Why are my rocker arms breaking??

[Wardcolorado]

So.... second time it's done this. The foot that rides on the camshaft has broken off the rocker arm. This is what killed it 5 years ago when I stopped driving it. Now... it did it again. #1 intake valve this time... can't remember what it was last time. I replaced all eight of the rocker arms with brand new dealer ones last time. Just swapped in one of the old ones this morning... but why??? I've never heard of these breaking before. I keep it below about 3500rpm -- usually more like 2500 to 3000, but sometimes 3500 when shifting.

Z

[BradMph]

When you replaced the rockers did you replace the rocker rod also. Did you replace the springs/spacers inbetween the rockers? Did you check the rod for clogged oilers? What rockers are you using. Tappet, hydraulic?? Do you adjust the rockers at any time?
Weak valves springs or saggy springs can cause the rocker to be slapped hard by the cam as the lobe comes around.
Could have a sticking/warped valve stem, in this case rockers can break everyday if the valve decides to stay shut and the cam forces the rocker to open it.
Something is sticking or siezing up to cause that to happen. The only time I broke a rocker was when the spacers between the rocker and the tension spring next to the rocker got worn down and the spring coil end dug between the rocker and rocker shaft. This siezed the rocker up from heat and snapped it.
Sometimes also if the valve cover is too tight on certain engine models, the rockers can actually strike the inside of the cover. Some valve covers have inner spaces that are pieces of sheet metal placed into the cover and used for PCV gases so oil isn't sucked up.

Bottom line, something is getting hot and seizing the rocker or some foriegn object is in there and finds a rocker. If there are absolutely no grooves on the rocker shaft that show evidence of damage, maybe the rockers are just a freak thing. I would bring the broken rocker to the dealer you purchased it and have them inspect it for a reason it broke.

[Wardcolorado]

Thanks

Yes replaced the rocker shaft as well when I put the new rockers in last time. They are the tappet type, not hydraulic. Just adjusted them about two months ago to specs. I'd say freak thing... but twice?

[camoit]

Can you give us a picture?
So it's not breaking in the center? Just the foot before it gets to the shaft ring. It must have been a casting flaw.
Other then that a sticky valve. Feel the valve and make sure it has some play.

[4D55 Performance]

It could be a lot of things but most likely it is due to improper engine maintenance or cheap Chinese parts. The valves need to be adjusted properly.

[thillskier]

AMEN 4d55 Performance. Maintenance.. Almost 100% a valve adjustment out of spec..and a LOT, IMHO. Where are you? U need someone to help adjust your valves (sorry, I realize you know this, just trying to get close by help!) Hopefully valve didn't bend (or ruin piston) and sacrificially broke! Yea Mitsubishi!! The cheapest (and easiest)component to replace is the part U broke! I can fix it if ur close (or have a private jet:)! hehe

[mikewarme]

Also had guys loose glow plugs in the cylinder before from their mickey mouse push button switch. Most people do not understand that if it takes too long to start engine holding the button for 30 seconds will not change anything. The tips turn into a ballon and they will break off when you try to remove them ! If the tip broke off than the valve could have hit the plug tip and broke the rocker since there is zero room between the 2 items. It will mash it into the piston generally and eventually vaporize. Also check to make sure your timing marks are all lined up! Also if your balancer and crank sprocket are shot at the keyway than your timing will change around. This if not fixed will fu#$ up your crank!

Mike

[Wardcolorado]

Well, it's dead now..... apparently I didn't get all of the pieces out of there from the broken rocker arm when I replaced it, and one jammed under a cam lobe and stopped the cam. Sheared the alignment pin off the cam gear and threw the timing belt.... of course it did this 700 miles from home (but only 10 miles from my destination). I left the truck there, and am trying to decide what to do. I have a spare engine I could pull the head off of. Or, I could get one of those cheap new 4D56T heads off of ebay ($600 from maylasia). Do they just bolt right up to the 4D55T block? Is it possible that this is a bum head for some reason?.... it failed back around 1995 originally (I think it was a dropped valve, but it might have been a bad rocker arm then too -- that was before I owned it) and was rebuilt, then had a broken rocker arm foot in 2005, then again in 2012 -- all within about 35k miles. Rest of the engine has always been good it seems.

It got 27mpg on the trip... was running really good, except for some electrical problems (which didn't affect the engine).