Rocker arms jumping off,

[red reading]

Rocker arm failure is down to the reasons below,

valve springs becoming soft with age,

un even shimming between the two valves it operates,

un even cam wear creating side thrust.


these engines will also break the rocker arms if they are over reved and the valves contact the pistons, this is a design that is designed into the engine to prevent (or help to) catastrophic engine failure.

to stop this happening when you are building an engine always measure the spring free length and compare to the manual,and also observe the spring compressed length when installed, you can adjust the compressed length by fitting shims to the cylinder head ( this will need to be done if the valves and valve seats have been reground definitely and if the engine is of high milage).

if the valve springs are smaller than stock length in the manual they will need to be changed.

aftermarket springs will also come with these figures so please observe them.

 

[Fast Guy]

What is the over rev rpm? I've missed plenty of gears on my standard engine and once even watched it rev clean off the clock. I got lucky though on that engine and never had a problem. (watch my current engine go, next time out.:doh

 

[The Doc]

Standard car will rev to first limit on fuel and ignition cut of 7440rpm seen many cars with stock healthy engines rev to 8000rpm, so if you are lucky 8500rpm before valve float and rockers then jumping off, if unlucky and the engine has sloppy tolerance and weak springs just hitting the limiter could cause a rocker to jump.

nothing would surprise me with your current engine.

 

[MarkTurbo]

The highest I've ever seen is 7750 ish on my apexi, that was going across the finish line at wiscombe as you need to hold 1st gear to the limiter.

 

[Fast Guy]

Standard car will rev to first limit on fuel and ignition cut of 7440rpm seen many cars with stock healthy engines rev to 8000rpm, so if you are lucky 8500rpm before valve float and rockers then jumping off, if unlucky and the engine has sloppy tolerance and weak springs just hitting the limiter could cause a rocker to jump.

nothing would surprise me with your current engine.

Bear in mind I was taking about a missed gear over rev where fuel and ignition cuts won't limit you. Just checked my rev counter and it goes to 9000rpm, so I must have close to or over that depending how accurate mine is.

Re my current engine, not sure what valve lift it has, but with all the head gaskets in there, it'll need to be a lot more than standard for the valves to have a chance of saying hello to the pistons.

 

[The Doc]

Yep I know what you were saying carl, I was just showing you the point that stock engines have known to be safe Clearence wise.

and re your engine, knowing who built it etc Clearence wise I am sure it is fine, bet they never set the valve spring heights though so that and lumpy cams could mean you get valve float in which rockers can still jump, or maybe you won't .....who know's till you try it.

 

[Fast Guy]

Well I give it 7500rpm plenty, but am reluctant to go over that. It would be pointless anyway as power is falling off, but my graph only goes to 7000rpm, so I don't know how fast it drops off after that.

 

[The Doc]

Prob quite fast as they would not bother revving the car any further than it needs, that's the way proper dyno boys do it to put less stress on the engine.