Question : 1995 Grand Prix 3100 LIM, Cooling, Heads, and Oil

[Lukeonia1]

Hi everyone... My '95 Grand Prix engine has Problems, I have a couple questions, and I'll take all the advice I can get.

The engine:

• 1995 3.1L V6, with ball-and-pivot rockers
• Loses coolant. I suspect the LIM gasket, because the engine looks wet around where the intake meets the block and heads.
• Runs EXTREMELY rough. Starts right up, but idles rough, hesitates, chokes, and stalls. My power is down the drain too. It also shakes.
• Had a broken intake rocker arm stud on Cylinder #4. Replaced it and now the engine runs better, but not by much.
• Has zero compression in Cylinder #4. Suspect the exhaust valve due to lack of excessive blowby or oil/coolant mixing.

The #4 intake valve seems to be functioning normally (it was stuck closed), but I think all that's done is screw with the oxygen sensor. Now the exhaust smells very gassy until the catalytic converter warms up.

So. Question #1: Does the exhaust valve seem like the likely culprit? It would account for the gassy exhaust and compression loss, and the engine did get fairly hot a couple times due to low coolant levels.

My working plan is to pull the heads off, and see what the deal is with those valves. I've come into possession of a '96 Grand Prix 3100 that had its oil pump go bad (it still runs, albeit badly). This brings me to Question #2: can I take the roller-rocker heads off the '96 engine and bolt them onto the '95 engine? I know the LIM gaskets will be different, but are the heads otherwise interchangeable? Also, Question #2½: can I expect those '96 heads to be usable? What kind of damage might have occurred to the head when the oil stopped circulating?

Oh, and Bonus question: I have another '95 GP with a bad transmission, and the transmission out of the aforementioned '96. I want to swap them; would it be easier to drop the transmission out the bottom, or raise the engine/transmission assembly out the top, swap them, and then lower the assembly back in?

[Azrael]

#1: A crack in the cylinder head can also cause compression loss into the intake, exhaust and/or coolant passage. You won't know for sure until the heads come off.

#2: The heads will be interchangeable. There really shouldn't be any difference in gaskets between those years except for the EGR valve. Just use a set for a 95.

#2.5: The only things to go wrong on a cyl head in the case of oil starvation are the valvestem seals. Any excessive wear on them will cause more oil to enter the cyl. Considering their age, at the very least have them cleaned, checked and pressure tested at a machineshop. There's no point doing all that work to find out they have other issues. Also, if you're planning on using the 96's roller rockers check them for metal flakes/shavings in the bearings and excessive wear where they meet the pushrod. If they look bad you can use the set from the 95 even if they're the older pivot-ball style rockers.

[Lukeonia1]

Well, the head interchange turned out to be a moot point; when I pulled the valve covers off that '96 engine, I found ball-and-pivot rockers. So, either someone else swapped heads on that engine, or that engine was not original to that car. I was a little disappointed that I didn't get to upgrade my rockers, but I got the engine+transmission free with purchase of another bad-transmission Grand Prix, so I can't complain one bit.

Anyway, I got the replacement heads bolted back on, now it's just a matter of getting everything else put back together without having any bolts left over!

[pocket-rocket]

I believe that there was a year where rollers and pivots was a toss up thanks to production changes mid year. I could be mistaken though.