What causes bent pushrods?

[Nick1994]

My dad has a 1999 Fleetwood Flair 30H RV that he bought 2years ago, around 76k miles. It has the Chevy 454 engine. In August he moved up to Oregon and drove it up there towing his FJ Cruiser, 4 mpg . In August before the journey he changed the oil, plugs, wires, cap, rotor, etc. On the journey it set a CEL for running lean (or rich? Can't remember) and it also has had a crack in the exhaust manifold, we thought it might be that. It's been running fine, except last week he said it wouldn't go over 10 mph, had a rough idle, and when giving it throttle it stumbles and bangs on the passenger side. He took it to an RV mechanic who said it had 3 bent pushrods and it runs fine now after the repair. How do push rods get bent? I'm not that internal-engine-savvy.

 

[JTK]

A hydraulic lash adjuster (lifter) that sticks all the way extended can bend a pushrod.

 

[ARCOgraphite]

overrevving usually.

 

[ARCOgraphite]

He need to get a old Suzuki Samurai or a Smart for a tow behind. That FJ is a fat piglet.

 

[Chris142]

Overrevving. All that weight pushing it down a hill usually.

 

[BrocLuno]

Bad lifter as stated above .. Or, it is the rocker arm not having enough slot clearance so that the arm stops moving and the cam/lifter does not. So if this engine ever had a cam change (?) and they did not install "long slot rockers", it might be close to the limits ... An over rev and lifters pumped up will put it over the limit. Or, it could be piston/valve interference due to a worn timing chain (long shot), timing jumped one tooth (also long shot, but still needs worn chain), or piston/valves set too close and carbon build-up has closed the gap (best probability) ... I would not drive it until I found out why? Find a tune-up shop with a bore scope and have them look in the cylinders. If it's carbon-ed up, get it cleaned (various ways). If it not carboned up, then it's mechanical ...

 

[SatinSilver]

That's like towing a 4Runner behind it as far as weight goes. Yikes!

 

[Nick1994]

Originally Posted By: Chris142

Overrevving. All that weight pushing it down a hill usually.

It took a lot of throttle to get it up the mountains to Oregon from Arizona, not sure what else he could have done. Also, it ran fine when he'd drive it around town occasionally the past couple months, he said it was all of a sudden. He doesn't drive like a race car driver so I don't think he was redlining it around town.

Originally Posted By: ARCOgraphite

He need to get a old Suzuki Samurai or a Smart for a tow behind. That FJ is a fat piglet.

He was moving, wasn't for a vacation. It was a flat tow too with a tow bar so no trailer weight.

 

[DoubleWasp]

As I said in the other thread, BBC engines are not exactly happy with high sustained rpms. Most of the time when we see BBCS with bent pushrods, it's either broken or soft valve springs that allowed pushrods to escape their position and be rammed into a new position after escaping the rocker, or collapsed lifters allowing the same. When we do the marine versions, we almost always replace the valve springs with something aftermarket that will take the beating, unless preserving a crate engine warranty. Collapsed lifters are nowhere near as common as broken or soft valve springs.

 

[BrocLuno]

Well, I assumed that broken valve springs were not the issue because the OP did not relay that info from the mechanic?? But maybe we don't have the whole story ...

 

[Kuato]

Credit to Chevy's 454 for operating that long with several bent pushrods! Yeah at high rpm you get valve float (valves stay open) and when they're in the way of the piston or other parts....well something's got to give.

 

[dishdude]

.

 

[ShotGun429]

heavy towing up a mountain (heat) can take out the oil film on the valve guides,Cast iron guides, steel valves, hangs them (valves) open off the valve seat, and Piston hits said valves and you end up with Bent pushrods, Just replacing pushrods may not fix your issue long term.

 

[DoubleWasp]

Originally Posted By: BrocLuno

Well, I assumed that broken valve springs were not the issue because the OP did not relay that info from the mechanic?? But maybe we don't have the whole story ...

I didn't get that impression either, just passing along info. Multiple bent pushrods definitely makes me think of valve float due to collapsed or semi-collapsed lifters. Part of me even wonders if low oil pressure allowed the lifters to leak down enough to set a few pushrods free. Not an easy one to hit dead on unless you're the mechanic who was on that engine.

 

[Nick1994]

Originally Posted By: DoubleWasp

Originally Posted By: BrocLuno

Well, I assumed that broken valve springs were not the issue because the OP did not relay that info from the mechanic?? But maybe we don't have the whole story ...

I didn't get that impression either, just passing along info. Multiple bent pushrods definitely makes me think of valve float due to collapsed or semi-collapsed lifters. Part of me even wonders if low oil pressure allowed the lifters to leak down enough to set a few pushrods free. Not an easy one to hit dead on unless you're the mechanic who was on that engine.

I posted all the info I got from my dad, sorry if it wasn't enough. I believe the gauge reads good oil pressure too, he filled with 10w40 MaxLife before the journey.

 

[MiKe3o]

I have seen the valve guides get a little rusty especially the exhaust side. The first start something has to give then it breaks loose. After replacing the push rod it never fails again, and could find no other failed parts. I saw this in motorhomes that do more sitting then driving

 

[benjy]

a quick search + a lot of reading will enlighten anyone who understands the basics the importance of a properly set up valve train + what can go wrong as wear occurs. its no secret the BB Chevys valve geometry was suspect!!!

 

[Johnny2Bad]

Of course BBChevy's can run at high RPM when built to do so, but that's not the motor they put in motor homes; you get a heavy duty truck motor instead, and I don't mean pickup truck motor, I mean bus motor, with maybe a 4800 rpm redline. Even with a closed throttle, going downhill with a load could cause engine over-revving, although I would expect that to be pretty fast. Any idea what the redline vs speed in gears works out to in his specific configuration? I would not be surprised to learn 80 MPH is above redline. Our company buses are governed to 65 MPH (OEM configuration), but if going downhill in gear with a closed throttle, will still go faster than 65.

 

[clinebarger]

Originally Posted By: DoubleWasp

As I said in the other thread, BBC engines are not exactly happy with high sustained rpms. Most of the time when we see BBCS with bent pushrods, it's either broken or soft valve springs that allowed pushrods to escape their position and be rammed into a new position after escaping the rocker, or collapsed lifters allowing the same. When we do the marine versions, we almost always replace the valve springs with something aftermarket that will take the beating, unless preserving a crate engine warranty. Collapsed lifters are nowhere near as common as broken or soft valve springs.

I agree......And BBC valves are extremely heavy! A spring doesn't have to lose much of it's seat pressure to lose control of the valve.

 

[Nick1994]

Originally Posted By: Johnny2Bad

Of course BBChevy's can run at high RPM when built to do so, but that's not the motor they put in motor homes; you get a heavy duty truck motor instead, and I don't mean pickup truck motor, I mean bus motor, with maybe a 4800 rpm redline. Even with a closed throttle, going downhill with a load could cause engine over-revving, although I would expect that to be pretty fast. Any idea what the redline vs speed in gears works out to in his specific configuration? I would not be surprised to learn 80 MPH is above redline. Our company buses are governed to 65 MPH (OEM configuration), but if going downhill in gear with a closed throttle, will still go faster than 65.

I haven't driven it or ridden in it, I know my dad isn't a hot rod driver but I do remember him saying there was a couple parts he did 70 mph and even 75 mph.