Posts
391
Joined
2/13/2013
Location
NE
US
Edited Date/Time
9/5/2013 6:20pm
putting a new pin and bearing on a crank for a 04 yz 125 and i cant find the gasket for the middle of the engine. between the two big cases.
question 1: is there something i should use other then a normal gasket?
question 2: should i use grease when pressing the new pin and bearing in?
any other tips would be helpful. this is my first time working in the bottom end of an engine
thanks
question 1: is there something i should use other then a normal gasket?
question 2: should i use grease when pressing the new pin and bearing in?
any other tips would be helpful. this is my first time working in the bottom end of an engine
thanks
Don't use grease.
If you freeze the complete crank after its trued it will be easier to press the cases together
Press the cases together slowly and spin the transmissions shafts as you put them together
The Shop
Watch them and read the run out on the gauge yourself.
You should put crank bearings in also.
If you put the bearings in the freezer the day before or several hours before needed they slip right in the case if the case is
Warmed till you can not lay your hand on it long.
If they hang up a c clamp or vice can be used to push them in,even a tap from a dead blow hammer.
When frozen they usually slide right in.
The case halves should slip close enuff together so you can use the bolts to pull it the rest of the way,
No binding here,it should slip together easy if you got all the shafts in correct.
It is important that the yamabond be on both case halves,a thin coat.
Especially around the crank,this seal must be correct,if it pulls air between the caes the engine goes lean and will fail.
I install new crank seals last ,wipe a litte oil on the lip and push in with fingers usually.
A piece of pvc pipe the right diameter works to push in seals.
Tip#2 DON,T take it to an auto shop!
Another huge mistake is people assembling the center cases. It is very easy to throw a nicely balanced crank out of whack(the smaller the CC the easier) assembling the cases by "tapping" them together back and forth getting it to slide down over the crank. Even the method of using your center case screws to pull the cases together evenly is butchery to me. You can use the same cooling procedure you used with your "cold" main bearings and heated cases by putting your assembled crank in the freezer. If you have heated your cases to install your "cold" main bearings, then you can allow a little time for your bearings to absorb that heat before sliding the crank into one of your case halves. Some cases and cranks are more of a "pressed fit" on one side and a "slip fit" on the other case side. Refer to a manual for your exact model(both sides may be a pressed fit"). Some people put the crank seals in before(make sure cases are not too hot), and some people do afterwards. The important part is not to harm the seal.
If your cases do not slide together easily on their own, you should have the proper crank pulling tool to finish the job.
With a good crank jig you can be very close when you press it together and need only minor taps with the brass hammer. Yamaha had a nice jig that they sold through their tool supplier but it was $600 back in 1978 but you could have the crank pressed together and be almost within tolerance. I have seen people spend an hour getting a crank zeroed and then when they get it all bolted together and it has some binding they hit the crank end with a hammer to free it up. why bother to zero it when they smack it with a hammer .DOH
http://www.eric-gorr.com/incl/pdfs/2%20stroke%20top%20end%20and%20perfo…
(all of it) and buy the factory manual. Buy whatever tools you need and go for it. If you are doing something that is ruining the surface and bending etc., you are doing it wrong. Really....read that Gorr article a few times as it has great advice and shows how to do it without hammering it. Also, either buy a new non Wiseco crank or have someone rebuild it. Use the search as I remember a thread about guys who rebuild cranks for a living
OH...WASH YOUR BIKE BEFORE YOU START
EDIT: I just noticed that the Gorr article is missing some pages...Damn. Buy the book it is excellent.
Freeze crank and bearings.
Heat gun to "relax" the cases for bearing and crank removal/install
Double, no triple check for washers, shims or spacers that are stuck to surfaces. This will save a lot of grief later, nothing worse than trying to pull out a tranny in one piece and hearing a "tink" as the 0.5mm spacer drops from somewhere.
Build or buy a crank puller, I built one for about $10 out of threaded rod, pipe and pvc.
Buy or borrow a flywheel puller, $12 from China on ebay
Always replace the main bearings and main seals when splitting the cases.
Pit Row
oh and what is the normal tolerance? this is my first time doing anything to do with the bottom end besides shifting linkage in a 98 kx250 (which didnt involve splitting the case) and before everyone tells me to take it in or have a shop do it, i want to learn how to do this myself. everyone has to start somewhere.
thanks
Get a Yamaha manual for that year and model, it will tell you side clearance and give you everything you need to know, if you don't have a manual then you are in over your head.
The one lesson you will learn by doing the crank by yourself without proper equipment and experience is that you will pay to have it done the right way when it blows up and destroys top ends, and even your cases.
Out of balance crank might be ok, but just don't install the powerband, because then it will vibrate real bad.
Post a reply to: bottom end