installing bearings in uprights

[onlyincanada]

Some technical tips please

I did a little searching on the net to find the various coefficients of expansion and found the following which was quite helpfull.

http://muller.net/mullermachine/docs/temperature.html


So last night I tried to install those hard to find SKF 633007 C bearings into the uprights in my RF82 .It seems to be a very tight fit , but did not have a good enough inside micrometer to measure it exactly, will head to a local machine shop to get the exact measurements if I need to.
I had the bearings in the freezer overnight and had the upright in the oven, at 275 deg for an hour or so ( wife was out shopping) and when I tried to fit it together the bearing was still too tight to drop in to place,
So my questions are.
How much can I safely heat the upright without risking softening the casting too much? It has just been powder coated so really don't want to use the torches on it.
Should I look at Dry Ice or Nitrogen to shrink the bearing more?
Dry Ice seems to be good at - 100deg or so but they recomend "disolving" the dry ice in 90% alcohol to ensure good "heat" transfer but I am concerned the alcohol will disolve the grease in the sealed bearing.

Should I just go ahead and "press" the bearing into place.

Help please.

Thanks in advance
Rick

[Larry]

...did they powder-coat the inside of the upright--where the bearing is supposed to ride? Usually these bearings will fit in with a minimum of effort (heat/cool or use a press). If your upright was powder coated on the inside, you'll have to remove the coating!

Larry Oliver
International Racing Products

[Tim FF19]

Using alcohol willl increase the heat transfer but the only difference is time. Just use the dry ice alone and the bearing will cool down within 1/2 hr -1 hr anyway. With alcohol you would be ready in 5-10 min. Be really sure the bore of the upright is polished with NO burrs. Coat the bearing with some kind of anti-sieze prior to pressing in. It should go together with no more than a light tap with a soft face hammer. Keeping the parts square to each other is everything. An arbor press is really helpful because it keeps the parts in line. 400F would be better for the upright except for the powder coat but 275 is way better than room temp. It is possible to do this at room temp if you have a press and you can keep everything aligned but you are on the right track with the heating and cooling.

Good Luck.

Tim

[onlyincanada]

The powder coating was properly masked and the inside of the upright looks clean and burr free.
I do need to make a "tool" to control the bearing as I put it in the upright, the cavity is pretty small amd deep and it was hard the first time to make sure it was straight without burning my hand, will do that better on the second attempt.
I really do think I just need to be more aggressive on the Heating/ cooling part of the equation.
I really am looking for a drop in fit as the last think I want to do is gall the casting.
Thanks in advance
Rick

[Scott Hanba]

I've made installation tools by taking the outer race of the old bearing and making an axial cut through the race in one spot so that it can flex in the bore and easily be removed. Works great.

[R. Pare]

Double check both the bore dimensions and the bearing. You need only about .001" interference per 1.0" of bearing diameter. It sounds like you have much more than that at the moment.

[LolaT440]

Bearings are pretty precise. If one came out, it should be correct for the new one to go back in. There should not be a need to check the measurements is there?

[Rick Kirchner]

Rick - don't sweat it if the bearing hangs up or cocks during installation.

first, buy about 10lb of dry ice and put it in the smallest cooler that will hold it and the bearings. Make sure there's nothing but a fine film of anti-sieze on the shell and then wrap them in aluminum foil and stick them in the dry ice. If you are using some kind of a press adapter or tool, throw it in there too, so you don't transfer any more heat to the bearing than necessary.

Fire up the old gas grill. Adjust the temp to about 375-400 degrees F - use a meat thermometer.

Put the uprights in there for about a half-hour or so.

Take an upright to the bearings and attempt to install. If it hangs, take the whole mess out to the grill and throw it in. in a few minutes you should hear the clink of a bearing falling out. While waiting, you can try on #2. Even if it doesn't just fall out, you can usually get it ouot with just a light rap of the upright on the bench.

Your only limiting factor will be the possibility of the dry ice running out. You'll need welder's gloves or those silicone oven mitts. Sometimes stuff sticks to the cold surfaces and causes a hangup. Really humid days can cause a pretty good ice buildup from condensation.

It's a bit tougher for me - I have to drive 90 miles to get the dry ice, so I always have to order twice as much as I need!

OBTW - powder coating the uprights is not a good idea, it hides cracks.

[R. Pare]

Bearings are pretty precise. If one came out, it should be correct for the new one to go back in. There should not be a need to check the measurements is there?

Theoreticaly, this should be the case, but theory and a buck won't even buy you a cup of coffee in some places. Some automotive replacement bearings are purposly made slightly larger to compensate for the expected housing growth - FAG in particular does this.

Thermal expansion of aluminium is about .0025 inches per inch for a 200 degree temp rise. If the bearing press fit on a 2.50 inch dia bearing is to be .0025 inches, then what he did - freeze the bearing as well as heat the upright - would allow the bearing to just fall in to place easily with a few thou to spare, buy ONLY if the replacement bearing was the exact same diameter.