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Hello.

There is a series of spacers, or washers, underneath the valve springs on my 216. So, while I dont know the technical terms, when I take off the spring, these washers are underneath the cap that holds the bottom of the spring on the head.

As Ive been working on the head, one of the things Ive noticed is that one of the valves does not have the same spacer as the others. Actually, Ive noticed several things wrong with the previous rebuild, including a missing boot and springs being on backwards.

How important is that spacer?

I imagine it keeps the spring at a certain height which affects tension and thus valves opening and closing. Is that correct? Any thoughts?

Thanks,

Judson

Judson,

I think you are correct about those washers/spacers being used to provide additional spring tension after a valve job.

Spring tension can be measured and appropriate washers are then put in (by a good re-builder).

Properly called a valve spring seat shim. Used to adjust installed spring height, which can be measured from the shim to the valve retainer with a metal rule. Should all then be to specs.

As mentioned above, another way to check is to actually measure spring load before installing the springs.

I think they were used to bring weakened springs back to spec. It would have been cheaper than new springs.

There is always some variation from spring to spring, especially when considering the whole installation (springs, seats, retainers, rotators). The springs are measured at assembly and shimmed as needed. Weak springs should be replaced.

However, springs made before the chrome vanadium materials became common could lose 25% of their spring load from normal operation. A good quality spring will lose very little over time.

Spring spacers are to correct spring installation hight variances. When the valve seat is cut, this makes the valve itself set deeper into the head. This also makes the stem side stick out farther from the head. With the stem sticking out farther, the spring pocket is now longer. To keep all the spring pockets the same length, spacers are added.
If the machinist cuts each seat to the same depth, then all the spring pockets will have the same amount of spacers, but if the machinists varies each seat cut, you end up with different amounts at each valve. Both ways work work just fine, buy cutting only whats needed to clean up each seat, you end up with the odd spacer counts. Some machinist will find the lowest seat then cut all the rest to the same depth, this makes assembly easier but can remove more material then needed.

Every valve spring has a load rating. Seat pressure is how much pressure the spring applies to the valve to hold it closed when the cam is NOT acting on it. Open pressure is the amount of force trying to shut the valve when fully opened by the camshaft. To keep all valves under equal force, spring shims are used to set the seat pressure to factory specifications. If the springs are getting weak and shims are used to compensate, you can end up with a coil bind situation. Coil bind is where the coils make contact with each other and form a solid mass, bent pushrods or broken studs are the results. At full valve lift, you should have clearance between each coil in every spring, ( .060" ) is the minimum amount you want.

When setting coil springs, a small, special tool is used to measure each one. ( http://www.summitracing.com/parts/cca-4929 )
Shims come in .015", .030", and .060" thicknesses, so being with in .015" is ideal, .030" is usually close enough. It you do not know the actual factory spring setting, next best thing is to set them all close to each other with out binding the coils at full lift. Shims also come in soft and hardened material. The hardened shims go up against the valve spring, softer shims go against the head surface. In high spring rate heads, the valve springs can wear away the cast iron or aluminum heads so the hardened shims prevent this. In your application, it's not going to be a problem.

Joe

Joe,

Thank you for your in depth response.

Do you think it is important to measure the tension on each spring before putting them back in? Basically, Ive taken apart the head to do a valve job because the car would not start due to what I believe to be low compression. Two cylinders had 0 compression, and the others ranging from 10-40 pounds. As Ive taken the head apart, Ive found a bent pushrod on the cylinder that was missing the spacer, as well as several springs that were upside down, and a missing oil boot. That is only on about half of the valves-the other valves I still need to check.

Good news is that most of the seats look fine. A few valves will need to be replaced, and a few valve seals, but again, do you think the spring tension could affect compression in that it does not allow valve to seal properly? And if so, what is easiest way to measure spring tension? You mentioned putting them side by side, but I assume that measures height and not tension.

Thanks.
Judson

Its unlikely the valve springs caused the low compression. It takes very little effort to shut the valves. The springs main purpose is to hold the lifter on the cam lobe. Even a very weak spring will can close a valve at low rpm. Tired springs show up as a miss at medium to high rpm. The weight of the lifter, push rod, and rocker arm is to much for the spring to keep on the cam lobe. As the rpm's increase, the lifter starts jumping off the cam, as it does the valve is held open, thus creating a miss.

A bent pushrod will limit valve lift, so low compression is a result. If you think about how the lifter rides on the cam lobe, it opens and closes as it goes up and down the lobe ramps. With a bent push rod, the length of that push rod is now shorter so the lifter doesn't start to open the valve till higher up on lobe ramp. Not only does not start to open till later, it doesn't open as far, plus it shuts quicker. This short lift cycle means less air for the cylinder and less compression.

You should also be looking for a bent valve or broken piston ring, both can cause little to no compression. Chuck the valves in a drill and spin the slowly looking for a wobble at the stem to head connection.

Go to local parts house and get some valve lapping compound. With a electric drill, you can spin the valves slowly while pulling them up against the seat, the compound will leave a nice dull ring where the two surfaces meet. If the valve is bent, it should leave a gap where no contact was made.
Another easy check after you lap all the valve seats is to assemble the head and poor a thin liquid ( paint thinner ) down the ports and see if the valves are holding. A very small seep is acceptable, drips are not.

A crude spring check can be made using a bathroom scale and wood blocks. The key is to compress each spring the same amount. Take two blocks of wood the same length and place on each side of the scale. If you have a piece of flat heavy steel, place it on the scale to spread out the load. Now place one spring on the scale and lay a 2x4 across it and the blocks of wood. You may need to adjust the hight of the blocks at this point, now stand on the 2x4 and see if you compress the spring. Adjust the hight till you get about 75 lbs of compression. Check each spring and write down your findings. I would expect them all to be close to each other. The is no need to know the springs actual specifications, you are only interested in how they compare to one another. If there is any doubt, new springs are fairly cheap.

Thanks, Joe. Great information. I appreciate it!