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Healey 100 -- Broken rocker and bent push rods !!!

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johnball

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So there we were driving down to Goodwood Revival at 6am on Sunday. Suddenly a large clattering and three cylinders. Took the rocker cover off and found the following:- rear cylinder exhaust rocker broken in half at the cam follower push rod end. Push rod bent and jammed in hole of the cylinder head. The inlet rocker has slid forward against the shaft spring and is resting on the valve spring washer, not the middle. Also the cam follower push rod is bent the same as the exhaust one - fowards. Suspected valves hitting pistons --- but no -- head now off and no visible damage to either pistons or head and valves !!!???. Now what I can not understand is why the rods are bent. The valves move up and down OK. If the cam followers had just jammed upwards, it would have just left the valves open and off the cam. The question is what happened first --- the exhaust rocker snapping ? or the inlet rocker sliding forward, but why the bent push rods ???.

Very lucky my, newish Dennis Welch aluminuim fast road head was not destroyed. Now have ordered an new 'roller rocker' set, plus 8 new rods to match.

What I do not want to do is install new Rockers, shaft and push rods and have same thing happen, as I have no sensible explanation of the sequence of what happened and why, except i do know rockers were the original 60 year old items, but the shaft was less than ten years old.
 
While you have moving valves now, is it possible that when everything is at running temperature that one or both stuck in their guides for some reason?? Or perhaps the cam followers for that cylinder stuck in the block with a valve open causing the piston to push it closed and bending the pushrod and perhaps jamming the other one. Really, needs to be something on either end of that parts chain failing to move to cause the pushrods to be put under more compression than normal. And I would expect the broken rocker would be a result rather than a cause.
 
If this is a recent head replacement, is there a chance of coil bind with the valve springs ?
 
Is it possible your timing chain jumped a couple of teeth?
 
I bent a push rod once when the rocker arm ball slipped out of the push rod cup. The valve didn't open, but the push rod got wedged in the hole. No damage done (that I could tell) other than the bent rod.
 
Sounds like the exhaust valve stuck and caused the rocker to snap and bend the rod. Once the valve stem cools off, no clearance problem and the valve is free. Intake pushrod damage is collateral?

I would remove the exhaust valve carefully and look for galling in the guide. Exhaust valves can heat up and seize rather suddenly. A little more clearance in the guide would probably correct the problem. You say it is a new head, so clearances are likely to be tight.

Good luck!
 
Johnball, My thinking is rocker loose on shaft. Slide off the top of the valve, pushrod couldn't push it, force of cam lift broke rocker and bent pushrod. In a race situation, or in necessity you would slam it back together and keep on going. But I would be concerned with what happen to the cam lobe and follower. maybe that can be inspected via the side covers. Dave C. (change oil too).
 
OK, so now have discovered the cause and consequence of the failure. The 60 year old exhaust rocker had the oil hole drilled through it too close to one edge. Finally it failed. The pushrod bounced up and down off the cam follower and was jammed but NOT bent. The broken bit of the exhaust rocker then got jammed under the inlet rocker and thus that pushrod was bent. The marks where it got stuck under the rocker are quite evident on the Dennis Welch ali cylinder head. Now I am having the DW roller rocker set fitted, but it appears that the cam I have may have a higher lift than thought.( it was from SC parts many years ago and was meant to be 100m spec but may be a 300 degrees higher lift than the current thoughts of 268 degrees and 0.252 inch lift ) The problem i have is that the valve springs are binding due to the long length of the roller rocker giving more valve push down, so I am having another set of thinner double springs fitted. Orchard Restorations in Heathfield, UK are doing a very good job of engineering the problem. Since I have had the car 20 years, I have decided to give it a birthday so they are doing other work while the car is in bits !!!!!!
 
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