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Author Topic: Pulley RPM MC8  (Read 2259 times)
rcbeam
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« on: July 02, 2011, 05:25:52 PM »

I made a previous post about loosing prime, and in that mentioned that my newly installed alternator does not work.  Probably should not do two subjects in a single post.  The P/O removed the 50DN and replaced it with a 75amp belt drive, being driven off the street side rear (fly wheel end) pulley.  The old alternator quit working, and I have been fooling with it and bad wiring for months.  I replaced it with a 150amp Prestolite alternator.  Today I finally finished it, got it all hooked back up and started the bus.  No voltage output from the new alternator.  So I've been thinking what in the world could be wrong.  I double checked my wiring.  The only odd thing about this new one is that is has an IGN terminal and needs to have 24v applied to it when the switch is on to excite the alternator.  I had 24v at that terminal.  Then I started thinking about the pulleys and RPM's.  I did not get to run the engine long enough to do any more checks, but I wonder if I speeded up the engine if it would have then put out voltage, which would indicate a RPM problem.  The engine ended up stalling and I suspect that I've lost prime.  So can't work on the alternator issue until I get that fixed.

In the mean time...  Does anyone know the RPM that the small (cam shaft I think) pulley turns on the street side rear (flywheel end) of the engine at idle?
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Russell
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« Reply #1 on: July 02, 2011, 05:33:09 PM »

Russell,

 Camshaft RPMs are the same as engine RPMs, so the pulley should be turning whatever your engine idle is set at, hopefully somewhere around 600-650 rpms.

Bob
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« Reply #2 on: July 02, 2011, 06:02:09 PM »

It should have produced some voltage even if it were low.  Does it have an internal or external regulator.  Hope it is "external" cause you want the alt to be sampling the voltage AT THE BAT PLUS TERMINAL and adjusting the alt output voltage accordingly.  Even the internal regulated models can have their sense line run out of the alternator for that purpose.  I don't know if they make CW and CCW rotating units but intuition tells me they do....been wrong before.

John
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« Reply #3 on: July 02, 2011, 08:13:03 PM »

As I looked into this recently I will throw in my 2 cents.
 Alts don't care which way they turn but the fan on the alt does.  they can have either CW CCW or "neutral/universal" fins on the fan.
 Pulleys and fans can be interchanged on most models to suit your needs.
 I believe if you have fully charged batteries and you are not providing a load, you may get the alt to act  like it is not charging.  turn some lights on etc  to wake it up.  Also rev it up a bit, sometimes alts have something inside that keeps them asleep 'til they hit a certain rpm, then they charge all through the rpms. 
Somewhere there must be the charts for different alts and what the cruising rpm on them should be.  You then do a little math and find the right (close) pulley.
Hopefully you only need to change one pulley, but of course 2 pulleys (drive and alt) may be required.    A good alt/starter rebuilder shop has all this info and the bits...
Have fun.
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luvrbus
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« Reply #4 on: July 02, 2011, 08:50:53 PM »

Camshaft drives only turn one direction on a 2 stroke right or left turning engines only time to worry about direction is a pulley on the crankshaft on a lefty engine that is the only part turning the opposite direction of a right handed engine

good luck
« Last Edit: July 03, 2011, 12:31:17 PM by luvrbus » Logged

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robertglines1
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« Reply #5 on: July 03, 2011, 11:05:52 AM »

I have one running off mine on my 8v92 and it does just fine at  a idle. for house system.   bob
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rcbeam
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« Reply #6 on: July 03, 2011, 01:16:20 PM »

I did some research online on pulley ratios.  Measured the driving pulley and it is 5 inches, with the driven pulley 3 inches.  If the bus idles at 600 (I have no way to determine what it idles at) then this is right at 999 rpm for the alternator.  I went to the prestolite site and looked up the spec on the alternator and the cut-in rpm is 1400, so I guess under 1400 it just rides along.  I played with some numbers and figured that if I can change this rear cam pulley to a 7 inch that would put me right at 1400 rpm @ idle of 600.  Also plugged in the numbers for 2200 rpm, figuring that would be the outside max the engine might ever do and that is still under the max continuous rpm for the alternator so I'm ok there.

