engine rebuild on 426

I did a search but couldn't find all that I wanted and posted this in the 250 forum but got nothing. I was reading about how much it would cost to have a place rebuild the engine. We bought a 00yz426 and a 02yz250f last spring used. I have no idea about the previous owners(regret not asking the dealership we bought them from) and how hard they rode them or if they replaced anything. We ride only on trails and only get to go about once a month at the most so we are not racing these things or using them a lot. anyways what im asking is:

should i think about rebuilding? I should be way over due right?

what should I replace? I know nothing about the parts i need to replace

How hard is it? Could I do it with little mechanical experience? I plan on doing the 03 cam swap this week.

How much $$$$ am I looking at if I do it myself? if I have a shop do it? whats tools will I need to purchase besides a torque wrench and about how much $$ are they?

are there any tutorials or anything out there besides the dirt rider one?=7

Thanks a ton.

No idea if you are overdue...depends on how hard they were ridden and how well they were maintained. The biggest worry, especially on the 250, is the valves, but even then, it's not a big worry. If the bikes are hard to start, valves tightening up may be the casue. Check them BEFORE you do the cam mod to see if they are in spec. If they are, no worries. If the bikes get harder to start, then check 'em again. Good rule of thumb is if you have to go more than 2 steps in shims to get them back in spec, it may be worth a look. If they go out of limits again in just a couple of hours, it's time to replace. Other things to look for are blue smoke (really, really rare) indicating rings are worn, and really excessive noise, also indicating worn top end or main bearings/rod bearings. These bikes are really stone reliable, though.

My 01 425 lasted about 7500 miles before the valves started to tighten on their own. I realy don't know how the guy I bought the bike from maintained it, but for the 3k I put on, it was oil and filter changes after every weekend of riding, and daily air filter changes. My son's 250 is still pretty new to us,...maybe a thousand miles since we bought it, and no problems.

These are pretty easy motors to rebuild if you take your time and follow the book. The book calls for a few special tools, but I found a way around them using normal shop tools and pullers. As far as cost, my 426 cost about 1350 if i remember right. That included new valves, cutting the seats, replacing a few guides, new big bore kit, new crank, main and balance shaft bearings, primary drive gear, and gaskets, seals, etc.

thanks for the info your answer was great. the bikes are both running great and always start great(a little harder when in gear though) I was just wondering about doing it to be preventative, but it seems to be quite an expense.

so your saying to check my valves before the cam mod? if they are off should i still do the cam mod and then just check them again? im doing it my 250f by the way.

so your saying to check my valves before the cam mod? if they are off should i still do the cam mod and then just check them again? im doing it my 250f by the way.

Yup, that's correct. Check the valves first to baseline where you are. (I believe most people who do two-fiddies don't have to change shims when going to the 03 cam) If you are out of spec to start, then you will know to keep a little closer eye on things. Then, after you get things set up with the new cam, run the bike for a few minutes (to "seat" the cam) and check them again. After that, depending on how much and how hard you ride, check them every couple of months or so, or if the bike starts getting hard to start.

Both the 250 and 426 are pretty tough bikes, and if you are observant, will give you plenty of warning before they let go. Grenading these mtors is really rare, and usually related to neglect of the valve train and/or not changingthe oil/oil filter/air filter frequently enough.

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