# Generator's Magnetic Center



## rock_breaker (Aug 10, 2015)

I am re-vamping a generating plant that was left at my shop with a destroyed engine. To do so I am replacing the scrap engine with one from the farm irrigation system. The outboard bearing on the generator engine also served as the front support bearing for the generator. The replacement engine has a 3/4" straight shaft consequently I have mounted a  bracket that supports  a flange bearing on one side and the generator front bell housing on the other. The replacement engine will turn the generator through a Love-Joy coupling.

Since I did not pay much attention to the rear bearing during dismantling my question is; how to find the horizontal magnetic center of the generator? There is no shoulder other than a plate holding a capacitor in the rear bell housing. The bearing is supported by an "O" ring midway through the bearing raceway. The Love-Joy coupling is a series 95 and can be adjusted along the axis of the shafts up to about 1/2".

A new base plate will be made to support the replacement engine and generator so there is potential for necessary adjustment. The damaged engine had two cushion mounts and the generator had one at the rear of the unit, I intend to support the new base plate with a cushion mount at each of the 4 corners.

Any help will be greatly appreciated.

Ray


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## JimDawson (Aug 10, 2015)

I think some pictures would be helpful here.  Normally small generators are mounted with a ridged connection between the engine and the generator housing.  It sounds like you are going to have the two mounted independently from each other.  The main thing is to keep the generator rotor centered in the housing.  Maybe take a close look at the original motor, and take some dimensions from that, maybe even use the original motor housing as the input end support.


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## rock_breaker (Aug 10, 2015)

I will have to learn how to do pictures, yes they will be mounted independent. The end bells on the generator have machined openings, the outboard end bell is machined for a bearing raceway. the one next to the engine has four holes that bolt the generator to the engine. The engine shaft has a taper that matches a female taper in the armature, the two are held together with a 1/4" rod  about 6" long that runs through a hole bored in the armature.  The engine shaft through the outboard  bearing is 1-3/8" diameter. I sawed the tapered end of the crankshaft off and have used it to get my alignment as accurately as I can along the axis of the units but am not sure about the location of the armature end ways through the stator. When the armature is pushed away from the engine it does seem to have a stop machined in the raceway.

Thanks for your help

Ray


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## JimDawson (Aug 10, 2015)

Normally the outboard bearing housing is what sets the axial position.  Maybe in this case, the axial position was set on the motor end.  The main issue is the brushes need to line up with the slip rings on the rotor, if they line up, that is the axial position of the rotor.  Given that you are making some major changes, maybe you'll have to come up with a different method of setting the axial location.


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## RJSakowski (Aug 10, 2015)

It sounds like, in modifying the engine/generator, you have destroyed your generator shaft registration.  It would be my expectation that the rotor would be centered in the stator windings.  Can you place shims equally between the stator and rotor to center it and locate your bearing center from that?  If you mount the rotor shaft bearing on a separate plate, it could give you some limited adjustability.  Once you find the sweet spot. you can drill and ream for positioning dowels pins for stability and ease of reassembly in the event you ever do a teardown.

Bob


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## SWARFEATER (Aug 10, 2015)

lube the lovejoy so it can move a little easier within itself. assemble the eng/gen and leave about 1/8 freeplay in the coupling, this should give enough for you to see the movement when its running, then adjust to suit. if not enough, make it 1/4.  I did some alignment on 10,000 hp GE motors that moved 5/8 after starting. btw most gens and motors move the shaft outward after starting, though this may not be true in all cases.


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## Tony Wells (Aug 10, 2015)

I've done some shaft/shaft alignments between large pumps and motors. I used a mag base and DTI to dial them in once they were secure. I mounted the pump on 4 jack screws so I had 3d alignment capability. Checking at least 2 places as far apart as possible on the "adjustable" shaft of the pump allowed me to get things within a couple of thousandths. Had nice, quiet, smooth units as a result. It took forever, but was worth it. In your case, you are facing a different problem, but with careful measurements you should be able to get close enough for the coupling. The polymer spiders are pretty forgiving.

Oddly enough, I have a similar project on the back burner myself. I have a Winpower genset that has a 12hp (I believe) gasoline engine. It's pull start. I hate that. I have a 16 hp cast iron electric start Kohler I want to swap in but of course all the dimensions are different. I suspect I'll have to start from scratch and build a skid to mount everything on. Pics when I tackle it. Maybe before winter.


