I'm re-assembling a Grand prix and have a basic question. Is the best way to install the new bearings into the uni-mount to heat the mount and drop in the bearings (and what temperature is best), or just press them in? Same questions about the wheel bearings into the front turbines. I don't want to crack the aluminum castings.
(02-06-2017, 12:26 PM)Ron Reaves Wrote: [ -> ]I'm re-assembling a Grand prix and have a basic question. Is the best way to install the new bearings into the uni-mount to heat the mount and drop in the bearings (and what temperature is best), or just press them in? Same questions about the wheel bearings into the front turbines. I don't want to crack the aluminum castings.
When I install ball bearings in any aluminum housing, I heat the housing to about 225/250 Deg. in an ordinary toaster oven. You can buy a Rival for around 30 bucks, and they work great. You can heat up your pizza rolls, too-if you don't mind the slight petroleum taste from kart parts! I've been using a toaster over for bearing install, paint bake, Etc. for over forty years. TJ
(02-06-2017, 03:29 PM)ted johnson Wrote: [ -> ] (02-06-2017, 12:26 PM)Ron Reaves Wrote: [ -> ]I'm re-assembling a Grand prix and have a basic question. Is the best way to install the new bearings into the uni-mount to heat the mount and drop in the bearings (and what temperature is best), or just press them in? Same questions about the wheel bearings into the front turbines. I don't want to crack the aluminum castings.
When I install ball bearings in any aluminum housing, I heat the housing to about 225/250 Deg. in an ordinary toaster oven. You can buy a Rival for around 30 bucks, and they work great. You can heat up your pizza rolls, too-if you don't mind the slight petroleum taste from kart parts! I've been using a toaster over for bearing install, paint bake, Etc. for over forty years. TJ
That's what I thought but i wasn't sure of the proper temperature. no problem with the pizza rolls, even a little paint taste could be an enhancement to us gearheads. Thx Ted........Ron
Some guys put the bearing in the freezer to cold shrink it, but I'm always afraid of condensation causing rust. Maybe I'm being paranoid?
Truth be told, I've put grilled cheese bread in my toaster oven so I didn't have to come back indoors to get it. Slight taste of paint....
Ted
.....um' time to check the label on powder coatings......no lead, no particular poisons, so maybe the rest mixed with the grilled cheese will pass right on through.......? Proceed at your own risk ......now you know why the lady of the house
casts an evil eye to those of us entering their domains with parts that need some persuasion ......
Ron,
The math is straightforward: aluminum grows right at .000012" per inch per degree. That's "twelve millionths of an inch — PER INCH… per degree.
An easier way to think about this is that aluminum grows: "12 parts per million". If you have a 2" bore, it will grow 24 millionths per degree.
Steel is half that. Right at 6 millionths per degree.
These numbers may sound intimidating or confusing if you're not used to working with them, but it's not a big deal. Let's say you have a 1-3/8" OD bearing you want to put into an aluminum front wheel hub. You take 1.375 (the size of the bore) and multiply it by 12. That equals 16.5. So the hub will grow 16 1/2 millionths per degree over ambient. That means that every 60° gets you .001" (16.5 millionths x 60 = just about .001"). If you carefully measure your bearing AND your bore at room temperature, and it has say... .0015" interference, you know that you need to heat the hub 90° over ambient to get the bore and the bearing to be "equal" in size. It's always good to have .002" to make a bearing nice and easy to drop in, so you need another 120° to get you that. 90° + 120° = 210° (over ambient).
So... on a 70° day, you will need to heat the hub to 280° (in this hypothetical situation) to have .002" clearance when you are ready to drop in the bearing.
I typically recommend NOT bothering to chill bearings -- steel only grows (or shrinks) half as much, so that same 1.375" bearing will only move around 8 millionths per degree. A good freezer will go down close to 0°F, but that only buys you a 70° drop at best, and that's only a bit over half a thousandths ---- not much!
The other thing I would recommend is using a regular oven not a toaster oven (if possible). Having an oven where the hub can sit and "soak" in the heat for a period of time is always the best way to make sure the piece is actually at that temperature. I have a dedicated oven that has 3/4" aluminum plates on both shelves, and once the oven has been on for a while at say... 300°F, those plates are up to temp, and you can just set your aluminum parts (hubs?) on the plate and it will be up to temp fairly quickly because the heat will transfer from the big plate into your small part very well.
