Yukon Dave

I have a problem. Let me tell you what I've done. I have a 6.2L with active fuel management with about 200,000 miles on it. I have replaced my timing chain and gears. I aligned the marks on the gears, rotated my crank twice and both marks are still lined up correctly. I even rotated the crank two more times just to make sure everything is lined up. I had puffs of smoke out the exhaust when I would first start my Yukon so I started to replace my valve seals after doing the timing chain. I am using air pressure to keeps the valves up and I have replaced all the seals (intake and exhaust) on the drivers side. I have not put the rocker arms back on yet but I just wanted to check and make sure all my push rods and lifters seemed to be ok, so I rotated the engine and now it will only rotate 1/2 turn on the crank bolt before it hits a "hard stop". I rotated the engine the opposite direction and it goes 1/2 crank rotation and hits another "hard stop". I can do this a few times, going back and forth from stop to stop until one time I do it, and it will go 1 full rotation until it stops again at the same place. It will go past the stop 1 out of 12 to 15 times that I rotate it. I am assuming that with 200,000 miles, there may be a ridge at the top of the cylinder walls. Do you think I am hitting that ridge and it just doesn't rotate thru it. Maybe, since I haven't put the resistance on the piston with the compression, that maybe the piston is moving just a touch higher causing the "hard stops". Not sure where to go from here. I don't want to button it back up and then have issues and have to tear it all apart again.

strutaeng

Did you also replace the camshaft? Maybe the new camshaft base circle is different such that different pushrod length was required? What else was replaced?

I don't believe it would be the ridge at the top of the cylinder bore because the pistons are still only traveling in the same stroke (assuming something bad like a spun rod bearing hasn't occurred, of course.)

Actually, even 200,000+ miles the LS engines don't really have that ridge if they were serviced regularly.

Yukon Dave

I did not replace the camshaft. This vehicle was purchased with about 165.000 on it. It does show signs of oil burning because all the covers had burned oil on them.
I just can't figure out why it was fine when i turned it over after the timing was replaced and then less than one hour later, after taking the rocker arms off, I have this issue.

I am also replacing the oil pump and pickup tube but I have not installed them yet. I wanted to get the timing done first.

strutaeng

I see.

So let's step back for a minute. What's the history with the vehicle? You've owned and driven it for around 40k it seems. Did it run good before? Any issues with it? Any CEL lights, noises, etc?

Why did you have to tear into a replace the cam sprocket and timing chain to begin with?

Yukon Dave

At idle, the oil pressure guage would drop and the oil light would come on. I first replaced the oil sending unit hoping it was bad but it wasn't. Then a friend of mine was talking about the oil pickup tube o-ring can break and cause the issue. I also looked online at all the "low pressure issues" sites and u-tubes. There were many things that could cause it so as long as I was into the o-ring of the pump, to me, it would not make sense to not replace everything that could have wear on it. Like I said earlier, it would smoke a little when it would start up so I knew the seals were bad. The timing chain had stretched but it was not excessive. It was not making noise. My intent, since I had to take it apart, I was going to replace the oil pump and pickup tube, the crank sprocket, the cam sprocket (which is adjustable valve timing), the chain and chain guides and all the valve seals.
The vehicle ran fine. no misses. It had a few oil leaks but I have all new gaskets for that. One thing I don't like about this engine is that you can't see the cam by removing the valley cover. the cam is only visible from below. The cam shows no sign that a lifter has had any issues. The surface are all the same width and do not show any scaring.
I just can't figure out what the issue is. I am trying to avoid taking the heads off because some moronic engineer has put two of the bolt where the exhaust manifold meets the pipe. directly next to the catalytic converter is and the stud is too long to use a regular socket on and not enough room to get a ratchet on a deep well socket.

strutaeng

Ok. I'm wondering if your VVT phaser (the cam sprocket gizmo) maybe didn't get installed correctly? I believe I've see one instance of the dowel shearing off as well on the LS1TECH forum. Someone with more knowledge about them than me please chime in.

Now about the low oil pressure. Was the pickup tube O-ring damaged at all when you removed it?

Yukon Dave

the o-ring was still intact as a whole circle. It was not broken but it was very, very brittle and broke in half in my hand once I got it off. The same thing for all the rubber inserts in the valley pan, all the grommets in the valve covers etc... When I pulled the pickup tube out of the pump, it was very easy to pull out. It didn't feel, to me, like it would be sealing very well. Just not what I'm used to with a normal o-ring type fit. It felt like it had shrunk up and was not rubbery at all.

I can take the VVT sprocket back off but since the rockers are not on the heads, would it really matter at all if the cam was not in timing correctly? None of the lifters have any pressure on them from the valves so they should just move up and down freely. That would make sense if the valve was interfering with the piston but the valves are all closed.
Is the VVT bolt a torque-to-yield bolt or can I re-use it. I bought a new one to replace the existing one just because I didn't want it to be sticking once I put it all back together. If I pull the new one out, can it be re-used. They cost around $100.

Just something else to keep in mind, all the moving parts are genuine GM parts. Some of the gaskets I got may be felpro or something like that but anything important is purely GM.

Something else I just thought of is that the VVT sprocket and timing gear were all tight when I rotated the engine twice to check my marks and at that time, all the rocker arms were still attached. This really went bad once I removed the rocker arms. (Baffled)

1FastBrick

iTrader: (17)

are all the spark plugs out?

Yukon Dave

Yes, all the plugs are out.

RB04Av

Might want to figure out, based on the point in the rotation where it stops, which cyls are at TDC at that time; and take a look into those spark plug holes with your borescope.