converting 6-71 direct drive Generator to belt driven Alternator, question etc.

[zubzub]

Hi I bought a nice Aux pulley drive:


 for the back of my 6-71 so that I could get rid of the huge useless generator back there:
 No pic of pre removal...but if you have one you know what it looks like.

The new P drive came with its own internal gear that is supposed to bolt to the cam gear:



The old Gen was driven by this internal gear, here it is in the engine:


Here it is out:



With the spacer:



This is what the cam gear looks like without an internal gear drive bolted to it:



The old gear drive won't fit the new P drive and the bolt holes on the Cam gear are larger than the bolt holes on the new gear drive.
The P drive housing bolts up OK and the spacing from driven gear to the cam gear face is OK:

but I will need to bore out the holes on this:

by 1/16 (old bolts 27/64, new drive gear 23/64.

This gear will not be pushing much....tops a 160 amp so I wouldn't mind some reassurance that it will have no trouble even though the wall of the gear will be 1/32 thinner.  Now that I write it down sounds minor....
Buddy who sold it to me said it would bolt right up, but my bus guy says it is from a 6V71, personally I have no idea but I think I can get it to work.
Can't return it as it was a liquidation sale....

My next concern is the size of the pulley....diameter is 5 5/16", (bottom of the belt V)....is this going to drive the usual truck alts fast enough?....IE is there a particular speed I should look to drive my new Alt at and will the aux drive pulley size allow that?  I know I should be able to change the Alt pulley, but presumably if I go too small I might get slippage.  As alway info links etc appreciated.

[bevans6]

It all looks good and real familiar.  the thin plate you called a spacer is actually the locking plate for the cam nut so it should go back on under the drive plate.  the pulley on my MC-5 is roughly 7" in diameter at the OD of the flange.  Remember the bigger the drive pulley and the smaller the driven pulley, the faster you go.  My driven pulley on the alt is roughly 3" in diameter, not having measured it lately.  You want to be running your alt in a good speed range for it's output curve.

my pulley has and needs four belts to drive the DN50 at it's rated 270 amps at 28 volts.  It's a power transfer thing, so you can take that and estimate how much power you can run per belt on a pulley - call it 1800 watts per belt.  You should be able to run a 160 amp 12 vdc nominal alt with one belt, based on that idea.

Good luck, it's looking good.  I just installed my pulley drive on my engine today, as a matter of fact, along with installing the rear crank seal, and fussing for a few hours with the front crank seal.  Came up with a small mismatch of parts that leave me with some new left-overs and some fettling and reusing of old parts, but that's life in the bus lane!

Brian

[luvrbus]

Pat, I don't think I would have used that drive for a 200 amp alternator DD has one a group 1700 something lol that bolts to the cam without the gears I have this thing about gears in the rear as you know but we use what we have 

good luck

[zubzub]

Oh yeah I forgot about that one..  Saw a diagram of it, seemed the simplest toughest design....never did find one for sale though.

[bevans6]

That is, except for the pulley, identical to the stock MCI setup I have to drive the 50DN.  The drive plate that bolts to the cam gear is identical to the drive plate for the compressor.  I sure hope it's strong enough.  Hard to get away from gears on the back of a Detroit...


Brian

[luvrbus]

Brian,they also used a aux drive with the slotted yokes and the fiber center you never  knew about MCI they did some strange stuff back there lol,I made the comment because of Pat's 6-71 inline.
FWIW Brian you will also see MCI's with a gear driven Eaton power steering pump instead of the Vickers pump yoke type

good luck

[bevans6]

Like you say, you never know!  My MCI has the Vickers style ear-drive power steering pump with the fiber disc to couple the drive to the pump.  I am going out to install it right now, actually.  One little thing at a time, in my spare time, keeps me sane sometimes...

Brian

[TedsBUSted]

Zubzub - Some random thoughts.
You might consider moving the compressor to the previous generator location, that would get your new alternator mounting location towards the rear bumper and away from the busy shift linkage area.

May be tough to find now, but some compressors used to have a thru-drive, with an accessory-drive  pulley located on the back of the compressor. I'm not sure of the capacity to drive a jumbo alternator and the compressor together but it would move your alternator out over the transmission.

Ted