Putting new piston in my 2011 YZ450 today. Any tips and tricks?

Never pulled the head off a 4t before. Anyone have any tips or tricks to make this as simple as possible? Thanks.

Read the whole procedure in the manual first. Then read it again. Then do it.

The biggest challenge will be compressing the oil rings. Always stuff rags or something in the crankcase under the piston to avoid dropping a circlip into the sump.

So I got it apart, everything went smoother then I had anticipated. Here are some pics of my cylinder. Is the vertical line a bad thing? It says in the manual vertical scratches are bad and to replace cylinder but you can still see the cross hatching so the vertical parts almost look factory. Measurements are all in spec 97.00mm. Thanks Grey. ImageUploadedByThumper Talk1418609714.011164.jpgImageUploadedByThumper Talk1418609727.385417.jpgImageUploadedByThumper Talk1418609740.134053.jpg

Those aren't scratches, just aluminum from the piston.

Clean it and ride happy

If you run a brush hone through it, it looks like it will clean up pretty well.  I circled the two areas that concern me the most.  If these two spots will disappear after less than 15 seconds total time with a silicon carbide hone (10 with aluminum oxide) you should be OK.

 

 

bore.png

If you run a brush hone through it, it looks like it will clean up pretty well. I circled the two areas that concern me the most. If these two spots will disappear after less than 15 seconds total time with a silicon carbide hone (10 with aluminum oxide) you should be OK.

Ok awesome, I did order a flex-hone with my parts luckily so I will do that for sure. Hopefully it cleans up. Thanks again, super handy being able to talk to someone with knowledge on this stuff.

I just did my WR and a friend recommended I insert the circlip on one side of the piston, then insert the piston w/rings into the cylinder while they are off the bike.  Then stick the cylinder / piston combo onto the connecting rod and insert wristpin / last circlip.

 

I did that method and it seemed to work pretty good.  Just make sure you stick a rag or paper towels into the case in the event you drop the circlip.

That works OK, but the problem is that the wrist pin bore is so close to the oil ring groove that the oil ring has to be down out of the actual bore and into the chamfer at the bottom of the sleeve, anyway, so you don't get as much help from doing that as you might want. 

 

Putting a couple of thin pieces of wood (or a single piece with a slot in it for the connecting rod) under the piston to give it somewhere solid to sit on while you work the jug onto it is another good approach.

 

The thing you really have to watch for is snagging the ends of the oil ring and rolling the ring out of the groove.

The cylinder looks like it should clean up very well.

I have access to a hone we can use tomorrow when you come to pick up the tank and exhaust for the snowbike.

See ya tomorrow bud!!

 

Craig

Got the bike back together and it runs great. The honing cleaned the cylinder right up. I broke it in for an hour on tires and then put the snow bike kit on. Put a good 4 or 5 hours on it yesterday and it didn't miss a beat. ImageUploadedByThumper Talk1419264514.586241.jpg

Got the bike back together and it runs great. The honing cleaned the cylinder right up. I broke it in for an hour on tires and then put the snow bike kit on. Put a good 4 or 5 hours on it yesterday and it didn't miss a beat. ImageUploadedByThumper Talk1419264514.586241.jpg

What's the name of that trail snowy. That's quite a bit of snow you got there.

What's the name of that trail snowy. That's quite a bit of snow you got there.

It was in a riding area in Fernie, British Columbia.

A good honing stone will make that cylinder look like new.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now