Bending / Breaking Pushrods

[Cudadrag]

I have recently been on a breaking or bending pushrods spree in my 451. The motor is 10.5:1 comp with solid lift can .590 lift. (Flat taps) Removing the heads showed no signs of valve contact with pistons. Valve springs have approx .050 left after full rocker compression. All have run flawless for 150+ runs (most 1/8 mile) but now seem to be breaking or bending. Damage can be to the rod or adjusting screw and seems to be random to cylinder or intake vs exhaust. What is also odd is that it does not matter if the engine is stressed or not. It can happen just reving up. No damage to Crane rockers

Could weakening valve springs cause this? Maybe causing valve float? When pushrods hold together there is no drop in car's performance.

I am certain this would be easier if I was smarter. Stupid is always getting in the way.

Thanks!

[rusty duster]

Are the rockers the old iron ones? How many threads are showing under the rocker on the adjuster screw?Are you getting a good oil supply to the valetrain?How much retainer to valve guide clearence do you have?

[fox]

Tired springs allow bad harmonics to create this damage.

[JVMopar]

How much clearence between pistons and valves? Should be 0.100"

I'd be checking everything out before you get to rebuild your engine.

I found out the hard way put valves though pistons and valves through cylinder heads.

Get some clay and check it out. Maybe a connecting rod streched?

[23T-Wedge]

Originally Posted by fox

Tired springs allow bad harmonics to create this damage.

This would be my guess, too. Just the beginnings of valve float can cause metal fatigue from the harmonics fox mentioned. .050" coil bind isn't a lot of cushion once they get weak. Did you notice what appears to be shiny polishing on the vertical portions of the individual coils? Keep us posted.

[Cudadrag]

A foot note to the problem: This actually began last year with just 1 adjusting screw breaking. All the screws showed 2 threads showing thru the rocker. The Rockers are those (Roller tipped) Cranes on a stock rocker bar. I replaced all the screws and pushrod early this year after more screw and push rod breakage with heat treated Smith Brothers pushrods (Same length 8.609") The Smith Brother Rods show only 1 to 0 threads past the rocker. That seemed to do the trick but now I just bent one of them. As far as oil once the push rod bends or breaks it gets pushed out and the lifter then pops out of it's galley thus a loss in oil pressure. Once replaced all goes back to normal.

I'm thinking the springs are just getting weak and need to retire. The springs came with the heads that were done by a local shop here in the twin cities. So I am unable to verify the age but assumed they were new. (There is that "assumed" word that always bites me at the end.) Heads worked very well for iron 452s until this push rod problem.

If I learn some thing definative I will certaintly forward. And please feel free to "Think out load" on this thread.

Thanks again everyone!

[23T-Wedge]

Cuda,
If the shop put the heads together, they might still have the work invoice, might show what installed spring pressure was, if so you could compare with what you've got now since you've got the heads off. What kind of rpm are you turning? Ever get into float? Sometimes harmonics from valve float can set up a hairline crack that won't show up right away. I had an adjuster break on a warmup in June, realized later it was the same rocker that an inner spring broke on last pass of last year. Might have been a coincidence but I've gotta think it worked on that rocker pretty hard when the spring broke. I know I'll be checking them a lot more closely from now on though.

[valiant64]

I'm betting on weak springs or bad valvetrain geometry. Smith Bros. pushrods should be strong enough, so I doubt that to be the problem.

[Cudadrag]

Well we replaced the pushrods in question with the same Smith Brothers. I found that the rocker shaft was too tight thus may have upset the geometry of the valve train. All is torqued correctly and seems ok. This still will not explain why the older Mopar Muscle push rods (Non heat treat and thinner walled) failed earlier this year. Maybe just a coincidence that those weaker just broke and then had the shaft too tight on the newer. (I know sounds like a stretch.) But for now we will see. Our next track test is not until 8-29.

[Cudadrag]

Well I broke another but this time in the garage just idling. I found that the adjusting nut and screw are backing out thus the pushrod falls off the rocker hits the rocker and bar then bends. I am replacing all the screws and nuts with a Smith Brothers set that has the 12-point nut and flange instead of just a flat machine nut.

My question is: Is there a torque setting these adjusting nuts should use for solid lifters? I am lashing at .028 intake .032 exhaust. I am guessing torque should about 25 lbs. I would be surprised if higher then that.

[pishta]

Lifter retainer type valley pan on my old 340 saved me more than once from total oil pressure failure if a lifter popped out, (bent 3 rods at once, then 2 more 2 months later) I pulled the shims out from under the suspected springs and never had a problem again. Might have been a band-aid approach to tired springs, but I sold the motor before I had any more problems.

[cudabob496]

when i have bent pushrods, it was because I was overrevving!

[Cudadrag]

Well got back from MN Brainerd's Muscle Car Shootout where in the first qualifing run I pushed a head gasket. We replaced the head gasket that night missing the 2nd qual run. Lost the first race (Time fell off a bit.) but the push rods held with the new(er) style nuts.

I know this sport would be easier if I had more talent.