I have made a few changes with regards to pulley size etc on both the engine and the miterbox on our MCI 5. This has been a result of rebuilding the miterbox and upgrading the pulley a few years ago but unknowingly at the time with a different size pulley then buying the only one I could get for the engine which I know is smaller than the original but now don't know the original of either. Does anyone have the original size of both or have any suggestions? What would be the optimun fan speed be for this 8V71 rig?
My upper pulley is 9in. and the lower is either 10 3/4 or 11 in. I believe both to be original to my 68 5A. I think i saw something in the book that said that 1700 rpm and higher is optimal fan speed for cooling.
MCI Lee,
I am not sure if the cooling system is the same on your 5 as it is on my 9 but with the 9's the preferred pulley is smaller which boosts the operating rpm's of the blower assembly by about 30%. I have an 8V71 and I completely rebuilt my cooiling system over the winter and I am so happy I went with the smaller pulley. It really is a remarkable difference. If you insist on putting a larger pulley back on , I still have my old one and you can have it although I think you may need a different length belt to run it. If your cooling system is basically the same as mine I would stick with the smaller pulley. If you ever decide to do a repower to a turbo model you will be wanting a smaller pulley as well.
Is the reason for your post that your bus is not cooling properly? If so, I would look at other possible explanations rather than the pulley.
Good luck.
Rick
My crank pulley is 9.25" OD and my blower pulley is 8.25" OD. 1980 MC-5C 8V-71. I find talking about the "smaller" or "larger" pulley hard to follow, without numbers the references mean nothing to me. I'm presuming the sizes on my engine are stock, but I have no way to tell.
Brian
Brian,
That is good advice. I will measure my old pulley and the new smaller pulley when I get home from work.
The parts places I shop at always refer to them as Large (OEM stock) or the smaller more desirable MC12 or 102A3 pulley that MCI went with exclusively when they started putting wet sleeve Turbo'd 6 and 8 cylinder 92 series heat sensitive engines in their coaches.
Rick
Rick, thanks. also, which pulley are you referring to, the crank pulley or the blower pulley? I would expect the sizes matter less than the ratios, as long as the sizes are reasonable for the belts.
Brian
Brian,
I am referring to the blower gearbox pulley. I have never been led to believe that the crank pulley comes in different sizes. Whenever I have spoken to anyone about the different options of the blower gearbox pulley or mitrebox pulley they have always been referring to the pulley attached to the blower gearbox.
I am not saying that the crank pulley doesn't come in different sizes, I just have never heard of it.
Rick
Well here goes,
keep in mind these are all on my 9 which may not be the same as your 5.
The part # on my old part is 6F-6-2. Both pulley are the same size (around 8 3/8") but the new style pulley has considerably deeper grooves.
The new pulley does not have a part #
hope it helps.
Rick
The only pulley I have heard any of the gurus talk of changing is the top one on the fans.
Smaller makes the fans spin faster, same as the gears on a bicycle.
I think it safe to assume there are no practical choices in changing the crankshaft pulley, or in the least, it would have been talked about as to how it wasn't feasible?
happy coaching!
buswarrior
I measured the pulleys I have on now tonight and they are engine = 9.25 and top pulley = 8.25. A quick spreadsheet puts the blower speed at 2242 at 2000 RPM engine speed. I am thinking that when I did the miterbox rebuild the replacement pulley was 3/4 inch larger than what was on it and that I started having some heating inconveniences. I then thought the engine pulley was worn and traction was a problem so I bought a new pulley from Luke and he said the size I had wasn't available. The only one was a 9.25 inch one. We got it and put it on. I think now that we had a 10.75 on the engine and a 7.5 ish on the top. Quick calc puts the blower speed @ 2865 RPM. That would be a 22% drop in fan speed. Is that enough to affect engine heating to the point I am at now? OK, to answer more questions: We also this past spring had new radiators built by Motor Missions in Las Vegas. I highly recommend them for quality work and quality products. I am confident the heat is not caused by the rads.
MCILee
http://users.cwnet.com/thall/fredhobe6.htm (http://users.cwnet.com/thall/fredhobe6.htm)
Lee,
The stock crankshaft or bottom pulley O.D. is 9 and 3/8" on my 1981 MCI which came equipped with the 8V71 and an Alliosn 754. The dimensions may or may not be the same as your 5 but I'm sure someone else here (where's Dallas when you need him...) would know better than I on that. Fred Hobe knows alot about our cooling systems he may be a good person to contact.
With that said,
Do you still have the original crank pulley?? If not, you might want to get the bottom pulley back to OEM before you start trying to figure this stuff out. When you change both pulleys at the same time you are losing your ability to have a baseline that is anywhere near where the designers had it. If you were to severely overspin the blower gearbox and the squirrel fans you might have some fairly serious unintended consequences. If I were you, I would try and get your bottom pulley back to stock. Then, if you still have the 8 1/4 pulley I would look to see if the belt rides even with the outside edge of the pulley or if the grooves are deep enough to let the belt ride roughly a 1/4 inch below the edge (that would mean you have the "smaller" more desirable pulley on top) but either way you are close enough to the stock setup that it should only overheat at that point under heavy load on a very hot day.
