Hitchcocks Forum

Rocker Failure

I’ve experienced failure so far of several Samrat rocker-sets after ~1000km each in my 1996 500cc Classic. The metal is worn away quickly off the top block and they get noisy – but they are bolted down at the correct 5ft-lbs and when bolted freely rotate. I have the larger exhaust valve, competition valve springs and Mr H’s Performance Cams together with high cap oil pumps.

I have also just seen that the new cams have ridges worn on the faces where the followers ride, and I’ve also found that the cam shaft bearing holes in the timing-chest cover are badly worn so I will have to fit bronze bushes.

I suspect that cruising at ~4000revs (~95kph on standard sprocket in top) the performance valve springs are floating and forming a coil-binding situation even though there is a total of 5-10mm of space between the spring coils before they bind when static. Sounds odd, but I’ve seen video of this on another make bike with description, elsewhere on the web. They say that valve springs can effectively coil-bind at the right harmonic speed even when they are not actually binding in a static test when the valves open. I suspect the cam-face ridges are due to this continual bouncing too as is the wear on the cam bushing.

If so, what to do?
I plan a new set of competition springs and the alloy spring caps.
Should I also take a millimeter off the head below the spring base plate to lengthen the amount of free spring length? Can I actually use the performance cams in the 500cc Classic without spring bind? And how the heck do I get cam bushes in the right place in the timing chest?

But more importantly, why is this happening? Surely I shouldn’t get coil-bind at such low revs?
Is it spring-bounce?
Any advice welcome!
Thanks, ChrisD

I sometimes wonder if sometimes something that is not broken has been repaired to such a degree that it is? ... Just the musimgs of an old dodger

Chris, have you cosidered some kind of lubrication problem?

"I have the larger exhaust valve, competition valve springs and Mr H’s Performance Cams together with high cap oil pumps. I have also just seen that the new cams have ridges worn on the faces where the followers ride"

I agree with both the former but in particular with Bryan.

It is quite possible that the samrat items are now trying to do a job they where not intended to do.

When you upgrade only part of a chain of items the weakest link will fail.

Hey Chris , I have the same set up more or less .
If the timing cover is that worn I would have a look at the part of the casting the oil pump spindle runs in , if worn badly I would buy a new timing cover .
The other thing is ..how well lapped are your pumps and how free flowing are your oil transfer holes and the pipe ? Did you drill out the tiny holes for the rocker bearing oil supply ?
My samrats are still OK after many thousands of miles , I fitted race springs to match my cams and our hosts recomend them so as not to bind and anouther important thing was to change the cam followers to the racing type so both were new to start off with as worn followers can wreck camshafts .
If you know for sure that your rockers are getting shit loads of oil something strange is going on and there have been storys of poorly made Samrats so our hosts make their own with much better tolerances and higher grade alloy .