|The MGA With An Attitude
Replacing a ROLLING ELEMENT BEARING -- UT-108
At 08:29 PM 8/8/03 -0400, Chuck Jackson wrote:
>.... So I decided I'd disassemble the hub .... But I can't figure out how to disassemble it. .... seemed logical that I should take the seal out first and it should come out intact. .... Is this just a brute force deal?<
Yes. Don't count on getting any seal out without damage. Always have new seals handy. Just get a BIG screwdriver and pry the old seal out like this:
>I also tried some light hammer-on-wood blows to the outer bearing, but nothing there, either. Does force on the outer bearing translate directly through the spacer and the inner bearing to the seal?<
No. There are shoulders inside the hub. Both bearings have to go in and out at their respective ends of the hub. The distance between the two shoulders in the hub is exactly the same as the length of the inner race spacer between the bearings. You can see a cross sectional drawing of the hub and bearings in the MGA Workshop Manual, page K.5, figure K.2.
>After the seal comes out, will there be any tips needed to get the bearings to come out?<
Standard technique for manually removing bearings. Use a long flat faced punch and "drift" them out from the inside. First I will tell you the traditional technique. Then I will tell you why it doesn't work here, and how to do it anyway. You would prefer not to hammer on the inner bearing race when removing the outer race from the housing. Similarly you would prefer not to hammer on the outer race when moving the inner race along the shaft. Either of these things will transmit the force of the hammer blow through the rolling elements (balls and inner races), which can create flat spots on the balls and cause spalling in the raceways, leading to rough running and early demise of the bearing.
The MGB uses tapered rolling bearings in the front hubs, where the outer bearing race is separate from the rest of the bearing. In that case, this is the only way you can remove the outer bearing race. When using a hammer and a single point punch, you tap a little at one point on the raceway to move the part just a little bit, maybe only a few thousandths of on inch at a time. Then you move the punch to a point 180 degrees around on the ring and tap it out a little there. You have to keep switching back and forth and tapping a little at a time to "walk" the bearing race out of the housing. If you hit it too hard the bearing race gets cocked too far crooked in the housing, jams in place to be hard to move, and starts taking a little bite to remove shavings of steel from the mating surface. If you do too much of that, or do it too many times, you mess up the housing so the next bearing you install will be loose in the bore. So you have to be patient and walk it out slowly in very small steps, which will take a couple of minutes for each bearing race.
With totally clear access on the outside, a new bearing might be installed quickly with a single push of an arbor press, as long as the bearing race is square with the housing. Otherwise you can install the new part with the same technique of walking it slowly into place with hammer and punch.
Now here's the hooker. The MGA front hub uses ball bearings in which the whole bearing is one piece that does not come apart. And the inner race bearing spacer is in the way inside of the hub to prevent access to use a punch to tap against the outer bearing race from inside. So here you have no choice but to push on the inner bearing race to remove the bearing from the housing.
Start with a large diameter punch that will just fit through the bore of the larger inner bearing. A wrench socket of appropriate size will work well. This needs some length, so add on a socket drive extension 6 or 8 inches long. Insert this tool (large end first) through the inboard bearing and into the inner race spacer until it seats against the inner shoulder of the spacer. Keeping the spacer as well centered as possible, tap gently with a hammer on the punch to drift the smaller outer bearing out of the hub. Again, if you hit it too hard you flat spot the bearing balls and raceways, so go easy on it. Tap just hard enough to make it move a small amount with each blow, and then keep tapping gently until the bearing finally moves out of the housing. This might take half a minute of so, but with a little patience you can remove the bearing without damaging anything, and the inner race spacer will come out with the outer ball bearing.
Then you get a larger diameter punch, about the size of the OD of the spacer. Turn the hub around and tap out the outer ball bearing from through the center of the hub in a similar manner. Again, tap gently, just enough to get it to move slowly, and have patience to drift it out without damage to the bearing. Having the bearings out of the hub is very convenient for cleaning and inspection and repacking. If you are very careful doing this, you can likely R&R the bearings at least a dozen times without damaging the hub or the bearings.
When reinstalling the ball bearings in the hub, you don't have to hammer on the inner races. Get a larger punch that will face against the outer bearing race and drift the part back into the hub nearly as gently as during removal. If you don't have a punch that large, you can still reinstall the bearings using the single point punch technique, but it will just take a little longer. For shimming the tapered roller bearings on the MGB, the outer bearing will need to be removed a few times, but only the inner race and roller assembly comes out, while the outer race stays in the hub. The ball bearings for the MGA do not require shimming. Just press those into place in the hub, solid up against the shoulders, and install a new inner seal (don't forget the inner race spacer).
Now remember the rule about which bearing race is press fit. Well, with special assembly design there are ways around that problem. The idea is simply to secure the bearing race so it doesn't move. In several places on the MGs where there is a ball bearing on a rotating shaft, it may be retained securely with a large lock nut, and maybe a locktab. The large ball bearing on the gearbox input shaft is mounted like this. It is a fairly snug fit on the shaft, but not a real tight interference press fit. Once you remove the big jam nut and locktab you can generally pry the bearing off the shaft with a couple of large screwdrivers. The gearbox center mainshaft ball bearing is mounted in similar fashion, slip fit and secured with a pinch on the inner race. For the MGA 1500 units there is a locking nut just behind the speedometer drive gear. For the MGA 1600 and MGB gearboxes there is a long tube spacer from that point back to the ball bearing in the tail end, and a large hex nut at the back flange holding all of those parts tightly together. Once the big jam nuts are removed the bearings can be pulled off the shaft without too much force. Score one for the good guys and the ease of maintenance on these old cars.
But some day you may run into a ball bearing that is a tight press fit on a shaft, or maybe one that wasn't intended to be but is just plain stuck. If you don't have a bearing separator tool, or if there's not enough space to get anything behind the bearing to pull it off of the shaft, then you need to get creative and figure another way to do it. In a pinch you can always cut a bearing off and save the shaft. You could use an abrasive cut-off wheel in a high speed hand grinder to cut completely through the outer bearing race in two places to remove the split halves. After that the bearing balls may simply fall out of the retainer cage, and the cage may be removed axially from the inner race. But a lot of bearing retainers have spherical nests for the balls, so even if you did cut away the outer bearing race the balls may still not come out. There is actually an easier way to get that far without even having to cut the outer race.
Remember the way the ball bearing is assembled? Inner race placed off center, load the balls in one side, center the race, space out the balls, and install the retainer. In this case disassembly is the reverse of assembly, and you want to remove the cage first. The ball retainer cage is most often held together with rivets. You can use a small grind stone in a high speed hand grinder to grind one end off the rivets, and then pry out the exposed side of the ball retainer with a screwdriver. Then the other half of the cage should fall back far enough to allow the balls to relocate inside of the bearing. Push all of the balls around to one side of the bearing, and you can move the outer race ring off center and remove it, while the balls all fall out, and the second half of the cage can be pulled off. Then you get a small abrasive cut off wheel and cut at least half way through the inner bearing race at just one point. Using a cold chisel and a heavy hammer you can then break the inner race at the cut point. Once the inner race is split it will expand just enough that it can be pried off the shaft with not much effort.
In many cases, getting the old bearing off the shaft is most of the battle. Installing a new bearing is a breeze by comparison. You can generally just slide the new bearing onto the shaft up to the point where it's just about one bearing width away from the final location before it gets into the press fit part of the shaft. Then you push it on the rest of the way with a large press, or drift it into place with a punch and hammer a little bit at time by tapping only on the inner bearing race. Having cut a bearing for removal in this manner just once, you will have a better grasp on the phrase, "Where there's a will there's a way".