engine and drivetrain 304° Cam and Double Valve Springs

[tomorrowcalling]

Hi,

Are double valve springs absolutely required when using 304° cam?.

Do you have to change the valve guide to a 318 to install double valve springs?.

Do you need different spring retainers for double valve springs?.

As background to my questions, I'm part way through a engine build for my rally car. I have the 304° cam, the double springs, and a nicely reconditioned head - but with the old style valve guides. I suspect I know the answers to my questions, but they're not the ones i'd like.......

[c.d.iesel]

Hi, = Cheers

Are double valve springs absolutely required when using 304° cam? = YA

Do you have to change the valve guide to a 318 to install double valve springs?. = YA

Do you need different spring retainers for double valve springs?. = YA , 2 RINGS INSTEAD OF ONE ON THE UNDERSIDE OF RETAINER

As background to my questions, I'm part way through a engine build for my rally car. I have the 304° cam, the double springs, and a nicely reconditioned head - but with the old style valve guides = SHOULD BE NEW GUIDES ! OR YER IN FOR TROUBLE

..... I suspect I know the answers to my questions, but they're not the ones i'd like....... = THEN IGNORE THE ABOVE.

Stage 2 Competition Engines

This is our most popular M10 performance engine. Lots of torque, smooth idle, rapid acceleration to 7000 RPM. This is a solid 150HP engine, yet when driven with a light foot can get up to 30 mpg. This engine utilizes dual Weber 40 DCOE's with Korman's 1 piece balance port intake manifold, Korman K-300 Camshaft, Bosch Mechanical Advance Distributor, Korman-Stahl Header, Dual Valve Springs, Chrome Alloy valve spring retainers, and Korman Rocker Arms. Connecting rods are lightened and balanced, cylinder heads are fully ported and polished. The engine is completely balanced and blueprinted. All boring is done with a torque plate for best cylinder roundness. Substituting the Schrick 292 cam yields an additional 10 horsepower. P/N 11002200

High Performance Dual Valve Springs

Includes center damper spring sleeve. Long life with revs to 7600 RPM. Will fit over 79> small valve seals. Must update guides and seals on older heads. No cylinder head machining required.

P/N 11341204N

[wegweiser]

I was told that for the Schrick 304 (don't know about other manufacurers) that the std springs are sufficient. (FWIW - Schrick's OWN literature may say otherwise!) Mine's a street car - but one driven VERY enthusiastically (yes....I've bounced off 7800 rpm more than once and cruise at 5000 rpm for HOURS!) I asked Eric Kerman - my engine builder guru - and he said - no worries with std springs...he may even have implied that the stock 2002 rockers and orig. 2002 rods were the weakest link. (...and FYI - I'm running S14 rods w. S14 crankshaft)

I've been told overly stiff springs can accelerate wear on the cam - haven't seen if this is true or not.

I'd be curious to hear others' opinions on 304 spring recommendations.

paul

[Harv]

Kerman built my head with a schrick 304 and used Crower double springs and titanium retainers.

John

[wegweiser]

hmmm.... interesting! I wonder why he talked me OUT of them! I had cash in hand - not cutting any corners, budget based solely upon his recommendations. ...and I said I wanted a MEAN street motor. (I asked if oversized valves were a good idea, too) ...again - he said "don't bother". Maybe he thought I just puttered around the country club in ole Emily at 1800 rpm all day long (wink!)

Ole Em's due for her first valve adjustment soon - maybe I'll take a gander at what springs are in there afterall!

S14 crank

S14 rods

machined fr. pulley

JB aluminum flywheel

Schrick 304

JE pistons 9.5 +/-

45mm DCOEs

E12 head

turbo radiator...keeps it TOO cool on highway

I'll report back after I pull the valve cover off!

Paul

[steve k.]

2002s get valve float at about 7500rpm. where is 304 power band and would you really be testing it? Though the parts that break are rocker arms, what causes the fractures is the pounding of the valves on the rockers due to valve float.

steve k.

[john_a]

Are double valve springs absolutely required when using 304° cam?.

No, you do not need double springs. Please refer to Schrick's remarks on the 304 cam spec sheet, they call for part number 002 02 090 which is SINGLE spring. There is an alternate double spring listed if you choose (outer 056 02 062, inner 056 02 022) but the double springs are not required. My first choice is the single Schrick (stock BMW springs should not be used.) This Schrick single spring is rated for 198 lbf @ 1.043" nose pressure, you don't need more than that (and the double set is virtually the same pressure.) There is no issue with resonance using Schrick singles with the 304 cam that would make a double spring required.

Do you have to change the valve guide to a 318 to install double valve springs?.

No, you don't have to replace the old style guide to use double springs, you only would have to machine the top of the guide to accept the newer seals. This is a lot simpler than replacing guides.

