Bent and Broken Push Rod 350 SBC

[LongBox]

69 GMC 910. 350 4bbl SBC, TH 350. Truck sat for 14 years, with apparently an occasional start. Truck was garaged all that time. Gasoline smelled pretty bad. Truck started, after some work on the ignition, and actually ran real good.

My plan was to use the old gas up, then fill with new, and do a tune up to get the dwell and timing correct. Started to run rough, then began to clatter.

Compression tested around 175, cold, throttle not blocked open, except for two cylinders. One was at 135, the other at 0!

Pulled the rocker covers, and found one pushrod not engaging the rocker arm at all, and one pushrod broken off and bent as well. See picture, which I hope shows up below.

Question, before I get into this any further, is what might have caused this? I'm wondering if the old gas varnished up the valve stems and guides? Or maybe ghe fact that it was not timed correctly (spark) did something? It was spark knocking under load...

New pushrod in photo for comparison.

[davepl]

Can't speak to the cause, but at the risk of pointing out the obvious, you're still missing a piece of that pushrod, are you not? So long as it's not in the engine somewhere...

Ignition timing couldn't bend a pushrod, at least not in any way that I can envision.

I wonder if gunk got into the lifter, plugged it up, it wouldn't compress, and that bent it. That's my best guess... gummed up lifter. If a chunk of carbon gets stuck in the valve that can also do it.

Check the bottom of that lifter for condition - if there's any suspect wear on that lifter, you likely have some on the cam as well.

[notsolo]

Long time ago friend's Buick,it had close to 100k on it. Vacuum line came off. Resulted in a bent push rod. That's what we thought at the time. He ran it hard. We replaced lifters and push rods, ran great after that.

[LongBox]

Yes, the rest of the lifter is down in the valley somewhere. Manifold off this coming week, and we'll see what we find. The engine oil pressure is good, even when just cranking for a compression test, the gauge goes to the middle. That doesn't mean there is no problem with the lifters, though, so while it's apart, we'll be looking at each lifter, each lobe, etc. Also want to make sure each valve and guide have proper clearance and action.

[hamjet]

it very well could have been a stuck valve. imagine for a moment if the valve did not close all the way you will have a lot of clearance which can allow the rocker to flop at an angle, once the lobe takes up slack, if the rocker hit the valve on the edge, it would put pressure on the pushrod at an angle. looking at the pushrod in the photo it looks like it bent right at the wear spot where it comes through the head.

[Mike C]

Originally Posted by hamjet

it very well could have been a stuck valve. imagine for a moment if the valve did not close all the way you will have a lot of clearance which can allow the rocker to flop at an angle, once the lobe takes up slack, if the rocker hit the valve on the edge, it would put pressure on the pushrod at an angle. looking at the pushrod in the photo it looks like it bent right at the wear spot where it comes through the head.

This. Running an engine on bad, varnished gas can cause valves to stick when it cools off. Then pushrod no longer is centered on rocker and it twists, bends or breaks.

[LongBox]

Originally Posted by Mike C

This. Running an engine on bad, varnished gas can cause valves to stick when it cools off. Then pushrod no longer is centered on rocker and it twists, bends or breaks.

I believe this is the cause of the problem. With the rocker covers off, and with a new pushrod in place, but not done up very tight, that valve does not move when the rocker moves. My mistake. It's going to get fixed properly, taking the head to a machine shop to make sure the valve stems/guides are all good, and we've gotta check those lifters and lobes, plus fetch that chunk of pushrod outa there.

I did put a container of injector cleaner that was on my shelf in the tank, but I guess that was not enough. I was too lazy to take the tank out of the truck and drain it out.

[1969c10joe]

did you oil prime engine? are we supposed to if the engine sits for a long time? even if its wellbroken in?

[GRX]

x3 on bad gas making valves stick stick. Have seen this happen many times. Smells like turpentine.

You may get lucky pumping various solvent through the system. If not, the proper fix is to take off the heads, remove the intake valves completely, and thoroughly clean the sticky varnish from the valve stems & guides.

[LongBox]

Update: After thinking about the engine issues and talking with other "car guys", I decided to let a shop take care of this. Going to send the heads to a machine shop to make sure the valves and guides are good, and not varnished up. Will check the lifters and cam lobes, and my question now is if there are issues with the cam and lifters, would it be advisable to go to a roller set up? If so, what would be a good recommendation? Torque and fuel economy are more important to me than high end power.