New here - looking for top end pointers - please!

[JimM]

Hello all,
Well it's time to rebuild the top end on my 00 YZ 250. It's running great, I just feel like I should.
Anyway, although I've never done this, I'm no dunce with a wrench, and I'm NOT paying the shop $340 plus parts!! If there are any good sites with pointers, tips and pictures to help me along, that would be great. Any pointers, do's, dont's "look out fo this or that" anyone wants to lend, that would be great as well. It seems like it should be simple enough.

One thing I'm confused on. I orderd a Wiseco piston. Then I find out on another site that all factory cylinders are not necessarily EXACTLY the same size, and various piston sizes exist on a given year and model. Well hell, I just ordered the "2000 YZ250 piston" !! Should I worry? I wasn't given any other options on the site except for "oversize" The guy at the shop told be Wiseco's are tighter than stock, and I should be just fine. I wanted more opinions though.
I'm the original owner, and the bike has not been raced or ridden hard. I ride in the woods, mostly at Lower RPM. I've probably put a years worth of riding on the bike, which is why this top end has lasted so long. I'm picking things up though this year, and after this rebuild I'll do it a bit more often.

Thanks for any help.

Jim

[DCox]

Hi Jim, welcome aboard.

Many can help you here . . . . However, one member by the name of Faded is extremely proficient in all-things-technical. He usually manifests himself with these types of posts, but in the event that he doesn't, PM him or you can offer a sacrifice of broken fiber reeds with a mixture of gas and premix at 40:1. That is sure to invoke him.

[RaceyCRF250]

just put in a google search, im sure things should pop up filled with pics and full descriptions!! either that or eventually your gonna need a service manual, that will take you step by step and you'll be riding in no time!

by the way, welcome to the second most addicting thing on the planet right after nicotine.(and no i dont know from experience, im only 16)

[brokenbones]

I just did the top end on my 01 YZ 250, it is alot easier then you think. Now that I have done it once, I think I could do it again in a couple hours at most. The real bugger of the whole thing was wiggling out the carb so that I could get the cylinder out. Make sure you remove the powervalve linkage from the kickstarter side of the motor before you start prying on the cylinder. And make sure you put in a new wrist pin bearing ($12.00 or so) and get the piston facing the right way when you install it (arrow on the piston pointing at the exhaust port). The wiseco pro-lite piston comes with; piston, wrist pin, circlips and rings. Cometic Gasket set ($25.00) not included, but needed. About the piston size thing, the standard size is the correct size for you. Wiseco pistons come with decent instruction too...Check for any damage on your cylinder walls and keep everything COMPLETELY free of dirt.

Good luck! Welcome to ATM!

[Roostman]

Your gonna have a little trouble getting the cylinder off more than likely. This is due to some water from washing your bike that gets under the cylinder mounting nuts and sits on the studs and dowels. The water rusts the dowels and studs and makes it a bear to get the cylinder off sometimes. If the cylinder doesnt come right off after you take the nuts off the cylinder studs, spray a little WD40 on the studs and let it sit awhile . You definately dont want to pry the cylinder off but you can tap lightly with a rubber or leather mallet in upward motions around the 4 stud locations to help break it free. Dont hit to hard. Once you get the cylinder up, place a NEW CLEAN terrycloth towel around the rod to cushion the piston when you pull the cylinder up. Use that same towel to stuff around the rod and fill the crankcase void to ensure you dont drop anything (especially the pin clips) into the case. THROW THE OLD WRISTPIN CLIPS IN THE TRASH IMEDIATELY AFTER REMOVAL SO THAT YOU DONT REUSE THEM. THEY WILL CAUSE A FAILURE FOR SURE IF YOU REUSE THEM. The rest is pretty simple and if you are mechanically inclined, wont be hard to figure out.

As for the Wiseco piston, Im not a big fan of them but many on here are. I like to stick with stock as there is not much if any to be gained by deviating from the stock piston. Others will tell you different but Ive talked with the guys at Pro Circuit and Tom Morgan about this and they concur that the stock is a great choice if not the best choice. Good luck and let us know how it comes out.

[JimM]

Thanks guys, just what I was looking for! Much appreciated.

Jim

[cr2504life]

Don't forget to put the gap on the circlips facing either up or down, they can fly out if you don't. Im not sure which is supposed to be better, i just know that your not supposed to put them in sideways. Good luck.

[Roostman]

It doesnt matter which way the circlips go in just that you dont have the open part of the clip lined up with the cutout on the piston (or youll have a hell of a time gettin them out in the future). It does help to put them in where it will be easier to get them out in the future....meaning dont put them where the opening of the clip is opposite of the cutout of the piston, cause this will be very hard to remove later as well.

[Dell30rb]

These guys have pretty much spelled it out...

Get a friend to help with installing the cylinder. You need to pinch the ring with your fingers and have someone else lower the cylinder down, so you can push the piston and ring (s) into the cylinder. Be careful to keep the cylinder straight when putting it on... do not twist it in either direction. The ring may snag a port and break.

[Roostman]

Face the opening of the clip at 6:00 or 2:00 I think would be the best for getting them out in the future. Usually the cutout for removing them is at 4:00. Whatever the case, make a side of the clip accessable to the removal cutout so that your able to bend the clip inward for removal......you follow me?