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## rock_breaker (Aug 11, 2015)

This project is a real learning experience, especially the feed back on this forum, your input is highly valued. A couple of lines here to provide better information. In the dismantle of the generator: the taper connection of engine to generator was new to me,  it does eliminate one bearing. There is a "plastic" fan on the engine end of the armature with no set screw or key, an interference fit that I don't want to mess with, that pretty much forces relying on the taper connection and a machined opening in the engine end bell housing. With some careful (check for fit after each .0005 doc pass ) a sliding but snug fit was accomplished in the new bearing support bracket the same approach was used on the a spacer ring in the bell housing. Both bores are 1-3/8" which is the diameter of the outboard bearing in the damaged engine.

I am working on getting pictures (a whole new learning process) and am taking the time to think things through as best  I can so the going is slow.

Thanks for your input.

Ray


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## Keith Foor (Aug 16, 2015)

Since you are aware that the generator armature was carried by the motor shaft why not pull the crank from the new motor and turn the correct taper on it the machine and drill the case of the motor, or create a mounting plate to attach the generator head to the new motor?  Another option would be to take the case of the original motor, machine it to be a front plate for the generator and make a new input shaft with the correct taper turned on it.  At the other end of the shaft, turn it to a standard size and cut a keyway for your lovejoy connector.  The problem with just using a lovejoy is it's not a direct connection and will allow the shaft to sag and possibly hit internally if not supported by other means.  
Now with all that said, and knowing a bit about generators, I would be looking at the bearing and casting design of the back end of the generator.  A number of the cheap, and not so cheap, consumer level generators were carried in a bronze and sometimes plastic bearing.  The life expectancy on these generator heads were in the hundreds of hours and were never designed for extended use.  The average Home Depot consumer generator is designed to drag out to run a refrigerator and a light or two twice a year for about 3 hours while power is restored.  Now without pictures, or a description of what size this generator is, I have no idea if it's one of these consumer units, or a big 12KW commercial head.  And don't let power ratings fool you either.  Just because it says it's 10KW, if it's running a 3600 RPM pull start engine, it's still questionable.  Case in point.  I have a 5KW Coleman unit for running stuff at a camp site and intermittent use.  It's got a 10 HP Briggs pull start motor and is loud and sucks fuel.  The other generator I have is a 4KW, from an RV.  It has a 20 HP twin cylinder Onan motor and runs at 1800 RPM.  It's quiet and uses half the fuel the 10 HP does in the same time frame.  It has 1000 plus hours on it and will go several thousand more because it's designed to be parked at an RV park, and fired up for a week at a time and runs off the 100 gallon fuel tank in an RV.  
The motor on it will fail before the generator head will give up... The coleman will spit the generator head long before the Briggs motor dies.  
So, long story short.  know that what you are trying to save and utilize is worth the effort.  It sucks to put time and money into something and then have it fail because it was never designed to operate in the manner you expect it to.


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## rock_breaker (Sep 8, 2015)

I know not having pictures sucks but at 82 the learning curve is off the chart. This unit is one of the lower quality short term operation 5.2 kw generators and the replacement engine is also repurposed (This is more of a fun and learning project). Yesterday I got the generator reassembled and ready to remount in the cart type frame.  The assembly has been changed from one piece to two pieces, thus the mounting (new) bracket and the 1 3/8" flange mounted ball bearing. I used a sleeve that fit the 1.375" shaft and the machined clearance hole in the end bell to get the armature centered sideways. The outboard end  of  armature shaft has a ball bearing that fits into a machined hole in the end bell.  It appears the end play (registration) is controlled at the pull rope end of the damaged engine so I will probably rely on the two 0.375" grub screws in the bearing to "hold" this dimension. The replacement engine has a 0.75" diameter output shaft that is 2.25" long and the taper starts 3" into the armature so a new longer shaft was turned to accommodate this length and also the additional length required for the flange bearing and support bracket. The large end of the taper is 0.875 while the small end is 0.650 a dial indicator was used to get the cross slide properly aligned.

I will report the finished results when it happens, have to take time out to get the trash out and get ready for Muzzle loading hunting season.

Have a good day

Ray


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## KBeitz (May 13, 2018)

For anyone wanting to do this just take the side cover off the engine and the engine crank.
Cut the crank next to the journal and mount the cover and sawed off chunk of the engine crank
back on the getset. The long bolt that goes through the generator will draw the crank stub tight.
Bolt the engine side cover with the bearing back fast to the genset. Your good to go.


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## KBeitz (May 13, 2018)

Hey... What happened? So many pictures....

I fixed it...


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## Silverbullet (May 13, 2018)

Pictures or not , the illustrations show a good way to do it. My concern is holding the generator end firm enough to keep it from shaking its way off  with one mount on the generator it relied on the motor to be bolted to it . Under a load it will twist itself right off a rubber mount . You'll need four on just the generator end.


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