FF-714 alternator support strut sanity check

Hi everyone,
I was just checking over the FWF kit directions yesterday to make sure I did everything. I found this bit: "Make the FF-714 alternator support strut shown on the alternator installation drawing. Adjust the hole spacing to fit your installation. The strut requires a slight joggle. Use a big bench vise and a big hammer..."

So I don't have the Van's alternator nor the alternator drawing, as I have a B&C 40 amp. I would assume this the same thing as the "tensioning arm" referred to elsewhere in the instructions, but it talks about "hole spacing" so I'm not so sure. The tensioning arm I'm thinking of has a big long slot and you put the metric bolt through it into the alternator. This thing:

Alternator

Looks good! Maybe a wide area washer would give you better contact under the tension adjust bolt.

Overtorque

Also be careful not to over-torque. Alternator threads are aluminum.

I believe the joggled bracket the instructions refer to is the one that goes between the forward alternator pivot and the starter motor. I assume that it helps keep both alternator pivot bolts acting in double shear. See picture below from my recent installation.

Jim Sharkey
RV6 Tip Up O360-A1A VFR
Fitting Cowl etc

jsharkey said:

I believe the joggled bracket the instructions refer to is the one that goes between the forward alternator pivot and the starter motor. I assume that it helps keep both alternator pivot bolts acting in double shear. See picture below from my recent installation.

Click to expand...

Yes, that might be it! The tech counselor also mentioned having seen a bracket like this.

Hmm, that pivot bolt is one long bolt on mine -- will probably be too short if I insert another thing in there.

Are other B&C 40 amp users installing this bracket?

Alternator Support Bracket

There are probably various support bracket designs depending on the alternator. For my installation, stock Van's 40 amp on an O360-A1A, a joggle or spacer is required. I had a bracket failure at about 450 hours because I didn't get the bracket in perfect alignment as can be seen. The offset in my case is about 3/8 s of an inch.

[/IMG] [/IMG]

I have the B&C 40-amp alternator as well. I am not flying yet, but I can hardly believe that a joggle bar is necessary. The alternator came with a mounting bracket and the slide-adjustmetn shown i the picture in the previous post. I installed it with the supplied hardware, and it sure seems snug as a bug to me. I gotta believe that joggle bar is for the van's supplied alternator. Somebody stop me if they have good hard info to the contrary.

erich weaver

Break sharp edges

ALL you guys make sure the bracket does not have sharp edges or burrs. By all means get some fine sand paper/de0burr tool and round those sharp edges on the tension arm.

Also when you wrap safety wire around the tension arm, it can wear a grove and make a stress riser and cause a crack.

Well I noticed that many are safety wiring the bolt head.

Is there a better way? I don't use safety wire on that bolt. The problem is that you are threading into the alternator.

I used a threaded bolt that goes thru the alternator threaded lug and protrudes enough to add a nut. The nut with a lock washer and optional cotter pin adds my security.

On the bolt head side/tension arm side, a flat washer and star washer. Don't use a lock washer against the tension arm because it leaves marks which can cause cracks.

With the torque and double nut method (the threads in the alternator and nut) the chance of it coming loose is reduced to an acceptable level.

You can always drill out the threads on the alternator and use two lock nuts. As some one pointed out the aluminum can strip and that is a good reason to use steel nuts.

If you do safety wire the bolt, try to not wrap it around the tension arm. Possibly you can add a tab (riveted on) to attach the safety wire.

Click

gmcjetpilot said:

Also when you wrap safety wire around the tension arm, it can wear a grove and make a stress riser and cause a crack.

Click to expand...

The B&C arm (at least) is steel, do you really think it would crack from a safety wire dent?

Good point, I do think so

Paul Eastham said:

The B&C arm (at least) is steel, do you really think it would crack from a safety wire dent?

Click to expand...

Yea. Vibration will wear a small notch and combo of stress, vibration, possible crack. I have seen so many cracks in steel tension arms you have to take notice:


Steel is stronger, but it does not have great crack growth properties. WHO knows what some of these parts are made of.

