Modified Chainsaw Method for Blower Fan Replacement

Don Foster got me thinking some years ago, or thereabouts, if there wasn’t a way to remove and replace or maintain the blower fans in the 240s and still leave something a little tidier in terms of a cover.

I do blower fans using a Dremel tool with a drywall bit.  These are the spiral or scroll style bits that are used in the famous Roto Zip tools.  I know this in itself is not a novelty as others have posted similar ideas, but herein lie a few twists.

Start disassembly by removing the console side covers as usual.  While removing front seats is great, you won’t be spending nearly as much time under the dash with this method so you may want to forego that.  Likewise you won’t need to unbolt half the dash support system, above-knee cross braces etc.  In fact, short of moving wires and taking off the covers, you won’t have to move much at all.  Under dash felts have to come off.  I usually put a big garbage bag on the floor too.  It catches the cutting waste.

To begin getting access to the interior of the heater housing, locate the center of the scroll housing on each side.  Keep in mind that the little injection pin, stud, nipple, whatever you want to call it, is not the center.  Once you have found the approximate center, use a compass to scratch or draw a 6” circle on the housing.  Adjust your center point to leave room on flat surfaces around the perimeter of the circle.  Hook up your Dremel and cut out the circle.  Be careful not to push the bit too far in and hit the fan blade.  You will find that the highest speed is NOT what you want on the tool.  If you build up too much heat the plastic melts instead of cutting.  Likewise not the slowest speed.  Try and keep the stepped cutting edge of the bit against the outside of the housing.  It’s a “feel” thing, I can’t explain it other than to say if you don’t push too hard, you can rest the spiral edge against the plastic.  Move as quickly as you can without forcing the blade too hard against the plastic and get the plug out right away.

The reason for starting with 6” diameter is to leave yourself some room.  Once the plug is out you may want to re-cut the hole slightly larger, but you may find you can use that extra half inch or so to re-center your hole so that the fan blade is easier to extract.

What makes the standard method of replacing the blower motor so difficult is that getting the outer scroll housings out past all the dash hardware is difficult.  But wait, there’s more:  The inner housing half is even tougher!  The beauty of this and Don’s method is that the housings stay completely in place.

Once you have a good sized access hole in the outer scroll housing, you can easily get to the clips that hold the fan impellers in place.Don’t lose them.  Don’t be surprised if the impellers don’t come off the shaft easily.  If the shaft has any corrosion on it, the impellers will stick.  Try some liquid wrench or other penetrating oil. 

On the left side, the motor will not fit through the hole in the inside half of the scroll housing.  Dremel to the rescue again.  You can remove just a few areas to clear the ears of the old motor, or you can make a nice consistent “all around” cut and remove the entire venturi through which the air passes on its way from the heater core to the impeller.  The venturi is the smooth, radiused inner edge of the scroll housing's inner half.

This is the only section of the original chainsaw method documentation that I take issue with.  It is said that removing the center of the inner scroll housing will be done at the sacrifice of some air flow.  In my experience, even if you remove the absolute minimum material to allow the motor to be removed, the air flow suffers quite a bit.  This is no doubt due to the combination of the lowered air velocity created by the larger hole and, to a greater extent, to the loss of the nice, smooth shape of the inner scroll housing.  You will notice a significant reduction in air from the left side vents in the dash.  What’s more, if you leave a bunch of ragged edges and loose bits hanging around, the fan will be noisier AND you’ll have less air flow.  Try and leave as clean an edge as possible by going back over it with a little drum sander in your Dremel.

If you have a problem with the decreased air flow, there is a way to repair the venturi, and I’ll get to that later.

Next, if the car is fitted with the old, original motor (most likely—or you wouldn’t be doing this), you’ll find that the new model won’t fit inside the old motor mount that is all the way inside the interior of the housing.  You need to get in there with the Dremel and a grinder bit, or a die grinder, and open it up enough to take the newer motor.  Early cars have raised areas on the mount that accept the feet of the old motor.  These have to be removed too.  I highly recommend you check out Art Benstein’s site, cleanflametrap.com for some great pictures (I hope Art doesn’t mind me mentioning his site).

I will not go into the actual motor replacement here--wiring and such.  It’s well documented on 100 other posts and sites.  One thing I will say:  If you are not replacing your fan blade retainers with new ones, make sure you tweak the old ones so that they slip tightly into place.  Even with your new, removable covers (to be described shortly) it’s a pain going back inside because your impellers are slipping due to loose retainers.  If the clips are very loose, they can fall off.  Hopefully they’ll just drop into the floor ducts.  If not, heaven knows where they’ll end up.  I often turn them over and re-use them that way—much springier.

