I know some places people get engines are from scrapyards and ebay/Craigslist/marketplace.
UPDATE: My DOHC is toast. Found a hole in the oil pan, which seems to have been caused by the connecting rod getting shot out, because it's not there. Cylinder wall has some nasty gauges, which look too deep to be fixed without shaving out tons of metal and using really over sized pistons. So now I'm looking for a replacement DOHC, otherwise the Stealth is creeping towards the scrapyard. (Or anyone willing to take it)
Would still love someone to explain the difference between the two 6g72 orientations though, I can't be the only one who was scouring the internet looking for a clear answer on that.
