PMG Frame Building Secrets

Building frames is something that evolves, it’s a combination of looking at other people’s designs and making changes to suit your needs. For the DIYer with limited tools, it’s always wise to look at early equipment as they spent a lot of time to KISS it.  A lot of this stuff was developed to be made simple, with fewest parts and common tools and materials.

I was talking to friend SW Lee in Malaysia, he’s a Businessman for a multinational company, but he worked at his Father’s side first to learn a lot about stationary power plants big and small. He also worked in a store that sold stationary engines and engine parts when he was attending College.  One day we were discussing a trick his Father had taught him about setting up a direct drive generator.  His Father constructed the frame where the generator mount was wedged in and could be knocked around with a large hammer until all was perfectly in alignment.  The shoulder bolts that held the generator to the mount were designed to fit snugly in the mounting holes.

Once all was in perfect alignment Lee’s Father would weld in the mount.  What he created was a generator where the gen head or engine side could be removed and then replaced without the worry of losing shims or the need to do a realignment.  All that one needed to do is use a shoulder bolt and a proper sized hole for both the engine mount and the generator mount to keep all in alignment.  This is an example of what you learn by doing, and you learn quickly to consult the man who has touched the work versus those who have never got closer than a CAD drawing. If you look back at my earliest pages, you will see my efforts to shim in aligments on direct drives.  I had to pay special attention to the shims, and put a straight edge across the coupler to verify all was ready to run if I took things apart.

SW Lee and his Father

SW Lee left, A Master of KISS right, "Lee's Father"

In our case, we are designing for the Do it Yourself-er who may not have an abundance of tools or building materials, in this example, we make use of a welder as they are everywhere, and most people have a friend who owns one.  If that’s not the case, it’s fairly easy to bolt a frame together, so just change your design a little.

I can’t tell you how many times I’ve been asked for all the measurements of generators and engines because some one wants to build the frame in advance of receiving the major pieces. This is usually a big mistake as it is so easy to miss something.  To ‘fab up’ the frame when you have all the parts is easy and quick, It’s a lot more fun too, because you are sure it all fits. Prebuilding the frame almost always leads to disappointment, something is taller or sticks out further than expected, or the measurements you were given was for an earlier model.  

Following is another KISS fabrication trick Lee’s Father uses.  Simply add the detail to the cross members so they nest between the rails ‘unwelded’.

a keep it simple fabrication trick

"Keep It Simple" applies to fabrication methods as well.

 Install the engine and use a bar and hammer to position the cross members and engine where you want it before you weld it in.  You will be able to date my frames as either pre or post knowledge of KISS assembly. Pictured here is a loved and reliable Yanmar with a single flywheel about the same diameter of a Lister type. It runs at 1000 RPM and is known for it’s long life and reliability.   


We start with a very basic frame.

Basic PMG frame

The three cross members are made of heavy Angle, I used a $59 harbor freight cut off saw with composite blade to cut the square tube on each side, and the angle iron. The angle iron cross pieces are 17 inches long, a notch was cut to allow one side of the angle to drop down between the side rails, while the top of the angle lays all the way across the square tube. I used the harbor freight saw to do this as well. In my case, I used a wire feed welder, and fully welded the pieces in place. The two angles to the left are spaced to assure that my engine mounting holes will fall in the middle of the angle iron tops, about 10.5 inches for the CF186 horizontal shaft diesel I will use here. We will be mounting our generator head to the right on this frame.  A mistake the beginner makes is placing a hole too close to the angle iron corner, and then finding it’s too tight to get the nut on the bolt on the underside. You’ll see nuts ground down on one side for clearance on some DIYer frames, it’s easy to avoid this problem when you do your layout and measure properly. 


Angle iron generator mounts, note they form slots for tension adjustment.

Angle Iron Gen Mounts, easily and quickly fabbed up with basic tools.

Simple to fabricate generator mounts made from two pieces of angle.

Making slotted holes is a problem if you don’t have a mill, in this step we make generator mounts the easy way by adding a wrap of masking tape around the bolts and then placing them in between as spacers. We clamp it together and add a small scrap of metal to each end and weld it to keep the proper width in the slot.


Adding the Generator mounts to the frame.

Here’s why you wait until you have the components BEFORE you fab. We place the generator in position and make sure it slides smoothly back and forth before we weld. There’s no guess work with this method. If the generator manufacturer changed the hole location on the mountingtabs and didn’t update the online drawings, you won’t be inconvenienced.  

After you have mocked up you engine and PMG, you will bolt the engine into the frame, then place your PMG on the frame and move it one way or another till it is perfectly in line with the engine pulley. Of course small adjustments can be made by moving the pulley in or out on the shaft, but running fairly close to the inside is always preferable. Only after you get your alignment sorted will you weld in these mounts. As you can see, you have a lot of latitude to move the PMG one way or the other, and since this angle is a lot smaller than the larger angles in the frame, you have room for the bolt head and washer on the bottom.


