50DN fell off?

thomasinnv · February 14, 2012, 07:41:33 AM

when you get the rest of the alternator off it would be a good idea to check the cam with a dial indicator. Friend of mine went through this a few years ago in his 4905. Ended up with a bent cam but didn't know it. Went through all the trouble to fix the grenade damage, then had to tear it all out again to replace the cam.

buswarrior · February 14, 2012, 08:13:07 AM

Failure to assemble the alternator correctly last time it was rebuilt?

There is a lot of vibration, proper torque specs, washers, thread locker, etc, I don't have the book.

Who does?

I'm thinking that there may be a whole lot of luck here? Let's hope that the drive is fine, the body of the alternator simply fell off when enough bolts backed off and/or snapped off in the process?

As noted, these big gear drive alternators have to be fed and watered correctly. That includes fresh parts, particularly the drive gear, and installation according to spec.

Both of which are busnut weaknesses, which leads to over reporting of failures in the hobby.

The right money spent on the gear drive, or the right money spent converting to a belt drive would salve the fears.

happy coaching!
buswarrior

Boomer · February 14, 2012, 08:14:32 AM

Well, the Delco 50DN is a nice piece of equipment but like most things requires maintenance and observation to get the best out of it. They were supposed to be good for 250,000 miles but I was never comfortable with that; we rebuilt ours at anywhere from 70K to 100K just to be on the safe side. The overhaul kits were a little over $200.00 in those days, and we could do it in house for a little less that a day's labor. As I mentioned, if installing the first time, the drive gear must be installed using a special alignment tool, which I bought from MCI. Some failures that can happen:

#1 would be bearing failure, especially in the alternator drive adaptor which was commonly used on MCI's. There are two bearings in that one and the adaptor adds another 8" or so to the weight of all that mass jumping around on the back of the engine. MCI installed a support bracket to stabilize the unit but a lot of operators never replaced it when the alt was reinstalled. Dumb.

#2 would be diode failure. This can cause enough parasitic draw to quickly drain your batteries if just one goes out. Insist on genuine Delco-Remy diodes, not third world.

#3 stator failure of some kind.

Insulators on the posts not changed at overhaul, getting hard and leaking oil.

It is also critical to securely anchor the hot cable. I have seen many buses that the cable was just flopping around in the wind. This can lead to the eyelet breaking off, and I have heard of instances where the cable arced on the alternator case and quickly burned a hole in it, pumping oil out of it and either destroying the engine for lack of oil pressure or starting a fire. Guys, secure that cable!

IMHO, there is no reason for motorhomers to continue to run the 50D unless you still have OEM air conditioning, or need to pull power off it to charge the house batteries. A nice little lightweight 70-100 amp alternator will do just fine.

I sure hope you do not find the worst case scenario when you get in there. Never seen the case separate like that.

Lin · February 14, 2012, 09:50:41 AM

Do you really need all the power that a 50DN produces? If things in the engine are okay and, like most of us, you can do with a lot less power. you might want to consider abandoning the 50DN and hanging a belt driven 100 amp alternator somewhere. Mine only has a 45 amp, 24v alternator which works fine. I would like it better if it were twice the power, but can't say I have ever needed it. I know there are several here the have 100+ amp alternators and are quite happy with them.

belfert · February 14, 2012, 10:07:00 AM

I have a belt drive 50DN. Am I still taking a risk by keeping it around? Could I still have gear train damage if the 50DN locked tight, or would the belt just break or burn up?

bevans6 · February 14, 2012, 10:51:26 AM

The belt drive version is fine. It uses exactly the same accessory drive design as the air compressor, just to a pulley mount. The gears that drive the hard-mounted version are what seem to cause most of the problems, along with not using the extra mounting bracket for added support. It's not really the alternator part that causes most of the problems, although it sure seems to have done so this time. As I understand it the gears that break are planetary gears to step up the RPM to drive the alternator at a multiple of engine speed. The belt drive pulley doesn't have that, it's just directly coupled to the cam same as the air compressor is.

The belt drive version just spins in two bearings. It doesn't have brushes, there are no real wear parts except for the oil seals, o-rings, insulators, bearings. The only way it could lock up is if the rotor exploded, which could happen I guess. About the biggest issue it has is it's so darn big.

