Broken valve spring

[Mick6186]

Went for a short drive in my newly recommissioned 130/5. All seemed well but noticed a strange ticking. Got back to my garage and when idling there was a ticking noise that was at cam speed, but occasionally missed a beat.
I took the cam cover off and checked the valve clearances. All were spot on 8thou except 4 exhaust which was 10thou. I noticed that the cam follower wouldn't spin in its mount. I turned the engine over by hand and the clearance when checked was now 120thou. Trouble I thought.
The engine is a tall block 1700 with L14 cams Cosworth springs and bigger valves and has covered about 500 miles since being built. It had stood for at least 12 years before I acquired it.
Upon investigation I found that the outer valve spring was broken which appeared to making the cam follower tight for its final travel.
I removed the valve springs and associated bits without removing the head and have now made a fixture which hopefully will enable me to fit new spring with the head in situ. Fingers crossed.
Anyone any ideas why the spring should have shattered?

[ericbushby]

My engine had been overhauled before I bought the car but had not been used for quite a while.
One spring broke soon after I got it going and some of the others had a reduced length when removed having been compressed all that (unknown) time.
A new set of springs should fix it.
Eric in Burnley
S3SE DHC

[rgh0]

Were the springs new or had they been in the engine while it sat for 12 years?

If new i would take a close look at the installed dimensions with the valve closed and at full lift to ensure the correct springs have been fitted. if they were old it may be due to the springs sitting under compression and constant high stress for 12 years in which case there may be other springs in similar condition

In either case i would pull the head off and do a more thorough investigation

cheers
Rohan

[avro]

Something to look out for !

The Cosworth valve springs haven?t been available for some years now and as l recall had to be fitted with a modified Cosworth spring retainer. The position of the spring seat on the retainer relative to the tip of the valve was some .060? higher than the standard retainer . This was so the spring which required a longer fitted length would not become coil bound on full lift when using a higher lift cam such as the L14.
There are springs now available from both QED (Q55) and Burton Performance (FL408) recommended for these cams but you will need to change the retainers if you are currently using the Cosworth items. It may not be possible to achieve the correct fitted length without an excessive amount of platform shims . The springs now available have less coils with a thinner wire section and as such are able to cope with the high lift cams but at a much shorter fitted length.

Hope this makes sense.

Good luck

Nick

[Elan45]

Rohan,

About 10 years ago, first race of the season, I broke 2 valve springs in my Formula Junior motor, A6 cam.. Since then, I release the rocker shaft over the winter so that the 2 valves held open by the cam are released. Not broken a spring since. But, of course we can't do that with our twin cam engines.

Roger

[el-saturn]

roger - if you untighten both cams (and maybe even loosen the cotters) on a TC, you get the same result, don't you?? sandy

[Mick6186]

Thanks for the replies. Very helpful. The engine was built by a guy I absolutely trust. He has built race engines for many years, especially in the twin cam era. He is now retired but remembers my particular engine!!
I will run the engine when the spring is replaced and if I have any more broken springs replace the lot. I will keep you posted regarding my fabricated tool to replace the springs!
Mick

[rgh0]

If the Cosworth springs are non longer available you may need to find a suitable new spring and retainer for the installed height and cam lift. You want around 60 to 70 lbs valve seat load and less than 200 lbs cam nose load.

People have replaced valve springs with the head in place by holding the valve up with either air pressure or a flexible rope through the plug hole and the piston at TDC and then making a tool that pivots off one of the cam bearing bolts to compress the valve spring so the retainer and collets can be fitted.

I have always found it easier and less risk to just take the head off as once the cams are removed head removal is about at 10 minute additional exercise

cheers
Rohan

[Elan45]

Yes, you can just release the cam caps on both cams and achieve the same effect, but a little more effort to make sure everything stays in time. On the pushrod FJ motor (I have ARP studs everywhere) I simply loosen the nuts and put the rocker cover back on. In the spring, I just retorque the head and then the rockers and on to other prep issues.

Roger