With newly rebuilt radiators and the 8 1/4 pulley on top and the OEM pulley on the bottom if you are still overheating and if are using an infrared gun and your gauges to verify temps, I would be looking at thermostats, water pump, air tensioner for the belt itself, wrong belt size and I would IR the exhaust manifold on each cylinder to make sure I don't have anything major wrong like one cylinder running alot hotter than the others..
You haven't decsribed the symptoms well enough for most here to be of help.
Is it overheating all the time or just on long pulls. What kind of temps are we talking here? 200 plus degrees?
What is the ambient temp outside when it overheats?
Are you towing a vehicle?
Are you running an automatic transmission ? If so, have you IR'd the transmission and its side engine mounted cooler during an overheating episode? Allison transmission's are fairly notorious for overheating the motor when they have issues because they share the same cooling sustem.
The thermostats and water pump are a quick diagnosis with an IR gun. The temp of the coolant returning to the motor should be considerably cooler when it re-enters the motor.
Lastly, have you checked the seals around the upper door to your fan assembly? That seal has to be as airtight as possible and all the seals around your radiators need to be airtight as well so you have virtually all the air that is entering the fan area running through your radiators.
There are also seals on both ends of the squirrel fan shrouds. Big rubber O-rings. Are they making a good seal with the shroud or are they brittle/ chewed up and allowing air to enter the fan around the seals?
I feel for you, there is nothing like white knuckling gauge watching to ruin a good bus ride...
Hope it helps.
Rick
I would do like Rick and check the bottom pulley there are tons of different size crank pulleys for the Detroit .
The standard being 9and 3/8 inches.
The reason people change the top is for price ever buy a 8.5 crank pulley from DD
good luck
The crank pulley is actually also a harmonic balancer, isn't it, he said, digging for his manual...
Bevans, no they are not the V71 does not use a harmonic balancer neither does the 6v92 and some 8v92 engines
good luck
looked it up in my DD manual, apparently while the 12V engines had a viscous damper pulley ($$$) the others had either a solid pulley or a rubber damped vibration damper pulley, which I see on mine, come to notice it. I've had the rubber dampers fail on race engines, from time to time. they aren't cheap either... So there is a possible difference to look out for.
Brian
The pulley and the harmonic balancers are 2 separate items some v12/71 just have a cap on the end of the crankshaft it all depends on the hp and application some have cam shaft balancers some don't. The 8v92 and the in line 671 use the viscous balancer also around 600 bucks from Detroit.
good luck
Just to keep it straight, if changing the pulley on the engine crank, the goal would be a larger pulley on that end to speed up the cooling fans.
Smaller on the fans, bigger on the crank, or some combination of that is the goal for hiking the air flow.
happy coaching!
buswarrior
I am confident the original was larger than the 9 3/8 we now have because it was a bit of a concern when I couldn't get the same size. It also was tough to get the belt between the pulley and the bumper stuff to change the belt. If these things happened fast it would be easier to remember but as most of you know these projects can stretch out for a few months and we have many other numbers running thru our heads!!! If the day is cool, say less than mid to low 80's it is usually not a problem. On one of the last outings I put new weather stripping in on the top door and made sure the gaps were sealed around the radiator. What are we towing? Last weekend was a 2004 F-150 with a jet ski trailer behind it weighing in @ probably 2000 lbs, ambient temp was about 90 degrees. On the way home at 75-80 degrees and not even a hint of over heat. Relatively flat ground with only slight but long 1-2 miles uphills and down. I am about to the point that I will take some temp readings next time out and if they prove to be correct with what I have read on the board here I will machine out a pulley that will fit in the space allowed and get a new belt and see what happens. At least get back to the fan speed I think I had way back when before I started improving things. LOL
Lee
Lee,
Think about giving ABC in Faribault MN a call to see if they can ship you out a new crank pulley. An earlier post from someone with an MCI 5 said they had the same one as I am running so it must be a good ground zero to start from.
If you kept the 7 and 1/2 pulley maybe try putting that back on and i'll bet you'll be just fine tempwise.
I know C&J coach have the smaller gearbox pulley in stock althought it will be considerably more than a used one.
Good luck and keep us informed as to how things work out.
Just to show you there is hope, I drove 350 miles a couple weekends back and I didn't look at the temp gauge more 2-3 times on the whole trip. That is a new concept to me.
Have a great day,
Rick
From the parts book; Pulley- Crankshaft (Std. Rear Axle) 8C-4-2. Pulley- Crankshaft (3.7 Rear Axle) 8C-4-3. Pulley- Blower Drive Prior to Coach Unit No. 5578, 6C-6-4. Pulley- Blower Drive Effective With Coach Unit No. 5578, 6C-6-79. Std. Rear Axle is 3.36:1 ratio, Optional is 3.7:1 ratio.
Forgot to add; V-Belt - Blower Drive for Std. Axle Ratio, 111" # 8B-27-2. For 3.7 Axle Ratio, 110" #8C-27-5