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  #11  
Old 01-07-2019, 06:57 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
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Remember why you want a good ground on the engine - to run the starter.

The starter has a very nice ground lug on it. The only engine ground you need is from the ground lug on the firewall to the ground lug on the starter. Use the same gauge wire that you run power to the starter.

Iíve seen the Vanís RV-14 engine mount ground setup - and wonder why they would do that when it is so simple to just ground at the starter.

Carl
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  #12  
Old 01-07-2019, 11:03 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
.

Iíve seen the Vanís RV-14 engine mount ground setup - and wonder why they would do that when it is so simple to just ground at the starter.

Carl
I guess there are different opinions on what is simple.
Running two heavy gauge wires all the way fwd to the start is not, in my opinion.
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  #13  
Old 01-08-2019, 07:34 AM
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Carl Froehlich Carl Froehlich is offline
 
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Originally Posted by rvbuilder2002 View Post
I guess there are different opinions on what is simple.
Running two heavy gauge wires all the way fwd to the start is not, in my opinion.
Sorry Scott, I have to disagree:
- The extra foot or so of wire weight is trivial.
- Old school ground straps run from the firewall to a greasy engine bolt are not weight free, but do create the potential for future maintenance issues. We need not perpetuate 1960 Cessna thought.
- Odds are that a plane that has a reluctant starter but a charged battery, the problem is a poor ground return from the starter.
- Considering other stuff a builder can inadvertent do to add ďhidden ground returnsĒ from the engine, failure to have a robust starter ground can lead to starter current finding itís way back to ground via some expensive piece of avionics.

As I said, just run a #2 wire from the common firewall ground to the nice ground lug on the starter and build on.

#2 welding cable is amazingly robust to abrasion and heat, and inexpensive. I use #4 to connect each battery and #6 for the alternator output.

Carl
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  #14  
Old 01-08-2019, 08:44 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Like I said.... differing opinions

Quote:
Originally Posted by Carl Froehlich View Post
Sorry Scott, I have to disagree:
- The extra foot or so of wire weight is trivial.

Get out your tape measure. The typical cable path from the battery/firewall area to the starter motor requires somewhere between 3-4 feet of cable (and the weight per foot of 2 gauge copper wire is not trivial), plus the biggest cabling pain in the engine compartment is properly anchoring wires / cables to the engine around the top of the engine sump. Running a ground cable all the way to the front doubles that.

- Old school ground straps run from the firewall to a greasy engine bolt are not weight free, but do create the potential for future maintenance issues. We need not perpetuate 1960 Cessna thought.

I don't think the starter area of a typical Lycoming is any cleaner than the aft rear of the engine case.

- Odds are that a plane that has a reluctant starter but a charged battery, the problem is a poor ground return from the starter.

I agree, but that problem can exist with any high power cable connection.... regardless of whether it is attached at the engine case or directly on the starter motor. With four bolts mounting the starter, I have never seen a ground problem at that location.
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