Now to see if I can take the pulley off the engine and if there is room for a 7 incher. 

The more I do the more I learn.

Do I understand what I'm doing or is my line of thinking all wet?
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Russell
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« Reply #7 on: July 03, 2011, 03:17:40 PM »

Russel,

You make perfect sense to me.  That may be a problem LOL  I would try for 7 1/2 or 8 cause you will not be doing a sustained 2200.  Hills and at the top of a shift.  Your alt is over engineered, no doubt.  Would an 8 incher over rev the alt at 2200?  What you are setting up with the 7 inch would be marginal at 6oo rpm engine.  If you have dead bats with that spec you would not be able to charge the bats at idle at all or the out-put would be weak.  I would want to be able to sit and charge the bats or at least not drawn them down with the inverter running an AC or the HW heater.

I hope they make those pulleys in any size you can imagine.

Good luck,


John
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« Reply #8 on: July 03, 2011, 05:08:44 PM »

John:  Thx for the reply.  I only figured up to a 7 but might be able to use an 8 and not overspeed the alternator, however I am not sure how much room I have where the cam pulley is located... will have to check for bolts, etc that would determine max pulley size.  Like you i hate the idea of the alternator not being able to put out current at an idle and right now, my high idle is all screwed up.

I googled "pulley ratio" and found several sites... took the first one and it had a neat ratio calculator... just plug in numbers and it tells you want you need to know.  http://www.csgnetwork.com/pulleybeltcalc.html

Russell
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Russell
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« Reply #9 on: July 03, 2011, 05:10:44 PM »

Russell, I don't think you are going to find a 7 inch pulley for that drive DD didn't make a large assortment of the auxiliary drive pulley sizes you may can find a larger pulley that will bolt on to the existing pulley where the 3 bolt holes are for pulling the pulley.
I would be looking for a smaller pulley for the alternator.
A 8v71 uses 5 inch front and rear on the cam drive the 8v92 uses a 6 inch I have a 6 inch blower drive if it that will help you that pulley is not a common pulley just found at any supply house it is a DD item.
Me personally I would be a little afraid of changing to a pulley on the back larger than the front one on the cam they are the same size for balance the best I can figure     

good luck
« Last Edit: July 03, 2011, 05:27:49 PM by luvrbus » Logged

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« Reply #10 on: July 03, 2011, 05:51:08 PM »

You can get yourself a Chinese hand held tachometer at Harborfreight for less than a hundred bucks. Good enough to see what your iddle is. Or to set your iddle or your max no load rpm speed.

JC
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« Reply #11 on: July 03, 2011, 08:18:45 PM »

I hate to think you are stuck....not with the minds we have here.  Clifford seems to have the solution with using a smaller pulley on the driven end.  Not quite the same and the belts wear faster.  Might explore "ganging" the belt(s) with the power steering or AC or compressor or?

You are welcome.  Didn't do much but share your concern for having some charge at idle.  Hope that can be resolved to your satisfaction.

John
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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
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« Reply #12 on: July 07, 2011, 06:18:40 PM »

Clifford:  Never thought about a different size putting things out of balance, but you may have a point.  With the driven pulley being only 3 inch, not sure how much smaller I can find, but that may just be my only option.

Thx everyone for your opinions.  This is what makes this group so great.
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Russell
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robertglines1
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« Reply #13 on: July 07, 2011, 06:32:03 PM »

As you know our diesel don't like long idle periods so charging while doing that shouldn't be a great concern. should it?
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« Reply #14 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.
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« Reply #15 on: 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
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« Reply #16 on: 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
« Last Edit: July 08, 2011, 06:31:20 AM by luvrbus » Logged

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« Reply #17 on: 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

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« Reply #18 on: July 08, 2011, 07:33:59 AM »

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
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« Reply #19 on: 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
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« Reply #20 on: July 08, 2011, 09:56:31 AM »

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

good luck
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« Reply #21 on: 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
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« Reply #22 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
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« Reply #23 on: July 08, 2011, 03:22:06 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
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The price of apathy towards public affairs is to be ruled by evil men." Plato
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« Reply #24 on: 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. 
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Russell
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« Reply #25 on: 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.
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