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06 WR250f Top-End Rebuild - Need Help

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Hi everyone, time to think about my 06 WR250f top engine rebuild and decided to do it myself.  I am a self taught bike mechanic so most of what I know is either from experiencing it or reading about it.

Been riding the bike for the second year now and I do not know how many hours are on the bike, I put about 60h myself and I have about 17000km on the speedometer.

 

From what I read so far I think I need:

- piston (plan to use the 08YZ high compression) - 5XC-11631-00-00 is for the 08 YZ (5NL-11631-20-00 for 06WR)

- piston ring set - 5NL-11603-00-00

- piston pin - 5NL-11633-00-00

- the 2 cylinder gaskets - 5NL-11181-00-00 and 5NL-11351-00-00

- camshaft chain? - 94591-53114-00 (just because I have the engine open, I know I need the flywheel puller)

 

And a few questions please

- do I need anything else? 

- checked/ shimmed the valves, how do I know when they are done? What needs to be done / anything has to be done to valves and cylinder head when replacing the cylinder?

 

Thanks in advance

 

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The factory service manual goes into detail for checking the cylinder head / valves - Requires precise measuring tools. My buddy opted to send his head out for inspection / repairs.

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From everything I've read here, shim the valves once and when they tighten up again, it's replacement time. Stock shims are usually .170 and around there, so if you replaced shims that were significantly smaller that that they may have been replaced before. It's a good idea to check the valve clearance often.

Oh, and get the seats cut by someone that knows what they're doing with a Serdi machine when replacing valves.

And replace the cam chain too.

Edited by not2shabby

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Hi there, I actually work for yamaha (technician) and did a top end on monday, you can get away with just a piston, rings,gaskets and a decent checkover providing your barrel and valves are in good condition, but if it was my bike and what I recommend to a customer is to replace the timing chain (cam chain) and tensioner, once your head is off hold it upside down put the sparkplug in and pour petrol in so that the valves are submerged (level with the top of the head) and let it sit for a few minutes if the level doesnt drop your valves are fine, i would also check what size shims anything under 1.65mm is on the verge of replacing a valve, then just look at your cams and rockers if there is a flat spot or they look badly worn I would suggest replacing them but leaving them wont hurt your bike either, just double check valve clearences, I Hope that helped a bit

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Also when it comes to shimming you can shim a bike a million times if you want as long as its not under .165

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Cams and rockers show no sign of wear, I have .18 shims on all valves right now, and they are all on the loose side of the range. I will know more when I open it up, it looks like the parts come under 200$ if the valves and head are fine.

Is there anything that has to be done to the cylinder once the piston is out?

Part of me tells me to do this so I know that the bike is in good shape. At the same time it works very well and shows no signs of burning oil. What is the expected life of a cylinder/ head anyway? One of my riding buddies with an 2007 450 has only checked the valve clearance once so far and he is not interested in rebuilding anything until it needs it. When does a bike need this?

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Hi there, I actually work for yamaha (technician) and did a top end on monday, you can get away with just a piston, rings,gaskets and a decent checkover providing your barrel and valves are in good condition, but if it was my bike and what I recommend to a customer is to replace the timing chain (cam chain) and tensioner, once your head is off hold it upside down put the sparkplug in and pour petrol in so that the valves are submerged (level with the top of the head) and let it sit for a few minutes if the level doesnt drop your valves are fine, i would also check what size shims anything under 1.65mm is on the verge of replacing a valve, then just look at your cams and rockers if there is a flat spot or they look badly worn I would suggest replacing them but leaving them wont hurt your bike either, just double check valve clearences, I Hope that helped a bit

 

I have worked in the trade for over 20 years and although a top end is a common repair most gloss over some imporatant steps - measurments. Service manual breaks down what to check in the cyclinder bore, it also gives all the specifications for the valves seats and guides. Sure plenty of wrenches simply use the eye ball micrometer but when a rebuild should go many many hours lasts half as long well....

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Just check that the piston sits tight in the barrel and make sure that you torq down everything correctly, you dont need arb measurements to tell you what your eyes can already see. I did a top end on a grizzly 700 FI which after the guy picked it up he decided to drain the oil himself,it ran 150 hours with about 200ml of oil and had absolutely no wear on the cams, rockers, piston or rings so I trust what i see with my eyes more than the book

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Good points, thanks. I am new to this but I have good mechanical sense and zero experience in doing this. I have adjusted the valves and watched a few YT videos, I have the tools, I am ready to go (I believe). Most probably I will wait until the end of the season as I do not want to be without a ride for too long.

 

Another newbie question: am I trying to fix something that it isn't broken? I know the recommendations of replacing at least the rings every 30h, etc. but the bike runs fine, I can say great!

I am not really racing the bike, I only participate in the off-road competition at my club and do trail riding at a medium pace.

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if the piston and barrel are in good shape ( pistons tight in the barrel, no scratches, scores, or burn marks on either and not bypassing oil.. generally just shiny and smooth looking apart from the head and top of the piston) you can quite easily just replace the rings, timing chain, tensioner and gaskets, that way you wouldnt have to spend so much but would still have peace of mind that you not going to jump the timing chain or one day start her up and see a cloud of smoke, just be VERY careful when putting the piston back into the barrel, no one wants to bend a ring

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if the piston and barrel are in good shape ( pistons tight in the barrel, no scratches, scores, or burn marks on either and not bypassing oil.. generally just shiny and smooth looking apart from the head and top of the piston) you can quite easily just replace the rings, timing chain, tensioner and gaskets, that way you wouldnt have to spend so much but would still have peace of mind that you not going to jump the timing chain or one day start her up and see a cloud of smoke, just be VERY careful when putting the piston back into the barrel, no one wants to bend a ring

 

Thanks, any suggestion on how to put the piston back in properly?

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If you stick to that guide you will be absolutely fine just two suggestions, when you remove your gear lever make a mark that lines up with the gap on the lever so you dont have to guess where it goes and MAKE SURE when you remove the flywheel that the woodruff key doesnt drop into the engine, a guy I work with had that happen and we had to split the motor to get it out

Edited by genocidal_josh

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Lol where the bolt on your gear lever is theres a gap so it can tighten? Make a mark that lines up with that and the woodruff key is what holds your flywheel in place

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Another bit of advice when you're putting it all back together. When you get to the point where the timing chain is installed and you are timing the camshaft, use your finger to act as a tensioner on the chain through the tensioner hole. Make your finger a manual tensioner And check the timing.

It's very easy if the chain slack is not removed to be off a tooth.

So, put your finger in the hole!

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