B&C vacuum pad alternator interference

I have a Barrett-built IO-540X(C4B5) which is a thing of beauty and I'm starting to do the back-end installations prior to hanging it. I'm intending to use a B&C backup alternator on the vacuum drive pad. I thought I was going to have trouble with interference with the oil system but, fortunately, swapping the spin-on adapter for an Airwolf remote system gave me barely enough clearance. *Heave sigh of relief*

Then I went to install the tach sender. It's one that is offset slightly but, even so, it will not fit with the backup alternator in place. One alternative is to cap the drive and use the tach feed from the Lightspeed ignitions, which is an option I'll explore with Aerotronics. But I prefer the independent sensor. So, before I give up, I thought I'd ask if anyone had run into this and what their solution was. Is there a close-quarters sender I'm unaware of? Thanks for any help offered.

You may be able to get a spacer from B&C for the alternator that will allow the tach sensor to fit. I have also seen some tach sensors that were mounted on the firewall with a tach cable connecting them to the tach pickup on the engine.

Short extension

I was not excited about the cable to the firewall so I made a short tube to move the signal generator enough to clear the B&C dynamo. Simple lathe job for the tube. But, you will need to modify a flex cable to correct length. I modified something from the "storage shelves" at the FBO.

Or - just don't install a Tach sender at all. Most engine monitors do just fine with a Mag or EI signal for engine RPM.

Carl

Carl Froehlich said:

Or - just don't install a Tach sender at all. Most engine monitors do just fine with a Mag or EI signal for engine RPM.

Carl

Click to expand...

That is what I did.

Aerotronics tells me that the G900X can only support one tach input, so if I take it from one of the LSE boxes, I'll lose tach when that box goes down. For instance, when doing a mag check. So that reinforces my preference for the mechanical tach. I think, so far, the cable to a sender on the firewall is the most likely.

Another possibility is to attach the backup alternator to the hydraulic pump pad - but I don't know if that is possible or recommended. The stud locations look the same but is the spline gear the same? With my luck, it would just create another interference anyway.