MGA Generator to Mini Denso Alternator Conversion
At 02:17 PM 11/20/2011, George Stringe wrote:
"I used a small one wire alternator I bought on line from DB Electrical on Ebay for $85. It is a Chevy mini Denso and is about 3.5 inches in diam".

A quick reminder here that the vehicle electrical system needs to be converted from positive to negative ground.

"I cut off a corner of the front plate so the alt would attach at the original post hole where the generator mounted. There was a hole out at the corner I cut off but I wasn't comfortable with the amount of iron around the hole to the edge of the plate. After cutting the plate and attaching the alternator to the bottom mount, I fabricated the top mount and adjuster out of an old alternator adjuster I had in my junk box. I cut the old adjuster to length and welded pieces to it to make it fit the existing top generator mounting hole. This will require a shorter length belt by about 3/4 inch".



Now that George has done this, I would like to say that I have always lusted after one of these small alternators, but could never bring myself to pay hundreds of dollars to buy one. But now they show up on eBay for under $100. Apparently there is an OEM application for a Honda Civic, and that alternator is actually made by Denso (as in Nippondenso or Nippon for short). Now there are a few more manufacturers for aftermarket replacement parts with different trade names. The most common one seems to be Powermaster. They make model 8162 for one-wire operation (battery wire only) or 8172 for two-wire connection (battery and ignition switch wires). The "other" brands often refer to these small alternators as "mini Denso style", also often referred to as racing or street rod alternator. The ones currently on eBay are intended as direct bolt-on for some Chevy engines (with the right brackets), and they weigh only 5.5-Lb (2.5-Kg).

My remaining issue is that this particular configuration is not a direct bolt-on for the MG engine, but requires some creative custom work for mounting. I think I would have found a different way from George's idea, primarily because I wouldn't want to cut down the front engine plate. After looking at his pictures and description I took a picture of my spare engine front plate for reference (the picture with yellow fan). Now it occurs to me that the hole he cut away on the engine front plate was the top bolt hole for the engine mount bracket. Hmmmm. Must send George a short message.

At 07:54 AM 11/22/2011, George Stringe wrote:
"No need to scratch your head. After I sent my last notes, I was out in the shop and decided to look at the spare engine I have sitting in the corner. About 2 nano seconds later, I uttered ..... ohhhhshit. .......... So stay tuned. I installed the engine mount on the new engine, minus the missing hole bolt, and I guess I have to a little repair work. Hey I get to weld some more!!! ;-) Basically I will start over from scratch".

We will review this again later.

Some additional information:
Refer to www.powermastermotorsports.com
8162 (1-wire black) - 28169 (1-wire polished) - 8172 (2-wire)

All are 93-mm mounting, 30 amps at idle, 50 amps max.
Idle speed is specified as 2400 rpm for the alternator.
Pulley ratio for street use is assumed to be 3:1.
Therefore crankshaft speed would be 800 rpm at idle.

The MGA has a relatively small crankshaft pulley, so this alternator may produce less current at normal engine idle speed. Alternator V-belt pulleys are available in 2.8", 4" and 5.25" diameter. Definitely use the 2.8" pulley for an MGA street car, and even then you may have only 2:1 drive ratio. You could set the idle speed up to 1000 to 1200 rpm, or just keep in mind that it will not make 30 amps at normal idle speed. This may be no problem at all for the MGA, as the car originally had a 22 amp max output generator that produced very low current at idle speed. Also the entire electrical system of the stock MGA seldom draws more than 20 amps total with everything electrical switched on (until you start upgrading accessories). Suggest monitoring the system voltage for a while to see what it does at low engine speed, and how well it works with moderate driving speed.

On 11/26/2011, George Stringe wrote:
"I milled a little off of the two mounting ears on the alternator. I used the adjuster bracket by taking the mods of my previous attempt and reshaped it a little. Not painted up yet but you can see the improved setup. Instead of the original belt I used a slightly shorter one. The original still works but the adjustment is within 1/8 inch of the end. The shorted one has room for stretch and still will go over the pulleys".