411 Engine noise

[Kevin H]

Originally Posted by Hunter

I assumed they where aluminium, they have BRISTOL cast or Machined into them.

In that case they are not original. Bristol used the the stock mild steel rocker covers that came with the engine.

The rocker covers on your car are an aftermarket item and it sounds like there isn't quite enough clearance at one point, OR there's something funny about that rocker arm!

Maybe the oil hole in that rocker arm is blocked and the rocker arm and/or the shaft has worn so that it's sitting up a bit higher? (although I can't imagine it getting that bad unnoticed).

Or perhaps someone has fitted non stock rocker arms?

The stock rocker arms do not have a bearing at the pivot point.

You can remove the rocker arms and shaft without removing the head, in fact I think you have to remove them to actually get at the head bolts.

However, when removing the rocker shaft it's important that it is unloaded evenly to prevent it being bent. Also make sure you keep the rocker arms in the same order, because they will all have slightly different wear patterns.

Once you have removed the rocker arms you may as well remove the push rods and make sure they're all straight

Of course if you go down this disassembly path it's a slippery slope, because there are all sorts of things you may as well clean and check. In which case it's probably worth investing in a book on rebuilding big block (B/RB) mopar engines

[Ronald G. Stephenson]

That noise is probably not due to the rocker arms hitting the valve cover, and could be something much more serious. A wrist pin will make that noise at some point on the RPM scale, and not at others. I would led someone who understands engines listen to the noise.

[Kevin H]

I must admit the fact that the noise goes away over 1200 rpm is hard to explain if it's the rocker arm hitting the cover.

But then if it was the wrist pin, aka gudgeon pin, why would the noise go away when the rocker cover is removed?

It is however worth erring on the side of caution, because if a gudgeon pin does fail it's usually goodbye engine.

[Hunter]

Thank you everyone for your advise its pretty much confirmed what I had suspected (but hoped was not the case).

My thoughts where lazy lifters and i was hoping to change these without removing the head. ie from the top with an appropriate tool.
If this is something that can be done, i will. If not, it will have to go to the local Bristol specialist. He can look at it when he has finished the 403 that he has had for over a year now (long story)

As for the rocker covers, im unsure where they came from. what I do know is its the last 411 made so may have had some goodies added at the factory, or someone spent cash on aftermarket pieces.

Thanks again everyone, a great forum with some very useful info. I have learned a great deal reading through the threads.

[Frenchy]

Since you say the noise disappears with the rocker cover off, and the cover has contact marks from the rocker, why not try 3 gaskets to increase the clearance? As I don't own a Bristol yet, I'm not familiar with the Chryser type of rocker arm mount - is it a shaft, or a ball stud that it pivots on? Reason I ask is, with a ball pivot, the rocker might go into a resonant vibration mode where it not only pivots front to rear, but also side to side. And maybe this happens at speeds below 1200 rpm, but stabilizes around 1200.
If you had access to a shop with a strobotach, they could synchronize the strobe flash to slow down and slow-motion the movements of the rocker, and you might see some unusual motion not visible to the eye alone. I once solved a lost motion mystery on a reciprocating experimental lab test with one of these instruments - it's just a variable frequency strobe combined with a tachometer so you know how fast it cycles, and can match or vary slightly its flash rate vs the rate of motion of an object. This might show the rocker "dancing" in an odd way which could vary its distance from the rocker cover.