Brian

brando4905 · February 14, 2012, 11:22:11 AM

Thanks for all the support and advice guys. I just sent it away on the hook. I didn't get the drive off to look real good at it, but what I could see of the gears through a hole inside the drive looked fine. I'll report back when I know something.

All I can say to any of you that have a 50dn is to check every bolt on that thing. I considered myself to be pretty good at the pre-trip inspections and general maintenance of the obvious, but I never thought to tighten the bolts holding the alt. together.

Anybody have any leads on a pulley assy. to replace the alt. drive?

gus · February 14, 2012, 03:44:46 PM

I agree with Len, this is a good time to switch to a belt driven alt of less output, those things put out much too much power for most conversions.

If those 1/4" bolts snapped off there should be some threaded pieces still in the housing or block.

Possibly all the bolts were never installed?

One thing for sure, I'm going to give mine a good check and if I ever have to remove it I'm switching to belt drive.

buswarrior · February 14, 2012, 11:57:12 PM

For balanced reporting, let's be sure we aren't scaring less experienced busnuts.

If your coach was sourced from a reputable fleet, the gear driven alternator was properly rebuilt, was installed correctly, and hasn't been hung on there for a gazillion miles, you simply need to pay attention to the nuts and bolts and evidence of leaks, like every other fastener on the coach.

As an alternative, there are many high powered, air cooled, belt driven alternators available and quite good for busnut use.

One popular place to rig up an alternator on an MCI is using the old air conditioning compressor drive pulleys.

While under way, charging the house bank after a night of boondocking, or running AC via an inverter are both good reasons to have a big alternator.

Those of us with older MCI, and the newer MCI enjoy belt drive alternators already.

happy coaching!
buswarrior

chev49 · February 15, 2012, 03:36:25 AM

I'm glad i have a belt driven alternator. In fact, i wouldn't mind replacing it with a 100 amp chevy alternator if it fails because i only use mine for charging the engine battery bank and headlight stuff. For 20 years i worried about watching the gear driven ones, and i got tired of that. Now all i gotta do is a simple visual check when im doing a preflight...

brando4905 · February 16, 2012, 05:05:38 AM

Well....my mechanic says there is no evidence so far of gear train failure, big relief. Alternator will need to be replaced and I have been researching my options. I really would like to replace the 50dn with something else, but I can not locate a pulley drive to swap out the gear drive. I have found this, http://www.ebay.com/itm/50DN-Gear-Drive-Generator-10459122-Kirks-New-Box-/270670436966, which seems to be a great deal if it is really a new alt. But I hate to put one of these back in when I don't need that much power. Any of you GM guys replaced your 50dn with an smaller unit?

Thanks,
Brandon

bevans6 · February 16, 2012, 05:56:00 AM

GM buses are 12v, are they not? That would make choice of alternator pretty easy. How much current do you need? do you have high current loads like OTR air conditioning (OEM or inverter running a 120 volt AC air conditioner). You can just take the old drive gear stuff off the engine and put on a blanking plate to cover the hole where the 50DN was. What are the other mounting/pulley options on your engine? On mine, the crank pulley is accessible, as is the cam balancer pulley, and there is room there to mount some fairly small alternator. You need to think about pulley sizes and alternator RPM's too.

Brian

brando4905 · February 16, 2012, 06:17:07 AM

I wish it was 12v, she's 24. I hadn't even thought about the other end of the engine, might be doable off the crank pulley/ balancer thingy?

Busted Knuckle · February 16, 2012, 06:27:54 AM

I have bought items from Kirk's over the yrs (several of the from ebay and some direct.
I have been extremely happy with the quality & service.

BK

bevans6 · February 16, 2012, 06:29:12 AM

The front end of the engine is where I would look. There are usually two pulley's there, crank and cam, both of a decent size so you can get a reasonable pulley ratio. If your fan is belt driven maybe you can utilize that somehow. 2:1 pulley ratio is OK, higher would be better, you want to consult the output curve of whatever alternator you are thinking of to see what the speed range it wants is, and also think about clockwise or counter clockwise rotation. 24v alternators are easily available, just not at rock bottom ebay prices for hot rods...

Brian