The V8 Owners Forum -

Has anyone ever had a rocker fail/break on them? I have heard that they can fracture underneath- I am assuming the valve end effectively breaks off.

I am wondering if it is worth polishing the undersides of the arches as I have a brand new set and rough edges on castings are always where cracks start, with a high lift cam and double valve springs there's more tension than they were designed for... Plus I'm sure it would only take a couple of mins with a couple of right wheels and buffing wheel in my workshop.

TC

I've only worked on standard engines, but have only come across one broken rocker in all those years.

Interestingly (well, I thought so) it had a misfire and a light tapping which the knowall doing the job insisted was a piston or big end, despite everone else telling him to whip the rocker covers off to have a look.

He took the engine and box out, and after removing the first rocker cover, found the end rocker was broken. He insisted there was another fault and proceeded to strip the engine down to the last nut and bolt to find it, without success. Tw*t!

As a general observation broken rockers are asociated with the valve or spring retainer hitting somthing. this can be a valve hitting a piston because the clearance hasn't been checked properly, or the push rod jumps out of its cup and causes the valve to open too far and hits the piston (or the cap hits the top of the guide) or the timing chain slips. This can be because of over reving leadind to valve train float. As a rule you have to have to have an very heavy valve springs and a very high lift cam to overload the rover rockers, generally installing this sort of set up you will be upgrading the whole set up.
Mike

I have a few snapped ones----- some with tips broken off and some with them split accross the bore

That might have something to do with your addiction to 7000-8000 rpm Mr Stuart

My first 3500 raced for 3 years with no failures of the original 100,000 mile rockers. My new rockers on the 4.6 have sharp casting marks around the arms as well. And they have been fine for nearly two years. I run a Blower cam and all the double valve springs etc with no trouble. But my engine does not really go above 5800 rpm.
On two occasions I have cocked up on my valve clearance calcs and bent a whole set of standard heavy real steel pushrods while the engine ran rough for about 30 seconds on startup and then started rattling. New set of rods and some shims and all good.

My biggest cock up was having 3 engines on the go at once. I fitted stock heads to the wrong engine. The heads were older stock heads that had not had the valve guides trimmed and capped with blue seals for the bigger cam as they should have gone onto an old pre sd1 stock engine with stock cam.
Therfore not enough available lift between the bottom of the valve cap and valve guide. The rods bent out of true by about 7mm in the middle. Those rockers are still in use 2 years later and are still fine.
I'm not sure I would have been that lucky if they had been moly rods though.

Do whatever makes you feel comfortable Tom.
I just buy them, stick them in and use them.

If I buy rockers from RS they tend to have rough casting marks. The last set I got from JE seem a lot smoother and a lot more shiny. And a better price too.
I've just dropped a set of heads into John at JE to have the guides shortened and machined for blue seals for a wilder cam. He only charges £40 a pair which I think is great.

Perry, I only live a mile from John Eales, if you fancy meeting up for a pint when you pick up your heads let me know.

mgbv8 wrote:That might have something to do with your addiction to 7000-8000 rpm Mr Stuart

LOL I may just leave them then- I'm sure you have given yours plenty of stick over the years Pel!!!

Provided the rockers are limited to a maximum engine speed of 5800 rpm, there should be no problem assuming of course that they are genuine parts.

I have heard of non genuine rockers being broken when taken out of the box.

I would also steer completely away from the pattern parts that come in the "blue box".

Ron.

RoverP6B wrote:Provided the rockers are limited to a maximum engine speed of 5800 rpm, there should be no problem assuming of course that they are genuine parts.

I have heard of non genuine rockers being broken when taken out of the box.

I would also steer completely away from the pattern parts that come in the "blue box".

Ron.

I regularly ran stock rocker arms to 7k and have hit 8200 on one occasion, and never broke one untill my timing gear breakage,

I have to admit to taking my old 3500 to over 8000rpm one day during an "incident" at the Pod. I launched hard and just as I shifted to 2nd gear under full power + 150 of gas a half shaft let go. The thing revved its nuts off, but only for a few seconds. As I came off the pedal I glanced at the tacho and she was on her way back down from 8300 rpm.
I thought I had cooked it for sure. But we put new shafts in and the following weekend we took her out and the engine was fine. Those rockers raced on for another 2 years before the 4.6 went in.
So they will take the odd bit of exessive abuse eh?