In other chain saw posts, the housing is patched back together using the removed piece of plastic and/or tape and/or other materials. The problem is that you removed 1/8” of plastic with your bit and you have to replace that with something.  Instead, run over to your local 99 Cents Only store (or the like) and find yourself some black, plastic, TV trays.  Any plastic about 1/8” thick will work, but for 2 x 99 cents, I’m for the TV trays.  In the accompanying photos, I used red ones. Trace a circle on the plastic that is 1” in diameter wider than the final size of the hole you cut in the scroll housing.  STOP!  Don’t cut yet.  First take a quarter and trace three ears on the perimeter of your circle.   Use ½ of the diameter of the quarter.  Where to put the ears?  Take a look at the hole you cut in the scroll housings.  Position your ears where there are flat spots.  These ears are what you are going to use to screw the new cover to the scroll housing (see pictures below).  Now trim out your new cover including the three ears.  Drill a hole in the center of each ear with a 3/16” bit.  Clean all the waste off the opening in your scroll housing and place the new cover over the hole.  Hold it in place and rotate until your three ears find flat areas to screw to.  If you have not cut out too much of your scroll housing, there will be plenty of room to mount the new cover.  Use something sharp to mark your three mounting holes.  Drill the scroll housing at those three points with a small drill bit.  3/32 is about right for #10 screws.

I use GE clear silicone household glue for tons of things and sealing the new covers is one of them.  Put a bead all the way around your new cover or on the housing.  You don’t need a huge amount.  I also circle the mounting holes on the three ears.  Put the cover in place and secure it with three, #10 sheet metal screws.  Of course the size of the screw is up to you, but make sure the screws do not bind in the holes on the cover,and do bind in the scroll housing.  If your holes are all aligned properly the new cover will sit plenty flat on the housing while the glue dries.  Don’t use much more than a ½” long screw, especially if your hole happens to be partially over the edge of the fan blade!  I use 3/8” long screws, #10s.  Don’t use flathead screws (countersink underside) or you’ll crack your new cover.

Going back to the air flow issue, there is a way to remove the motor through a butchered left side inner scroll housing and still get your air flow back up to where it should be—or nearly so.  Before you move ahead with this, do whatever is possible to vacuum out as much of the plastic garbage from inside the matrix housing as possible.  Vacuum the matrix itself, there will be pieces in it and they block the air flow.  Be ready to be disappointed though.  No matter how much you vacuum, you will have plastic bits in your teeth for the first week or so after the job is done.  It seems unavoidable.  If you have a light colored interior, and this is your mate’s car (gender non-specific) be ready to be bitched at (even males can bitch).  You may even want to wear safety glasses the first time you turn the fan on after finishing!

Now, about repairing the venturi:

Start by locating a plastic funnel with a top diameter that is similar to the diameter of the entry to the old venturi.Just measure the inside scroll housing.  We are going to use a piece of the funnel to recreate the venturi.  Keep in mind we won’t have that nice sweeping curve, but at least the opening into the heater matrix area will be back to the original size.I think you wind up with about 80% of the original flow or better.How important is this?  In my opinion, with the old venturi destroyed, the air flow out the left vents is less than half what it normally is.  Just a thumbnail estimate.  To figure out how much funnel you need, measure the old venturi that you cut out.  Trim off a piece of funnel that leaves you a “small end” the same size as the old venturi center opening.  Clean up the edges and make sure it is “square”.  If necessary, trim the top edge of your new part so that it fits nicely into what’s left of the old venturi allowing a smooth transition.  Finally, to create a somewhat smoother “small end”, I put a piece of plastic door edge molding on the small end's edge.  This provides at least somewhat better flow over the edge than just the sharp plastic would.  I think.  It seems like a good idea, but I’m not an aerodynamicist.  I always glue the edge molding to the funnel with super glue for good measure.

Position the new venturi in the inner scroll housing.  Make a few test runs and trim the big end as necessary.  You want it to fit right down in there.  Once you are satisfied, glue it in place.  You could even screw it in place to be certain it will never fall out.  Of course never is a long time.  Since 240s last, what, 8 gazillion miles, you may have to do this again in 2064 or so.

That’s the lot of it!  

The first time I changed a blower motor was in 1992 on our beloved 242GT.  I simply could not believe how much trouble it was.  In the last three years I’ve done no less than five of these beasts.  Not all of them required changing the motor.  The first one was a Bertone coupe and I did it the old way.  Hated every minute of it, it took me over 6 hours, and I remembered the 242GT vividly.  I swore I’d never do one like that again.  Next one was this new method and I was done in less than four hours.

Not all motor noises need a new motor! On my 91 245, for example, I cut out the right side (which is easier) and found that the bearings on that side of the motor were the cause of my very minor noise.  I lubed the bearing and the motor has been virtually silent since, almost a three years now.  I would highly recommend using a stethoscope or other tool to listen to each side of the housing and see if you can pinpoint the noise first.  If the noise is minor, or very occasional, just lube.  If there is louder or constant racket you may have to change the motor.  The best part is that once you’ve done both sides, you can maintain the motor with a minimum of fuss.

Right side with the lower dash felt, glovebox and side cover removed.  It's a good idea to bundle all the wiring harnesses up and out of the way.  Black tarp is a large garbage bag to catch the detritus. 

The left side is more difficult just because there is so much more "stuff" in the way.  Harness tied out of the way.

The OEM motors are grounded via the large, black wire to the floor via the bolt that holds the sheet metal support shown here.  The new motor's harness exits the top of the heater housing.  If, as I do, you choose to relocate the ground wire somewhere more convenient, don't forget to replace this bolt---it goes through the floor.

