Van's Air Force
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Engine mount ground?
- Thread starter rvdave
- Start date
The engine should be grounded to the mount by 2 straps. Also, the powder coat should be removed from the mount faces before attaching to the firewall. Then you technically don't need the extra ground you are running. However, I did exactly the same, just because........
rleffler
Well Known Member
Step back and look at the bigger picture. What are you attempting to ground and why? Also to identify and understand any potential failure points.
I ran a ground from the alternator(s) (primary and backup)to the large bolt on the forest of tabs and from the engine as well. Almost everything in my RV-10 is grounded directly to the forest of tabs on one side of the firewall or the other. The lights in the wing are the only items I have grounded locally.
There are multiple ways to accomplish the grounds. The important thing is that everything is grounded. If the engine becomes isolated from ground of the aircraft, some ignitions and many sensors won't work as intended.
Auburntsts
Well Known Member
Bob is spot on. For example, I accomplished the same thing as Bob following a similar concept, but different route. In may case I ran a single strap from a convenient engine case bolt to one of the engine mount's grounding tabs and a second strap from that same tab to the big bolt on the firewall side of the forest of tabs.
Bill Boyd
Well Known Member
electrons will find a way home
Or more to the point, if the heavy-duty high-current engine ground strap fails, then sensor leads and control cable sheaths will be forced to carry large currents when the starter is next used, and this isn't good. Their magic smoke will come out. Redundant straps sized for starter motor currents are a sound idea. If you only have one, inspect it regularly, and consider adding a second.
Or more to the point, if the heavy-duty high-current engine ground strap fails, then sensor leads and control cable sheaths will be forced to carry large currents when the starter is next used, and this isn't good. Their magic smoke will come out. Redundant straps sized for starter motor currents are a sound idea. If you only have one, inspect it regularly, and consider adding a second.
Birkelbach
Well Known Member
I ran one large wire from the (-) terminal of the battery to the forest of tabs and one braided strap from that same stud to the first engine case bolt I came too. Ground everything to the forest of tabs except maybe position / landing lights. If the ground strap comes loose smoke will probably leak from the ignition wires the next time the starter turns. If you install it properly and take a look at it every now and then, you won't have any problems. No need for redundant straps. Take care of the ounces and the pounds will take care of themselves.
I don't know what the benefit of grounding the engine mount would be.
I don't know what the benefit of grounding the engine mount would be.
N941WR
Legacy Member
Bill Boyd is correct. The question is, what will your alternate ground path be?
A primary strap from an engine bolt to you forest of tab ground is ideal for a primary path.
Your secondary path should not attach to any of the bolts used for your primary path. The reason is that if one bolt comes off, you have lost both paths.
In my case, after studying this at length, I realized that braded stainless oil and fuel pressure lines provide a secondary path, a pretty good secondary path. While people scoff at this, there is no worry of explosion or fire as any electrons using those hoses will pass round the fluids, similar to a faraday cage.
One other thing, does the 10's engine mount have a tab for a grounding strap? Neither of my engine mounts had such a tab.
A primary strap from an engine bolt to you forest of tab ground is ideal for a primary path.
Your secondary path should not attach to any of the bolts used for your primary path. The reason is that if one bolt comes off, you have lost both paths.
In my case, after studying this at length, I realized that braded stainless oil and fuel pressure lines provide a secondary path, a pretty good secondary path. While people scoff at this, there is no worry of explosion or fire as any electrons using those hoses will pass round the fluids, similar to a faraday cage.
One other thing, does the 10's engine mount have a tab for a grounding strap? Neither of my engine mounts had such a tab.
Auburntsts
Well Known Member
Yes, in fact Ithe mount has 2 tabs.
Ok just to clarify some things. Your engine mounting frame is attached to the firewall at six points, making grounding contact at each mounting point. There are two straps that mount
from the engine to the engine mount, which grounds to the firewall. So is this a proper install or ?. Why the ground straps from the engine to the firewall or firewall forrest tabs. is this just different methods or Am I missing something.
from the engine to the engine mount, which grounds to the firewall. So is this a proper install or ?. Why the ground straps from the engine to the firewall or firewall forrest tabs. is this just different methods or Am I missing something.
Each contact point is a location for resistance. The lowest amount of contact points are two. The more resistance, the more error you will have in gauges. And lower cranking power to starter.
The flow of power from the battery is from the -- to the +....... Make it a good one.
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As I see it, if you have removed the powder coat from the engine mount faces and have a good contact and have installed the engine to mount grounding straps, it should be good. However, a poor ground is going to cause all sorts of problems, probably difficult to track down. So, most people seem to add a further strap - I ran a #2 from one of the engine strap points to the firewall ground. That way, I reckon to have 2 independent possible paths for the ground.
I think the feeling is that this is a critical item so some redundancy should be applied.
I think the feeling is that this is a critical item so some redundancy should be applied.
My apologies, Im not trying to hijack this posting, but I did have additional questions on the grounding.
I have basic forest tabs (metal groupings of 10 tabs). My intent was to mount them on one of the angle stiffeners that run diagonal on the firewall. Installing them in a row along the top lip. This would be for my instrument grounding point. It makes sense having a strap from the engine strap point to the firewall. Would a stainless steal bolt through the firewall with the engine grounding attached to the bolt work good. Would two seperate bolt points and not remove the powder coating from the engine mount work better. Or as far as removing coating from the engine mount, should it be done to one or two, and since there are six, is there a preferred mounting point that should be the ones that has the coating removed.
I have basic forest tabs (metal groupings of 10 tabs). My intent was to mount them on one of the angle stiffeners that run diagonal on the firewall. Installing them in a row along the top lip. This would be for my instrument grounding point. It makes sense having a strap from the engine strap point to the firewall. Would a stainless steal bolt through the firewall with the engine grounding attached to the bolt work good. Would two seperate bolt points and not remove the powder coating from the engine mount work better. Or as far as removing coating from the engine mount, should it be done to one or two, and since there are six, is there a preferred mounting point that should be the ones that has the coating removed.
Carl Froehlich
Well Known Member
I re-read the posts on this and conclude we have a classic circular conversation.
To the original post - there is no reason to ground the engine mount. There are many reasons to not use the engine mount in any engine ground scheme. In practical terms however the engine mount will be at firewall ground potential.
Ground the engine where you have the most current draw - at the starter ground lug. Use a #4 wire from the starter ground to the firewall ground (if you use the forest of tabs for this ground you kill two birds with one stone). This also provides a good ground for the alternator. Ground the battery(s) to the cabin side of this firewall ground.
Carl
To the original post - there is no reason to ground the engine mount. There are many reasons to not use the engine mount in any engine ground scheme. In practical terms however the engine mount will be at firewall ground potential.
Ground the engine where you have the most current draw - at the starter ground lug. Use a #4 wire from the starter ground to the firewall ground (if you use the forest of tabs for this ground you kill two birds with one stone). This also provides a good ground for the alternator. Ground the battery(s) to the cabin side of this firewall ground.
Carl
