Think a hone will fix this

[focker811]

Just pulled the head and cylinder on my 06 yz450 and this is what the walls on the cylinder look like... There are two scuffs/scratches on the ex. wall.

What would cause this?

The bike has guessing around 300 hours with no major work just air filters and oil changes.

I am planning on putting in a new oem piston and timing chain

[yz007f]

It might but you really wont know until you try it.. It is kinda hard to tell from this picture without having it in your hand.

[ForsheeMS]

IMO the cylinder should be replated. At 300 hours the piston was likely worn beyond spec causing piston rock and wear to the cylinder. It takes a special diamond hone to do anything to the Nikasil plating. Even if the scoring cleans up the cylinder will probably be out of round.

[CaptainKnobby]

You can get those Flex hone's for nickisil plates. They are a flex ball hone and I forget what grit but they cost like $50.00 some bucks.

I think this is the size and grit you need (not positive) but I believe. i would have to research a little. i was thinking of the stuff like a year ago and knew all what I needed to hone my 06, like size ball hone,grit.

I believe the 06 cylinder width is 95mm +or- I would have to look in the manual to be sure.

This place would have the hone you needed.

http://www.enginehones.com/334320ao.html

[grayracer513]

You can get those Flex hone's for nickisil plates. They are a flex ball hone and I forget what grit but they cost like $50.00 some bucks.

A ball hone won't fix that. What caused it? Debris in the oil, most likely, or possibly a low grade oil failure. The 300 hours may have had something to do with it, too.

[Family Man]

just buy a new cylinder.

[CaptainKnobby]

A ball hone won't fix that. What caused it? Debris in the oil, most likely, or possibly a low grade oil failure. The 300 hours may have had something to do with it, too.

What would he have to do? Have it bored over so many thousandths? or just have to have it replated?

[tek_01]

What would he have to do? Have it bored over so many thousandths? or just have to have it replated?

Ill take a guess here, If you measure the cylinder and it is within spec than you can hone it and see if the scratches come out. If it is not in spec or the scratches dont come out you can either bore it over a couple thou, get it re-plated and buy a slightly oversize piston to suit the new bore size OR get a new cylinder which would probably be the best way to go.

Someone chime in if im wrong

[CaptainKnobby]

That why I asked. i dont know how much these cylinder cost or to have one replated. i do however know what one would run to have it bored over.

In the long run he would be better off to get a new one with that many hours on it

[grayracer513]

There are no oversize pistons. Either it gets plated and finished back to standard, or they make a big bore kit out of it.

[tek_01]

Motosport.com have the OEM cylinder for $253

I think plating costs close to the $200 mark and about $30 for the bore that's why if it were me id get a new one at those prices.

EDIT: Millennium have a cylinder exchange program that might be worth considering if you want to save $50

Core Exchange Under 54mm Single Cylinder $194.95 ($100 deposit until you send your cylinder in)

[grayracer513]

Core Exchange Under 54mm Single Cylinder $194.95 ($100 deposit until you send your cylinder in)

The YZ450 bore is 95mm

[tek_01]

Doh! i dont know what i was thinking there

In that case it is a little bit more and probably not worth it under the exchange program

[focker811]

I took it to a mechanic friend of mine an hour north of me and he was able to run a stone hone and cleaned it up. its still in spec and looks pretty good. The piston did not look too bad or as bad as the the cylinder.

A new oem piston kit is on its way so we should be good.

[cbwood]

Just did mine it looked very similar. It checked out nice and round. We took .002 total off bringing it to the high limit on the tolerance (.004 cylinder to piston). If the piston is ok you could just re ring it for $40 replace the gaskets ($50) and go for the season. All that said a new cylinder is $300 and could last the rest of the life of the bike. Alternatively search the web for Millennium they can weld retreat and hone for $200-$300. Also remember if the bottom end needs some love your 1/2 the way in and could also freshen it up.

[grayracer513]

Piston clearance is less of a concern than the integrity of the plating, which is not more than a thousandth or two thick. If you have refinished the cylinder out to .002" over it's original size, the remaining nikasil layer is going to be quite thin. At higher hours on such cylinders, the chance of a plating peel or wear-through is increased.

[mkporn]

Piston clearance is less of a concern than the integrity of the plating, which is not more than a thousandth or two thick. If you have refinished the cylinder out to .002" over it's original size, the remaining nikasil layer is going to be quite thin. At higher hours on such cylinders, the chance of a plating peel or wear-through is increased.

Do you ever feel you are talking to a brick wall??

[grayracer513]

Do you ever feel you are talking to a brick wall??

Why do you ask??

[cbwood]

Thought we agreed the plating to be .0025-.004. Depending on the initial application possibly much greater.

http://www.enginebuildermag.com/Article/36521/machining_new_metals__nickel_silicon_carbide_coatings.aspx

[grayracer513]

When did "we" do that? The initial coating is laid down on a bore that is perhaps .004-.005" oversize. The bore is plated until it is undersized, then precision honed to size. If the original bore was .004 over, and finished exactly on its original center, the plating will be a uniform .002 thick. If it is later honed for wear to .002 over (the service wear limit), and is still on center, the plating will then be .001 thick, and it should, in an ideal world, be able to wear another .0015" before it's taken out of service, right?

That works OK until any of the wear or refinishing goes off center even .001". Do the math. Remember, I didn't say it would fail, I said it was more likely to.