Crank install advice

[jredding]

Hey guys,

About to tackle my first bottom end rebuild.
I'm after some on advice on the best method for installing the crank.

Option 1: Crank puller.
I've seen these on Ebay but they're a bit pricey. Thought i'd get some advice before diving in.
https://www.youtube.com/watch?v=4B5Gf06QrTo



Option 2: Heating bearings.
I saw this in alexbrown64's yz125k build thread http://forum.ozvmx.com/index.php?topic=36259.msg375743#msg375743
Heat sockets up and expand the inner bearing race, slide the crank in.
I'll like this method but it seems to good to be true. hah



Option 3: Hit and hope.
Just smack it in with a mallet...

Any help would be ace.

[matcho mick]

chuck the crank in the freezer (when the missus is out  ) then heat the bearings with the sockets should do the trick,think all the methods have been thrashed out on here before??,

[crossedup2]

There are several ways of doing this but the simple way is always the best.

So check out this youtube site by Ken O' Conner. https://youtu.be/iKeg7z4x5JQ

I've used this in the last 5 rebuilds and it just works so easily

Peter B

[evo550]

I fit bearings to crank first, by heating bearings and freeze crank, mains just slide on, then put the whole assembly back in freezer, give it a couple of hours and it will just drop into cases without heating them.

[Lozza]

There are several ways of doing this but the simple way is always the best.

So check out this youtube site by Ken O' Conner. https://youtu.be/iKeg7z4x5JQ

I've used this in the last 5 rebuilds and it just works so easily

Peter B

Poor old Ken needs to jump into the 21st century

https://www.youtube.com/watch?v=2GGr8wsxhZI

Thats the only way to do it

[jredding]

There are several ways of doing this but the simple way is always the best.

So check out this youtube site by Ken O' Conner. https://youtu.be/iKeg7z4x5JQ

I've used this in the last 5 rebuilds and it just works so easily

Peter B

Thanks guys! Looks like i'll be heating up those bearings and slipping the crank in. Sounds easy enough.
Here's to hoping it all goes to plan.

[Tomas]

Also, not many old bikes have used liquid gasket materials. When liquid gasket is used in motor that originally used paper gasket, you may end up puting axial pressure on bearings and that may cause them to fail. Paper gasket usually counts for about 0.2-0.3mm not sure how thick liquid gasket is when compressed during assembly.

[jredding]

Are you suggesting that if a bike originally used a paper gasket it would be wise to use a paper gasket on the rebuild?
The bike is '74 YZ125a. I don't have my manual handy but i'm pretty sure they used liquid gaskets. I could be wrong tho.

[matcho mick]

Thomas is generalising JR,some do,some don't have centre gaskets,we're talking early stuff,spanish do,but it's handy they have shimmed cranks so you can flick the gasket,you go right ahead & use liquid gasket on your YZ,good luck with the build,

[MaxPower]

Poor old Ken needs to jump into the 21st century

https://www.youtube.com/watch?v=2GGr8wsxhZI

Thats the only way to do it

I'm not being sarcastic, I'm really asking, Isn't there a reason cranks aren't made so a slip fit of a main bearing isn't possible?

[Momus]

Poor old Ken needs to jump into the 21st century

https://www.youtube.com/watch?v=2GGr8wsxhZI

Thats the only way to do it

I'm not being sarcastic, I'm really asking, Isn't there a reason cranks aren't made so a slip fit of a main bearing isn't possible?

Slip fit means there is the risk of the journal spinning against the bearing inner bore and destroying itself against the much harder bearing. On the drive side of cranks the primary gear is shouldered against the bearing inner and nutted tight. This enables dissasembly. On the magneto side  it is usually a light draw fit to stop spinning and perhaps to dilate the bearing inner slightly to give the correct running clearance.

[Lozza]

Poor old Ken needs to jump into the 21st century

https://www.youtube.com/watch?v=2GGr8wsxhZI

Thats the only way to do it

I'm not being sarcastic, I'm really asking, Isn't there a reason cranks aren't made so a slip fit of a main bearing isn't possible?

Depends on who made it. Most high end two strokes are slip fitted from the factory. Rotax has been doing that since the late 70's