You start with a sheet of 3/16 inch metal or thicker, cut a few holes, and few hole slots, add a few pulleys and you have a generator that will put out AC or charge a 48 volt battery string with some respectable output.
In my opinion, it’s best to avoid the flat head engines. There are now plenty of 6- 6.5 HP OHV engines for cheap; and you should pass on the flat heads, they burn too much fuel and don’t last nearly as long as these newer and better OHV models.
Since the PMG ships with a serpentine pulley, you only need buy one more for the engine, and a serpentine belt.
Add some angle and sides to the plate, or mount it between your wooden frame, and your ready to run.
But some will ask, why build this??
A labor charge for a small repair on a lawn mower will junk it in a hurry. And there are a lot of good engines sitting on mower decks with problems.
An excellent example is one of the Honda OHV equipped engines (not the OHC), these Honda OHV engines have gone many thousands of hours, and they are fairly fuel efficient. I’m sure there are others that are great engines as well.
Fact is, the first thing that fails on a hardware store generator is the generator, not the engine, so building something like this could be a real advantage, and finding spare engines should be a snap! Maybe if you’re an off gridder, you have a few spare engines?
Harbor freight is currently selling a 6.5 HP horizontal shaft engine for $129.00. For those that have experienced faults and loss of electrical output in small generators, they are buying two of these engines, (one for a spare), and using them to drive the PMG, and/or car alternator for battery charging. It’s easy to configure for one or both on the same frame (a value play). Some remind us it was the failure of their generator head that failed them last time, and investing in a generator like this allows the mounting of nearly any horizontal engine, and running it in hard times. If you buy the PMG with its 4.2 inch stock serpentine, you need only buy another 4.2″ pulley, and then go to NAPA or any other auto parts house and ask for the serpentine belt you need. Remember, those last digits are belt length, 425 at the end would be a 42.5 inch belt. Simply wrap a string around the pulleys, measure how long the string is, figure how much shorter or longer it can be, and call the auto parts store to see what they have in stock. Most stores near me can get about anything in 4 hours, or you can find lots of belts under the hood of cars and trucks in the junk yard. Get familiar with cars and trucks that use the shorter ones for auxiliary equipment, one long serpentine is typical, but many have added another drive pulley and a short belt for various things. Two bearing generators and air conditioning compressors have been run off the same serpentine belt. The automotive type compressor has an electric clutch, and it free wheels when not in use. In their home built setup, AC components from a car or truck are used to cool a room, and the rather significant losses from mechanical to electrical, and electrical to mechanical energy at the other end are avoided. This can result in a lot more cool for any given amount of fuel burned.
There are a lot of durable engines out there to be reused, some have tapered shafts as there are many generators that failed and the engines was pulled off the Gen Set. Could the engine be redeployed? I have wondered if it’s possible to ‘press off’ the electricals on the Gen side, and use the gen side shaft as an adapter to convert the taper shaft to a straight shaft. I am sure I’ve seen these conversions, just not sure that’s how it was accomplished. When using a tapered bushing like used with our pulleys, I doubt you even need a key way, the compression of the taper bush should transfer enough torque to twist the shaft! Bob Otey presses out motor shafts and makes longer custom shafts for specific applications all the time. This gives me hope it’s easy in the typical big box generator application if you have a press. One engine I like is the 11 hp Honda that was used in 5kw construction generators. I have heard a few stories of Hondas of this design reaching a rather amazing 10,000 hours of running when they were deployed as battery chargers in off grid locations. One report of this was from an editor of a monthly publication that’s been around for a long time, but I would imagine the running RPM was reduced. We can do that with the two bearing generator and set the drive ratio we want and don’t need run it so fast.
I have a Honda OHV engine of similar design that refuses to die. It has lived 4 times longer than what most people expected out of it.
BTW, I see a number of posts looking for adapters to convert a tapered shaft to a straight shaft, since these single bearing heads often use the same size tapered shaft, an adapter might be a good part to make and sell on Ebay…. Yes, California’s “All Knowing” CARB will likely cause manufacturers to accept their even higher standards soon. There’s talk that next year’s big box store generator will have a catalytic converter on it and cost you 20% more. It might be a good idea to provide this handy part to allow us to recycle the stuff made prior that isn’t crippled by CARB.