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Old 12-03-2019, 10:32 AM
TimO TimO is offline
Join Date: Feb 2005
Location: Wisconsin
Posts: 651
Default B&C Alternator on IO-390 Bracket Issue

After just installing B&C BC460-H alternators, I ran into a consistent problem in mounting on the RV-14's IO-390 and I thought I'd mention it here in case any of you used that alternator on your install.

The issue is this: When you order the alternator for Boss mount, you choose if you have a dual groove or single groove pulley, and that determines which U-shaped boss mount bracket you get. The 2 brackets they have, have slightly different fore-aft hole alignments that determine how well the V-Belt centers in the grooves of both pulleys. If you are not in alignment you will for sure wear the belt worse, but also have a much higher chance of belt breakage.

When I ordered my alternators, I ordered the standard Single groove bracket because that's what I have on both my IO-390 and IO-540. My IO-540 is a narrow deck older engine, but my IO-390 is new from Lycoming in 2015.

In fitting the alternator to the engine, the only way you will get a good accurate look at the alignment is if you use some sort of alignment tool. Eye-balling won't get it, because you can move your head around an convince yourself that you're off to the forward side, dead on, or off to the aft side, all by just moving your head a little or switching eyes. Fortunately the alternators ship with a flat but dog-leg bent adjuster arm that makes a decent tool to verify the alignment. You can lift the alternator to its highest position, and run that tool around the large pulley and see where it hits in the alternator pulley.

On my IO-390, it hit about 1/3 of the way up the aft side of the v-groove slope. I tried multiple brackets to verify that they were drilled accurately and it was the same story. B&C gave me the hole measurements for their 2 brackets and based on the measurements I was skeptical that the dual-groove pulley would work also. It moved it twice as far as was needed to make it proper. I then went to do the install on my IO-540 and had the same issue but it was more severe. (which was good, actually)

So I had them send me 2 of the dual-groove pulley brackets. The dual groove bracket moved the hole exactly the right amount for my IO-540, which made that perfect. But, the dual groove bracket indeed moved the alignment too far on the IO-390. So, I was left with the only real solution(s) to be either:

1) Grind the alternator mounting hole on the alternator case and shim the alternator to align. (This would mean I permanently changed my alternators dimensions)

2) Elongate the holes in the Boss mount bracket to allow proper alignment.

I opted for #2 for now, but, it's an imperfect fix because now you have to worry about the bracket sliding forward if something shifts, so you would want to find a way to prevent that movement.

There is an option #3 that I'm going to explore and that's to see if I can get them to produce a 3rd bracket that has intermediate hole spacings, or, if I can have a bracket sourced that has no holes drilled. The down side to this is, if you drill them yourself you'll want them to be perfectly accurate because any mis-drilling will result in a potentially twisted alternator alignment that would also not be good. Also, one of the 2 holes is elongated by default so you'd have to drill and elongate that hole if you wanted it done as all other brackets are made.

I just wanted to mention it here, because I can't be the only one that this will affect, and if you just blindly installed your alternator without verifying the alignment, there's a high likelihood that yours is off too. My original Plane Power 60A alternator was perfectly aligned using the default bracket so the engine itself must be fairly standard, but I'm really not sure if B&C is perhaps fully aware of the various hole spacings that may be found in the field.

I will be doing a full write-up on the project when I get time and there will be pictures at that time.
Tim Olson - CFI
RV-10 N104CD - Flying 2/2006 - 1400+ hours
RV-14 N14YT - Flying 6/2016 - 350+ hours
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Old 12-03-2019, 11:46 AM
MS19087's Avatar
MS19087 MS19087 is offline
Join Date: Nov 2006
Location: West Chester, PA
Posts: 779
Default Thanks for this info

Tim - Thanks for this information. I was planning to use the B&C alternator. Perhaps if enough of us reach out to them they will address this issue. Its always something . . .
RV-9A; Built, Flown & Sold
RV-14A; Building
2022 =VAF= donor
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Old 12-03-2019, 12:18 PM
Ender Ender is offline
Join Date: Dec 2017
Location: Marion, IA
Posts: 80

Sorry dumb question. I assume you are talking the main alternator mount, not a backup on the accessory pad right?
Building RV-14A
Flight Test Engineer
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Old 12-03-2019, 02:44 PM
Bavafa Bavafa is offline
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,670

Thanks for posting this. I am just finishing my first annual and the visual inspection of the belt did not show any abnormal wear. Of course during the installation, I paid attention to see if it lines up but I only did it visually and it appeared to be right on the money. Of course as you said, visually has the good chance of error so I will take a closer look as my cowl is still off.
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - SOLD
N258SM RV14A - IO390EXP119 - in progress
Dues paid
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Old 12-03-2019, 03:38 PM
TimO TimO is offline
Join Date: Feb 2005
Location: Wisconsin
Posts: 651

More info:

Yes, this is the main alternator mount, which on my IO-390 is a Boss mount. My Standby alternator fit fine with the standard oil filter. Beware that depending on your hoses that you buy, it may take a little different routing for the oil cooler hoses. Mine worked, but I did have to work a little to make sure they didn't cover the alternator vent holes on the standby.

