Broken Valve Spring

[David2269]

My Stag developed a misfire, it seems a valve spring is broken following an investigation to check the valve clearances. Any tips or guidance on how to replace the springs, and if there is an easy way to do this, would be appreciated. Is worth replacing all the valve springs as one has suddenly failed? The car came with no history and the engine that came with the car is an ESS, so a replaced at some stage.

[richardthestag]

Ouch... I recently replaced a broken valve spring on a Rover v8 by getting the impacted cylinder close to TDC i.e. both valve closed.. fed a load of washing line rope into the spark plug hole and wound the engine to TDC on that cylinder until I felt resistance whilst hand winding the engine. Then I used a tool (big socket) to bang down on the top plate of the valve spring and use a magnet (attached to the side of the socket) to catch the collets. Refitting was way less easy. I needed to create a brace which ended up being a very used rocker shaft which I bolted to the engine using the original pedestals . I then used the ring end of a spanner to compress the spring top plate and dropped the collets back into place. Took me an hour.

Stag V8 valve springs are recessed into the head, I think the above method is still achievable BUT you may need a tube to sit between the ring end and the valve top plate... Then of course you will need to manufacture some sort of bar that sits 2" above the top of the valve that you can then lever against.

Seems like a shed load of work but probably less than removing the head..

That said, if the spring has broken then fair chance that the upcoming piston on that cylinder would have gone proper Tyson on the reluctant valve.. So head would need to come off anyway

[flying farmer]

I think the first thing to do is see if the valve has got bent from hitting the piston. A simple way of checking is to remove the spark plug and use a length of rubber hose (half inch heater hose works well) to blow into the cylinder. It will be fairly obvious if the valve is bent as it won't hold any pressure. I use this method for diagnosing dodgy valves and poorly sealing piston rings. Blowing by mouth is sufficient.

If you have a bent valve it is head off time.

Removing the old spring might be possible using the method Richard mentioned above, replacing the spring retainer will require some imagination and probably the construction of a tool to do the job.

If you manage to remove the old spring and find any signs of rust pitting on the spring ( not uncommon if engines have stood for years), then I would definitely look at replacing the whole set

[jbuckl]

I think the first thing to do is see if the valve has got bent from hitting the piston. A simple way of checking is to remove the spark plug and use a length of rubber hose (half inch heater hose works well) to blow into the cylinder. It will be fairly obvious if the valve is bent as it won't hold any pressure. I use this method for diagnosing dodgy valves and poorly sealing piston rings. Blowing by mouth is sufficient.

If you have a bent valve it is head off time.

Removing the old spring might be possible using the method Richard mentioned above, replacing the spring retainer will require some imagination and probably the construction of a tool to do the job.

If you manage to remove the old spring and find any signs of rust pitting on the spring ( not uncommon if engines have stood for years), then I would definitely look at replacing the whole set

Indeed, rust pitting on a valve spring is a primary reason for a fracture propagation. Regular fatigue on a valve spring takes many millions of cycles. Think 200,000 miles plus.

most valve spring failures are due to manufacturing defects (material inclusions) , over revving or corrosion.