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Old 02-08-2011, 08:00 AM
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Difference in measured vs calculated coil bind clearance

I calculated the coil bind clearance on the 383 I'm building as .112"

The formula I used was as follows:

Installed Height - (Coil Bind Height + Net Lift) = Coil Bind Clearance

I just mocked-up the head and measured with a vernier caliper and got .070"




That's a big difference. I've heard that higher ratio rockers sometimes give more lift than they're supposed to, but I'm using Scorpions which have an excellent reputation. An extra .042" of lift would equate to a rocker ratio of 1.66 instead of the 1.6 they're supposed to be.

Is such a variation in the rocker ratio common (for these brand rockers), or is my measuring technique off?

At the moment, it's looking lucky that I didn't keep the Comp 986-16 springs I originally had with an installed height .050" shorter, as I'd be at .020" coil bind clearance right now!

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Old 02-08-2011, 08:29 AM
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You have done the math correctly, but you are measuring it wrong by trying to measure between two coils like you are. You would have to measure the gap between all of the coils on one side of the spring and add them together to come up somewhere close, but that would still be an incredibly inaccurate way to go about it. It may also be the inner that stacks solid first.

Easiest way to verify the coil bind height of the spring to see if it matches published specs is to compress it down to a solid stack in a vice or a press and measure the true length when stacked solid. Then you will have a solid verified number to use in your calculations.

I don't know if this is still common practice, but it used to be suggested to compress all of the springs down to solid stack in a vice before installing them. This was a trick to extend the spring life in the old days, as a stress relief process I guess. I don't know if this is still the hot tip with modern spring materials used today though, haven't heard of it in a while.
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Old 02-08-2011, 08:38 AM
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Thanks, I did wonder about that... wasn't sure if the clearance was total clearance between all coils, or if it was the clearance between any 2 coils. So, looks like I've actually got more coil bind clearance than I calculated by the looks of things. At least the math is correct. Guess I could measure lift at the valve with a DTI on the retainer, but don't think I'll bother... the cam is the right grind and the springs are set at the correct installed height.
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Old 02-08-2011, 08:43 AM
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What you want to determine, is that there's about 0.060" or so between the coils- including the inner springs. You could go a little tighter than this- but this provides a bit of cushion, and is what I shoot for.

Use a wire feeler gauge- it will allow better access than trying to use calipers.

More: http://www.lunatipower.com/Tech/Valv...pringTech.aspx
and http://www.kmotion.biz/instht.htm
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Old 02-08-2011, 09:00 AM
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Interesting... the Lunati link implies that the clearance measurement is taken between a single set of coils.




Is that diagram a bad representation? ericnova72 said the coil bind clearance equates to the total of the clearances between ALL the coils.
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Old 02-08-2011, 09:15 AM
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I can only speak for myself- and I use 0.060" minimum between coils as my target. Slightly less is OK- but cuts into the "cushion" I like to maintain.
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Old 02-08-2011, 10:16 AM
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David Vizard says "The most prominent cause of cam lobe failure is spring coil bind. On assembly, make sure the valve can go to full lift and still have at least .05 more lift available. If the coils clash together during high speed operation, the springs will lose their force far quicker and may even break."
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Old 02-08-2011, 10:42 AM
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Everything I've ever seen says a minimum of .050 between coils. If you had .050 TOTAL, then at max lift you would only have .008-.010 between coils. Go to youtube and search for valvespring slowmo's (or something like that) and watch how much springs move around while an engine is running. You'll be shocked!
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Old 02-08-2011, 11:00 AM
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The spring harmonics or "surge" has to be taken into account. You don't want the coils to touch each other during operation, so what seems like an excessive amount of clearance is needed.

In an "on the edge" race set-up, much less might be used. But in these cases, the valve springs are considered to be a disposable commodity- like spark plugs.

Anyway, the bottom line in this case: The spring application is correct. The spring installed height is also correct. So, unless the rocker ratio was changed, the springs will function as they should. But it's ALWAYS a good practice to actually, physically measure the clearances to verify them to be adaquate.

From a previous post:

Here's a list of some areas that need to be verified to be OK.

There is no substitute for physically measuring everything.

Here are a few things that need to be checked/verified on the top end of the engine. Not everything here applies to your build, it's just a general guide, and is not all-inclusive:
  • Springs for installed height
  • Coil bind (>/= 0.050" to 0.060” between all coils)
  • Retainer to seal/ valve guide boss at full lift
  • Retainer to rocker
  • Trunnion to stud boss
  • Piston-to-valve clearance (both before and after TDC on overlap)
  • Push rod to guide slot in head (if used)
  • Can use EITHER self aligning rockers OR pushrod guide slots in head OR guide plates, not two or more of these at the same time
  • ”Rails” of self aligning rockers (if used) to retainer
  • Rocker to valve tip (by adjusting guide plates if used)
  • Rocker slot to stud (if using stamped/cast rockers w/pivot balls)
  • Proper geometry (push rod length)
  • Rocker/polyloc to valve cover or baffle
  • Camshaft endplay
  • Distributor shaft and gear endplay
  • Distributor gear material compatible with cam material
  • Hydraulic lifter preload or solid lifter lash setting
  • Timing set phasing
  • Cam gear to crank gear alignment
  • Cam gear end play if roller cam
  • If using the SBC OEM roller lifters and retainers (aka dogbones), lobe lift must be kept below 0.354” so the lifters don’t lose contact w/the retainers
  • Cam lobe to connecting rod on strokers

