I am getting a little worried, but hopefully there is more to reading spring specifications than meets the eye.

Currently using a COmp Cam 292H-10 camshaft with 1.5 ratio rockers.
(hydraulic, flat tappet).

The lobe lift is 0.334“, with a valve lift of 0.501“.

Lifter pre-load is set to about 0.020“ cold.

The valve springs that are currently loaded are Federal Mogul VS-739R.
According to a few sources, the maximum lift is 0.480“.

http://www.northernautoparts.com/Pro...ctModelId=2297

I was told that these springs were rated for much higher lift when I bought
them.

Closed Height - coild bind height = ~ 0.540"

If this is all true, shouldn`t my springs bind? The engine runs quite well.
I`m confused as to why my engine hasn`t exploded...maybe I`m just on
the edge of bind?

You can rest assured the engine doesn`t start until I figure out what is going on!



I am scared...hold me!

 

Comp recommends a 986 or 987 spring for that cam.

If you run the numbers:

http://compcams.com/Technical/Curren...ML/329-338.asp
(use page 338)

986 gives 132# seated @ 1.750 in. and 280# open @ 1.250 inches. Coil bind is 1.150 or .100 past open point on your cam.

987 gives 121# seated @ 1.800 in. and 293# open @ 1.300 inches. Coil bind is 1.150 or .150 past open point on your cam.

The VS739R gives 110# seated @ 1.700 in. and 287# open @ 1.200 inches. Coil bind is 1.160 or about .040 past open point on your cam.

Both Comp springs are 1.43 dia. vs 1.264 for the VS739R. You may need to enlarge the diameter of the spring pocket, but that's not an expensive operation.

If it were my engine, I wouldn't use the VS739R springs. I suspect you'll see some dead canaries if you do.

 

Thanks Jon.

(Edit spring part number)
The cam card specifies 986-16.

Long story short, I had these springs installed before I purchased the cam
and only ran them for one season. The valve springs were shimmed which
also leads me to believe the coil bind will come a little sooner!

I'm not going to play any games after seeing the VS-739R Specs. If I had
a valve float condition, it would pump the valve up another 0.020" and that
would screw me for headroom on the spring (~ 0.010 - 0.020" depending on
the shim)!

 

Hmmm...I can't find 968 as a Comp spring number. I bet it's meant to be 986.
Dyslexia strikes the cam card writer!

 

No, I'm just blind.

It IS 986-16 ( I was initially backing your previous post) but I messed up.

In addition, I'm pretty sure my heads will accept that spring diameter (Sportsman II), so that's a plus.

I'll have to find the MFG spec.

 

Be forewarned, CC springs are notorious for spring pressure, not meeting specs. Consider this, if open or closed pressure is marginal.

 

Sportsman II heads have a little "recess" for stock-sized 1.25" springs which adds to their actual installed height. Probably got shimmed just to bring it back up to it's 1.70" installed height spec. You're right- they will take up to, I beleive, a 1.55" spring right outta the box with the pockets that Dart cuts into them.

There is absolutely NO substitute for measuring actual installed height. You can do it with a fancy-schmancy valve spring height mic, but I used to set all mine up just using a small vernier caliper and some VERY careful measuring and re-checking a bunch of times.

It's not necessary to be perfect down to .001" for a street motor but you better be between 0 and +.010" from spec (never go too short unless you know for sure why you are doing it).

Having a valve spring pressure tester is also nice but too expensive for the average weekend wrench. I lucked into mine and have found it to be invaluable over the years. Setting up valvetrains is something most weekend warriors do in minutes. Pros spend hours on them. I find the more time I spend on the the valvetrain the better (and longer!) the motor runs.

 

One other thing.... I have used single-coil 1.25" springs, almost identical to yours, with very similar Comp 280 Magnum cam and did so successfully. They don't have quite the pressure that the recommended springs do, but the spring itself weighs less as do the smaller retainer and locks. My concusion: the lower mass of the smaller parts means the spring doesn't have to work as hard to keep things under control. I was seeing a total difference (retaner plus 1/2 of the spring's weight) on the order of 22-25g lighter. And it's all mass that's right there on top of the valve- where it counts most.

I guess I should throw in my standard disclaimer that I don't RECOMMEND doing this, but it has been done.

BTW- I looked at the specs on your current springs posted above..... you have .040 of travel left before you hit coil bind, assuming everything is measured and spec'ed out perfectly. But that's a little too close for my liking. I don't come anywhere inside of .050 from coil bind ever. Obviously, it's working in your motor right now, but you're close. Another reason to put the right springs in.

 

Cool thanks guys.

My reason for posting was due to the specs I found on the springs.

Why would the MFG rate the springs for 0.480" lift? Is this because
the pressure at the rated valve lift is correct for a gross valve lift of
0.480"?
My valves are cut down for the valve job which makes them slightly lighter.
That would go well with what you're stating about reciprocating mass and
less work for the springs.

I am a little concerned now because there is only 0.040" of 'headroom'.

With 0.501" valve lift, the spring height at that point translates to about
1.200" spring height. Coil bind happens at 1.160"

With the shims, 0.020" + of pre-load (<valve float conditions! )and any thermal expansion, I must be
knocking on hell's door?!

 

To answer your first question, it is rated for .480" lift, as this is considered safe max, in regards to coil bind. Does not have anything to do with pressure. As noted by someone else, you are close to coil bind. Based on the mfr. suggested max lift (.480") figure, you are closer (to coil bind) than what they consider safe, and recommend for that particular spring.