best way to change bearings

[tom galdys]

Ray's tool is fantastic. He should sell them. Tom

 

[David Bryant]

Thanks for the heads-up on temperature, this was my main concern- ie. tweaking the temper of the aluminum casting.

Looks like 250 - 300 degrees F is probably safe range.

 

[Shane Midkiff]

Hey Jim,

I did some research on the material a few years back and maybe you can comment on this as well. Most small engine's .12 to .45 the case does not need to be heated up more than 250 degrees (f) for proper expansion to change out the bearings and 225 degrees (f) will do as well. Some larger case's or stubborn bearings need a little more heat but 275 degrees (F) will do just fine and is still in a safe range.

Shane

 

[Jim Allen]

Hey Jim,

I did some research on the material a few years back and maybe you can comment on this as well. Most small engine's .12 to .45 the case does not need to be heated up more than 250 degrees (f) for proper expansion to change out the bearings and 225 degrees (f) will do as well. Some larger case's or stubborn bearings need a little more heat but 275 degrees (F) will do just fine and is still in a safe range.

Shane

Shane,

The amount of heat required will depend on the amount of press fit used to hold the bearings in their housings. Engines, such as the Nelson, use heavy press fit amounts (.0004" to.0005") with very high clearance bearings. When considering the machining tolerances possible, even low press amounts (.0002" to .0003"), could easily present a problem. Heat the thing very carefully with a butane torch in the bearing area as someone has already stated.

Jim

 

[moparbarn]

good info so far . one thing i need to add is where to apply pressure to bearings when installing them. when pressing a bearing on a shaft, apply pressure to the inner race only. when pressing a bearing into a housing - pto or crankcase, apply pressure to the outer race only. most bearings are an easy fit on the crankshaft, so i prefer to install them into the case first. the object is to not let the balls in the bearing take the load of installing it. they are not designed to take the sort of loads put on them from installing. they are designed to accept loads when rolling, & in contact with the full arc of the races, while bathed in oil. a bearing in motion actually "hydroplanes" on a thin film of oil. stop the motion, & the oil offers NO protection. transferring the loads of installation across the balls makes them take the load on a VERY small surface (the edge of the race), & while not rolling, which will not allow them to transfer the pressure properly. this can cause flat spots in the balls. it can also cause the races to distort & get dimples in them, where the balls pressed against them. failure is almost gauranteed, in a short time......this info can be applied to ALL bearings, big or small, needle, roller or ball.

 

[David Bryant]

What do you use to insert bearings into case? A circular tool(only contacts outer race)?

What about alignment (installing bearings without crankshaft)?

 

[Daniel's Racing]

No need to freeze or heat the whole case in a oven. Freezing the bearing will only draw heat out of case instantly should you not seat it quickly enough and does very little to reduce the diameter besides the condensation water contaminating your new bearings.

The easiest and safest method is to just use a heat gun and blow the heat directly through the bore for 30 seconds and the bearing will go in easily without having to play hot potatoe with a 300 degree case.

 

[moparbarn]

What do you use to insert bearings into case? A circular tool(only contacts outer race)?

What about alignment (installing bearings without crankshaft)?

yes, any sort of "mandrel" will work. deepwell mechanic's sockets work great !

 

[glenng]

No need to freeze or heat the whole case in a oven. Freezing the bearing will only draw heat out of case instantly should you not seat it quickly enough and does very little to reduce the diameter besides the condensation water contaminating your new bearings.

The easiest and safest method is to just use a heat gun and blow the heat directly through the bore for 30 seconds and the bearing will go in easily without having to play hot potatoe with a 300 degree case.

I'm supprised nobody else mentioned the water condensation when freezing- as the bearing returns to room temp you can see it "sweat". Freezing does little to "shrink" small parts but is nec. on larger stuff with more press fit.

 

[Joe Warren]

I use a torch & a pair of vise grips, Empty the engine out of all parts, clamp the vise grips on the engine mouting rail to hold the engine case.. heat the case in areas around the brgs 1-2 minutes. keep moving the case. Dump the brgs out on a clean rag. Brake clean the case & wipe out if needed. Have all rotating parts already cleaned and ready to go. heat the case again, drop the brgs in.. they should fall in fully. Install the crank & check rotation. Always check crankcase o`rings or gaskets both can cause problems later. if it is a CMB engine? with rear crank case brg cover i like to install this cover while the case is still warm But the rear hsg room temp. Torque the crankcase bolts, Install flywheel & collet, Check engine rotation while tightening the collet...Constantly check for easy rotation as you assembly the engine to make sure there are no binding issues. Use Quality Brgs.. I have Won a lot of Races with BOCABEARINGS.com products. Use after run oil in the engine & always clear out cooling water jacket free of water after running. Wrap the engine up in a paper towel or rag No plastic bags.......

 

[SayMikey]

My method has been:

(A) Placing case (w/old bearings installed) into pre-heated oven (I believe approx 250 to 350 degrees F), heat for X number of minutes (I believe 10 to 20min)

( B) Slide new large inner bearing onto crankshaft

© Working swiftly Carefully remove case from oven (using mitt). I carefully tap on the outer case with safe object (I use wooden spoon), old bearings should fall out.

(D) Quickly slide crankshaft into position with large inner-bearing in place. Slide outer-bearing onto crankshaft front-end. Slide flywheel and collet onto crankshaft, hand-tighten cable collet nut. Bearings should self-position

This is the way I've been doing it for years.

I also use this method,using the crank really keeps the bearings straight and no binds after cool