I'm just hoping to prevent headaches for any of you who also use that alternator on your build. My guess is that with the misalignment, you would be able to go a decent amount of time with a belt installed, but you would still have more wear. Of course, with V-drive pulleys you would want them aligned very well. I really don't think it's something that is easily eyeballed. The error as far as I can see, is just under .10". Something around .093, but it was almost impossible to measure without another set of hands.

I did share the information with B&C today in hopes that they perhaps come out with another bracket version for their product line that will work with the IO-390 perfectly. They're going to share the info internally.

Here's what I shared with them today, that has some at least halfway decent photos:

If the link is broken some day when you're surfing this thread, just let me know. This was planned as a temporary link, but I'll have a bigger write up that includes most of it later.
Tim Olson - CFI
RV-10 N104CD - Flying 2/2006 - 1400+ hours
RV-14 N14YT - Flying 6/2016 - 350+ hours
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Old 12-04-2019, 06:51 AM
bobnoffs bobnoffs is offline
Join Date: Jul 2012
Location: n. wi
Posts: 881

taking a shot at redrilling your holes in a new piece has no guarantees they are going to come out perfect. if you get a good fit with the bracket with elongated holes maybe part of the hole could be filled in with weld and redrilled for your perfect fit with no chance of slippage.
Bob Noffs
n. wi.
dakota hawk/jab 3300 built and flying. sold 6/18.getting serious about the 12. in the hangar now as of 10/15/19
RV-12 kit as of 9/13
RV-12 airworthiness cert. 11/30/2021
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Old 12-04-2019, 07:51 AM
RViator60 RViator60 is offline
Join Date: Nov 2019
Location: Southport, NC
Posts: 89

Sorry if this sounds like a dumb question....I just ordered my YIO-390 from Lycoming for delivery next Sept. Doesn't it come with the alternator? Is the B&C a replacement for what came standard?
Marty Guinn
Based at KSUT, Southport, NC
- flying 1973 PA28-180 (N55087)
RV14A Build Log
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Old 12-04-2019, 08:09 AM
TimO TimO is offline
Join Date: Feb 2005
Location: Wisconsin
Posts: 651

I agree that re-drilling wouldn't be the way to go. Only if someone had a machining system, perhaps. I thought about filling in the holes with JB Weld. That would be simple enough. Filling them in with actual weld wouldn't be too bad either I guess, I could do that. B&C said that the holes are put in during the step where the part it bent, so it's not possible to obtain one from them that is un-drilled. That's fine by me because I'd either rather get one that was drilled perfectly, or fill those holes as we're talking about.

Regarding the other question: No, your new engine does not come with any alternator on it. It will come with a starter though. The alternator is something that you can either get from Vans or anywhere else. I'm not sure if it's included with the FWF Kit. Someone else maybe should chime in on that. I excluded mine from the kit and ordered it myself, if it is. So then you have 2 popular choices. B&C, or Plane-Power. Plane-Power is sold by ACS or Vans or many other places. B&C is sold by ACS or direct or some other places as well.
Tim Olson - CFI
RV-10 N104CD - Flying 2/2006 - 1400+ hours
RV-14 N14YT - Flying 6/2016 - 350+ hours
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Old 12-04-2019, 08:49 AM
McStevens McStevens is offline
Join Date: Sep 2019
Location: Edmonds, WA
Posts: 143

The holes on the bracket look slotted anyway, so what then is the issue with redrilling?
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Old 12-04-2019, 09:05 AM
mountainride mountainride is offline
Join Date: Jan 2018
Location: Golden, Colorado
Posts: 60
Default alternator failure

My first 60A plane power failed at 12 hours on the 390. It stopped charging and went to battery voltage with the field energized normally. Overnighted a replacement and that worked fine for the next 15 hours. On the last flight I was only getting 13.5 volts on climbout. I returned to landing and once on the ground with boost pump off the voltage went back to 14.5 I pulled the cowling and inspected the alternator/belt tension and it looks fine. Thats above battery voltage but I was assuming the PP would hold 14.5 volts for for its rated amperage. With the boost pump on I am still pulling less than 15 amps on my system. I have a call in to Hartzell again but haven't been able to get a response in 2 days either by phone or email.

I am going to see what I can do about getting rid of this alternator for good and going either the autoparts route or B&C. This alternator has grounded me 2 weeks in a row. I would prefer to go internally regulated to simplify my wiring. I am trying to figure out exactly what alternator will fit in the standard mounts. I also would like to not have to pull my prop to change the belt if I don't have to.

Will the B&C work with the same belt? Is there a list of parts I need to order?

Will the Denso-210-0637 work the plane power alternator belt? I just need to order the boss mount from Vans?

What about the suzuki samurai alternator? Will either of these work as a drop in replacement? What is the output voltage on these? My EarthX put outs 13.1 volts so I would like to have a voltage around 14 if possible.

RV-14 N303XC : Flying
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