Ignition CDI Brackets

[SWeidemann]

Can someone share information about what type and thickness of stainless steel I should use to fabricate mounting brackets for re-locating my CDI units on a 912 ULS? I would expect a metal composition that tolerates lots of vibration and heat without fatigue would be best, also what thickness? McMaster Carr carries quite a variety.

Thanks much,

Skot

[Dave S]

Scot,

I can't speak to the specs for the bracket material; however, I would like to offer a related consideration based on some list members experience with single point ground failures where optional brackets are used.

Be sure both ignition module grounds (not talking about the P-leads) run all the way back to the engine block. There have been cases where grounds run to the top of the bracket have resulted in ignition failure where a bracket has cracked - i.e. cases where the two ground wires were too short to go to their original point at the manifold so the bracket was used to continue the ground to the block - a cracked bracket can shut off both ignition modules since the ground is through a single conductor (the bracket).

If you search "ignition failures" you can probably find the situations I am refering to (912 Rotax) .

Sincerely,

Dave

[HighWing]

Skot,
Dave's advice is good. I ran separate ground leads to hard points on the engine. With that said, I would strongly recommend 4130 steel for the brackets rather than the stainless. I did have one stainless bracket fail on my first Model IV, and really can't think of a real good reason for stainless unless it is corrosion prevention, but that can be taken care of with something as easy as a couple of squirts of Rustoleum. 4130 is formulated for its tougness.

For the mounting, I would probably use the 3/4" width X .063" offered by Aircraft Spruce. You can buy a 3 ft length for cheap and probably request cutting to one foot lengths for shipping economy. If you feel you want a little more beef the .071" would be the next size up.

[SWeidemann]

Dave & Lowell,

Good comments both. I do like the idea of 4130 for bracket fabrication. The factory brackets are a little less than .08 inch thick (and in reading the FWF instructions there is no reference to stainless steel). SS got stuck in my brain because some of the brackets on the old engine were stainless. And yes, I intend on making grounding redundant with braided ground straps too.

Thanks, Skot

[HighWing]

In re-reading my post, I think the one inch strap might be my choice. A little more beef with very little added weight.