These two pages describe the process used to convert from a
Prestolite Alternator to a Toyota Alternator on a Lycoming O-360 Boss Mount wide
deck.
The unit described puts out an approximate 60 amps continuous duty.
(we're not done testing it yet)
The common units being sold today for these conversions do not usually have the correct internal fan installed. They are also generally not rated accurately for continuous duty. We recently tested one of the "60 amp" units purchased from Vans Aircraft. At about 40 amps the armature core exceeded 200deg C.
We found that this unit would directly use the stock steel boss mount Lycoming bracket and can be used as is. The only thing is, it will run a little hotter, and you can't adjust the voltage output.
So in this installation I chose to modify several things. I replaced the internal regulator and brush assembly to use an external adjustable regulator. And I put a different rotor in it so that the attached centrifugal fans would function at maximum capacity. Most automotive engines spin the reverse of airmotive.
The following part numbers are Lester part numbers, which is the numbering system used for many aftermarket parts.
#13754
Toyota Camry LE 1997-on 90 amp alternator
#1493-91CCW Honda 91 mm rotor with fans and aft bearing
#46-82200 Terminal Block, used on some Chrysler models
#39-8201 Brush holder
The pulley I used was the stock Prestolite pulley used on most Lycomings
# PU-672.
This had to be modified via a lathe, removing most of the aft extended
boss portion and some of the front extended boss portion.
The first few photos show the parts and the new
alternator.
This last picture above shows the back cover removed with the brush assembly, internal
regulator and rectifier exposed. This is accessed by removing the three nuts and
one ground lug on the back cover. Note: the area of the back cover below that
has two square holes for venting the internal regulator will need to be modified
to allow the terminal posts to come out there.
These next two show the rubber boot removed from the brush holder and the brush
assembly with the internal regulator. The round plastic cover is kept with the
new brushes but it doesn't slide into them like the old one. It gets trapped
between the lower and upper rubber boots by the back cover.
This shows the back without the brushes and regulator. Note the red rubber
boot that you don't want to forget to reinstall like I did. There are also gray
boots for the armature winding leads that come up to the rectifier. These are
also easy to forget.
This shows the pulley nut and pulley removed. Its a 22mm and
I used and 1/2" air gun to
knock it loose.
In these images the 4 case nuts are removed as well as the four screws holding
the rectifier leads in place.
The next one shows the rectifier removed.
Remove
the gray boots and the case will then split leaving the wire armature with the
front half, and the field rotor with the rear half.
The old rotor may be gently tapped out of the rear case by supporting it at the split line and using a small center punch on the rear dimple of the rotor shaft.
These next images show the backside of Honda rotor (left) next to the Toyota
rotor (right).
As you can see the Honda rotor has the fan positioned correctly for
centrifugally moving the air from the front and rear inlets to the side outlets.
Other than the fans they are identical.
These below show the rear rotor bearing I found on each
rotor. The one off the
Toyota was deeper so I used it, but it wasn't necessary.
This bearing is only supported radially in the rear case. Rotor depth is set by
the front bearing.
This allows for the rotor and case to expand differently as they warm up.
I don't recommend changing this bearing unless you have a fairly specialized
bearing puller to get that sucker off.
