The International Cessna^® 170 Association

As I am putting my 53 together, I noticed that there appears to be no ground strap from the engine mount to the airframe. Since the mount is isolated from the firewall by rubber, is not a strap necessaary? Thanks for the comments!

George

From what is shown in the parts book, there is a battery box ground strap, 90412007-1, (bonds to airframe), and engine mount bonding strap, 0550100-7,( the latter being attached to the engine and engine mount). From that it appears that all the grounding is done to the airframe its self rather than relying on the engine mount for a ground. That being said, I always have a ground strap from my engine mount to the airframe. Hopefully I haven't missed a ground strap in the drawings. Jon

Both the battery and the engine should be grounded directly to the firewall with proper cables.

gahorn wrote:Both the battery and the engine should be grounded directly to the firewall with proper cables.

And the best place to ground the engine is under one of the nuts that hold the starter to the accessory case, right? And the other end of that ground strap should either go directly to the battery negative terminal, or to the same point that the battery negative terminal is grounded to the firewall, so that the starter's current load is conducted as directly as possible through cables big enough to carry that current easily.

John

Jon,

From what I have been able to determine, you are correct. I too noticed the strap from battery to firewall and strap from engine to mount.

Circuit as I understand it. Power to engine, engine through strap to mount, mount to firewall?, firewall to batery neg through strap. Unless I am missing something, there should be another strap to complete the circuit as the mount to firewall junction would be a poor conductor. I can make a strap but would like to find the correct part number first if I could.

Thanks

George

The arrangement pictured below has worked for me since 1982 and 1500+ hours of flying. Your mileage may vary. Put one at each engine-to-mount bolt, and one from each mount-to-firewall bolt. .020 to .025 aluminum, as best as I remember, maybe .032.

Miles

Miles has the "proper" grounding setup. Altho he might have trouble with that nice paint job getting good grounding A ground strap (like the one on the neg. side of the battery) from the back case to the fire wall is the best but not in the IPC so in theory shouldn't be there.
brad

As I said, no problems in almost 25 years... no paint in the mount hole.

Miles

PS: Before anyone notices and points it out, in the picture of mount on the engine the bolt looks loose; it is. The engine is still on the build-up stand. I was installing the mount to the engine and the bolts hadn't yet been torqued.

Thanks all for the help! I made up a strap to go from the lower right mount bolt direct to the firewall location that my battery ground strap is fastened to. 5 people, 5 different solutions!

George

[quote="cessna170bdriver"]As I said, no problems in almost 25 years... no paint in the mount hole.

Miles

Just kidding Miles, I know if anyone has every thing thought out, it would be you!
brad