Sufficient Grounding with Motor Mount?

[CharlieWaffles]

Now that I am down the road and have mounted my engine quite some time ago I've come across a small tidbit of information that would have been handy to know BEFORE mounting the engine mount/engine. I did nothing special to remove the powder coat from the pads on the engine mount before they were bolted to the airframe.

So I'm beginning to wonder if my engine mount will provide sufficient grounding to the engine when a braided ground is run from the engine to the mount. Is there a resistance value I should check for with my multi-meter between the engine case and airframe ground? An acceptable range would be a good reference.

[scsmith]

I would recommend attaching a ground strap to the aluminum stiffening angles that form the structure of the firewall. I would not recommend clamping a ground strap to the engine mount tube, even if you remove the powdercoat from the pads that mate to the airframe. JMHO

[Andrew M]

What Steve said. The only grounding straps I have seen run to the engine mount, were a tab welded on the mount for that purpose. Go with an engine to airframe ground, which is very common in the certified world.

[N941WR]

Removing the powder coating where the mount meets the fuselage won?t do much good because you still have the vibration isolators that are made of rubber.

You MUST put a ground strap from the engine to the fuselage. Otherwise, the current generated when you hit the starter will travel through all the other little wires (EGT, MAP, etc.) and burn them up.

It is also good to provide a secondary ground path. In most cases, the oil and fuel pressure lines will work just fine.

You can see the ground strap in this overhead picture of my engine installation. It runs from the forest of tabs on the firewall to a case bolt on the engine.

[Walt]

Originally Posted by N941WR

It is also good to provide a secondary ground path. In most cases, the oil and fuel pressure lines will work just fine.

Not sure what was meant by the above but the braiding on the fuel and oil line is for protection, if it has to act a ground, the braids will be glowing in a matter of seconds and burn through your lines

I strongly advise you go with dual ground straps, one from battery to airframe and another from the battery to engine case.

[Mike S]

Originally Posted by Walt

I strongly advise you go with dual ground straps, one from battery to airframe and another from the battery to engine case.

The OP is building a 10, so a seperate ground from the battery to the engine case is problematic due to the rear battery. Just a firewall to engine case ground line is enough in the 10. Be sure to get the firewall end where it is connecting to structure, not just sheet metal.

For a firewall mounted battery, good advice from Walt.

[BobTurner]

I followed the plans, no problems. Just remove any powder coating from the tab where you attach the ground strap fom the engine. The mount is well grounded to the firewall structure by the large bolts which attach it to the firewall. Those bolts pass thru the mount where it was stripped of any paint when you used the holes as a drill guide.

PS. The resistance must be much less than 0.1 ohm, less than a typical multimeter can measure.

[Mike S]

Originally Posted by BobTurner

Just remove any powder coating from the tab where you attach the ground strap fom the engine.

Early mounts did not have the tab on the mount.

Dont know what year the OP's kit is, but the tab may be there, or not.

[CharlieWaffles]

My mount does indeed have the tabs.

[Pat Stewart]

My battery is in the back so it is grounded to the airframe. I also used two of the braided grounds straps, one from the engine to the tab on the mount and the second from the engine to the firewall.

Pat