A 'big' paper clip is right at 0.050" OD wire- and can be used (after the thickness is verified) as a 'feeler gage'.
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Old 02-08-2011, 11:36 AM
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Lets do the math on these springs

installed height 1.7
minus coil bind 1.125
----
difference .575
max lift .52
.055 total coil clearance

I count a minimum of 4 coil gaps. If each coil gap had .050 clearance the max lift on these springs would be installed height minus coil bind =.575
minus (4 coil gaps X.05= .2)
leaving max lift at .575-.2 = .375

http://www.competitionproducts.com/products.asp?dept=58
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Old 02-08-2011, 11:49 AM
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Quote:
Originally Posted by bnun12
Lets do the math on these springs

installed height 1.7
minus coil bind 1.125
----
difference .575
max lift .52
.055 total coil clearance

I count a minimum of 4 coil gaps. If each coil gap had .050 clearance the max lift on these springs would be installed height minus coil bind =.575
minus (4 coil gaps X.05= .2)
leaving max lift at .575-.2 = .375

http://www.competitionproducts.com/products.asp?dept=58
Yep, the math gives total coil bind clearance. So, on that basis, the total clearance measured across ALL coils should equal the calculated figure.

Looks like the Lunati diagram is incorrect, as it implies that EACH coil should have .060 clearance with its neighbor.

Think I'll measure net valve lift with a DTI on the retainer and see what I come up with... that, at least, will tell me the ACTUAL ratio my rockers are giving me (assuming that lobe lift is exactly as Comp Cams state).
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Old 02-08-2011, 12:03 PM
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Just found this site, which confirms that coil bind clearance should be the total of the clearances found between ALL coils...

http://www.burtonpower.com/tuning-gu...ng-timing.html

Lunati (and some others) should change their diagram. I think this is a point that is easily misunderstood if you're actually MEASURING coil bind clearance and the cam companies should clarify the correct procedure in their tech docs, as there is ambiguity with the way many of them describe the procedure.
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Old 02-08-2011, 12:20 PM
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From Comp Cams' The Truth About Valve Springs:

Quote:
Installation

1. Before installing the spring on the cylinder heads, check the installed spring height (Diagram A). This is the distance from the bottom of the retainer to the surface where the spring rests on the head. The valves, retainers and valve locks will be used in this step. First, install the valve in the guide, then install the retainer and valve locks. Pull the retainer tightly against the valve locks while holding the valve assembly steady.
Measure the distance between the spring seat and the outside step of the retainer using your height micrometer (Part #4928 or #4929) or a snap gauge and a pair of calipers. Repeat this procedure for all the valves and record your Information. After you have measured all the valves, find the shortest height. This will become the spring’s installed height on your heads. If your combination includes a dual or triple spring assembly, it will be necessary to allow for the inner steps of the retainer.

2. Once you have determined the shortest installed height, it will be necessary to use shims to obtain this height (±.020” is acceptable) on the remaining valves. These are available through our catalog or at any of
your local COMP Cams® dealers.

3. Before removing the retainers, measure the distance from the bottom of the retainer to the top of the valve seal (Diagram A). This distance must be greater than the lift of the valve. If not, the guide must be machined. This is a very common cause of early camshaft failure.

4. Once the valve springs have been installed, it is important to check for coil bind. This means that when the valve is fully open, there must be a minimum of .060” clearance between the coils of both the inner and outer springs. If this clearance does not exist, you must change either the retainer or the valve to gain more installed height, or change to a spring that will handle more lift or machine the spring seat for extra depth.

5. Always check for clearance between the retainer and the inside face of the rocker arm. This will be most evident while the valve is on the seat. Rocker arms are designed to clear specific spring diameters, so you should check to see that you have the proper rocker arm/retainer combination. This situation can also be the result of improper rocker geometry and may be corrected with different length pushrods or a different length valve.

6. To aid in the engine breaking process, spray the springs, rocker arms and pushrods with COMP Cams® Valve Train Assembly Spray (Part #106).

Breaking In a Spring

1. It is important for new springs to take a heat-set. Never abuse or run the engine at high rpm when the springs are new. Upon initial start-up, limit rpm to 1500 to 2000 until the temperature has reached operating levels. Shut off the engine and allow the springs to cool to room temperature. This usually will eliminate early breakage and prolong spring life. After the spring has been “broken-in”, it is common for it to lose a slight amount of pressure. Once this initial pressure loss occurs, the spring pressure should remain constant unless the engine is abused and the spring becomes overstressed. Then the springs must either be replaced or shimmed to the correct pressure.
A possible explanation of the discrepancy is that the amount of movement before coil bind is not a total of 0.060" multiplied by how many coil gaps there are, or in what constitutes a "coil gap".
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Old 02-08-2011, 12:30 PM
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I'm gonna tell you right now that if you run a valve spring w/=/< 0.010" between the coils at max lift, you will have problems, unless you replace the springs after a short amount of run time.

Didn't you just say you thought you had 0.070" between coils, w/the springs set at the correct installed height?
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Old 02-08-2011, 12:34 PM
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Quote:
Originally Posted by cobalt327
I'm gonna tell you right now that if you run a valve spring w/=/< 0.010" between the coils at max lift, you will have problems, unless you replace the springs after a short amount of run time.

Didn't you just say you thought you had 0.070" between coils, w/the springs set at the correct installed height?
Exactly right!
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