What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Starting Issue

Tankerpilot75

Well Known Member
Starting Issue - additional help requested - see pg 3

I’ve had slow starter rotation since I purchased my RV7A. This last week I upgraded to an EarthX ETX 900 battery with 400 CCA, and while it definitely spins the engine better, it’s still usually takes engagement of the starter more than once to fully engage the starter. My guess is there is some significant resistance between the battery and the starter.

My questions:

1. Can a bad (failing) firewall starter solenoid cause sufficient resistance to cause this type of problem? If so what would be the symptoms?

2. What about the cable between the battery and the solenoid, can a bad cable cause sufficient resistance to make the starter reluctant to engage?

3. Same question about the cable between the solenoid and the starter?

How would you go about narrowing down the problem area and if it is the starter solenoid where would you source one? I hate to keep buying parts to address this issue.
 
Last edited:
What brand/model of starter is it? Sounds to me more like the starter. Check the sizes of cables going to the starter and make sure the engine is properly grounded to the airframe.
 
Most of the items you listed could cause slow starting.

What starter are you running and what are the cable sizes between your battery and starter?
 
I’ve had slow starter rotation since I purchased my RV7A. This last week I upgraded to an EarthX ETX 900 battery with 400 CCA, and while it definitely spins the engine better, it’s still usually takes engagement of the starter more than once to fully engage the starter. My guess is there is some significant resistance between the battery and the starter.
My questions:
1. Can a bad (failing) firewall starter solenoid cause sufficient resistance to cause this type of problem? If so what would be the symptoms?
2. What about the cable between the battery and the solenoid, can a bad cable cause sufficient resistance to make the starter reluctant to engage?
3. Same question about the cable between the solenoid and the starter?
How would you go about narrowing down the problem area and if it is the starter solenoid where would you source one? I hate to keep buying parts to address this issue.

Yes to all questions. First thing in troubleshooting slow starter is to check all connections and make sure they are all clean and tight. Don't forget the ground cables. They carry the same current as the positive cables.
 
FWIW I’m had the slow start problem. I just chased the rabbit from solenoid to key.

After replacing the firewall solenoid and starter solenoid with new units (cheap price for how much labor is involved I figured why not) as well as checking and renewing all connections problem solved.

Never really figured out root cause because the firewall solenoid was a little off and some connections looked shoddy but no real smoking gun other than I feel better now and my plane starts in 2 blades now.
 
Mine was too small gauge of wire from the contactor to the starter, I had 8 AWG, 4 AWG worked 10 times better. Of course it doesn't burn through either like my 8ga did. I increased the ground size later as well.
 
Ground strap vs cable

What’s the difference between a “ground strap” (mesh wire strap) and “ground cable.” Is one a better conductor than the other? My RV7A currently has a ground strap from the negative post to the firewall.
 
What’s the difference between a “ground strap” (mesh wire strap) and “ground cable.” Is one a better conductor than the other? My RV7A currently has a ground strap from the negative post to the firewall.

Do you have a cable (or strap) from the engine or starter back to the firewall? If not, the starter circuit is completing (grounding) back through a very inefficient and random path.

But to answer your question, a strap is supposedly a better grounding mechanism than a cable.
 
Last edited:
Starter ground

Cable or strap, makes no difference assuming they are both the same equivalent gauge.

I run the same gauge welding cable for both the starter and stater ground (note - starter ground - not under some greasy engine bolt). Take you pick, either #2 or #4. The ground goes from the big common firewall ground bolt to the starter ground.

Welding cable is very flexible and the insulation is amazingly durable. I did a torch test to compare welding cable insulation to Mil-Spec wire. The welding cable came out better.

Good quality US made welding cable is available on Amazon and many other places.

Carl
 
Do you have a cable (or strap) from the engine or starter back to the firewall? If not, the starter circuit is completing (grounding) back through a very inefficient and random path.

But to answer your question, a strap is supposedly a better grounding mechanism than a cable.

My ground is from the battery (via strap) to the firewall. I will need to confirm this but I don’t believe there is a ground directly from the firewall to the engine. This could be the problem! I’ll check this out and let everyone know. I appreciate everyone’s input.
 
Problem

My ground is from the battery (via strap) to the firewall. I will need to confirm this but I don’t believe there is a ground directly from the firewall to the engine. This could be the problem! I’ll check this out and let everyone know. I appreciate everyone’s input.
It may not be "the" problem but it is definitely "a" problem to resolve.

Adding a good ground is not hard. I followed electric Bob's recommendation to have two ground straps from the engine to the FW/Battery.

http://www.rv8.ch/ground-point-on-firewall/

img_2648-1024x1024.jpg


Some recommend the ground should come directly from the starter, which is also a very good idea. My grounds attach to the back of the engine, and with the EarthX battery, starting is very crisp.
 
Too often the ground cable from the engine to the airframe ground point is made of standard aircraft wire in some large gauge. Large gauge aircraft wire is waaaaaay too stiff, the result being loose crimps and broken terminals.