Pete
I've been building Mac and Bend engines since 1960, and used to use the regular shop oven in Pop's lawn mower shop. Once I moved into a mobile home 40 miles from the shop, I knew there was no room for a shop oven, so I bought a toaster oven for small engines. I live in a fairly large house now, but the little toaster oven still works just fine for the few engines I may build each year. I've never had the first hint of trouble using the cheapie oven to install bearings in my Macs and West Bends. I leave the engine block in the oven for from 40 minutes to an hour, and the bearings drop right in. It's also good for heating the bearings before dropping them onto the crank. There's no force required to install bearings onto the crank, and the assembled cooled crank and bearing drop into the heated block of their own weight. Most vintage karters are retired and are not wealthy, so we make do with simpler tools. TJ
Ted,
Understood on the oven. :-)
fwiw: I bought a gas wall oven that was near brand new at a Goodwill store for $50 about 15+ years ago. I made a little roll-around cart that holds a 5-gallon propane bottle underneath, re-valved the oven for propane, and have been using it all those years. It was a very inexpensive solution for my shop, and had years where it would run all day every day at 350°F. My only concern with the toaster ovens I've used is that some models don't have really good temperature control, and I like being very careful to never go over 350°F on anything made out of aluminum.
PM
(02-07-2017, 02:55 AM)precisionmetal Wrote: [ -> ]Ron,
The math is straightforward: aluminum grows right at .000012" per inch per degree. That's "twelve millionths of an inch — PER INCH… per degree.
An easier way to think about this is that aluminum grows: "12 parts per million". If you have a 2" bore, it will grow 24 millionths per degree.
Steel is half that. Right at 6 millionths per degree.
These numbers may sound intimidating or confusing if you're not used to working with them, but it's not a big deal. Let's say you have a 1-3/8" OD bearing you want to put into an aluminum front wheel hub. You take 1.375 (the size of the bore) and multiply it by 12. That equals 16.5. So the hub will grow 16 1/2 millionths per degree over ambient. That means that every 60° gets you .001" (16.5 millionths x 60 = just about .001"). If you carefully measure your bearing AND your bore at room temperature, and it has say... .0015" interference, you know that you need to heat the hub 90° over ambient to get the bore and the bearing to be "equal" in size. It's always good to have .002" to make a bearing nice and easy to drop in, so you need another 120° to get you that. 90° + 120° = 210° (over ambient).
So... on a 70° day, you will need to heat the hub to 280° (in this hypothetical situation) to have .002" clearance when you are ready to drop in the bearing.
I typically recommend NOT bothering to chill bearings -- steel only grows (or shrinks) half as much, so that same 1.375" bearing will only move around 8 millionths per degree. A good freezer will go down close to 0°F, but that only buys you a 70° drop at best, and that's only a bit over half a thousandths ---- not much!
The other thing I would recommend is using a regular oven not a toaster oven (if possible). Having an oven where the hub can sit and "soak" in the heat for a period of time is always the best way to make sure the piece is actually at that temperature. I have a dedicated oven that has 3/4" aluminum plates on both shelves, and once the oven has been on for a while at say... 300°F, those plates are up to temp, and you can just set your aluminum parts (hubs?) on the plate and it will be up to temp fairly quickly because the heat will transfer from the big plate into your small part very well.
Pete
I'm gonna have to go with a toaster oven also. Hey Pete, being a retired engineer myself (industrial), I enjoyed seeing the math. Cool stuff. I was wondering about cooling the bearings also but now I don't plan to. The all for response.
Pete, good idea on the portable oven/fuel source. My problem is space. With a couple karts in the garage, plus one under fabrication, the workbenches and my Jeep, I've run out of room! I'm with you on not heating aluminum parts over 350 F. I don't ever heat engine blocks or crankcase covers over 250 F, so no issue there. As a retiree living on SS, with lots of hospital and doctor bills still to pay, I'm not comfortable spending any more money until the new Photon is ready for the track. Hopefully, Doc will give me clearance to run the new beastie once it is ready! It's good having members who have a working knowledge of engineering principles as you do. I'm a retired aerospace mechanical designer myself, and all the learnin' and 50 years of practical experience help out. What's even more helpful is the deep well of knowledge possessed by the vintage karting gang! My Pop once told me that if you don't know the proper way to do a thing, know a friend who DOES know! Ted