HELP- WHY WOULD A VALVE SPRING BREAK ?

[comper88]

Hi,can any one shed any light on why a valve spring would break,my mates just phoned and told me that his 3.5 V8 is running really rough and sounds like its only on 6 or 7,the only thing he had done was fit an advance module for the LPG side of things,prior to this the motor was running fine and has only just been rebuilt,on investigation his mate looked down the filler neck and there was half a valve spring looking back at him so off came the rocker cover and the valve spring to No2 cylinder is in two bits + a very bent strengthened push rod,whats the odds of the the spring breaking or could it have been the colletts that broke,by the way it was only a single spring and not a double,if we can replace the bent push rod and some how put the new valve spring on( without having a converted spark plug with a compressed air fitting on)does any one think it may not have damaged the piston,or is this just being hopefull any way i think the head and inlet manifold will have to come off and have a proper look see,the trouble is he wants to drive it to Germany on Thursday

[ian.stewart]

What machine work has been carried out to the engine, what cam is installed, were the springs checked for spring bind??
90% certain piston to valve interferance has occoured, thats the normal reason for pushrods to bend, unless the pushrod has slipped out of the lifter and into the cam oil way and has been squashed by the cam rotating.
the collets can be removed by removing the plug. pushing a length of clean rope down the bore, retaining the the other end. wind up the piston untill it hits the rope, you should be able remove the collets and springs without risc of the valve dropping into the bore

[comper88]

Hi Ian,not sure what engine work done as i did not help with the rebuild on this one,still trying to get my own V8 sorted out,i do know that it was a non standard cam and heavy duty push rods, new bottom end and new rings etc,having just spoke to his mate on his way home he now tells me that the oil pressure light was comming on so either tick over not quick enough or something bad has happened down in the sump,or could it be the rocker arm not sitting right and loosing oil pressure through the rocker shaft,also don't think that the push rod holes in head would have been opened out for the new heavy duty ones, do you think the push rod may have got caught up on the casting in the head thanks for the rope trick down the cylinder,not thought of that one,i used to use compressed air to push the valve up.

[katanaman]

Sounds like its toast to me and needs a good look at, at least the head taken off but I dont like the sound of no oil pressure.

[comper100]

Hiya all

I am the chap that went down to inspect it tonight. I think the oil pressure was done to the fact that there was no resistance as the rod was out and oil was just pouring from the rocker shaft. I think the can had bent the rod also as it has sliped down into the valley when i removed the rocker cover.

The springs weren't tested for bind but i have used loads without failure under much more abuse, thing is this happened on tickover too. A 100 mile trip was completed no worries the week before

Cheers Nige for the post

Its bugging me too!

[ian.stewart]

what about rocker shaft oil hole alignment.

[racer]

Hi,can any one shed any light on why a valve spring would break,

Valves springs break. There are many reasons and only a few of them would require you to think much more than simply replacing it and any other damage.

However, in this case, it could be the non-stock cam. If it is a bit too wild and the springs weren't matched to it in quality and fit..then breakage is an expected consequence.

racer

[comper100]

Yeah that could be it really, just a case of old springs and a hefty new cam

Either way it is fixable but i think it needs to stay in the country and get a few proof miles on it before its goes any great distance!

(Ian the rocket alinment was fine too when done )

[HairbearTE]

My money is on coil bind. Too much lift and stock springs reduces clearance between the coils during cam lift to unacceptable margins. Throw in the likelyhood of your block and/or heads having been skimmed at sometime in the past and you may have had no clearance at all! Springs are available with one less coil than stock to allow more lift without this happening. The rover has a non adjustable shaft mounted rocker system and because of this small changes to the geometry of the system (eg. by installing a new cam) create issues elsewhere. How long are your pushrods for example? If your cam has increased lift on a stock base circle then you would benefit from pushrods slightly shorter than stock or shims under the rocker pedastals. True, the hydraulic lifters will absorb small variances in the valvetrain but put together the extra lift, possible machining to heads etc. and the fact that the rockers may not be shimmed correctly and its not suprising when a stock spring breaks on an RV8.