Fan talk

[Geom]

As we continue to try and assemble all the parts needed for our engine rebuild, one item (surprisingly) continues to elude us.

We've been able to source most of the parts we need -between the local shop and, of course, Luke.

But the radiator fan is a whole other matter.
The current fan is a variable speed, clutch controlled, 7 blade, plastic fan.
Neither the local shop or Luke were able to find an exact replacement for the current fan.
It does not appear to be a "standard" bus fan.

In talking with Luke, his suggestion was just to replace the fan with an entirely different fan.
He suggested just skipping the variable speed fan, and going with a direct drive fan of equivalent diameter as the radiator shroud.

I'm inclined to agree with him (as we discussed the pros and cons).
-While a constant speed fan will likely run the engine cooler than ideal, when cold; the thermostat should still be able to manage the internal temp of the engine and keep the engine from running "too cool".
-Removing the clutch assembly removes yet another component that could fail
-During hot conditions a constant speed fan should (in theory) provide the best airflow -by not having an intermediary piece controlling rotation speed
-Instead of a 9" blades, centered around a 9.5" diameter hub, a direct fan should have longer blades providing more actual fan-blade surface to move air
-The original bus came with a constant speed fan (granted that was on an 8v71)
-(Perhaps not that important but,) I can get a metal blade (vs plastic) fan.

So I wanted to post the same question here to get additional thoughts and see why choosing a variable speed fan would be desirable over a direct drive fan -before I pulled the trigger on a different fan.

Thanks in advance,
George

[luvrbus]

Have they tried Flexxire, fans are a huge draw on HP so choose wisely,which ever fan you choose the manufactures specs for the spacing between the fan and the radiator is important shrouds are just 1/2 of the picture

good luck  

[Geom]

Thanks for the info Clifford.
I was afraid you might say something like that, lol.
Of course the answer can't be easy 

Based on what you've said, and the additional research I've been doing; a constant speed fan sounds like a bad idea. The problem is, no one seems to be able to find this fan or an equivalent diameter fan (which really surprises me ).

I even contacted the previous owner (2 owners ago), and he said he doesn't recall where the fan came from, but was sure he got the engine and fan together as part of a "known working" crate engine from DART (Dallas Area Transit). So at one time this was a "city bus" engine. And since it's left turning (now, previously that was at one point a right turning engine), I have to assume it was a GM city bus ?

Is this a clockwise or counterclockwise rotating fan? I'm assuming CCW, since it's a left turning engine, but I'm not sure.

The search continues, I suppose 

Thanks
George

[Geom]

...
Also, does the number of blades make a difference?
Is there a reason to choose a 7 blade vs an 8 or 9 blade fan?

I found this Horton outfit online. They sell a whole bunch of different fans.
But they don't have any 7 blade fans that are CCW (assuming this is a CCW fan).
But they do have 8 and 9 blade fans that are within the same diameter.

Plus, how close to the shroud should/can the fan blade tips be? As little as possible or within a certain tolerance?

Thanks again,
George

[Utahclaimjumper]

 If you have a decent shroud (close fitted) the distance from the rad is not critical as long as it sits fully into the shroud.>>>Dan

[luvrbus]

The standard seems to be 1/4in inside the shroud from the longest front tip and 1/4 spacing around the shroud,you don't install the fan fully inside a shroud   

[brmax]

I agree as above, the center plate of fan is typically center of blade twist and usually at the shroud edge, so half in my op.
In vehicles that move or twist in work as trucks and dumps I don't think anything is wrong with a fat finger between the shroud and fan.
I was curious what type or method of fan clutch you were looking for, like hydraulic, air engage only, ecm controlled something, or a weight type. I may have missed a post on this one
Floyd

[Geom]

...
I was curious what type or method of fan clutch you were looking for, like hydraulic, air engage only, ecm controlled something, or a weight type. I may have missed a post on this one
Floyd

I guess I don't really know what I'm looking for, except perhaps not ECM.
The current one seems to be some sort of thermally controlled friction clutch, but I'm not certain of that.
It's driven directly off of the crank (no pulley).
There are no part numbers or any identifying tags, etc on the fan or clutch.

I'd be looking for something that was equivalent or better.

I looked into the Flexxaire fans, and whoa those seem to be seriously over-engineered, quite complex (with A LOT of possible failure points), and most importantly mucho-mucho-moola, lol  .
That's probably not in scope. But a decent, variable speed clutch, equivalent to what's in there would probably suffice.