The inner spring ID is too small to fit over the old style seal.

The Schrick double's inner has an ID of 15.6 mm

The old style valve stem seal has an OD of ~ 17 mm.

The new style valve seals are just a bit over 14 mm.

Never replace guides if the are not really worn, it takes to much cutting to get the valve seats concentric again, the valves get sunk too deep & flow suffers. Most new guides are crap, they make them too loose on their ID. I always prefer to find a head with good original guides that has not been messed with.

Do you need different spring retainers for double valve springs?.

Yes, the retainer needs to fit properly on the ID of both springs, it will have a "step" that should match the springs. An aftermarket retainer can change the installed height of the spring, so be certain you know how to properly setup valvetrain if you are getting in to mix & match combinations. You have to get the installed heights correct.

[tomorrowcalling]

I assume to machine the old style valve guides to accept the new seals you'd have to remove them and turn them on a lathe, wouldn't you still have the same concentricity issues as installing new ones?.

Having said that does anyone have details of the top end of new style guide that I could give to a machinist?.

Further web browsing has seen the suggestion that standard retainers can be used if a few thousands is ground out of the id of the inner spring, can anyone confirm or deny (sounds a little suspect to me)

[Guest Anonymous]

I assume to machine the old style valve guides to accept the new seals you'd have to remove them and turn them on a lathe, wouldn't you still have the same concentricity issues as installing new ones?.

No, you do not need to remove the guide to machine it for the new style seal. The machinist uses a guide cutter tool that pilots off the guide ID, and produces the required diameter to achieve the 0.010" - 0.020" press fit to anchor the seal. This seems like a large interference fit, but remember the seal is metal with rubber clad where it fits the guide.

Having said that does anyone have details of the top end of new style guide that I could give to a machinist?.

Don't perform any machine work on your parts based on something you've read on the internet. Purchase one new guide and bring it to the machinist for a sample -- the guide is not expensive at all. The seal ID around the guide is nominal 10.5 mm, same fitment as many VW, but spend the $3 it cost for one guide to have a sample.

Further web browsing has seen the suggestion that standard retainers can be used if a few thousands is ground out of the id of the inner spring, can anyone confirm or deny (sounds a little suspect to me)

I would have thought based on your original post where you wanted to know if you absolutely had to use the double spring, that you were not so fixated on using them unless you had to. As previously pointed out, Schrick tells you the answer = single spring #002 02 090.

You cannot use the stock retainer with Schrick double springs. The outer spring has an ID too small for the stock spring retainer, and there is no proper way to hold the inner. You need retainers to match the spring diameters. FYI, the stock retainer is a perfect fit for the Schrick single spring.

Grinding any part of any valve spring is a recipe for disaster. Even a small nick can cause breakage.

What double springs do you have, are they Schrick or someone else?

Do you know the specs on your springs to be able to set them up properly?

It looks like you want to spend more money & time to install double springs than it would cost to get the Schrick singles. Are you sure you've got good reasons for doing it that way?

[bevans6]

When you talk about single vs double springs, remember that single springs can and should mean PERFOMANCE oriented single springs, not stock springs. That's been pointed out already but bears repeating. Many serious race engines are now using single springs with a beehive shape, the variable diameter does the same job that the inner spring on a dual setup does - remove harmonics. The inner spring is NOT there for rate, it's just there to change the tendency of the single spring to react to a harmonic frequency.

You can use stock valve caps with double springs, you do need to cut them to fit the inner spring. I do that, but then again I'm a pretty decent racing machinist. If you don't happen to own a lathe and know how to use it, it would be cheaper and better to buy the right caps to match your springs.

Concur with the advice to cut the existing valve guides to suit the smaller (and far better) valve seals. Again, I would do this myself, and I would make the tool to do it, but any competent machinist can do this for you.

As far as valve float is concerned, the cam has an awful lot to do with it as well as the springs. Stock cams can often float the valves at a lower RPM than a performance cam with the same valves and springs, simply because the performance cam has greater lift than the stock cam so the spring is more compressed and there is greater control over the valve.

As far as street driven vs race is concerned, there is a great difference between driving around town and occasionally getting up to 7000 rpm, and never getting below 6,000 rpm and spending most of the time between 7000 peaking at 7800. If you got 50 hours or 5,000 miles out of your street engine before you needed to do a total rebuild, you'd be very unhappy...if I get 50 hours out of a race engine, I'm very happy!

Cheers, Brian

[tomorrowcalling]

Thanks for everyones input, I've spoken to my local machinist about machining the valve stems in place, he's done it before so that's not an issue (you learn something new every day!). New steam seals are on order, just need to track down some suitable retainers.

All I need to do now is ask my wife for an increase in my allowance....