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Discussion Starter #1
Just bought a 2007 400ex and the motor is a little rarely at low end power so i want to rebuild top end. What is a great top end rebuild kit including all parts including cam.
 

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Well there isnt really a "kit" including everything. You can have ctracing build your engine and it comes with all that stuff. Or you can buy ebay sets that are a bunch of different brands of parts all sold togeather. I would suggest buying what you want individually. It always ends up cheaper in the long run that way. Honestly piston brand is all about preference. I have a wiseco. Gunna be putting a CP in on my next build. I have installed JE. Ross. Pro X. Namura. They are all ok. I would highly suggest a crf450 timing chain. And stud the head with either gt thunder hd studs or something similar. Dont buy into the ARP crap they sell for this motor. They dont do anything to solve the actual problem and thats the head studs pulling. Not stretching. I really like my magnum cam. But i have used hotcams. Webcams. Whitebrothers. And gt thunder. All are good. Dont go above .350 lift unless you plan to do shortened valve guides. Be sure to use a good mls head gasket. I like cometic. Havent used anything else and wont ever for that. Make sure when you get the cam you find out if they require hardfaced rocker arms. Also some require high rev springs. I like kibblewhite for those. I run them and have beat them hard without any problems. You will want to find a good engine machine shop for all the work. You can bore your stock sleeve to 87mm no problem. I wouldnt suggest going any further even though some do. Just seems sketchy thin at the bottom. The 87mm is thin enough to be alittle scary at first. But i have put my build through a copious amount of abuse and its held up no problem. Did my build coming up on 5 years ago and the stock crank has just decided to start letting loose. Thats why im switching to CP as they were the only ones who would make me a custom 87mm stroker piston. Welcome to the forums and keep us posted on what you decide to go with. And post up pictures along the way.
 

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Discussion Starter #3
Is it cheaper to bore the cylinder than to buy an aftermarket cylinder. Is the stuff on eBay mostly low quality Chinies stuff or is it good stuff that is up to par with honda. I would like to mostly stay with Honda parts but i bet they dont make big bore stuff.
What's the 411 with studs? I am new to this but have noticed some stud talk. What is a good direct replacement stud that does not need retapped? Whats wrong with OEM?
Who makes good cams?
What can go wrong with bottom ends on these engines and how can i tell it is going bad?
If I go big bore should i go 416 or 440? What sizes is there? Dont want to stroke at this time.
As for cam, what works good with stock springs and rockers?
 

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Aftermarket cylinders are knock offs. Cant beat just boring what you have. Thats what i did and it worked well. Prices are all depending on the machine shop you find. I pay my guy 40 bucks to bore and hone and hot tank it. But he is a family friend.

Studs themselves arent the issue. They pull the threads from the cast heads and the only way to fix it is to drill and re-tap deeper and courser threads. I like gt thunder. Jeff Snure is a good guy and does good work. Lots of guys on here and all over the world that have used his services.

Lower stage hotcams and magnum cams are the only ones im aware of that dont require hardface rocker arms and high rev springs. I suggest high rev springs for any cam. Im not running hardface rockers with my magnum cam and it has been perfect for almost 5 years. They look brandnew still

If you go big bore go 416 or 426. Stay away from the 440 kit. Nothing but reliability issues out of that bore. Almost impossible to keep from over heating. Im doing a 416 bore stroker so it will be a safe 440. No overheating or reliability issues.

My crank is starting to knock at rev limter. And right when it comes down from it. I know my motor like the back of my hand since ive rode/raced it so long so i caught it very early in the process of death. That oil change i struck gold. That was the confirmation.
 
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