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Old 07-18-2016, 11:42 PM
Reilly Reilly is offline
Join Date: Oct 2008
Location: South Africa
Posts: 60
Default Slow cranking speed


I would appreciate some views here for a potential cause.

Some background:

Purchased a RV9a last year with 555 hours on. 0320 carb engine.
No problem starting.
Had PIO in Jan which resulted in a nose over and substantial damage. (Beautifully repaired now)
The engine was removed and tested and fitted back to the plane.

The only problem that I have with it is that the first start of the day it is a struggle to start.
The one thing that I noticed is that the engine cranks over very slow. Almost like the battery is nearly flat. It has a new battery fitted.

Before I got it back the Company that fixed it said that my battery was on the way out and wanted to fit a new one which they did.

It has one magneto and one e-mag. My understanding is that if the power from the battery is too low then the e-mag turns itself off which means its trying to start only on the one magneto.
It sounds like it has a bit of spark and wants to fire but just does not catch.
Eventually it will start after about 8 or 10 attempts and then it starts ok for the rest of the day.

The engine has new rings and bearings but I doubt it has increased compression to such an extent to as cause such slow cranking.

Battery mounted on the firewall.

I don't think my old battery was on the way out. I think that after the re-installation something changed which caused the slow cranking and they assumed it was a weak battery. Battery shows good strength on the EMS.

On start I only have fuel pump switch on and Dynons come on with master.

Will check that all cables are tightly fastened and good earths.

Would really appreciate some views from those with more technical knowledge than me please.
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Old 07-19-2016, 02:41 AM
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titanhank titanhank is offline
Join Date: Aug 2007
Location: Friendswood, Tx
Posts: 362

I had the same issue with my -6. Replace the starter solenoid. They are prone to pitting on the contacts and will cause slow cranking.
10-1 pistons
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Old 07-19-2016, 05:23 AM
Kevin Horton's Avatar
Kevin Horton Kevin Horton is offline
Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357

Try cleaning and tightening all power and ground connections from the battery to the starter. That fixed the slow cranking issue I had on our aircraft.
Kevin Horton
Moses Lake, WA, USA
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Old 07-19-2016, 06:48 AM
David Bell David Bell is offline
Join Date: Jun 2009
Location: Broussard Louisiana
Posts: 116

After experiencing what appeared to be a very weak battery, I found the battery ground strap attach point to the airframe to be extremely loose. I torqued the bolt down and the slow, weak cranking hasn't happened again.
David Bell
Broussard, Louisiana
Flying RV-7 N711RT
Sold RV-4 N22755
Awesome 4/7years
Based: KLFT
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Old 07-19-2016, 07:41 AM
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JohnInReno JohnInReno is offline
Join Date: Jun 2005
Location: Prescott Valley/Chandler AZ
Posts: 351
Default Cables

My -9A had starting troubles that were eventually traced to bad crimps on the supplied heavy wires. As others have said, check those connections. Put them in a vice and pull hard.
John Morgensen
RV-9A N946PM 600+ hours since 2013
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Old 07-19-2016, 09:25 AM
luddite42 luddite42 is offline
Join Date: Mar 2010
Location: USA
Posts: 443

I onced fixed a weak starting issue by replacing the engine to airframe ground strap.
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Old 07-19-2016, 09:33 AM
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Mike S Mike S is offline
Senior Curmudgeon
Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,268

Previous replies have pretty much covered the common areas to look at.

Keep in mind that an electrical circuit is like a circle-------whatever comes out of the battery must get back to the battery. A small amount of electrical energy gets used/converted to heat, but most will need a good solid supply side path, and return path.

Good luck.
Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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Old 07-25-2016, 10:57 PM
Reilly Reilly is offline
Join Date: Oct 2008
Location: South Africa
Posts: 60

Thanks guys. Will check all wires this weekend.
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Old 07-25-2016, 11:24 PM
tim2542 tim2542 is offline
Join Date: Aug 2009
Location: Redding,Ca
Posts: 633

Check the wires and the whole system the easy way. Put a DC volt meter on the battery negative post and the positive lead on the engine case. When cranking you want to see less than .1~.2 volts, if more than that start moving the positive lead back towards the battery one connection at a time until you find the
what's developing the voltage.
Check the positive side the same way, measure between the positive battery post and the starter terminal. This side typically has more connections plus a couple of relays so let's give it .3 volts or so.
As a previous post mentioned, a good chance you'll find the starter relay generating a lot of voltage drop.
Tim Andres
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Old 07-26-2016, 08:18 AM
kaweeka kaweeka is offline
Join Date: May 2011
Location: Roseville
Posts: 376

Sky Tec has a pretty good troubleshooting diagram that backs up what has already been said...... just in pictures. I like pictures.
RV-9A N435KR, Vans calendar March 2018
LIO 320 B1A, Dual LS Plasma III, AFP injection
G3x touch
Roseville, Ca
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