Engine mount to fuse/battery ground

[georgemohr]

Engine mount to firewall/battery ground

Hi all!

There appears to be no clear ground path from the engine mount to the battery using Vans FF kit instructions. There's a ground strap from the engine ground lug to the motor mount, but nothing to the firewall and/or battery.

The stock setup seems to rely on the engine mount bolts to ground to the airframe structure to provide this path, but there are no steps to ensure clean metal to metal contacts between either the AFT face of the motor mount surface, OR the AFT face of the interior structure that the motor mount nuts would come in contact with.

I know lots of builders suggest an additional strap from the engine direct to the firewall/battery. I'm thinking of going this route, but I honestly don't understand how the stock setup has a decent ground?!

Regards,
George

 

[DanH]

I know lots of builders suggest an additional strap from the engine direct to the firewall/battery.

That feeling may stem from the use of a short WH-P25 cable in early -14 kits. Way too stiff for a run that short, so the eyelet broke, or loosened at the crimp. You can still see the cable in some drawings. I don't know when it was switched to braided strap.

Germane to your question, it's real hard to go wrong adding a good braided strap direct to the battery negative. Although an electrical path through the mount structure may be adequate, that welded tab makes me nervous.
.

 

[Mel]

I agree with Dan. With all the powder coating on the mount, I'm a lot more comfortable with a cable running directly between the engine and the firewall or negative battery terminal.

 

[Bavafa]

If memory serves me right, the mating surface of the engine mount is not powder coated. If it is, then it ought to be cleaned and with six points connected to the FW, it ought to establish a good ground.
But as Dan has mentioned, it ought to be long enough to provide the needed flexibility it needs.

 

[PhatRV]

I used the braid ground strap and bolt the other end to the ground bus. I since added one more ground braid strap as a redundant backup.

https://vansairforce.net/community/showpost.php?p=1499474&postcount=4

 

[georgemohr]

Ok thanks for the input here folks. I'm going to have a 2AWG braid made to go from the battery negative post to the engine block ground lug.

Not sure why the instructions leave the quality of this ground up to chance. At least some words about ensuring a clean metal contact by removing paint and powder coating should have been included?

 

[mturnerb]

Ok thanks for the input here folks. I'm going to have a 2AWG braid made to go from the battery negative post to the engine block ground lug.

Not sure why the instructions leave the quality of this ground up to chance. At least some words about ensuring a clean metal contact by removing paint and powder coating should have been included?

I did one like you describe but attached it to the bolt on the firewall where the battery ground (negative post to AC ground) connects. Instead of braid I used heavy gauge cable with crimps.

 

[lr172]

If memory serves me right, the mating surface of the engine mount is not powder coated. If it is, then it ought to be cleaned and with six points connected to the FW, it ought to establish a good ground.
But as Dan has mentioned, it ought to be long enough to provide the needed flexibility it needs.

I did this on my 10. Made sure the contact side of each attachment was clean steel and also left the insulation off the contact area of the firewall attach points. Have a clean ground path from airframe to engine via this plus the plans ground strap arrangement. IIRC, I put dielectric grease in that area to avoid rust and the issues it would create.