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Top end job

7 posts in this topic

okay heres the deal

I have owned a 1998 yz400f for about a year now. Two sets of rings and gaskets came withit.I hae been doing frequent oil changes and proper maintenace on the bike. Riding season is over for me in Canada and i was wondering if i should de-glaze the cylinder and slap on some new rings?

thanks for the help

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I could be mistaken, but I think that this would be a rather detrimental action...to your cylinder I mean. If memory serves me correctly, the cylinder wall is plated, hense deglazing it would surely make it unhappy. You could simply change the rings though, providing that the cylinder wall tollerences are in check (end gap on the new set of rings, ect.). Good luck.

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It's OK to d-glaze the clyinder, even if it is a coated cylinder. Just use a 400 grit

sand paper run it up and down the cyl in a circular motion a few times and all will be

good.

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Originally posted by c dawg1998yz400:

okay heres the deal

I have owned a 1998 yz400f for about a year now. Two sets of rings and gaskets came withit.I hae been doing frequent oil changes and proper maintenace on the bike. Riding season is over for me in Canada and i was wondering if i should de-glaze the cylinder and slap on some new rings?

thanks for the help

I have owned 5 yzf's, the first was a '98

both me and my son raced it to death and at the end of the season the lower con rod bearing went out. So I had to pull the engine

apart. The bike still ran strong it was just

real noisy. To make a long story short, these

are four stroks and if you bike runs good

and don't blow blue smoke I would't touch it.

If you just want something to do check the

valve clearnce thats always fun.

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I pulled down the top end in my 99 WR 400 after approx 4000 miles to put in a 420 kit. The parts that came out of the bike were in perfect condition the rings were in spec, cyclinder in perfect condition very low carbon build up it was the best lookng 4-stroke top end I have ever seen in 29 years or riding them.

It it runs good does not blow blue smoke, use oil or water--leave it alone and ride it till a observable or loss of power problem is identified.

Clark

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cdawg1998yz400,

I was mistaken, as I was not aware that one could safely deglaze a plated cylinder and I apologize. This is why this site is awesome, one can constantly learn from the collective.

I've done this many times (deglaze and re-ring) to my XRs as a quick and cheap rebuild. However, if you do so, I would still caution you to check end gap tolerances, both before and after. In most engines, the normal action of the ring and piston moving up and down the cylinder wall will shave off miniscule amounts of metal. This obviously increases the diameter of the cylinder wall ever so slightly over time and in some cases, quite dramatically, though I don't yet know how bad the 400 and 426 are in this area (ex. Ford Escorts are notorious for wearing the cylinder wall to an elliptical shape). As you know, when you deglaze, you also remove a small amount of metal from the cylinder wall as well. It is easy to go over board when deglazing. I have had an XR engine that was just under the high end gap tolerance before a deglaze and just slightly beyond tolerance after. Being lazy and cheap, I threw it together anyway, though in hind sight, I should have just bored it and bought a new piston because after the break in period it felt like the same old tired engine. I guess in your case, it will depend on what the numbers are, but let us know how you make out.

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