How can a main dealer break a rocker?

[raw cerb]

Had my 406 HDI in for a cambelt today. I received a message saying that they broken a rocker, and need to order one in.

How the hell can they break a rocker? Is it possible that they fitted the new belt incorrectly, and screwed up a rocker, (and probably valves too)? Any ideas appreciated, as I shall be calling them for an explanation first thing in the morning.

[rich 36]

Perhaps someone knows differently,
I'd never even heard of broken rockers outside Le man
until shortly after when one broke on mine
Thankfully being Flat Six piston merely shoved valve to one side
and no lasting damage,

not sure the effect on conventionsl layout engine,


got a picture somewhere

[Mikey G]

I'm pretty sure the 406 HDi engine doesnt run rockers, it should have direct acting cams on buckets.

Maybe they broke a tensioner? then again replacing them is normally part of the belt change nowadays.

[SneakyNeil]

Yes if they got the timing out or didn't tension it right and it jumped a tooth or whatever then valve to piston contact can often break rockers.

If they're lucky they didn't bend any valves... if it isn't running spot on when you get it back ask for a compression test!

[wildoliver]

rich 36 said:

Perhaps someone knows differently,
I'd never even heard of broken rockers outside Le man
until shortly after when one broke on mine
Thankfully being Flat Six piston merely shoved valve to one side
and no lasting damage,

not sure the effect on conventionsl layout engine,


got a picture somewhere

Rich if it is a 911 engine the rocker is designed as a weak point anyway in case of failure, it is a lot chaeper to replace a rocker than valve/piston!

[raw cerb]

just got it back. I reckon that it broke on first start up after fitting the belt. The heard it, and instant misfire followed. They assure my that they have checked and rechecked compression and diagnostics.

I would say that it is running fine now. The sticking valve bit bothers me, but if the truth is known, I reckon that they fitted the belt incorrectly. If the valve stuck, I assume it'll do it again!

[rich 36]

wildoliver said:

rich 36 said:

Perhaps someone knows differently,
I'd never even heard of broken rockers outside Le man
until shortly after when one broke on mine
Thankfully being Flat Six piston merely shoved valve to one side
and no lasting damage,

not sure the effect on conventionsl layout engine,


got a picture somewhere

Rich if it is a 911 engine the rocker is designed as a weak point anyway in case of failure, it is a lot chaeper to replace a rocker than valve/piston!

Thats in some ways nice to know,
I was sort of happy it'd done nothing much to anything else

[cptsideways]

I bet they bent a valve by not manually cranking the car over or winding it over with a long bar. I'd ask for a thorough inspection.

[That Daddy]

It would have to be some sticking valve,that story they have rolled you is crap,they timed the engine incorrectly,they should just come clean
& deal with it

[I Cooke]

wildoliver said:

rich 36 said:

Perhaps someone knows differently,
I'd never even heard of broken rockers outside Le man
until shortly after when one broke on mine
Thankfully being Flat Six piston merely shoved valve to one side
and no lasting damage,

not sure the effect on conventionsl layout engine,


got a picture somewhere

Rich if it is a 911 engine the rocker is designed as a weak point anyway in case of failure, it is a lot chaeper to replace a rocker than valve/piston!

That doesn't say much about what Porsche thinks of their mechanics!

Personally I would expect even slight valve/piston contact to result in damaged valves, but then I've only seen it a handfull of times. If engine has fired and contact has occured then you aren't looking at one valve but all of them on that cam.

[wildoliver]

It actually has nothing to do with their mechanics?

It is as an over rev protection. I've stripped a couple of 911 engines that have been buzzed and other than the broken rocker there has been no damage to valve, piston or guide.

Seems to work!

[raw cerb]

It broke down yesterday on the M25. Why? Because the induction pipe came off because it had not been screwed on properly!!!!

Although engine runs fine now, the dipstick now pops out. The oil level looks high, so hopefully its as simple as that. I fear worse though.

[I Cooke]

wildoliver said:

It actually has nothing to do with their mechanics?

It is as an over rev protection. I've stripped a couple of 911 engines that have been buzzed and other than the broken rocker there has been no damage to valve, piston or guide.

Seems to work!

Really? That suprises me. I would have thought that when the engine runs over speed the valves might bounce or not return quickly enough and hence hit the piston. How does the rocker become stressed? Surely the cam timing is still intact?

[wildoliver]

If you take a look at a 911 engine then it becomes fairly clear how they work. they shear across the pivot point.

[I Cooke]

I see, I'm not saying that I don't believe you at all, I know very little about Porsche engines. I was just curious as to exactly what causes the failure in the first place? Valve/piston contact would surely leave some evidence, especially if failure happened due to overspeed! Every case I have seen has at least rubbed the carbon off the top of the piston. At this point I would definately rebuild the head..... Or is it that the rocker cannot not cope with the extra load of running beyond maximum speed, hence failure may occur before valve contact?

Unless the timing is out, there should never be a point where the cam, rocker, valve and piston are all locked together.

Edited by I Cooke on Tuesday 27th March 12:46

Edited by I Cooke on Tuesday 27th March 12:47

[wildoliver]

They tend to fail at about 1000 above redline I believe.

Rubbed carbon wouldn't bother me, it isn't hard to remove. On a 911 or other hemi head engine it may be a different story depending how much rubbing had occured, as the valve would have been pushed to the side however slightly, but 9 times out of ten unless it is belt/chain failure a lot can be got away with.