Tools needed: Solenoid wrench, Spark plug viewer

In the last article I wrote about taking the solenoid apart and putting it together.This time I will discuss what you are looking for as far as wear and damage.I will concentrate on the nitrous solenoid here but the same techniques apply to fuel solenoids.

The sealing material on the solenoid piston is made of two basic materials, Teflon or rubber, depending on the manufacturer and the application its intended for. I will call it rubber for simplicity’s sake but the rubber is some hi tech stuff with various chemical makeups to withstand the cold nitrous. The rubber is generally black in color but there are some new wave cryogenic materials that have a red appearance. The Teflon is white in color.

There are four things that can damage or destroy a solenoid piston: fuel contamination, extreme pressure, crud, and plain old wear and tear (with the later being the most acceptable). The others are preventable.

Rubber has the advantage of providing a good tight seal and has rebound capabilities, up to a point. It has memory in other words and will return to its original shape and position. This is a good thing as far as flow consistency. The downside is that while it can be made impervious to nitrous it is susceptible to bloating from some fuels. There is no free lunch. What is resistant to fuel is junk for nitrous. The bloating will shut down the flow of nitrous or shut it off completely. This condition is pretty obvious since the engine goes flood rich due to lack of nitrous. What you will find upon inspection is the rubber swelled up in the middle of the sealing ring. Extreme cases will look like a little mountain. If you set the piston out in the air it may well return to its normal state and be reused. If not, replace it.

How does fuel get to the nitrous solenoid? Usually this happens on plate systems. The hot fuel fumes after shut down will track back through the nitrous bars to the solenoids and condense back to a liquid state. This can be avoided by mounting the nitrous solenoid so it is above the plate, making it harder for the fuel to get to the piston. This stuff isn’t smart enough to run up hill. Fumes will, but condensed liquid will run back down hill or evaporate. If you are curious about the fuel you use and its effect on the rubber, just put the piston in the fuel for a while and see what effect, if any, it has. Most fuels are not a problem, but some will make it go bloated. And this changes from year to year as race fuel manufacturers constantly tinker with the fuel to make it better. That means more or different chemicals we really don’t want to know about.

One would think that a little swelling is not a big deal but it has to do with how a solenoid works. Lets say our sample solenoid has an orifice of .110 and piston lift of .040 of an inch. If the rubber swells .020 of an inch you now have a reduction of 50% lift and a 42% loss of effective orifice diameter. This happens because the total lift of the piston is the same and the material is swelling in the opposite direction. So you can see it doesn’t take much to mess up your tune-up.

Now don’t get too shook up about fuel contamination. The rubber material keeps getting better as time goes on and this doesn’t happen everyday on every system, but you now know what to look for.

Teflon is an inert material and as a result is not affected by any fuel or nitrous. This would seem the obvious choice for a nitrous solenoid but it has a downside also. It has no memory and will pound itself deeper and deeper into the sealing ring, thereby reducing flow as time goes on. This has the same effect as rubber swelling: loss of lift/flow. The other problem is it has a tendency to hold any crud that gets by the filter system possibly causing a leak. Because the Teflon has no memory or rebound qualities it can cause a potential leak. I don’t have a problem with Teflon as long as the above problems are considered and implemented in your maintenance program. I think Teflon is fine for race cars that have a rigid maintenance schedule. In other words they are checked, changed, or adjusted with regularity. Adjusted? Some pistons have the Teflon exposed out the end and after running the Teflon can be trimmed back in a lathe and reinstalled. For the street machine or bracket car that goes many laps between maintenance I would stay with the rubber style pistons.

Extreme pressure happens to a lot of racers. A nitrous solenoid may be only capable of opening against 1200 lbs of pressure. If one puts a hot bottle in a car he may find the solenoid will not open until the bottle is cooled down or pressure is bled off by a purge valve. BUT the purge valve may not open either. You may have to bleed off some nitrous to get the bottle pressure within reason or lose the race. Now the piston could be exploded at this point doing one of two things. It will either plug the solenoid orifice or leak like crazy, the later being the worst case. I have spent time pulling rubber out of the bars of a nitrous plate. This should demonstrate how much power is involved with extreme pressure. As always, start the engine first, then slowly turn on the bottle. If the rpm jumps, shut the bottle down and turn the car off. If a leak happens, pull the plugs, and open the carb, spin the engine over (ignition off) and let the nitrous evaporate before running again.

I see most of the blow ups—and this happens with Teflon also—on the small solenoids used on street machines and purge valves. If you have a street machine and you leave the bottle on while the car sits in the hot parking lot, your bottle pressure goes sky high. Extreme cases are hatch back cars. The cure for street machines and race cars is when done using the nitrous shut the bottle off and purge off the excess nitrous. You will add years of life to the solenoid piston. The other tool is a pressure gauge on the bottle. This should be checked before turning the bottle on. Street machine owners should also study ways of insulating the bottle compartment.

Crud should never happen but it does. If it makes it to the piston it will tear up the material and most likely lodge in the solenoid making it leak. Street machines and bracket cars should have some kind of filter on the nitrous and the fuel systems. There is absolutely no excuse for getting crud in your solenoids. Your nitrous filling station should also have a filter on it. See Clickety Click, Chapter 1 for an example of a bad filling station day.

Race teams that have a solid maintenance routine do not run filters and this is fine. I don’t run filters on my own car but again, I emphasize the term Maintenance.

Wear and tear happens. These are mechanical objects and there is no way around it. You may need to use your spark plug viewing light to see the piston up close. You might see little tears as well as crud and a normal rise of the material in the center. These should be replaced. A bracket racer with good records can probably predict when its time to change due to e.t. slow down. If one is in a qualifying situation at a national event and low e.t. is critical for every round, then pistons should be checked before leaving home. Every maintenance schedule is a little different depending on amount of use and total flow. I know of some pro users that are fanatical about new pistons before eliminations.

I threw the word maintenance around a lot here and I hope I made the point. Personally, I think if a racer is not willing to do maintenance and filter his fuel and nitrous before putting it in the car might as well take up recycling as a career, because there are going to be a lot of experienced parts to haul to the dump.

Solenoid maintenance is simple and crucial to the tune-up. Just Do It!!