[JimM]

I'm pretty sure I understand, however....
I'm going to print this out and have it by my side while I'm doing the job. I actually need to see what you guys are referring to. I've never pulled one of these things apart before. I'm sure it will all make sense as soon as I see what I'm dealing with.
Thanks for help!

Jim

[Faded]

DC, thanks for the plug. It looks as if I got beat to the punch though! Everyone has brought up some excellent points and reading through there isn't much left to add. I'll put in my $0.02 to add to what has been said, but some things I do are not neccessarily required, but I'll include them anyway (designated with a *).

• Before dissassembly take the time to clean everything to reduce the chance of dirt falling in the engine.
• "Before" compression test.*
• Measure squish clearance using a piece of 0.125" solder (if I've never had that particular motor apart before).*
• Remove and clean carb, set float level and record jetting specs.*
• Remove head and check for warpage.
• Remove cylinder, and as others have said, DO NOT PRY THE CYLINDER OFF! Use a mallet! I just had the base of a '99 CR250 machined (0.010" off) because the previous owner tried prying the cylinder off.
• Look for signs of scuffing or any unusual wear on cylinder bore and piston skirt(s).
• Take your time to disassemble and throughly clean your powervalve and its associated parts.
• Clean cylinder (soap and water), deglaze the bore (use soap, water and a scotch brite pad), remove debris (rinse followed by compressed air), and reoil with a light layer of oil and some paper towels. Keep running paper towels through the bore until they come out clean.
• Check ring end gap on old rings.*
• Check the ring-end gap on your new piston rings (YOU MUST DO THIS). Place them in the cylinder (1 at a time) and use the new piston to push them down evenly 1/2" from the top of the cylinder. Use a feeler gauge to check the ring-end gap, should be @ 0.012". If it's less pull the ring out and draw file a little off, and then reinstall and recheck. Repeat this process until you get your 0.012" (on both rings).
• Use a little assembly lube (or premix) on piston pin bearing when installing your new piston.
• Circlips should be new, and installed in either the 12 or 6 o'clock postion, no exceptions. If not the clips can work themselves out and cause major engine damage.
• Don't install the piston backward (arrow toward exhaust port)
• Torque the head studs in a star pattern (1,3,5,2,4,6) to specified torque.
• Don't overtorque the head studs!!!
• Recheck compression.*
• Recheck squish.*

Wiseco makes the piston as a 'one size fits all', so they're no need to worry about if you got the right one or not. The Wiseco piston is also forged as opposed the the stock cast piston. It will tend to grow more during warm-up, so take your time to heat cycle it (let it idle for 10 minutes and then shut it down and completely cool off) two or three times before riding it. Always be sure to give the bike adequate time to warm-up everytime you ride. It is possible to put a cold bike under enough load to make the piston expand faster than the cylinder. Good luck, if I think of more I'll let you know.

[JimM]

I've come to the right place I see.
You guys have upped my confidence level a ton...

Jim

[brokenbones]

Ok I guess I better clearify the "pry it off" statement I made. There are better places to pry on the cylinder then where you are going to have to put a gasket or seal it. I meant slight pressure not a 4 ft pry bar. It is like everything else, you have to be carefull. If it comes off with just the mallet, that's great!

Don't install the piston backward (arrow toward exhaust port)

You are saying the arrow DOES point toward the exhaust port, correct?

[Faded]

Originally posted by brokenbones
Ok I guess I better clearify the "pry it off" statement I made. There are better places to pry on the cylinder then where you are going to have to put a gasket or seal it . . . .

. . . . You are saying the arrow DOES point toward the exhaust port, correct?

Where on the cylinder do you have a spot to pry with that doesn't have a gasket or get sealed? : Remember you're dealing with aluminum (read: SOFT!). The one I'm working on looked like they used a screw driver and I'm sure thier intent was to pry gently, but damage occured regardless.

Yes, I meant to say the arrow should point at the exhaust port when the piston is installed correctly.

[brokenbones]

Well of course there is no seal between your intake and the tranny. There are places to pry if you are carefull. Like I said if it comes off with a mallet, great, if not pry. Generous amounts of WD-40 or another penatrating oil are definatly recommended.

[Keetoman393]

Moved to the Knowledge Base at the request of another member Good advice!

[wFo250]

DC, you were not kidding.....Faded Is The Man. He could easily dismiss JimMs' inquiry as a tired subject, as he must have answered the same question a hundred times, he is still carving out well crafted advice.BRAVO! BTW JimM, you can search through past related posts from the home page, Checkitout!

[JimM]

Yep, much appreciated!
BTW guys, I've got my parts. I have one question before I begin. Do I need a ring compressor?

[Faded]

Originally posted by JimM
Do I need a ring compressor?

I have yet to "need" one, generally you can just use your hands and a little patience. If you can round up an extra set of hands it makes things even easier. Just make 110% sure that the rings are in the grooves and properly aligned with the pins so you don't risk catching one on a port. Try not to twist the cylinder on the piston, this can allow one end of the ring to pop out into a port. Also make sure the rings are installed properly, some have an up side (usually the print on the rings goes up) but read the instructions to be sure.