Jump to content
Sign in to follow this  

Help w/ xr250 big bore

Recommended Posts

So here it is. I have decided my 01 xr250 deserves a wiseco 277 big bore kit. My questions are these:

I see several kits offered, some with gaskets, some without, some with a top end bearing and others none. The gaskets are an obvious need but is the top end bearing something that is needed? Is the bearing hard to change?

Anyone know of any machine shops in the east or south sf bay area to do the boring that they trust?

What are the hidden costs with doing this big bore kit?

I am thinking of new valves, valve stem seals, and whatever else since it will be apart. What else should I consider? Cam chain?

Forgot to mention that I have done the Gordon mods already (header welds, air snorkel, jetting)

Thanks for the input

Share this post


Link to post
Share on other sites

ya, im sure someone will correct me if i mis-inform. i believe the bearing you are refering to is the wristpin bearing, its a 10 dollar part. so get it! hard to replace? No. once you plull the piston its the needle bearings that are in the small end of the connecting rod. they just slide right out, make sure you lube when you put all the new parts in.

Share this post


Link to post
Share on other sites

i have an 86xr250 myself, ive also been toying with the idea of going to 277.

from what ive learned, going to 277 is good cause you still have sleeve left for another bore, it doesnt need case matching as like you do when you go to 300. you can still use the stock carb at 277 too,.

ya, defunatley look at the vavletrain. is your cam chain tensioner fully maxed? noisy? if so replace both cam gears and the chain,

look at XRs only i think think their 277 kit comes with a cam too.

keep us posted on this one.

tony

Share this post


Link to post
Share on other sites

:bonk:

Xr's dont run a bearing in the top of the conrod. they are a steel on steel, which is one reason why XR's need good, fresh oil!

really???? hmmmm never knew that. thanks. goes to show you how far ive been into mine.:smirk:

Share this post


Link to post
Share on other sites

I have done several 277 big bores using the Wiseco piston kit with gaskets, good quality stuff. I always check the wrist pin bore in the rod to make sure it is within spec, a new pin comes with the kit. As said, there are no bearings or bushing for the pin. It is a bit pricey, but I always install new Kibblewhite valves and springs (or R/D springs) along with new seals. have seen very few well maintained engines that needed the guides, but check them and replace if necessary. A new cam chain is also a must, it is usually the first internal part to wear out in an RFVC engine. Possible hidden cost could be worn cam & rockers, bad crank & bearings, cam chain guides, chain tensioner,etc. depends on how well the engine was maintained. Check with some local enthusiasts on finding a reliable machine shop. The piston to cylinder clearance is critical, make sure that the specs supplied by Wiseco are adhered to.

Share this post


Link to post
Share on other sites

Thanks for all the info. I will definitely look into all that stuff. What about the valve seats? Is there anything specific to look for there ???

Share this post


Link to post
Share on other sites

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
Sign in to follow this  

×