2 Stroke, how to install crankshaft

[770]

im doing a overhaul on my 125cc 2 stroke engine. i have already put in the bearings in the crankcase. i then put my crankshaft in the freezer for about 12 hours and then tried to press it in with a press with no results. do you guys have any suggestions? Would it be safe to heat up the bearings with a blow torch?

[skatefreak]

With my NSR125 it was a case of bearings in the freezer/engine casings in the oven - bearings dropped right in.
Crank in the freezer and it dropped most of the way in.
Tighened up the crank cases and it pulled the bearings along onto the shaft.

This may or may not be the right way of doing it and I have not got round to running the engine yet (finishing panels is a nightmare!).

Best regards

-Jvr

[Pete.]

Put a spacer in between the crank webs and press on the main bearings. Heat one side case and drop in the crank. Build the gearbox and other bits into that crank casing, heat the other side and drop it on, press home. Remove crank web spacer.

Check out the coefficient of expansion of steel and aluminium. Freezing steel has about half the effect of heating aluminium but since the bearing is smaller the overall difference is less.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[andy_uk]

Depends on the engine...
Mine is (apparently) supposed to have the bearings fitted on the crank first (after heating bearings in the oven etc) then use a puller to pull the crankshaft into the casing.
Only one side needed this though, the other just needed the casing warming slightly and tapping on gently with a wooden mallet.
____________________
Aprilia Classic 125, GS500E, ER5-A1, ER5-C4, ER6 & an XJ6 project frame...

[770]

In the manual it says that i first need to install the bearings inside the crankcase. (Which i already have done.) then it says "install the crankshaft into the pre-heated bearings". Should i use a blow torch?

[770]

In the manual it says that i first need to install the bearings inside the crankcase. (Which i already have done.) then it says "install the crankshaft into the pre-heated bearings". Should i use a blow torch?

[biker_bob]

Blow torch on the bearings while they are in an aluminium case seems a bit dodgy to me. Could melt / distort / crack the case. The bearing will get a bit bigger and it's already in a tight hole.

If you're going this route I'd put the whole casing in the oven (with dinner to save wasting energy ;o) ) and wind it up to max. Aluminium melts around 660'c, you oven will only go up to about 250'c while a blow torch will go up to nearly 2000'c, easily enough to melt ally.

Did you actually use a proper press? I used to do it with a hammer and block of wood or use a vice as a press. Now I have a 2t press so they go in truly square and it's a LOT easier. Just support / bear on the bearing inner race using a tube.

[Pete.]