A good size to start with for the housing cutouts.

The passenger side is easier to work on.  Draw your circle with whatever works for you and is easy to see.  I use a pencil insert on my compass.  You may find, at this point, that the side of your motor that is squeaking is the right side.  If so, you may be able to postpone the more serious surgery by lubricating your motor through the new access hole.  However if you find that the motor cage is damaged, it's time for the whole nine yards.

The left side is always tougher to figure out.  Since there is more wiring in the way, I like the cover to "disappear" under the dash vertical support a little bit.  This means you cannot draw the entire circle of course. I will usually leave a "flat spot" near the support.

Use your imagination and try a few different locations for the hole before you scribe your final cut line.  Remember that you need to be able to get the impeller out, but you also need flat areas to seal your new, removable cover to.  And, last but not least, you need to be able to get to the line you draw with the cutting tool!

Tool of choice. 

Cut with care and the right side will give you a nice, clean circle that needs little clean up. 

Right side:  Notice that on the top right edge of the open hole there is still plenty of room to mount the new cover.  Not so on the lower left.  It's a trade-off.  The more you leave, the more room you have to attach the cover to, but the harder it is to remove the impeller.  I could have left--maybe-- another 1/8” or so on the lower left.  More room for glue!

Everything about the left side is difficult, even taking pictures.  Top right, the hole is very close to the frame.  Bottom right the hole is not exactly round, but close.  I "detoured" at the last minute since I was going to run out of flat area to attach the cover to.  This side is not as well centered over the impeller either.  You will have to slip your new cover behind the dash frame in the upper right area.  Not a problem, there’s room.

A pair of mechanic's picks works well to remove the impeller retainer clip.  One lifts the end out of the recess in the impeller, the other pulls the clip off the motor shaft.  Put something like a rag into the recess below the impeller.  If the clip drops off, you'll have to disassemble the floor ducting behind the carpet to get it out.  Unless it pops upwards.....

Don't lose that clip!!

This is the critical photo.  The difficulty in cutting the left side results in a more ragged opening.  Clean that up!  More importantly, this photo shows the venturi cut out of the left side inner scroll housing.  Now you know why I said “butchered”.  It’s very tough to get in there and cut cleanly.   The white part inside is the mount that the motor bolts to.  The old motors fit right inside the circular opening.  The newer motors are larger diameter and require that you enlarge that white plastic part’s inner diameter.

Not visible:  Up and toward the front is the rubber grommet through which the new wiring will run to get to the switch and power supply. 

Before building the new venturi from the funnel, get in here with a different grinding tool and clean all the rough edges off.  Leave things as smooth as possible.  This will aid air flow and decrease noise.  It will also save your hands while you are grinding out the motor mount!

Why are the harnesses all hanging in the way again?  I accidentally cut the wire tie with the Dremel.  I can't stress enough the high level of care one needs to exercise on this side.  Everything is in the way and one has a tendency to get a little careless.  While I didn't amputate the tip of my index finger, as it appears in the picture above, I did manage to nick myself quite nicely on this side when the cutting bit slipped out of the housing.





The door edge trim is a nod to smooth air flow.  Glue it in place!  It usually comes with some adhesive down in the groove, but you don’t want it coming loose inside the motor housing and behind the impeller, where you can’t get to it easily.  

Next step is to create the removable covers.  While I like the PVC TV trays, I’m sure there are many alternatives.  Don’t use anything too brittle as it will split while you are cutting, drilling, mounting etc. I like to find something with some flexibility.  These pieces are about 1/8” thick.  Anything too thin won’t stay flat while the adhesive is drying.



Note the ears for mounting.  I drill these with 3/16" holes and mount the cover with #10 screws.  You don't want the screws to bind in these holes during installation.



Glue on the housing?  Glue on the cover?  Your choice.  I think this way avoids smearing.  Note in this shot that I have re-insulated the expansion valve plumbing for the AC on the far right.  I replace any damaged butyl tape and then wrap it with silicone tape where it comes through the center console side cover.  Looks nicer than the bare butyl gum.  Also, cable ties won't cut through the silicone tape--makes for a nice clean wrap.



I use an electric screwdriver here.  If you feel insecure about alignment, use the cover to mark and pre-drill your holes before applying the silicone or other sealant.  Make sure the holes you drill are smaller than the screw size!  Usually I just hold the cover in place over the sealant without having pre-drilled the scroll housing.



Nice?  The black ones in my wagon look like they are factory parts.  Not bad for an amateur!



Once again the left side will have you scratching your head, if not pulling your hair.  Once it's complete though, it really does look neat and tidy.  And yes, I did replace the missing cable ties later. 


I recommend letting everything dry for a few hours before testing.  Hopefully you checked your electrical before putting the covers on. The drying time will give you the opportunity to put on your hazmat suit to protect you from all the stuff that will come out of the dash vents the first time you turn on the fan, but more important, because of the glued-in venturi repair/funnel, you definitely want everything dry before using the fan.  I expect the air flow could dislodge a funnel that is not completely set.