Rocker Arms

[ahalfacre5]

Hey guys..


I searched but didnt find much. I found 2 broken rocker arms today, and i need to know how exactly to replace them. can someone link a write up, or youtube video, or something? and what else should i look at while i have the valve cover off?

[vpilarrt]

Are you sure the timing belt didn't let go and crash a piston into the valves? Are they on the same cylinder?

[ahalfacre5]

I'm 98% percent sure. It started up just fine before I took the valve cover off, and it wouldn't run without a timing belt correct?

[MR 325]

Well, you need to start by removing the cylinder head from the engine.

[JCarp90]

Well, you need to start by removing the cylinder head from the engine.

This.

[digger]

i know people who have done it with the head on put i wouldnt try. will give you a chnace to refresh a few things in the process.\\

get a bentley

[jeffnhiscars]

If your timing belt did not jump you have to ask why those rockers broke. If its metal fatigue then you can figure others are not far behind so just replacing 2 without going through the head as suggested, may just be throwing good money after bad.

[digger]

post some nice macros of the fractured face of the rockers if you can

[jlevie]

What to do depend on which rockers broke. The rockers at either end of the head can be replaced w/o removing the head. Other than that the head needs to come off.

[jeffnhiscars]

What to do depend on which rockers broke. The rockers at either end of the head can be replaced w/o removing the head. Other than that the head needs to come off.

Even if that were the case, what are the chances that 2 rockers would just break without a larger problem lurking somewhere ?

[jlevie]

Even if that were the case, what are the chances that 2 rockers would just break without a larger problem lurking somewhere ?

I have seen broken rockers on street cars with automatic transmissions that seldom, if ever, saw the upper end of the rpm band. That suggests something other than just pushing the engine as the cause. My theory is that a past history of a lack of timely valve adjustments is the cause. Excessive valve clearance increases the impact forces of the rockers and that repetitive loading can eventually result in fractures. Adjusting the valves every 15k (or better yet every 10k) will help prevent failure. And if you have the head apart polishing the arm of the rockers that supports the eccentric fork will remove stress risers and decrease the chance of a failure.

So no, it doesn't necessarily mean that there is a larger problem.

[TobyB]

Excessive valve clearance increases the impact forces of the rockers and that repetitive loading can eventually result in fractures.

This.

Also, weak valve springs on an engine that gets used 'spiritedly' but NOT abused....

t

[jeffnhiscars]

I have seen broken rockers on street cars with automatic transmissions that seldom, if ever, saw the upper end of the rpm band. That suggests something other than just pushing the engine as the cause. My theory is that a past history of a lack of timely valve adjustments is the cause. Excessive valve clearance increases the impact forces of the rockers and that repetitive loading can eventually result in fractures. Adjusting the valves every 15k (or better yet every 10k) will help prevent failure. And if you have the head apart polishing the arm of the rockers that supports the eccentric fork will remove stress risers and decrease the chance of a failure.

So no, it doesn't necessarily mean that there is a larger problem.

I think we are saying the same thing.

By a larger problem I meant something suggesting more than replacing the 2 broken rockers is called for. I would consider metal fatigue, which occurs over time just as you describe, to be just such a problem. If those 2 rockers broke from fatigue, which as you say could be from poor maintenance or even from stress due to excessive wear, then all the other rockers will IMHO be in line to suffer the same fate.

Once the head is off most of us would clean up the valves, deck it etc "while we are in there". If it were mine (and at the moment it is cause I have a head in the shop), I'm just saying I would not reinstall the old rockers.

[jlevie]

Yeah, in that sense we are on the same page...

[SkiFree]

This.

Also, weak valve springs on an engine that gets used 'spiritedly' but NOT abused....

t

And it's not helped by the fact that the oem eccentric arm on the bottom backside of the rockers are so thin. It all adds up.