A certain popular kit manufacturer puts them in their firewall forward kits. If you have one, give it a flotation test at your first opportunity. If short span, replace it with a braided strap from B&C, Steinair, or similar. For longer spans do as Carl said and use finely stranded welding cable.
 
Too often the ground cable from the engine to the airframe ground point is made of standard aircraft wire in some large gauge. Large gauge aircraft wire is waaaaaay too stiff, the result being loose crimps and broken terminals.

In this respect, what is different between the ground strap and the starter's fat wire?
 
In this respect, what is different between the ground strap and the starter's fat wire?

the strap uses a large quantity of very thin wires. The battery cable (or thick gauge Tefzel) uses a small quantity of thick wires. The thinner the wire, the more it can flex without cracking or loosening inside of a crimp. Traditional battery cables requires support. A ground strap does not. Welding wire is very similar to a ground strap; Just braided vs. round and insulated.

Larry
 
Last edited:
the strap uses a large quantity of very thin wires. The battery cable uses a small quantity of thick wires. The thinner the wire, the more it can flex without cracking or loosening inside of a crimp. Traditional battery cables requires support. A ground strap does not. Welding wire is very similar to a ground strap; Just braided vs. round and insulated.

Larry

What I was getting at was why is a fat wire used as a ground strap more susceptible to problems than a fat wire used in the starter circuit?
 
What I was getting at was why is a fat wire used as a ground strap more susceptible to problems than a fat wire used in the starter circuit?

The starter wire is usually quite a bit longer than a ground strap meaning it has more room to flex as well as more opportunities to strain-relieve it. In my case, I have the starter wire secured to the engine mount to prevent strain at the firewall solenoid terminal and I have it secured to one of the sump bolts to prevent strain at the starter terminal.

Also, we have no choice but to use insulated round wire of some sort for the starter feed, but since the ground wire doesn't need to be insulated the strap is simpler and lighter...

Skylor
 
Update

I drove my hour to the airport to again look at the ground situation and the starter solenoid.

Ground: The negative battery terminal is grounded to the firewall. Where the top left engine mount attaches to the firewall is a ground wire going to engine attaching via bolt just under the left magneto. This looks like a solid ground - checked with a multimeter, there was no noted resistance.

Starter solenoid: This aircraft appears to have two solenoids ganged together. The positive cable from the battery attaches to the top solenoid. A cable from the lower solenoid runs to the starter. The bottom solenoid has an interesting setup with a jump wire between the two smaller posts.

Based on a private pm I decided it was worth a shot to replace the lower solenoid. Installed the new solenoid and wired it just as before based on a picture I took (see below). Did a test starter engagement and it immediately started cranking strongly. Since I was in the hanger and didn’t want to actually start, I disengaged the starter but it kept cranking until I turned off the battery switch. Tried a second time - same result. What a surprise!

I’m thinking maybe the old solenoid was jumped between the two smaller post by the previous owner/builder because he knew the lower solenoid had failed (just speculation) and that jump between the two smaller post just closed the relay.

Here’s my questions now: Why would there be two solenoids ganged together? If there should be two solenoids then why are the two smaller solenoid post on the lower solenoid jumped together? Don’t you normally touch those two posts together when trying to jump a car starter?

Please look at the attached picture and tell me what you see and help me figure out why my starter doesn’t disengage until I turn off the battery switch.
 
Last edited:
Solenoid wiring

appears to be standard setup for later RV's. Upper solenoid is master solenoid, all power to aircraft generally runs through this. Lower solenoid is starter solenoid, current only flows when starting. Regarding starter won't disengage, check that jumper as cross the small terminal, don't believe that should be there. Is it possible that jumper is a diode that isn't wired or working correctly?

Type of solenoid determines how it is to be wired, lots of variables. It can be determined which sol you have and the proper wiring for same. For now disconnect jumper and see what it does. Wiring diagram available from Vans and the solenoid manufacturer. Lots of information and help available.
 
Starting Issue Resolved

Regarding starter won't disengage, check that jumper as cross the small terminal, don't believe that should be there. Is it possible that jumper is a diode that isn't wired or working correctly?

You were right, the jumper wire with the new solenoid was the problem! Removed the jumper (wasn’t needed with new solenoid) conducted several continuity and starting tests and declared Victory! The EarthX battery engages the starter and definitely spins the engine much, much better than the old PC680. My goal accomplished!

As the second owner (non-builder) of an RV it’s always a learning curve when working on it. Some times I look at the build quality and the build decisions made by the builder and truly am impressed. Other times I discover things that make me question whether a little more attention (maybe less libation) would have significantly improved the build. I’m sure the next owner will feel the same way when he/she works on the airplane after my ownership ends. This is a great little RV and only getting better as upgrades are made.

Thanks to everyone who helped me resolve this issue and educate me on starting systems.
 
Back
Top