How deep to cut 74 fan housing for newer alternator?
 

I bought a remanufactured alternator for my '74 2.7, but when trying to install it I found that it is a little longer than the old unit. I've read earlier earlier posts that suggest cutting the fan housing deeper to accommodate the newer alternator. Does anyone know the depth of the cut that needs to be made? I don't have the old alternator to compare (prematurely sent back as core). BTW, the old alternator was a 55a (bosch I believe, but no brand markings, just a "germany" marking) with an external regulator and the remanufactured one is a Bosch 70a with external regulator.
Thanks
Bart

I think you will be better off replacing the housing with the correct one for the new alternator.

second that..if it ain't a perfect fit, expect it to be slightly crooked and have fan blades rub the housing.
ryan

What they said !!!

Thanks. Unfortunately, fan housings seem to be very expensive/hard to find. My best bet may be to try to retrieve the core and have it rebuilt, although from some earlier posts it sounds like several people have succesfully modified their fan housings.

clearance for the fan/blades is tight in the housing..you'll know if it isn't right pretty quickly by the rubbing. good luck on shaving it (magnesium part i believe)..let us know how it turns out.
ryan

Simple Solution.......
 

Bart,

Your problem is you got the wrong alternator size/configuration. And don't make it more complicated by machining your alternator housing to fit your new alternator. Just get the right size replacement alternator and sell the wrong alternator.

You will end up ahead than trying to utilize the wrong part. Just my two-cents.

Tony

I agree that the smartest thing is probably to to go back to the original alternator, but I am having a hard time fnding the same size with an external regulator (Any ideas on where to find a 55amp external regulator alternator?) Also, I woud like to upgrade to a 70amp model. There are several previous posts from people that have had success with the fan housing modification. How risky is the modifiction to the housing? I'm not a machine shop expert, but I would think that a good shop could maintain the same angle in the housing.

hi bart,
i have the original 55 amp marchal alternator that came in my car..just had it rebuilt a few months back..uses the external alternator. i agree that a 70 amp would be nice..sometimes at night when i have my lights on, etc., i literally have to turn down the volume on my stereo due to the load being just high enough to make it cut in and out..a royal pain.
ryan

Bart,

The cut is 9.3 mm deeper than the 55 Amp alternators ...

I have a lot of experience with this. . when I bought my 911E race car I was surprised to find the warning lamp on all the time. I pulled the alternator, a 55A Motorola/Marchal that was correct for the year, and found no brush holder! Hard to hook up a DF wire when you don't have a DF terminal at all!

So I bought a 1260 Watt Valeo for a Carrera, internally regulated. Guess what? Too long! So I bought a 901 "5R" casting fan shroud from a mid-year car. Guess what? Too long still, and needed some material machined off the BACK of the shroud to make the bolts fit. After an hour of hearing damage from grinding it, I went ahead and bought the correct Carrera fan shroud, a "930. . .4R" and it finally fit.

Anyway, I'm going to revert back to original shortly. To do that, you need to find an original motorola/marchal alternator, and the VR is available from this Wayne fella. Ebay is a good place to find them, or check with a local rebuilder.

Now, if you have some proceeds from the sale of the other alternators, I suggest you buy a high-output Bosch that fits your original fan shroud. These are available from Wayne, but a good reference to which one you need can be found here:

http://www.**************/alternators.html

If you are doing concours and need a stock-appearing Motorola VR, be sure and measure the voltage "set-point" to be sure you don't blow the Bosch alternator up! The old factory admonition, "use same brand of regulator and alternator" is due to the fact that the different brands have different characteristics, and the voltage the VR uses to excite the field is different-- if you have too high an excitation voltage, your system voltage will be too high, which could lead to a boiled battery!

I use a Transpo solid-state reg which is adjustable. It cost $12, so I have two of them. Using a screwdriver you can precisely adjust the output voltage AT THE BATTERY to compensate for any voltage drops along the way.

Good luck!

Thanks Warren, that is exactly what I needed.

I made this modification to fit a late model Carrera Alternator to an early housing. I had my machine shop mill of 3/4" where the alternator sits in the housing. It now fits just fine and everything is sqaure.

-Britain

Before:
http://www.britainsmith.com/Porsche/...9_0027_JPG.jpg

After:
http://www.britainsmith.com/Porsche/...0_0034_JPG.jpg

Assembled:
http://www.britainsmith.com/Porsche/...8_0028_JPG.jpg

That's a nice looking fan Britain. Is it new or did you clean up an old one? Mine is pretty oxidized and I'm thinking about how to spruce it up while I have it off.

It was pretty bad when I got it. I had it sandblasted and powdercoated.

-Britain