Aluminium Casting, Heat Or Cool To Remove Bearings

[megadodo]

One for you engineering types out there. One of my far too many projects is to get a ride on mower up running from 2 scrap ones. I now have a chassis that I can drive around but it wont cut much grass as the the bearings in the cutting deck are shot. I have, to my surprise, managed to sort out replacements despite them being a mix of metric and imperial in the one bearing? There are 2 but they sit in an aluminium housing that bolts to the deck. I thought about drifting them out but I remember something about the assembly needed to be heated or cooled to allow the bearings to removed more easily but I cant work out which route to take. Which do I do and why please, before my head explodes with the thought process behind it?

[Shaft]

Heat in the oven to expand the aluminium.

This will expand further than the bearing due to the CTE differences.

[fry61]

Or if inner race of bearing can be removed -- deposit a ring of weld inside the outer shell -- when cool outer should just drop out as the weld has caused the shell to shrink when the weld metal cools.

[andyparry]

Ally expands at about 13 parts per and stainless at about 9 parts per. Depending on the fit of the bearing into the housing, you may need a couple of hundred degrees of difference between the two. For a 30mm bore, 200c would increase the bore by 0.08mm by my reckoning. The trick is to stop the bearing going up in temperature as well! If you can, leave a big cold bar in the bearing to act as a heat sink for the bearing.

 

See http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.htmlfor more detail.

[Guest peter2b2002]

Ally expands at about 13 parts per and stainless at about 9 parts per. Depending on the fit of the bearing into the housing, you may need a couple of hundred degrees of difference between the two. For a 30mm bore, 200c would increase the bore by 0.08mm by my reckoning. The trick is to stop the bearing going up in temperature as well! If you can, leave a big cold bar in the bearing to act as a heat sink for the bearing.

 

See http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.htmlfor more detail.

heat the deck as quick as possible to stop the bearing from fealing the heat and as said wet rag inside the bearing or wrapped arround the bar

peter-2b

[Guest mower man]

Hi when repairing many of these machines [ they are all very similar ! ] in a previous existence normal procedure was thrash them out with a 2 lb hammer and bronze or brass drift ! ,never came across one that was any trouble , all the other methods mentioned could be used if needed but never had one that awkward ,we are talking hundreds by the way in 9 years ,warm the casting if you want, smash the bearing and use a mig or arc welder which ever takes your fancy ,usualy the shaft for the blade boss is furtled any way so replacements may be needed . Mainly I worked on Euro twin cut machines but like whit goods the same or very similar one where badged in a number of makes ! mick now you know where the name comes from

[megadodo]

Thanks all, I'll see if I can get the bearings out tomorrow, the new ones had arrived by the time I as home. Mick, thanks for the heads up, I was a bit worried the casting wouldn't take to having the bearings just drifted out! Luckily the shaft is in good condition and the new bearings slide nicely onto it but the part the blade fits to that goes on that shaft has a chunk out of it so that's my next stumbling block assuming I swap the bearings without cracking the casting!

[Guest mower man]

Blade boss is virtualy a sacrificial part if the blade hits some thing hard the two pins /lugs break off and on a twin bladed deck blade clash can result! if a single blade type it just wont cut properly as ever take your time support the casting properly and hit it square and FIRMLY ! dont tip tap If you were closer I'd come and show you ! mick

[megadodo]

Job done, knocked out the inner race of the broken bearing and that allowed me to drift the opposite bearing out, that of course allowed acces to the remains of the other one. Both came out with a couple of firm blows. I even managed to rig the blade boss back together. Just 2 new woodruff keys for the jack shaft and I'll be mowing the grass whilst sitting down! Thanks for the help folks.