Emergency: Where'd my Pushrods Go??

[PeasAndCarrots]

1986 Chevy G30 w/ 200k miles.

After confirming there was nothing wrong with left bank of cylinders, removed rocker cover on right back of cylinders to see whether a collapsed lifter was causing an exhaust valve not to open (see previous thread here: http://www.thedieselpageforums.com/t...ad.php?t=36159) and discovered the #2 and #4 rocker shaft was broken at the #2 cylinder bolt, and the #4 cylinder rocker shaft bolt was broken. Lifter pieces can be seen in the pushrod gallery. The #2 cylinder pushrods are nowhere in sight.

We're trying to figure out:
1. Where my muh****in pushrods?
2. What else might be broken/damaged (cam, pushrods, valves, piston?)
3. What was the failure mode/what broke first/how do we prevent it from happening again?
4. How do we fix it?

-Joe and Christy

[wthif]

They are on their side, resting. Look real hard and you should find them on their side in the lifter gallery.

I had an engine that had obviously destroyed a rocker in its past, as evidenced by the dent in the valve cover. The previous owner just bought new pushrods and left the old ones down there. I wouldn't do this because the other pushrods had worn quite a bit because they were rubbing against the falling ones.

I would think you could get them out with a good flashlight and a magnet. Also check the condition of the other pushrods you might need to replace a bunch of them.

Someone else will have to reply with the fix and what to check.

[john8662]

I'd probably pull a head and see why it did what it did. Most times it's not a matter of a faulty part that failed causing this. For example; bad pushrods, bad rocker arm shaft, etc.

Since you've already pulled the head on one side, complete this by pulling the head on this side too to make sure that everything is ok. Check for bent valves (as a result of this damage) and evidence on the pistons and inspect the gasket for leakage that could have caused this.

These are not common failures, but with anything over 200k miles, it's all possible.

Keep plugging...

Glad you're getting to the bottom of why it runs the way it has been running.

J

[PeasAndCarrots]

Thanks for the replies, y'all. Pulled the head and found the #2 piston was up at the top of its travel (#8 down towards the bottom). The missing pushrods were found sleeping sideways in the gallery.

My intuition is that the piston let loose first, causing destruction all along the valvetrain.
*Camshaft looks ok (from Christy's limited observation).
*All four of the #2 and #4 lifters were in pieces. Will be pulling oil pan for the other chunks.
*#2 and #4 pushrods will be replaced, 'cause they're chewed.
*None of the valves were visibly destroyed, but we will be checking them. The exhaust valves did leave marks on the #2 and #4 pistons.

Moving forward:
*Should I replace the #2 and #4 rockers, as a precaution?
*What is the usual failure mode of piston/rod assemblies? Is the crank likely to be damaged? (Please, God, no!)
*Are the lifter pieces all likely to be in the oil pan; if not, where did they get stuck and how do I get 'em out?

Thanks again for the guidance.
-Joe & Christy

[john8662]

Why wouldn't #2 be at the top? Unless it doesn't move when roating the engine, or you can push it down when it's in a position (indicating connecting rod or piston wrist pin failure (not the pin itself, but the casting in the piston that holds the pin).

#2 and #8 aren't paired cylinders (don't fire at the same time) #3 would be at at TDC for it to be paired...

Anyways...

Yes, most likely the pieces have made it to the pan, they would get hung up on the rotating assembly otherwise, be able to find them though.

You're a trooper though. I know what you're going through in a van, worked on one some.

So, what makes you feel that you have a piston failure? Just curious, cause I'm not sure that's clear in your previous post.

[PeasAndCarrots]

Thanks for pointing that out, John - I realized when I woke up that they might not be paired, and spent some time looking at the firing order (90° between firings, right?). This is the first V8 I've ever worked on, I'm typically a 4-cylinder guy and I'm used to seeing inner paired and outer paired. When we changed the left bank head gasket, the cylinders just happened to be in a location where #1 and #7, and #3 and #5 happened to be in the same part of their travel and I didn't think about it. So when I pulled the right head and saw the middle pistons at the same height towards the top, the back piston towards the bottom, and the front piston near TDC, it just looked "wrong."

My gut reaction to realizing my rotating assembly might be fine was, "that's great!" but now I'm wondering, if it wasn't from hitting a piston, what caused the valvetrain apocalypse? Is it possible that an over-torqued rocker shaft bolt started it all and simply took 15,000+ miles to fail?

[350Tacozilla]

it could have been a bad pushrod or rocker shaft itself (or maybe bolt like you mentioned) I have had the rocker studs pull out or break on other motors before (never a 6.2) but anything is possible.

I would basically take this time while motor is out and do a small rebuild if you can afford it.. if motor doesnt have ton of miles you could let the bearings and rings etc alone leaving the short block alone but have the heads machined flat, valve seats ground and check if a valve may be bent, all new gaskets etc... also maybe arp head studs


edit i also wanted to add... clean the motor out really well pull oil pan and clean it out wipe down the rotating assembly, rotate motor by hand and scrub each cylinder wall if your not going to pull it apart no motor ever blew up from being too clean

also one little tip I have done (chime in anyone if you think this is bad idea) I use lucas oil stabilizer as a assembly lube except for cams always use the correct lube for cams... but when you are done cleaning put a small line of lucas around each piston,if you put new oil pump or clean and inspect old one.. pour it full of lucas before installing it.. that way even if it sits for awhile before being installed and fired up everything has a coating of lube on it... the lucas just seems to stick longer than normal assembly lube... also any time you arent working on the motor throw it in a new garbage bag or cover it with a new one each time you never know what dirt can get in there while your away and heads are off