Thanks
George

[Iceni John]

I'm now putting the finishing touches to my complete replacement of my bus's entire cooling system  -  my bus has had an overheating problem for several years, and after almost not making it up CA 138 this year I decided to bite the bullet and just renew everything.   In addition to having a new radiator core made (10% larger surface area and 28% more tubes, this time dimpled), I had Multi-Wing make a new fan to replace the archaic old 6-blade metal fan that looks like it came out of some pre-WW2 Soviet tractor.   The new fan has 9 adjustable-pitch aerofoil blades  -  Multi-Wing said that a 12-blade fan would pull less air than a 9-blade for my 26" diameter size because the blades would be too close together.   Sounds plausible to me.   I had the new fan rotate the opposite direction than the old one to improve airflow out the bottom of the shroud where the radiator's air mixes with the air flowing under the bus, but that's not something you can do with your setup.   (I was having QCC make a new hydraulic fan motor anyway, so it was no big deal to have everything turn the opposite direction.)   I also riveted a 3"-wide strip of 1/16" aluminum onto the inside of the radiator shroud's lip  -  the new fan blades now sit entirely within this duct to better control radial airflow off their tips and lessen turbulence inside the shroud.   I have about 7/16" gap between the blades and the duct, more than I would like but there's nothing I can do about that apart from maybe attaching something like a strip of 1/4"-thick foam onto the inside of the duct to reduce the fan clearance to 3/16"  -  the closer the better.   (See how close aircraft turbine blades are to the engine cowlings?   You can't get a gnat's pube in those gaps.   It's all to do with maximizing airflow and reducing vortices and turbulence.)   Needless to say, all air gaps between the radiator and shroud have been sealed, however tiny they were  -  I need 100% of the air to go through the radiator, not just 90-something percent like before.

I've also installed a Thermal Dynamics remote transmission fluid cooler with electric fan to reduce the heatload into the engine coolant.   Several folk here have done this and report that it lowers the coolant temperature by a few degrees.   I'm not sure that spending $1000 for the cooler and three new transmission fluid hoses is cost-effective for only a few degrees difference, but at this point I'll try almost anything.   The hydraulic fluid cooler has also been relocated so now it's not in front of the radiator  - I don't want anything there that will block airflow and heat the incoming air at all.

I don't know how much of what I've done is practical or even possible for your bus, but maybe it will give you some ideas of what can be done.   I'm close to being able to start the engine for the first time in four months, the time it's taken me to do all this work.   Maybe this weekend I'll hear the sound of a Detroit again in the RV storage yard where I've done all this work.   Keep fingers and other body parts crossed.

John      

[TomC]

When I bought my bus (AMGeneral) the 8V-71 had a belt driven direct drive radiator fan. The mechanic said it was hard to keep the belts tight, and he had a gear drive setup. I switched to the direct drive gear driven fan drive-advantage was the fan turned right handed because of the opposite rotation from the two gears. Hence a fan was easy to find. I have an 8 blade metal fan-don't have to worry about that wearing out (I imagine Cliff has seen otherwise). Good Luck, TomC

[luvrbus]

Metal or plastic fans both work,I just don't like direct drive without a clutch.Believe it or not 2 stroke are just as hard to heat in cold weather as they are to cool in hot weather and both cold and hot running engines can damage it.

I would always change my Tstats to the fully closing type in the winter because older Eagles ran a direct drive fan and they ran to cold in the winter.

Ever notice the trucks with a radiator covered in the winter.I damaged a 8v71 running it 140* for a 1000 miles one time cost me a over haul, never did that again.Go with a fan clutch George keep it around 170* in the winter or they have a short shelf life along with your Allison as they don't like the cold either   

[RJ]

George -

I have a stock GMC metal blade fan for a 4106 in my storage unit that I'd like to get rid of.

In addition, I've got a completely rebuilt Torus unit - the hydraulic fan clutch that drives the fan - in a box ready to be shipped.

If you're interested in either, send me a private message.

FWIW & HTH. . .

[luvrbus]

I spoke with George this morning what he is describing to me ,he has a direct drive from the engine no Torus drive ,then a Brog/Warner Viscous drive clutch (guessing the brand)the fan bolts to the Viscous drive clutch,and I have seen this setup before on the later GM and Grumman/Flex transit buses .

George I chased the Viscous clutch down and found those lol but my price guess was way off the 2 places I found want almost $1400.00 for the clutch alone just check yours if it's not leaking and becomes harder to turn with more temperature then you are good. there are several different of the clutch fwiw any good Truck supply will have it or can match it I found it at PeterBuilt and online