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Another Slow Starting Thread

Manchu16

Active Member
I have read a few of the threads on slow starting. Many go to voltage drops or bad starting solenoids.

The first start of the day, I get a hang on the compression stroke but it muscles through and I get a start. All other starts during the day crank like normal. I have manually rotated the prop before my first start and I still have the same slow start. I dont recall the slow start when I first purchased the plane, but it has been getting worse.

I don't see any significant voltage drops (followed the skytec starter troubleshooting) and I have a new 680 that is strong. My understanding of both solenoid and starter issues is that they can happen cold or warm. Before I start replacing parts was hoping there were other tests I could perform to nail it down.
 
cables

Have you checked all the high current cable ends and crimps and connections, including the ground straps? That is an easy check that won't require replacing anything initially
 
I saw this many times on our flight club Warrior due to corrosion on the ground cable. Cleaning it with wire brush, making sure all ground connections to engine, firewall and battery were clean and secure always fixed it.
 
Connections are tight and clean; checked 2 weeks ago. Meter shows solid connection as well. Temporary ground run to the starter didn’t help either.

Because this is only happening during the first start of the day, my initial thought was a cold battery, which I ruled out by exercising the battery by loading it up and charging it like the airplane would before making my first start of the day. No joy.

I would assume a loose connection or corrosion should show up every start or at least more than the initial start of the day. But pure assumption on my part, which is why I appreciate everyone’s input. No doubt this has been a learning exercise
 
Depending on the starter, it might be a good idea to check with the manufacturer to see if they have some hints. I'd guess this is not the first time they have been presented with this problem.
 
Warm engines spin easier (i.e. requiring less amperage) than cold ones, so that possibly explains the variances you see. Likely issue is not enough current getting to the starter. Problems with Positive and negative cables and terminals all the way from Battery to starter can do this, as can the solenoids. These have two copper plates that come together and allow current flow. They can wear and reduce contact area, reducing available amperage delivery. There is typically one on the firewall and some Skytechs also have one on the starter. These type of failures are not that uncommon with solenoids; Most go for decades, but some die in a year or two if a burr causes a hang up.

You need to measure resistance of both pos and neg circuit from batt to starter and all should be .1 ohms or less. That still doesn't assure full amperage. If a #2 cable has 100 strands and 75 of them are broken at a failure point, resistance will be 0, but current carrying capacity will be 25% of rated capacity. Bad crimps are similar. Wiggle and pull tests help find that.

Larry
 
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Wire wound starters like the B/C or NL draw about half the current of a PM starter.
 
Double hit

I replaced the starter solenoid in the skytec and it helped the sluggish start, but still not great. A few weeks ago I swapped out the vans starter solenoid on the firewall and that took it the extra mile. Cranks like crazy now on my 680.

Last week I put both solenoids to the scalpel, ok the cut off wheel. Both of the solenoids showed significant pitting / arcing. As a precaution, I replaced the diode on the vans solenoid to hopefully delay future pitting. I did try to drill the rivets out to gently open the solenoid, but they were pretty gunked up. Wasn’t planning on reusing them, so pulled out the bigger artillery.
 
I replaced the starter solenoid in the skytec and it helped the sluggish start, but still not great. A few weeks ago I swapped out the vans starter solenoid on the firewall and that took it the extra mile. Cranks like crazy now on my 680.

Last week I put both solenoids to the scalpel, ok the cut off wheel. Both of the solenoids showed significant pitting / arcing. As a precaution, I replaced the diode on the vans solenoid to hopefully delay future pitting. I did try to drill the rivets out to gently open the solenoid, but they were pretty gunked up. Wasn’t planning on reusing them, so pulled out the bigger artillery.

You have found the solution but these components should be checked via voltage across them at starting current. The resistance only method is not always accurate. Or use your Seek thermal camera just after starting. I just got one and stumbled on a hot extension cord connection at the hangar while walking around the plane for another reason.
 
I replaced the starter solenoid in the skytec and it helped the sluggish start, but still not great. A few weeks ago I swapped out the vans starter solenoid on the firewall and that took it the extra mile. Cranks like crazy now on my 680.

Last week I put both solenoids to the scalpel, ok the cut off wheel. Both of the solenoids showed significant pitting / arcing. As a precaution, I replaced the diode on the vans solenoid to hopefully delay future pitting. I did try to drill the rivets out to gently open the solenoid, but they were pretty gunked up. Wasn’t planning on reusing them, so pulled out the bigger artillery.

diode only protects from arcing on the switch. It does nothing to stop arcing across the main contacts.
 
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