I'm not sure I like the idea of putting oil on it.
The Correct Way To Install Bearings
- Thread starter Vintage Engine Repairs
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Exophysical
ArboristSite Operative
I use oil on pretty much every bearing I install. Anything that is going to help the bearing seat easyer is going to reduce the chance of damage.
I understand that, but bearings do spin in chainsaws occasionally.
Exophysical
ArboristSite Operative
Bearings typically spin because either the bearing, shaft, or housing is damaged/ worn out. Its a bit of a catch 22 I guess, I'll keep using oil.
jeagan
ArboristSite Lurker
No, don't use oil on bearing races. Never. Bushings are another story. No oil on bearings.
Red loctite lubricates just fine. Don’t have to worry about them spinning in the cases
In instances where both contact surfaces are hardened (crank and bearing), you can install them using a press or puller with less risk of damage.
However, when dealing with softer bores (like magnesium or aluminum), forcing the bearing will damaging the pocket, however small it may seem. Sometimes it may be unavoidable (e.g., already installed seals between both races that could potentially melt with heat?), but even then I’m not convinced with pre freezing and rapid cooling they’ll come close to melting (>120c). Where at all possible, it’s sensible to maintain factory clearances…
Forcing bearings in these instances changes it from interference to a locational fit and eventually a sliding fit leading to movement between the outer race and pocket, vibration and increasing the risk of a spun bearing. At that point the only lasting solution may be replacing the cases. I’ve used retaining compound in some instances if the fit is still a snug locational fit (after some excellent advise from @pioneerguy) but i wouldn’t feel comfortable if the bearing could be pushed in by hand..
There's a bigger picture here too: scraped-off pocket material can stop the bearing fully seating, especially in the 034, 034 super, 036 & 360’s where the clearances are so damn tight (they seem to be the tightest I’ve come across). Also, in saws that have thin magnesium housings, ones that rely on a web / lattice of magnesium bracing for structural support in lieu of more material and lastly where the oil pump bolt drillings are, can all crack under pressure.
Adding oil to the outer race isn't going to cause a spun bearing if the interference fit is maintained; magnesium absorbs oil quickly, and cases are saturated anyway. However, pressing a bearing with oil might increase risks? I’m not sure..
High direct heat for about 60 seconds to reach 185c allows every bearing I’ve ever done on ope engines to drop in smoothly without altering clearance or damaging paint—it's efficient without downsides.
Ultimately, the method you choose has to work for you, but forcing components unnecessarily has led to damage in my experience and I wouldn’t do it any more, both to my equipment or customers.
I’ve yet to try freezing bearings using liquid
refrigerant from the air dusters and gently warming the case, but again, I don’t think it’s necessary if you follow the steps in the video.
However, when dealing with softer bores (like magnesium or aluminum), forcing the bearing will damaging the pocket, however small it may seem. Sometimes it may be unavoidable (e.g., already installed seals between both races that could potentially melt with heat?), but even then I’m not convinced with pre freezing and rapid cooling they’ll come close to melting (>120c). Where at all possible, it’s sensible to maintain factory clearances…
Forcing bearings in these instances changes it from interference to a locational fit and eventually a sliding fit leading to movement between the outer race and pocket, vibration and increasing the risk of a spun bearing. At that point the only lasting solution may be replacing the cases. I’ve used retaining compound in some instances if the fit is still a snug locational fit (after some excellent advise from @pioneerguy) but i wouldn’t feel comfortable if the bearing could be pushed in by hand..
There's a bigger picture here too: scraped-off pocket material can stop the bearing fully seating, especially in the 034, 034 super, 036 & 360’s where the clearances are so damn tight (they seem to be the tightest I’ve come across). Also, in saws that have thin magnesium housings, ones that rely on a web / lattice of magnesium bracing for structural support in lieu of more material and lastly where the oil pump bolt drillings are, can all crack under pressure.
Adding oil to the outer race isn't going to cause a spun bearing if the interference fit is maintained; magnesium absorbs oil quickly, and cases are saturated anyway. However, pressing a bearing with oil might increase risks? I’m not sure..
High direct heat for about 60 seconds to reach 185c allows every bearing I’ve ever done on ope engines to drop in smoothly without altering clearance or damaging paint—it's efficient without downsides.
Ultimately, the method you choose has to work for you, but forcing components unnecessarily has led to damage in my experience and I wouldn’t do it any more, both to my equipment or customers.
I’ve yet to try freezing bearings using liquid
refrigerant from the air dusters and gently warming the case, but again, I don’t think it’s necessary if you follow the steps in the video.
