Bearing temps frustration.

[Vintage Engine Repairs]

Hi,

I have noticed how the older machines all have a much sweeter bearing to pocket fit.
I’m working on an engine from the 50’s and you literally need no more than 100c and the bearing will fall out.
In the 60-70’s the chainsaws seem to be around 130c, still fine, nice snug fit but temperatures that won’t damage anything.

From the 80’s onwards the pockets are so bloody tight and need temperatures of 185c or more to get them in. It’s a pain in the arse and so unnecessary. If you don’t use heat you can end up cracking the pocket, gouging the pocket or poor alignment. If you use heat you can overheat the races and balls, in fact everything and chances are you’ll get the bearing stuck half way and have to pound it out. Why?

.

 

[deye223]

Are you freezing the bearings

 

[Vintage Engine Repairs]

Are you freezing the bearings

Na I don’t find it makes any practical difference honestly.

 

[ironman_gq]

Freeze the bearings. It's not how hot the case is that makes them drop in, it's the temperature differential between the two that makes the fit. If you're heating the cases to 185C and using bearings that are 20C you have a 165C temp delta. If you freeze the bearings to -20C you only need to heat the case to 145C.

I've rebuilt quite a few drivetrains that have bearings in bores or shafted bearings. In my experience a hot bearing won't drop on the shafts without quite a bit of persuasion from the drive sleeve, if I freeze the shaft the bearings will drop right on without any tapping or hammering.

 

[sean donato]

We used the heat freeze method all the time at the machine shop. Worked very well. I do the same thing with case bearings at the house. (Don't tell my wife lol)

 

[Dean-O]

I freeze the bearings every single time I’m doing a case split. Makes it so much easier just did a 362 a month ago, froze the bearings heated the case half’s with heat gun and dropped them right in.

 

[Huskybill]

I have a arbor press and a 12 ton hydraulic press with the clamshells for removing bearings. I also have The Husqvarna assembly tools for most saws with the disassembly clamp.

Check very closely when using heat as it cools the bearing can push out.

When I built Bullard turret lathes we installed the large timkin roller bearing, frozen well below zero. On the larger 144” chucks we used dry ice.

 

[MagraAdam]

is it because over time the metallurgy has gotten better to reduce the expansion/contraction of the metals, so that the cases don't crack if left in the snow or expand unevenly on the exhaust side etc? Excluding the bearing removal, it sounds like a good thing on paper? would it reduce the need to warm up the engine before use?

 

[buzz sawyer]

I would think that with higher rpms and running temps, a tighter fit would be needed.

 

[Chainmale]

Magnesium, and aluminium alloys would only expand and contract a fraction of what steel and iron do

 

[frank_]

Magnesium, and aluminium alloys would only expand and contract a fraction of what steel and iron do

is the reverse of that surely ?
plus older engines are a lot less stressed

 

[MagraAdam]

is the reverse of that surely ?
plus older engines are a lot less stressed

I believe you're right

https://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

 

[Canyon Angler]

Magnesium, and aluminium alloys would only expand and contract a fraction of what steel and iron do

Actually, aluminum and magnesium alloys expand/contract about twice as much as steel for a given Δt ...

https://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

 

[Mad Professor]

Coefficient of expansion:

Aluminum 13
Magnesium 14
Copper 9.8
Cast Iron 5.8
Cast steel 7
Mild steel 6
Nickel alloys 6-8

 

[Chainmale]

Oops Sorry, seems I stand corrected.
At least I've learnt something from it

 

[Canyon Angler]

This may explain why Guadaost found that chilling the bearing made far less difference than heating the aluminum case.

Still, chilling the bearing can't hurt and might help...I once had to replace a bearing on the arbor shaft of my Powermatic table saw, and freezing the shaft helped (some)...tho it still needed the BFH...

 

[Huskybill]

I run a richer oil ratio. I don’t believe in 50:1 mix.

 

[Vintage Engine Repairs]

I’ll do a deep freeze and see what it measures in dia before and after.

 

[Vintage Engine Repairs]

Ok, starting diameter is 28.00mm at room temp

It’s in with the ice cubes in the freezer and I’ll re measure it once it’s been 24 hours.

 

[Mad Professor]

If you can get a hold of some dry ice that will get you -78 oC. You can also make a dry ice bath with ethanol/grain alcohol, that will cool the bearing down quick.