rocker shaft

[Astro]

Hello,

does anyone have an idea how this could happen during the first hill climb this morning? Valve clearance has been 0.40mm and the rockers are all still ok!

[dklawson]

I zoomed in on the end of the shaft in the picture and changed the contrast a bit. There look to be a few "beach marks" on the top of the break that suggest a rapid fatigue failure.

If this was a hardened shaft I would suspect residual stresses and a head that may not be perfectly flat, pedestals that are not all exactly the same height, or a rocker shaft that was slightly bent before installation.

[Astro]

it was a C-AHT436 from Spares, a 1.5 Hi Lift forged rocker assembly on an old, but really good reconditioned Arden head. It was running about 500kms competition within two years. Now suddenly the motor just did 6000 instead of 8000 and 5km later there was a clacking noise. Therefore I am not sure when it broke and how to explain these marks. Might a standard rocker shaft be a better solution?

[Spider]

Yeap, had that happen before.

In our case it was the lack of finish quality from the drilling that started it.

<Edit: I know this suggestion will no doubt make Mark cringe, however try a set from MED. I don't know what much of their other stuff is like and I'm not too interested in debating it, however I can say that I have been running several sets of their Rockers (in 1.3 and 1.5 ratios) after suffering breakages like yours and also broken rocker arms. IMO the MED Rockers are well made and given very good service, I think they are also attractively priced too.>

[Astro]

Thank you! But I am still not sure what to do. Two years ago I had trouble with long push rods from MED and they never answered. In the meantime I am running a short stroke engine and can use standard push rods and have no more problems. OK, in three weeks we will do Vuillafans Echevannes and the engine should work.

P.S. just looking on their HP. Does they have any forged assemblies? With a period G2 car under FIA regulations, we cannot use roller rockers!

P.P.S. just visited a specialist. It's a fatique failure. It will happen again and it doesn't matter how thick the wall of the rocker shaft will be. The end of the rocker shaft should be supported like those ones. viewtopic.php?f=4&t=6303 Today there seems no one to offer a classic solution, it's just MED with their LDX rockers made from aluminium. Perhaps anyone knows where to get a classic 1.5 rocker assembly with supported ends? Otherwise we try to build something like this. Thank you.

[carbon]

The Windsor roller rockers from mid-80's also had very neat looking 'W' pedestals to give extra support to the rocker shaft.

I used to think this was a bit of overkill but maybe on reflection they got it right...

Link : http://www.manumolding.co.uk/motorsports

Does anyone know if Windsor still sell these rocker pedestals?

[Astro]

After all quoting Nick Swift "Thick wall rocker shafts have been the standard engine tuner’s choice for years but the quality of the steel and the all-important heat treatment has been getting worse. These rocker shafts do break, usually they snap at the NO 1 post and the mayhem caused by the loose pushrod and rocker is expensive." it is not a rare problem. There seems to be two solutions. Either a very high quality rocker shaft or, as Jim Whitehouse did, fixing the ends by two more rocker shaft posts.

[carbon]

More rocker shaft mayhem on the Aus Mini forum : http://www.ausmini.com/forums/viewtopic.php?f=2&t=89734

Must be open season

[5portsrock]

For the ease of use and cost why not just life the shaft? So many hrs running and just replace it.