Poor Cranking? Check Your Solenoid!

[Ironflight]

With close to 1600 hours on the Valkyrie, it is no surprise that some of the original components might be ready for replacement. For the past few months, I have noticed some intermittent starting (actually cranking) issues on some flights. I remember a few months back when I hit the starter switch, and got nothing but a ?click?. But when I tried it again, it cranked fine?.so I kept an eye on it, and kept flying. Occasionally, the cranking seemed slow?but then it got better. Again, I watched it. Just before this current trip, I gave a call to SkyTec to see what they thought about the performance of the starter, and they (rightfully) said that they have had great luck with the Flyweight installed on the airplane, and that they would be happy to go through it if I sent it in ? but they bet it would be fine.

Well sure enough, it worked just fine all the way to Oregon ? and then on the ramp at Aurora, all Louise got was that ?click? ? over and over. SHe and Joe rolled it in to the Van?s hangar, and we pulled the cowl. I grabbed a piece of hinge pin and bent it into a ?U? shaped jumper wrapped it in a rag, and jumped across the solenoid terminals ? and got the best cranking prop I?ve seen in a long time! Now seeing as I was sitting in the mother ship?s hangar, I had a hunch that it might not be hard to find a brand new starter solenoid?.and I could even save on the shipping! Sure enough ? Daryl had one in my hands by the time I had pulled the old one, and we were putting things back together in no time. I can?t say enough good things about the ?magic door? in the back of the Van?s hangar. Rap on the door and say ?1/2 box end??and one magically appears?.

The Prototype Shop guys seem to have a good life!

I saved the old solenoid, and will do an autopsy on it when we get back to Houston ? I expect to see burned and pitted contacts providing a high resistance. Pictures when I have them?. In the meantime, if you have a lot of starts on your system, and you are experiencing problems, it might be a good time to suspect the solenoid- they are actually pretty cheap!

Paul

[Walt]

Solenoids are an often overlooked source of problems. They "usually" give some warning signs of an impeding failure such as slow cranking like you experienced or intermittent operation (you will see this when you first activate the relay and nothing happens, it takes a second or third time of activating it to get it to work).

I also replace these in pairs, if the master or the starter relay fail, I replace them both. These are relatively inexpensive parts that play a critical role in aircraft operation.

[humptybump]

Is the a better than average chance that my "one blade, then it just stops for a second or two, then multiple blades and start" - is solo iod related ? I've already changed the battery.

[rocketbob]

Why bother with an external starter solenoid when there's one built in the starter. A few millohms of resistance at 350A equates to a drop of several volts across the circuit. So what if the starter cable is hot all the time, its hot to the starter solenoid. As long as the cable is supported correctly it will never be a hazard.

[DanH]

Originally Posted by rocketbob

Why bother with an external starter solenoid when there's one built in the starter. A few millohms of resistance at 350A equates to a drop of several volts across the circuit. So what if the starter cable is hot all the time, its hot to the starter solenoid. As long as the cable is supported correctly it will never be a hazard.

Agree. Requires a switch rated for 20+ amps or a relay, but it works great. I use a rewired Skytec NL series, with a 30 amp automotive relay triggered by a start button (with hidden cutout) on the stick.

http://www.skytecair.com/Wiring_Diag.htm

[barryrv10]

It is important when you tighten the nut on the stud, that you back up on the locking nut so the stud does not turn. The connection inside the solenoid is two flat surfaces and if the stud turns you loose that good connection.

[Ironflight]

First, I tend to agree with the guys who say that we should think about doing away with the starter solenoid, now that we are all using non-Bendix starters. Heck, Sky-Tec actually comments on their page that they don?t know why Van?s still show them on their drawings. Well, some habits die hard?.and rewiring takes time, so maybe I?ll get rid of mine someday. In the meantime, here are some autopsy photos:

This is the solenoid with the top ripped off. Looks Ok from this vantage point:




Ahh?.but take out the plunger and take a look at the contacts! They are nicely pitted ? and not symmetrically.

Originally Posted by barryrv10

It is important when you tighten the nut on the stud, that you back up on the locking nut so the stud does not turn. The connection inside the solenoid is two flat surfaces and if the stud turns you loose that good connection.

I think Barry hit the nail on the proverbial head!




And here is the ?underside? of the plunger contact ? note the pitting, and the fact that it clearly rotates during its life:




I cannot believe how much changing a $21 part changes the character of a 1500+ hour airplane! Whereas I was beginning to think I had to baby it on every start because it barely got over TDC, now I can once again practically taxi on the starter. The thing is, these go bad gradually over a lot of hours, so you just don?t notice how bad it is getting ? like boiling a frog. So if you have a slow starter ? think about changing your solenoid (or eliminating it). And remember, we have to put SOME parts in to keep the aviation economy going?

Paul

[scard]

Thanks very much for the tear down report. I think I'll get that on the list of time limited replacement items.

[Steve Barnes]

I KNOW WHAT I AM DOING THIS WEEKEND. For some time now, I have had slow turn over speed or not at all. Some times I have to turn the key several times to get through one compression stroke. I just replaced the battery, but didn't make any difference.

Steve

[N8RV]

Thaks, Paul. How often do you boil frogs? Just wondering ... :-)