to bore or not to bore? Lost soul here, need guide


Sep 29, 2003
Hello, first i would like to say i am new to DRN and the forum. Thanks for having me.

Second, over the weekend i found a 01 CR250 for $1000 that some guy was wanting to get rid of. After talking with the guy, he said it needed a new top end. I figured for a couple hundred bucks i could throw in a new top end and be on my merry way. So i bought it.

I got it to the shop and tore it down. Yes, it needed a new top end...I started tearing the carbs out and there was a 1/4" ring of dirt and grease inside the "intake"... Well i took the piston out and the cylinder sleeve walls are pretty torn up. Well now i have to determine what course of action to take.

My goal is to have a awesome running, reliable, low cost(install and upkeep) bike.

I figure i have 2 options. I need your help deciding which is the best for me and my goals.

Option 1 - buy a new cylinder, piston, rings, gaskets, bearings, etc and basically make the bike stock.

Option 2 - bore it out, installing a larger piston kit, etc.

I am not a rookie when it comes to ridding, i do have a shortfall when it comes to bike repairs. My friends tell me to pay tht $400 and get a new Nicasil cylinder, others tell me to bore it out and install a larger pistion.

What are the pros and cons of getting it bored? what other things do i need to be concerned about when doing this upgrade? Do i need to upgrade any other parts?

your advice is very valuable to me. Help me if you can


May 3, 2000
This was a good first post. In my opinion you can't go wrong with a an overbore now a days. Eric Gorr(A sponsor of this site) does quality work for half the price of other shops. I would recommend going to a 265 cc over bore and port job. The 265cc is very reliable. This cost arounds 400 bucks and includes a top end. To me the only con about a big bore is when you sell the bike. I would get suspicious on to why a person got his/her engine bored. Also now that you have the top end off check your connecting rod. How is your connecting rod. Is their play?? For a 1000 bucks you got yourself a steal if it only needs this amount of work.



Damn Yankees
Nov 21, 2000
North East USA
I'd recommend just getting the existing cylinder re-plated. US Chrome does an excellent job and it is less than half the cost of a new cylinder, not to mention the plating quality will be much better. They can weld up any gouges or cracks before they re-plate.

If you found dirt in the carb then that means dirt is in the main bearings so plan on replacing them too along with the seals.

Before you run it for the first time after rebuilding it find out how the dirt got into the engine. Check the entire air intake boot and filter seal.

Good luck and congrats on the good buy :) and welcome to DRN :)


Dec 10, 2002
Do you know why the cylinders are plated? It's to privide a wear resistant surface. If you install a cylinder without plating, you will quite possible have to have it re-machined and a pision fit, each top end. In theory the plating allows the majority of wear to be on the piston and rings, and not the cylinder.


Jan 22, 2002
this is what I do when I buy a used bike that needs tlc.

dont worry abot riding this year, hurts to say it but take your time and do things thorough this winter. Get yourself 3 manuals if you have little mechaincal experience. the factory honda manual for yor bike<cant be beat for well illustrated pictures of assemblies and torque values of the bolts A clymer manual is very good at explaining what needs to be done to someone who isn't a mechanic and Eric Gorr's Performance handbook is the best and being able to tell you what you are looking at, why you are looking at it , and what is the problem ,what can make it better.

engine gets completely rebuilt, con rod , mains, transmision bearings everything. send the cylinder & head off to Forward Motion if you want an overbore and port work done or send the cylinder to US Chrome and get a stock replating.since it is a Honda a new crank might just be worth it compared to rebuilding it<honda cranks are inexpensive and hard to rebuild without the proper set up>

In a well organized fashion remove all large assemblies from the frame and repaint it. rebuild each individual component as you reinstall them. new bearing and seals as needed for the chassis,suspension and wheels.

peruse these forums for specific information about your bike that people did/ have to do and ask questions if you dont see whatr you need to know.

if you are patient, careful and meticulous , and you do most of the possible work yourself you could easily have yourself a basicly brand new 01 cr250 for next spring for under 2500$ Be meticulous with your maintenance,air filter always cleaned, gearbox oil changed often, pistons once a year or however often you may need them and repair any damage as it happens and you will have a nice bike for long time.

Sounds like it is a great deal if you spend your time and money wisely now.

Welcome to DRN

No trolls, no cliques, no spam & newb friendly. Do it.

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