Conical valve springs

[ECR]

Just read an interesting topic via SELOC about conical valve springs. The spring is wound so that the distance between each coil is different and the diameter at the top of the spring is considerably less than the base.

Varying the distance between coils reduces the harmonics that are often the cause of valve spring breakage (each coil has a different harmonic to its neighbor) and because the spring is smaller in diameter at the top, the valve spring retainer can be smaller (less weight to move) and there is also less weight in the spring at the point which moves the most distance.

 

It seems a simple idea that could be applied to all performance engines.The link below gives a fuller explanation.

http://www.superchevy.com/how-to/engines-drivetrain/1410-conical-valvesprings-story-behind-the-coils

 

 

[Shortshift]

Interesting, Roger. 

When I was digging around to learn more about Duratec R500 engine specs last year, I came across a reference to CC having introduced conical (or tapered) valve springs on their R500 engine builds from around 2010/2011; I don't know whether this can be relied upon to be factually correct, though.  It was claimed that their change in approach was in response to a number of valve spring failures which (allegedly) a few people had experienced with their earlier R500 Duratec engine builds.

James

[Golf Juliet Tango]

As we are talking about truncated cones here, I think that "tapered" means the same as "conical" here.

I accept that it might be a non-conical taper but doubt it.

[ECR]

Yes, look at the link

(you pedant    )

[7 wonders of the world]

The OE versions were in this format as were the Cosworth upgraded ones too.

An additional reason for failure is also fretting on double spring set ups as the springs bow slightly under compression allowing intererence between inner and outer coils.

 

[Shortshift]

"The OE versions were in this format as were the Cosworth upgraded ones too."

Are you talking about the fitment of conical springs here, and to Duratecs (when you mention OE versions)?  Just getting a bit lost...

James

[7 wonders of the world]

Yes, stock Ford springs were single conical (Beehive) design and Cosworth used this design albeit in different heights and rates in their modified versions, with Ti top caps.

[The_ASH]

Most interesting, thanks for posting, will pass link on to some other people.

[7 wonders of the world]

http://www.burtonpower.com/cosworth-hd-valve-spring-set-ford-duratec-he-i4-to-11-5mm-lift-kk3459.html

[ECR]

According to the above mentioned article, one of the reasons for a double valve spring was that as well as increasing load, the slight interference fit caused the inner spring to act as a damper to reduce resonation

[7 wonders of the world]

The main reason aside from increased poundage was to alter the resonance frequency so valve bounce became less of an issue or could be tuned out of the engines useable rpm range.

[Shortshift]

I am still struggling to follow some of this.

So, what type (specification) of spring was fitted to the early R500 Duratecs that (allegedly) were prone to early failure?  Were these early engines built with conical springs and did they fail (and if so, what were they replaced with?) or were the conical springs introduced as the solution to breaking springs (and, if so, what was the spec of the pre-conical springs that had the history of breaking)?

Can anyone clarify this?

James

[7 wonders of the world]

Not sure who built or now builds the engines, ISTR Simon @ Ultimate Performance did the CNC head work and offered upgrade kits to R500 spec for Duratec owners but the springs in this kit are not necessarily the same as ones the CC supplied engines.

Think the R400D used conventional Kent Cams valve springs and retainer (singles).

As to the actual cause of the failures and the numbers involved no idea I'm afraid, spring type, material, heat treatment, poundage, many factors for consideration here. 

[Shortshift]

Thanks 7 wonders... 

Maybe someone else might know (the valve spring history)?  My understanding is that CC removed and then stripped the heads on the standard Duratec engines before sending them to Simon (Ultimate Performance) for the CNC work, and that CC then rebuilt the heads with the uprated cams, valves, springs etc (and fitted uprated pistons to the lower half of the engine, etc) before reassembling the unit.  Would be interesting if anyone knows definitively what type/spec of valve springs were fitted during the rebuilds, both in the early days and on the later (post 2010??) engines.

Anyone know?

James

[Rob Walker]

I understand that the early conical springs were supplied by Kent Cams and that these were later replaced by the Cosworth Conical springs.  Kent  told me in 2016 that they had now changed their spring material for this application.

[Shortshift]

Thanks Rob - helps to complete the picture.

James

[7 wonders of the world]

Interesting Cosworth who offered 2 different spring sets, both conical have now stopped produce the high capacity version (circa 13.5mm lift), tried extensively to get a set a while back.

You can still buy the lower capacity set though.

[Shortshift]

Probably going a bit off topic here but I found my own notes, drawn from various sources, about the history of R500 Duratec valve springs which suggests that conical springs might not have been used initially but were possibly introduced around 2010.  Can't be sure of accuracy but the notes read as follows:

Valve springs:

 

CC - initial engine builds using single spring but reports of spring failures; reportedly revised spec from CC in 2010/11 timeframe, possibly introducing conical/tapered spring

 

Alternative - double springs available from Kent (VS59) but some failures known and they are said to be very aggressive on cam lobes

 

Alternative (2016) - SBD have developed their own double spring and cap set with dual rate springs (straight, not conical)

Are the Cosworth springs seen as further alternatives, or are they the conical spring that was introduced and fitted by CC from 2010/11 to address the initial failure problems?

James
 

[7 wonders of the world]

AFAIK the Cosworth versions were developed for their own range of tuned crate engines and race series engines in various formulas.

Would like to know why the high capacity version is no longer available though.

[Shortshift]

I thought that Cosworth did most of the development of the R500 Duratec before Caterham Cars took it in-house for the final stages...

James