I'm done with my cam install and I'm upgrading the valve train. I'm using comp 918 springs. I also purchased a barrel micrometer for checking the installed height. I say that like I know what it means....sheesh. I have reviewed shoebox's install guide and I'm still confused about the valve spring height measurement. Let me see if I have this right. I install the new spring locator put the micrometer on next, then top it off with the retainer and the lock. I then open the mic until it's snug . The box the 918's came in said the installed height is 1.80". If the barrell mic measures 1.80 am I good to go? Do I have to do this for every spring? How much could the measurement be off without harming the engine?

 

Sounds like you have it. The mic installs in place of the spring. Make sure the retainer and locks are well seated (pull up hard on the retainer). You screw the mic out to get the reading of the installed height. I'll let someone who has good experience with spring pressures answer your question about height variance and effects.

 

Ok does your spring mic look like this?

Last page all the way on the right (pg 349)

http://www.compcams.com/Technical/Cu...ML/340-349.asp

If that's the case and you are using the comp retainers you might be really low on the actual installed height.

BTW what is the cam?

Bret

 

The installed height listed in the specs is not an absolute value. It is just a representative number. You might chose to install the spring at say, 1.85" if you needed to accomdate more lift, for example. This would be fine, provided that the seat pressure at that height was in the appropriate range. Similarly, if you need more pressure, you might install the springs at <1.80". Provided that you still had enough room to accomdate the amount of lift involved.

Rich

 

As Bret said, the retainers for the 918 springs don't sit on the mic like
a larger diameter retainer would. You will need to consider the offset
for the smaller retainers and add it to the measurement on the mic. For
my install the retainers contacted the first step on the mic which was
.150" lower.

 

That is the mic I have and the cam specs are as follows: 236/242 .555/.576 112+4 LSA

 

Ok, notice how the retainer sits down in the step in the mic.... well you have to subtract that step (.150) from your measurement.....

JUST LIKE TRUEDUAL SAYS...

for your setup the minum installed height you can have is 1.711" but 1.750" to 1.800" is better, but I would say if you get to 1.750" you will be fine.

As you noticed that will mean the spring mic has to read 1.860" or more for the springs not to hit coils and go BOOM!

Bret

 

Thanks for the responses. How often does someone actually have to adjust the install height? If it's too short do you add shims under or on top of the seat and what if it's too long how do you shorten it up? Do I have to repeat the measurement 16 times or will one measurement do?

Bret and Truedual: Let's see if I understand this. If I get a measurement off the mic that reads between 1.86 and 1.95 I'm good to go. This is considering the 0.150" for the mic.

 

I think you are misunderstanding "installed height". This is the height at which you want the srping, not some arbitrary number. But to get them to the desired height, you will need to shim the springs. Due to random variations, each spring typically needs a diiferent amount of shim. Some will need none. IOW, when you measure, you have to measure them all and they will all be slightly different.

Take a look at http://www.mustang50magazine.com/howto/24453/ which contains the following:

In order for valvesprings to properly and consistently close an engine’s valves, they must be installed at a consistent installed height--the distance from the bottom of the valvespring retainer to the bottom of the valvespring, with the spring installed on the cylinder head. Installing new springs at the height specified by the manufacturer usually ensures that the springs develop the proper seat and open pressures without going into coil-bind (the coils stacking solidly during valve lift). However, because even springs in the same batch vary slightly, some race engine builders install the springs to achieve a specific seat and open pressure, even if the exact installed height varies slightly from spring to spring.

When valves and seats are ground during the cylinder-head reconditioning process, the valve stem sticks through the head farther, thereby increasing installed height and reducing spring pressure. Normal wear also decreases the spring rate. Lowering the installed height can compensate for any decrease in spring pressure, so long as you don’t approach coil-bind.

The procedure for figuring out and correcting installed height is similar whether you seek to install all the springs at a given exact height, vary the heights slightly to compensate for variations in spring tension, or compensate for sunken valve seats. It was explained to us by the experts at Jim Grubbs Motorsports.

Checking and Correcting Installed Height

First, install the retainer with keys on the valve stem to be checked. Retainer thickness varies somewhat, so from this point onward always keep the same retainer together with the same valve as a matched set. Measure the distance from the bottom of the retainer to the spring pocket floor. If the measured distance is greater than the desired installed height, add enough valvespring shims to reduce installed height to the proper dimension. When shooting for a uniform installed height (rather than a specific pressure), try to get all heights within 0.005 inch of each other. Shims vary slightly due to their nominal thickness, so if you have enough shims and mic them all, you can get pretty darn close!

Spring-locating cups are more stable than plain flat shims. Mandatory on aluminum heads to keep the spring from galling the head, cups can also eliminate the need to excessively stack standard flat shims, as well as help locate and hold the spring in place.


If the measured distance is less than the desired installed height, there are several solutions:

* Machine the spring pocket deeper. On stock heads, there’s the risk of cutting through to the internal coolant passages. Special stepped cutters are available to minimize the problem. Even if you don’t run into water, deepening the pocket on a fully prepped head limits the amount of material the head porter can remove from the port roof without excessively thinning the casting.

* Install longer valves. This is a good solution if you plan for it ahead of time when spec’ing out the engine combo, but it’s expensive if you’ve already bought a set of valves. Longer valves alter the valvetrain geometry, so you’ll probably need custom pushrods too.

* Install offset valve stem keys or retainers. The aftermarket offers 0.050- and 0.100-inch offset keys and retainers for adjusting installed height. These usually eliminate the need to deepen the pocket or (if the initial installed measurement was much greater than spec) stack an excessive number of shims. But raising the retainer may cause rocker-arm interference, and there’s no room for a lash cap.

Avoid Coil-Bind

Uncorrected coil-bind quickly destroys a valvetrain. The dimension at which the spring’s coils all stack solidly should be at least 0.050 inch greater than the cam’s total valve lift, minus any lash if you’re running a solid cam. Each spring component of multispring assemblies should be checked separately, and then all the components should be checked together as an assembly. The previous installed-height fixes are also quick and dirty fixes for a coil-bind condition, but when they’re used for this purpose the final spring pressures will end up below the desired spec. The proper fix for a coil-bind problem is to find a suitable valvespring that accommodates the valve lift generated by the camshaft.

Retainer-to-Guide Check

Anytime you change the cam, valves, rocker arms, or retainers, check for interference between the valvespring retainer and the valve guide tops (or PC-style seals, if so equipped). The distance from the retainer bottom to the top of the guide (or seal) should be at least 0.050 inch greater than the cam’s rated valve lift (minus the lash if using a solid cam). If the valve stem seal height is the cause of insufficient clearance, you can often substitute a different seal type or brand. Sometimes the guide itself can be shortened without any serious problems. Otherwise, you’re looking at a combination of offset retainers and keys and more shims and/or longer valves--with all their attendant drawbacks.

 

Rich, Thanks that's a very helpful article. I still have a question that was not answered in the article. When using the micrometer do I keep turning it till it won't turn no more? It makes a huge difference in the measurements I get if I just turn it until it's snug.

Thank you all for your replies.

 

Well, you don't force it (it's not a wrench). but the spring exerts a lot of pressure, so I would go towards the side of "till it won't turn any more".

Rich