Dual vs single conical valve spring kits.

[Blunny]

I have a 450cc (05) Husaberg & there is an after market supplier selling a dual valve spring kit as an upgrade promising better lobe / cam bearing wear, less seat pressure, less valve wear and quieter running. (OEM is a single conical spring).

I was given one of these kits, so I started researching to try and understand why these dual valve spring kits are "better". All the research on the innernutz achieved was to get me more confused. So many theories for and against....

Now, I know nought about this stuff, is it a worthwhile mod to install the dual spring kit? what is the advantage?

Thanks.

[aidan]

In simple terms-

The dual valve spring is used to avoid valve bounce by minimising harmonic resonance in the valve spring.

At certain rpm the harmonic frequency of a valve spring will match the rate at which the valves are being open and closed. This leads to valve bounce.

Using two springs prevents this because they each have a different harmonic frequency so while one is in its harmonic rpm range the other spring won't be and will continue to operate as normal.

A big single spring needs to have high seat pressure to move its harmonic range above the rpm ceiling of the engine, whereas dual spring can use lower seat pressures.

Don't know if what i've written is 100% correct but i'm sure someone else will chime in

[Blunny]

Thanks Aidan.
The main benefit they (husaberg.org) talk about is the easier life that the top end has with the dual spring lower seat spring pressures. A few commented on a better throttle response and slightly more power, so it could be a good thing.

[Bushmechanic]

Aidan has it right, there is also the effect of damping from the 2 springs rubbing together that helps in being able to run a lower seated force with a dual setup BUT to take advantage of this you need to be able to install them at a length that lowers the seated force.

the kit from the UK has the same coil count overall lengths and wire diameter as the KTM atv DVSK if you got either one free it was the right price

they are not the same springs though, the atv spring kit has lighter retainers and a slightly lower peak force, it is also only $66 US

http://www.partspitstop.com/pages/EC...3036028044%2F1

edit $55 here

http://www.ktmpartshouse.com/fiche_s...er=83036028044

both the UK and the KTM ATV kits are too long to be installed in a stock head properly at a length that will actually reduce the seated force over oem, they do reduce the peak force but not by much and they are heavier than the oem conicals

the kibblewhite DVSK for the KTM rfs engines on the other hand is short enough to be installed correctly and has less peak force than the other 2 by about 10% for the same seated force, the springs are lighter and the retainers are Ti and lighter again.

depending on the ex rate they are cheaper than the UK set. the KPMI number is 96-96000 get in touch with DJH on ktmtalk for a set or you may find some on ebay. specs here http://valvetrain.kpmivalvetrain.com...ycle/96-96000? i got mine on ebay for about 160 delivered

Ive tested all 4 spring types, the kibblewhites are hands down the easiest to fit and offer the best performance, noticeable gain up to 1/4 revs over the other 2 DVSKits.

the main advantage of the UK and ktm duals is they offer redundancy if a spring fails. if you want a significant performance gain or you want to reduce the loads on the valvetrain by a worthwhile amount you need to get the kibblewhites

the absolute best IMHO would be a conical (lighter) that can provide a high enough seated force to minimize valve bounce and a low peak force while still being made good enough not to fail.

there is a french tuner who swears by pac racing single springs, ive not tried them yet

http://www.performancewholesale.com....nt/article/230

I'll dig up the figures regarding all the forces and weights lateron.

[Bushmechanic]

these figures are measured in a stock head with uncut seats and stock valves on brand new springs, they are what you get if you just get the kits and install them

nose pressure measured at an additional 10mm lift similar to the stock cam profile.

oem conical seated 72lbs, an additional 10mm lift gave 238lbs

kibblewhite duals seated 72lbs and 200lbs peak

KTM ATV duals, seated 80lbs and 228peak

UK duals, with 0.1mm thick shims as lower springs seats (my idea, doesn't work) seated 76lbs and peak 232lbs. FWIW it is claimed that their seated force is 87lbs... if it were then the peak force after 10mm lift from there is over the oem 240lbs

another shortcoming of the UK set and the atv springs is that safe useful lift from their as installed height is limited to the stock 08 cam profile ONLY!

the weights are:

oem conicals, retainer 11gm, spring 40gm

kibblewhite duals, retainer 7.75gm, springs 37gm

KTM ATV duals, retainer 13.25gm, springs 54gms

UK duals, retainer 13.8gm springs 56gm

an added advantage of the kibblewhites is that if needed you can machine the lower spring seat and install them at a longer spring length (equivalent to about 39mm including retainer and seat) for a seated force of only 60 lbs, an additional 10mm lift from there gives you 180lbs peak.

without longer valves or a serious seat re-cut it is not possible to install the other 2 dual kits at a length that reduces the loads on the valve train by a useful amount but if you have a set they are worth installing for reliability and piece of mind.

[Blunny]

Thanks Bushy, great info & exactly what I wanted to hear. The KPI kits look to be the best option. I don't mind buying a new set as even if the kit I have was free it still is not a jump forward.

I'm a long term berg owner but I cant be bothered going onto the uhe.org site to ask these questions. One man kind of dominates....shouts down, and generally behaves like a duckwit. I have bought a few items from him but I cant handle his attitude.

How is your big bore tractor going? I am thinking of developing my 06 450 further, eg. diet, refine the engine (vibration, engine noise, a bit more rev for grasstrack).

I wanted a 70 degree bike, rode 2 and was so impressed I bought a YZ 250 2st....

[Bushmechanic]

No worries Blunny, the UHE moderators indicated i would be banned if i made reference to a certain vendor or posted after him

under those conditions it would not be possible to make the above information available to those who need it, the mods didn't want to do anything themselves and although i haven't posted in it for ages they recently locked my build thread so I no longer contribute there.

the 700 is going very well, Ive been playing around with the heat treatment of the gears, oem is a tad brittle. i put some of them in an oven at 250deg C for an hour and got them to about 55hrc. have also tried sending some off to get cryoed but that didn't work out so well.. .lasted an hour before the hardfacing flaked off but they were second hand so im not sure if they would have failed anyway.

been running a knobby rear too over winter which reduces the loads on the box

got an old 550 engine im slowly turning into a 650 with a 20mm head packer, have hit a bit of a snag though as the cases have been annealed by the fire that killed the bike so i have to heat treat them, 540 deg for 4 hours quench and age next day at 180deg...

work is getting a CNC mill so head packers and other custom bits shouldn't be too time consuming in a few months.

on your 450 you could balance the crank to 62% I reckon that would help a lot with the vibes, you could also fit 1mm oversize valves (KW) unshroud the head around them and matchport the intake/exhaust tracts, could bore out the carb and go a 8/07 or hot cam for more overev but unless you up the compression the bottom end will suffer.

[Bushmechanic]

Bit more info Regarding the KW springs.

the "correct" springs are KW # 96-69000 for the KTM RFS 400, 520, 525 and 540 up till 2007. the springs listed for the 450 are different

springs only RRP is $54.20 for a set of 8

Titanium retainers RRP $108.67

hardened steel base washers RRP $30.59

as a kit as I wrote you can sometimes find them listed cheap on ebay. they are often listed for the KTM "ATV" or 525.

if you need some in a hurry obviously rocky mountain ATV is the go but the price for a kit there is $197

[Blunny]

Thanks Bushie.

I'm still in 2 minds on what to do with the 450. The YZ250 2T has been a very big eye opener & the berg has been getting no love since the jap tart turned up.

The poor Berg might have to be asked to quietly leave the premises via ebay.

[Bushmechanic]

I can understand that, stock pre 09 berg is a pig compared to sweet jap lightweight. you'd have far more fun play riding on the the 250.