Top end rebuilds on modern Four Strokes

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7/19/2018 8:12 AM

Anyone have experience doing these? It's just about the only maintenance item I've shy'd away from doing. I really want to learn how to doit, I just don't want to get in over my head. I'm pretty good with mechanical things but I know how important it is to be perfect on this one. I learned on YouTube how to take apart my forks, replace seals, etc a few years ago and have done this for myself and friends successfully quite a few times. How hard can it be doing a top end?

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7/19/2018 8:14 AM

Imo the hardest part is getting the clips on the piston wrist pin without dropping them in the bottom end. Otherwise its really easy. Grab all the parts and some assembly lube and youre good to go. Follow the service manual to a T.

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7/19/2018 4:11 PM

4 stroke top end are the same as 2 stroke top ends except the valves. You need to be able to check your valves. A feeler guage can be used on this. But you need to make sure your valve seats are sealing correctly because if your valve seats are out of wack then it doesn’t matter how perfect your valves are. Shops use a leak down test usually to see if any air is being passed through the valve when the valve is seated but I don’t own one and so I would have to go by my eyes but I have never been taught anything about it and so I don’t do them. That’s literally the only reason why I don’t do 4 stroke top ends. If you can have somebody check your valve seats or show you how then it is easy. Pull head and cylinder, check cylinder and valves for any wear and then check your service manual (can be found online) to make sure everything is in spec. Then lubricat everything and put it back together.

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7/19/2018 4:36 PM

Best answer to the above post is to have new valves and your valve seats recut. To me thats a part of a top end every so often

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7/19/2018 5:32 PM

If you have never rebuilt an engine before, even a lawn mower engine then dont try it. Its one thing when your moped locks up going 30 on the street but its another situation when your dirtbike locks up going up the face of a jump. But if you do venture into it then remember these few things. Get a very good torque wrench. Always replace timing chain. Make sure you use a rag or i prefer surran wrap to cover the crank opening so you dont drop stuff down in there. Make sure you have a manual. Make sure all timing marks are aligned to spec. On the flywheel they can be confusing. There are 2 marks, one is your tdc mark. Make sure you identify that in the manual. Follow the manuals specs for torquing the head and cam cap bolts. Make sure the cam cap bolts are tightened in the right order. After assembly run the engine and recheck torque. I hope iam not missing anything.

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7/22/2018 6:52 AM

You should always check the bore if it's in specifications. Overall pretty easy.

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7/22/2018 8:16 AM

Difference between doing 2 st & 4 st Top ends is cam chain tensioner and aligning the cam chain to specs. 4 stroke has more rings and you need to line each at a different open space

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