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John400

98 YZ400F head problems

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Hey everybody, I have 98 yz400f with head problems. I took the top end apart and found the one of the buckets had wore a grove in the head. I was going to buy a used head for it, I also heard that I should replace Not exactly sure if it's the wrist pin or rod because they would break if you would bore the cry lender out.

So here is the question can I put a 426 cyclinder and head on the 400 bottom end or would I be better off just buying another. 400 head??

Thanks for your help!!!

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yes I own a 99 model.

 

u can put a 426 cylinder and head on and it will fit fine.

 

however I recommend using a new con rod for a 426. its a stronger rod and would ensure greater reliability.

also change crank main bearings

 

if buying a used head, get the valve seats cut, and vacuum test them, theres a lot of ppl who do dodgy valve cut jobs.

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Okay, this might sound like a dumb question but can I just put a 426 sleeve in my cylinder? I'm guessing not I will need a 426 and also a new carb. Not real sure what all I would need to do just thinking about my options and what would be better for the money

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None of the YZF engines use sleeves.  The bore walls are the same aluminum as the rest of the cylinder, plated with an extremely hard compound called Nikasil. 

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yes you can sleeve it.

there are sleeved available for early yz.

 

however they will either be steel or cast iron sleeves which are not near as hard as the Nikasil plating on an aluminium cylinder.

you can do it but it will wear quicker

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Sleeving is as expensive as boring and re-plating to standard size, and produces inferior results.  I have on idea why anyone would do that.

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Okay, makes sense, I found an 01 head, jug and cams for a good price, what years will fit on my 98 bottom end.

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All of them as long as it's a 426.  However, you need to understand something about the crankshaft if you're going to do this: to use the 426 95mm piston, you will need to change to a 426 connecting rod and rod bearing.  The wrist pin size is different between the two.

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Not sure about the cost of the new cylinder vs replating the one you currently have but la sleeve charges 250 to replate your cylinder and take it back to the stock bore or another size if you choose. I just had mine done through them and had a great result but they do take a few weeks to send it back I have the contact info if you're interested

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wasn't their a 450 piston that has 400 pin size to fit a 400 rod in a 426 bore?' it may have ended up higher compression? grey knows it all . but really why cheap out on a 400 rod only to put more stress on it because of a bigger piston 426 rod is the way to go if your set on making it a 426 don't risk wrecking your whole motor because you wouldn't spend an extra 120 on a rod

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I agree, when I do the work it will be done the right way. I don't want any issues because parts I should have or should not of used.

Thanks everybody for the advice!!

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The 450 wrist pin is the same size as the 400, and you could do that.  But the fact that you can do something doesn't make it a good idea.  That's why I didn't mention that.

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Not sure about the cost of the new cylinder vs replating the one you currently have but la sleeve charges 250 to replate your cylinder and take it back to the stock bore or another size if you choose.

here in Australia it cost $450.00 to replate. and only 2 places do it.

here in AUS it cost half as much to sleeve than to replate.

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