With alignment proven, we weld in the mounts top and bottom.

Generator Head test fit done, we weld in the brackets on top and bottom.


PMG generator mount, note, the cement floor does not give good contrast here, but the pairs of angles that will support the generator head are evenly spaced and were checked by temporarily fitting the generator head and assuring that the pulley on the engine and on the PMG were aligned. Once done, I tack welded in the angles, and now that we have verified all, we fully weld in the mounts.


Basic frame completed, engine and generator mounted.

Basic frame complete, careful attention paid to pulley alignment. A steel straight edge comes in handy.

It’s hard to see just how much movement is allowed in PMG adjustment, but close to three inches! Using some sheet metal channel, we can quickly build a a shield around our belt drive.

This is the heart of a frame, there’s all kinds of things you can add, but remember, it is best to mount gauges and all the items you can reasonably mount elsewhere off the frame, or if it is a portable generator set, then use rubber isolators for panel that gauges will be mounted on. Remember, if you are going to use this as a portable unit, and you have electric start, make room for a battery box.

If you look at a completed generator, it can look like an overwhelming job to make it, fact is, it’s fun and a great hobby. Now if you look closely, you’ll note that the following video clip shows the above generator with some easily constructed square tube frame added. Note on one side there’s a removable horizontal piece of the frame. This allows use to remove the engine and replace it. Note that we need NOT use the same engine, we can readily use a variety of horizontal shaft engines to power our DIYer PMG, all we need is the PMG and Utterpower pulleys, used or new engine and we’re ready to build.

Don’t want to go to all the trouble? Go to your local shop that handles chain saws, lawn mowers and small generator repair. Out back there’s generally a pile of Generators that can not be economically repaired, simply offer the operator a few dollars for the whole thing or part. This is how I found the power panel for this build, but it’s easy to make your own, and that’s another story. Sometimes you can remove the Generator and reuse the engine and frame to power the PMG.  Construction generators are often wonderful sources of donor parts. 

Here’s the YouTube video of the above generator with a few pieces added.  I cut the square tube with a $59 composite cut off saw, but it’s quick enough with a new blade in a hand hack saw. My wire feed welder is a favorite toy, and once you own one and play with it, you’ll realize there’s little you can’t make or repair.  With a wire feed you can even join sheet metal by backing it with with a big piece of steel, you owe it to yourself to have a wire feed welder.

But what about that hinge plate setup you may have heard about? Well, it sure did work well here on our test engine.  One of the advantages is you can set it up where you just pull the rod out of the hinge and you can quickly remove the mount and the generator head for access to the engine, or to move it to another prime mover very quickly.  Following is an example of the hinge plate, some will design using the weight of the PMG for the tension, if you study the direction of rotation, adding load can actually help apply a little more tension.  If you engineer it right, you should be very happy with the results.  There are now several PMG owners who have used the hinge plate design and they are totally happy, you can add a spring for tension if it suits your needs.


Pull the rod out of the hinge and remove mount and generator in 30 sec.

Shown here fitted to a Lister type, generator and mount can be removed in seconds. Engine flywheel is CCW rotation from this view.

This ought to get you started thinking about how you will build yours, it’s the beginning of ideas, not the end.  KISS is a philosophy, it really does take time to evolve simplicity.  Anyone can make the process or the machine more complex. Many thanks to Lee and His Father for the valuable DIYer tips.

Look here for small engines, you might be surprised what you can buy for the money..

Visit the utterpower PMG pages.

All the best,

George B.

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3 Responses to PMG Frame Building Secrets

  1. Joseph Bolton says:

    I like the link for the small air cooled 10hp diesel engine! One thing I wish the Lister 6/1 could be is air cooled. Just out of curiosity, I looked up typical Hp, BMEP, and torque profiles on diesel engines and made a spreadsheet that calculates Hp at rpm. This 10hp engine, if it follows 95% of diesel engine power profiles, will still make 6hp at 1900 rpm’s since BMEP increases to a point as rpm’s decrease. With a heavy enough pulley or different flywheel, this could be a reliable little machine if engine life increases significantly at these lower rpm’s, all things being equal. The engine might not cool as well as it does at full rpm, but it might cool just fine too since a lot of heat comes from friction at 3600 rpm’s. Either way, it is a cute engine. If I could make a new flywheel for it and run it well at 1900 rpm, I’d try using it as a backup for the Lister 6/1 any day.

    • George B. says:

      You are right, 1900 might be ok, you are making less heat at that speed, maybe you use a non contact thermometer to check cooling fins and exhaust temp and full load? The Onan flathead gas twins were designed to run up to 3600 RPMs I believe, they were used at 1800 for a lot of Onan RV 4000 watt 120VAC generators, wonder what the mods were if any? I have found a few of these where the previous owner had cranked them up to 240 AC output, 3600 RPM 120hz, I assumed they were using it to run a welder or similiar, but who knows?

  2. Pingback: DIYer Soon Wah Lee, Reporting in From China |

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