My tension arm is steel (what heat treat I don't know), has a joggle bent into it for alignment and it way thicker than a generic 1960's chevy tension arm. It also looks thicker than than B&C from the picture. It's from a Niagara Airparts alternator kit. I noticed the edges where sharp and deburred them. Really that is standard procedure, right, nothing special.

I am not using any safety wire and counting on the lock feature of washers and "jam nut".

Not saying it is right or safety wire grooves are bad or going to cause cracks, just a thought. I do think any notch or "dent" should be avoided as much as loose bolts and nuts, but that is just me.

Really the whole tension arm affair is 1950's car stuff. The geometry, design of the tension arm, lack of positive bolt retention (place to safety wire) make it not "aircraft" quality. Clearly its a weak area, so every little bit helps.

One problem, you can't torque the bolt up in the aluminum alternator housing. Torque (friction) is a VERY good way to keep things put. Go to GE or P&W jet engine factory. They don't put safety wire on anything because it just can't be installed. So they use super strong bolts and torque them heck for stout.

Just different ideas. Good point. Short answer, I don't know but I respect that tension arm and want to baby it. I see more cracks than loose bolts.

I am not anti-safety wire but what about Loctite and tabs. You could bend up a little aluminum tab to cradle around the tension arm with tabs to keep the bolt from turning. You could make a batch and replace them every time you take the alternator off, which should be rare. I just think the way the safety wire looks is kind of marginal. It is a tough place to deal with and respect not having bolts come loose but is it really needed? Can you do something else? Each to his or her own.

A Bit Confusing....

I think that there is a bit of confusion here...the original poster really is asking about that short little bracing link that goes between the starter and the alternator. This really does stiffen up the assembly, and I have seen many alternator bracket failures in my Grumman days when people forgot to install it. I have also seen several installations on RV's where people didn't have it - but these were airplanes that hadn't flown yet. unless you are familiar with how the alternator should be hung on the front of a Lyc, it's understandable that you wouldn't know about it.

The little link is actually easy to make (with a big hammer and a big vice), and yes, you'll have to have a slightly longer bolt, but I wouldn't want to operate very long without it - you run the risk of really wallowing out the holes on the alternator or the alternator mount. I won't say that it happens to everyone, but I've seen it happens enough to make the link a real good idea.

Paul

Doha

Ironflight said:

I think that there is a bit of confusion here...the original poster really is asking about that short little bracing link that goes between the starter and the alternator. Paul

Click to expand...

I think he was asking how does it look overall and what we thought. Doha.

If you are talking about the short link between starter and alternator bracket it is a good idea how ever it was originally made for the case mounted alternators that hung way down. Some people do get away with out it. I agree with you should have have one. Not sure how that affects tension arm cracking but I think it would help reduce stress and stabilize the alternator mount.

You can see the short strap these pictures (standard in the Plane Power alternator kits):

Ironflight said:

I think that there is a bit of confusion here...the original poster really is asking about that short little bracing link that goes between the starter and the alternator.

Click to expand...

Yes I was, thank you for bringing us all back on track.

So now that I know what it is (though I am a little uncertain how necessary it is) -- can anyone provide construction details? What thickness stock, etc. As I said I don't have the Van's alternator drawing so I don't have these details.

I would also note that the B&C alternator install instructions do *not* mention the use of this part.

Thanks -
Paul

No joggle bracket necessary on B&C alternators

I e-mailed Tim Hedding at B&C about the joggle bracket along with the picture posted earlier in this thread that showed it. This was his reply:

"No such support "link" is required on our belt drive alternators. We use high-strength steel brackets, lighter alternators and very close rotor balancing. Therefore our alternators do not need the extra support from the
starter."

erich weaver

erich weaver said:

I e-mailed Tim Hedding at B&C about the joggle bracket along with the picture posted earlier in this thread that showed it. This was his reply:

"No such support "link" is required on our belt drive alternators. We use high-strength steel brackets, lighter alternators and very close rotor balancing. Therefore our alternators do not need the extra support from the
starter."

erich weaver

Click to expand...

Hey, thanks a lot for letting the rest of us know! I was about to email them.

Paul