If one was to go back prior to 07 and read all the threads on this site concerning pulling crankcases together over bearings already installed on crankshafts there was no one using heat to swell the cases. I posted a thread about using heat to install bearings and it freaked many members out. The replies were mostly concerned with burning paint,discoloring of the cases and melting bearing spacers. Most all threads back then was about using long bolts or all thread to draw the cases in over the bearings ,that subjected the balls in the bearing to sustain a heavy side load. There were also many that were just driving bearings in with presses or hammering them using sockets. After a lot of the uproar died down there were a few mentions of others trying to use heat and it soon became the norm, using many different sources of heat and also the temps themselves. Some Stihl saws use a steel reinforced pocket for the bearings on the clutch side so they take a bit more heat to expand them than the mag or aluminum cases. I have yet to see a bearing damaged by heating the cases and if one has everything pre sorted and laid out in handy fashion the whole job can be done in 30 mins or so.. Dolmar taught us to heat the cases and install the bearings in their pockets first, then slip them on over the crank, this worked well but Stihl
advises to install the bearings on the crank first, then draw the cases on over the bearings, either way has worked well for me since I was well versed in using heat to swell metals from my time working in the machine shops and in the marine repair yards as far back as the early 70`s.
advises to install the bearings on the crank first, then draw the cases on over the bearings, either way has worked well for me since I was well versed in using heat to swell metals from my time working in the machine shops and in the marine repair yards as far back as the early 70`s.
I have heated the case halves in an oven to 200 degrees and frozen the bearings after reading about the bearings just "dropping" in. If it made much difference it did not jump out at me.
Sidecarflip, Thanks for all that. Don't know what your prognosis is but sure hoping and Praying you can beat the big C.
OT
In my experience, the temperatures achievable in a home freezer for metal shrinkage won’t lead to a measurable required reduction in pocket temperature. For instance, freezing a bearing to -15°C might allow you to fit it in at 180°instead of 185°C. In practice, there's no appreciable difference, at least with a propane torch. Initial alignment of that bearing has a bigger effect than a few degrees of expansion here.
I only freeze the bearings to reduce the chances of annealing the cages and balls. If I’m heating thick cases which will retain the heat longer and I accidentally go to, let’s say, 240°C due to either inaccurate temp gum readings or emissivity on shiny cases and annealing starts at around 200°C for the bearing cage, it doesn’t sit well with me.
I will attempt to replace/repair anything on my saws apart from bearings, seals and splitting cases. I have tried on two saws, both times I failed to get a proper seal, failed pressure test with time / parts wasted. I've learned my limitation and now I have a friendly mechanic who does these aspects for me (while I watch). These types of repair take real skill to get everything seated properly and you probably only develop this from working regularly on a variety of saw brands.
We do the Fahrenheit thing over here usually. Quite different from 200C.
Interference fit is usually .001 to .0015 (in our measurement USA). You can look that up in a Machinery's Handbook. Between heating the parent casting boss and a deep freeze, that is easily obtained without the use of liquid N, which a layperson cannot obtain anyway. You could 'bathe' the bearing in solid Carbon Dioxide, aka: Dry Ice, which you can obtain.
One thing that is often overlooked or not even thought about with the fit of these bearings is that the case actually expands a fair bit when the engine is run , the case absorbs some of the heat and a bearing that was loose at the install at room temp will be even more loose when the engine is at operating temp,when run on long extended cuts such as bucking large diameter trunks or milling situations the cases get quite hot and the bearings being made mostly of steel do not expand as much as the mag or aluminum crankcase.
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The temp would be 392F
not sure why you think liquid nitrogen can't be had by anyone. Just need to stop by any welding supply/gas shop that has it here and walk out with a dewar (or roll the larger ones). Wasn't any issue to get it when I worked over the road either, no matter where I was.
On the bearing mounting subject, just about every mfg has books with procedures detailing how they reccomend bearing installation.
Skf
https://www.skf.com/us/support/mounting-instructions
Nachi
https://www.nachi-india.com/services/bearing-installation
Skf
https://www.skf.com/us/support/mounting-instructions
Nachi
https://www.nachi-india.com/services/bearing-installation
There are restrictions imposed by our new administration concerning the public possession of cryogenic gas now. I get mine from my air-gas compressor station but I have a commercial account with them. We now reside in a 'protect the public from themselves' society. Cryogenic substances now have additional controls on them, not like before and it is dangerous if not handled carefully. Just like the the large (over 125 cubic foot) bottles of compressed Oxygen and why I have my large bottles filled, my Oxygen bottle for my O/A torch is a 250 btw. In fact I have all my bottles filled as I own them all, outright. That includes all my 125 cubic foot 75/25 bottles, my 100% Argon bottles as well. They all have my company name painted on them and I have special tags that go on them to notify the compressor attendants not to exchange, but fill only. I have and own at the minimum, 2 bottles of each flavor on hand all the time, kept in an outside bottle rack. I use a lot of gas as a rule in the shop when we are in production and that is now.
