Repairing Cracked Hubs
A brief update on the December cover story about the B.D. Tillinghast half-breed: Tillie has finally made her journey across the pond, arriving safely the beginning of December. At some point her crate suffered a close encounter with a fork lift, evidenced by two neat holes punched through the end wall of the crate, just either side of the head of the engine, but not causing any damage. Dismantling the crate was cold, but fun, and by the end of the day Tillie was sitting on our trailer.
Now to business. Some time back I ran an article about running an engine with a flywheel that had a cracked spoke. Much of the discussion at that time centred around safety issues, but this time we have a different sort of crack, on the hub, and the solutions presented were interesting, as one might expect. As ever, the following comments reflect a variety of opinions that surfaced during this discussion.
I just got the cracked flywheels from my 2 HP earl-style Galloway back. They were repaired by a welder who has 20 years experience. I made sure the flywheels went on easy, inserted the key, and as soon as I started tapping it in, it cracked in both places again. The other wheel seems to be okay, for now. Anyway, I will go with this for now and look into new cast flywheels when I win the lotto.
Rest assured gang, THIS WILL NOT RUN IN SHOWS OR PARADES.
That wheel can be welded, but it will need to be in a hot bed to stress-relieve it 'til cold, and it should have a lot of peening while cooling - DON'T run it cracked.
I have seen a flywheel that had a cracked hub come off the crankshaft at a show, which I gather is the problem given the description of the fitting and subsequent cracking as the key was inserted. Shrink a ring on it and be done with it!
The idea of using a 'sweat ring' brought out a lot more questions and answers, starting with exactly what it is, before progressing to how to fit one and the best material to use.
A sweat ring is a piece of round metal, heated to a high temperature and placed onto the outside of a round metal object, which is usually cooled before applying the ring. A good practice is to turn the object, in this case a flywheel hub from a Galloway flywheel, so you get a good surface. After placing the ring onto the object, let them cool down naturally meaning just leave it until it is cool. This same principal can be applied to a sleeve, but the OD of the sleeve would be five to 10 thousandths larger.
If one were to fabricate a sweat ring, what kind of steel should be used? I was thinking about using seamless pipe, but don't know its characteristics. I need to do a little more research on the cause of the cracks.
Plain old garden variety hot-rolled steel works well. Pipe, whether it has a welded seam or is seamless, will work, if it can be found in the right size. The ring should be about a 1/4-inch thick and as wide as possible. Put the flywheel in the deep freeze and warm the ring up to a black red. Drop it on, making sure it is in the right place, and let it all cool/warm to ambient temp.
A ring shrunk on the hub is a good repair. The centrifugal forces placed on that hub are minor compared to those placed on the rim.
While I don't feel this flywheel would ever explode, I don't think it will stay in place on the crankshaft. Since it is a Galloway flywheel (i.e., rare) it is worth repairing. That said, it is worth repairing correctly.
I believe it was suggested that CRS was a suitable ring material. I would recommend you use a good, readily available alloy with good heat-treating characteristics, such as 4140. I also recommend using at least pre-hardened 4140, or even better heat treat it to Rc 40/45.
Realistically, you can make this ring .002 to .010 interference fit. If you use dead soft CRS, the higher interference fit is a mute point, because as the ring cools the hoop stress will exceed the yield strength of the CRS and the ring will stretch, thus limiting the amount of available compression you can put on the hub.
However, if you use a heat-treated alloy, that ring will tolerate a much greater hoop stress before failing/yielding.
What this boils down to is that by using a high-strength ring you can make a much smaller ring to do the same job. This will allow the repair to be inconspicuous, and with a little effort the repair could be made to match the original contour of the hub. Equal attention should be given to preparing the hub. The hub should be turned to allow 100 percent contact to the ring - if not, the ID of the flywheel will become egg-shaped.
Another way to shrink your flywheel hub is to shoot a fire extinguisher at it. We have done this at work when we need to cool something fast. It's not as good as dry ice, but does work
Can someone provide some info for the proper interference for a sweat ring?
