Pulley RPM MC8

bevans6 · July 08, 2011, 04:53:40 AM

Speaking of the stock alternator pulley diameters on the MC-5 engine, the drive pulley is 7" diameter and the driven pulley is 3.5" diameter. This is the stock cam position accessory drive and the pulleys are for four 1/2" belts. The 7" is as big as you can get without having to clearance the bellhousing, there is just enough clearance to install the belts. This is for the 50DN, which charges just fine at idle.

Brian

luvrbus · July 08, 2011, 06:24:56 AM

Brian, where are measuring the pulley at I went through all my group numbers and cannot find a 7 inch drive for a 8v71 they list 3 sizes for for the standard cam drive on the right bank and each one has a different drive coupling one drive takes a different cam and cam gear and 1 size for blower drive

good luck

bevans6 · July 08, 2011, 07:09:13 AM

I am just measuring the OD of the pulley, so not where the belt rides or anything tricky like that. They are MCI parts, I believe. The part number for the engine pulley is 7F-3-50 and the part number for the alternator pulley assembly is 7F-3-53, which includes the unobtainable splined inner hub. They are grooved for four belts. The engine pulley fits on the shaft of the accessory drive, which I think is a standard Detroit part, and has a special tapered sleeve/bushing that fits over the shaft and locks onto the key in the shaft.

Brian

JohnEd · July 08, 2011, 07:33:59 AM

Quote from: Chopper Scott on July 07, 2011, 08:52:08 PM
You have to run the engine enough rpm to turn the alternator fast enough to exicte it to make it charge. If the alternator is a one wire type it won't charge until it gets turning fast enough. If you start it and never get above idle it's not going to. Rev it up and then let it idle. I have a 24 volt and a 12 volt alternator on my rig and they both act the same. They just need some rpm's to excite them and then they work great.

In my 54 years of dinking with car and light truck stuff I have never heard anything like that. Old generators needing to be phased are excluded from that statement. Not for a moment arguing with you, Scott. Rather, making the point that this a point of education and also my having led a sheltered life in many ways, I guess. Thanks for that information.

John

JackConrad · July 08, 2011, 09:50:16 AM

We installed a "one wire" 24 volt air cooled alternator on our MC-8 (8V71) running of a accessory pulley that was installed where the OEM gear drive alternator had been. We noticed it would not charge until we revved the engine up a little. Once that was done it would continue charging, even at idle. The alternator also had an additional terminal that could be connected to the ignition switch (powered only when the ignition switch was on). When we connected that wire, the alternator would start charging immediately, even at idle.
I was told by a person at the alternator rebuilding shop that the alternator has to spin at a certain RPM (I forget that number) in order to self excite or it can be excited by connecting the other wire to the ignition. Jack

luvrbus · July 08, 2011, 09:56:31 AM

He has the standard pulley that worked with the 50D so it should work

good luck

zubzub · July 08, 2011, 01:56:12 PM

know for a fact that on by VW Van bosch alts untill I kick it up the alt is not charging (round 1,200) had 2 alts in the van both behaved the same way. Actually managed to kill the bat and stall the engine one fine winter morning when I started the van, turned all the fans on full, then went back in to have breakfast while the van warmed up......was warm but dead (fresh kill?) when I went back out

bigjohnkub · July 08, 2011, 02:05:45 PM

John Ed. , Self exciting(one wire) altenators are very common on farm tractors. Have to rev up engine then will charge at idle. Hope this will help.

Big John

JohnEd · July 08, 2011, 03:22:06 PM

Quote from: bigjohnkub on July 08, 2011, 02:05:45 PM
John Ed. , Self exciting(one wire) altenators are very common on farm tractors. Have to rev up engine then will charge at idle. Hope this will help.

Big John

Hey Bro. How are you? Good to hear from you.

I ain't arguing for an instant. Lots of stuff I have never heard of and lots more I am starting to notice I have forgotten LOL

Be well, thanks for the info,

John

rcbeam · July 08, 2011, 05:41:20 PM

According to the specs on the alternator, it's cut-in speed is 1400 rpm. With the pulleys I have not, I would have to bump the idle up to 850 or 875 to have the alternator charge. If my high idle worked right that would be fine for while parked and at startup, etc. I guess with 2 new 8D batteries, and no coach heat/air, I might not have to worry too much about not charging at idle speeds.

Chopper Scott · July 08, 2011, 05:54:53 PM

Without all the coach electrical stuff you'll be fine as you already stated. Just try and rev it up until it starts charging and then let it return to normal idle. It still should keep charging. It just needs that higher rpm to get it going.