There is no hard and fast rule here. The greater the interference fit the larger the ring required to support the resulting hoop stress. Here at work I shrink rolling mill sleeves onto shafts with .015 interference! But that hoop stress is supported with a ring of 4340 or H13 alloy steel at an Rc hardness of 43-45. The cross sectional area is 9-inch square. The sleeves have an OD of 12-inch, an ID of 8-inch, and are 4-1/2-inch wide.
I'm betting .002 interference will be just fine.
Made a few measurements on a 3 HP Herc last night. The hub is 3-3/8-inch OD. Maximum width ring that could be shrunk on is 3/4-inch. If the hub(s) were cut 3/8-inch deep/side the new hub diameter would be 2 5/8-inch.
Yesterday I speculated on .002 interference fit. I am upping that to .006 after looking at this.
Someone asked about split hubs. If you are lucky enough to only have to ring one side, then shrink the ring on after the flywheel is back on the crankshaft and clamped. If having to do the inside, too, clamp the flywheel on a piece of TG&P, then turn both sides/hubs. Then unclamp and remove TG&P. Fabricate a wedge (with slide-hammer provisions) to support the gap (but not expand it) after you shrink the inside ring on. Once the flywheel is on the shaft, use a slide hammer to remove the support wedge, tighten the clamp bolt, then shrink the outer ring on.
I have spent many years repairing all manner of farm equipment with all kinds of cast-iron pulleys, sprockets and gears. Many of these run at fairly high RPMs (1,500 to 2,500). Over the years I have had to make repairs with out the best tools or supplies for the job. I won't present this as 'the way,' only as how I would likely attack this problem if it were mine on, say, a high-speed combine pulley and I wanted to be very sure of it.
First off, I would turn the hub with a shoulder for a ring on both sides. Next, I would bore the center out well beyond the keyway, but leave as much meat as possible. Then I would braze the cracks, both inside and out, followed by reboring the inner bore. At that point the cracks should still be well brazed but the surface back to clean cast. Next, I would turn a loose press-fit sleeve for the bore, but leave the inside hole under-size. After pressing it in I would braze it in place from both sides. Bore the inside to shaft size and cut a new keyway in the sleeve. The sleeve should be twice as thick as the depth of the keyway. Lastly, return the shoulders and shrink on a couple of heavy rings. I might even be tempted to braze those, too. If I did I would maybe turn them and the shoulders with a slight taper and press them on tightly. Cool the flywheel and heat the ring well.
Has anybody ever considered putting a 'tire' on the outside of a flywheel? If one would fabricate a steel tire or band such as they did with wooden carriage wheels, I would imagine the flywheel could still be used with less chance of explosion, possibly making it a functional engine?
I'm not sanctioning what was done, but I know a fellow who shrunk a tire onto a flywheel on a 3 HP Fuller & Johnson. In order to make both look the same, he put one on the opposite side, as well.
This engine appeared to have been rolled down a mountainside. The guy found it all busted up and half buried in the mud alongside a creek. One of the flywheels was in many pieces. He found everything except one spoke.
In as strong a statement I could make I warned him not to attempt to reassemble the flywheel. He was determined and wouldn't let what anyone said stop him. At that juncture I said he should at least shrink a tire onto it. He paid attention to that advice, at least.
To replace the missing spoke he went to the local salvage yard and broke one out of a wheel he found there. After everything was welded back together and the tire shrunk on, he hooked the engine to an electric motor and tested it by deliberately running it over its rated speed. He says he will never run it in public (but, when he passes from the scene, I wonder what the possibly unsuspecting, subsequent owners will do?)
I, being new to cast iron, appreciate this more than you can imagine. I love this little Galloway. It did run, prior to restoration. But there are so many people here in Helena, Mont., who want to see this baby, I've just got to make it safe. Bottom line - I need new flywheels.
The information given here by contributors to the Stationary Engine List was interspersed with comments about safety aspects. As these were covered in the previous article about cracked flywheels, this time I focused on technical information. But for the owner of the Galloway , the safety aspect had to take priority, and it did.
Happy New Year to all, and thanks to GEM for letting us share some of the discussions we have via the Internet with you.
Engine enthusiast Helen French lives in Leicester, England. Contact her via e-mail at: Helen@insulate.co.uk. Join the ATIS mailing list at: http://www.atis.net