Piston&cylinder?

Do you think these are reusable. They look pretty good to me, just some light scratches, nothing that you can feel. I haven't checked the piston cylinder clearance yet bc I couldn't find my gauges or my caliper. From the looks of the crank I will be getting a new one.

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Let's start with the crank. Your first YZF tear down is it? Everybody freaks the first time they see the bluing on the crank throws. But it's OK, it's just part of the manufacturing process. Normal.

Notice that the rod shows no sign of being nearly that hot, nor does the side bearing. The manual shows how to measure the installed crank for wear.

The piston looks nearly perfect, but it should be measured all the same. Also check the ring grooves and the pin bore.

The cylinder needs a close look. You should have it measured for wear by a good engine shop that has experience using a bore gauge. It also definitely needs at least a good deglazing. The measurement can be made either before or after the hone job, since a bottle brush hone won't change the size of the cylinder measurably. Precise measurement is critical because the tolerances are so small with a plated cylinder. The Nikasil plating on the bore is very thin, and the maximum allowable variance from dead straight and round is only .002".

The rings are clearly worn. The second ring is showing a bright edge where the moly filling has worn off the edges of the channel it's filled into. You were going to replace those anyway.

Thanks gray, I did a compression test on it and it was leaking into the case real fast so I figured the piston and cylinder was worn but didn't appear to be once I took it apart. The valve clearance closed up to. 04 on the intake valves so I'm gonna put a head I bought on it and get this one rebuilt with steel valves. I don't have a clue as to what brand this piston is but there's what appears to be a serial number on it. What does it look like to you? Thanks for helping!!

Does it have "ART" in raised letters on the underside of the piston crown?

No I cleaned it up and it has this on it.

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That printing reminds me of the Wiseco pistons. They print out the part number of the piston on the face with dots for the letters. That and they always end in the bore size- 95 mm. The part number is similar in style to the wiseco stock bore part number 4785M09500. Definately not a Vertex nor a JE. I googled your number and nothing came up.

The piston looks good, but I'd replace it while you have everything apart for peace of mind. Do u have any idea of the hours on the bike? These 450's last a long time with regular maintenance but I'm not one to push it, especially how cheap pistons and valves compared to a $1500-2500 catastrophic failure.

You do have some scoring in that cylinder. definatley have seen worse been used, but like gray said have it measured. Does any of the scoring or marks come off when cleaned? If you decide to replace both I'd highly recommend the 478 kit. nearly the same price as a stock bore cylinder and piston. I was gonna have my cylinder re-plated and replace the piston, but I got the whole kit for the same price and got some performance out of it as well.

Just sent my cylinder to millennium for replating, having a hard time figuring out what piston to get.

I've been thinking, I'm putting about 600 to 700 bucks in the top end of this thing. I'm thinking about going ahead and doing the crank and bearings and seals in the bottom end to and basiclly have a brand new engine in the old 426. I don't know if it would be a good thing to do bc everything in the bottom seems to be in good shape(less the clutch basket is showing some wear). What do you guys think I should do? I've got awhile to think about it cause millennium sent me the wrong wrist pin for some reason.

That printing reminds me of the Wiseco pistons. They print out the part number of the piston on the face with dots for the letters. That and they always end in the bore size- 95 mm. The part number is similar in style to the wiseco stock bore part number 4785M09500. Definately not a Vertex nor a JE. I googled your number and nothing came up.

The piston looks good, but I'd replace it while you have everything apart for peace of mind. Do u have any idea of the hours on the bike? These 450's last a long time with regular maintenance but I'm not one to push it, especially how cheap pistons and valves compared to a $1500-2500 catastrophic failure.

You do have some scoring in that cylinder. definatley have seen worse been used, but like gray said have it measured. Does any of the scoring or marks come off when cleaned? If you decide to replace both I'd highly recommend the 478 kit. nearly the same price as a stock bore cylinder and piston. I was gonna have my cylinder re-plated and replace the piston, but I got the whole kit for the same price and got some performance out of it as well.

Thanks for the help, figured out what piston it is, wiseco 13.5:1. I'm just going back with wiseco stock compression and stock bore.

Thanks for the help, figured out what piston it is, wiseco 13.5:1. I'm just going back with wiseco stock compression and stock bore.

If you are using the stock bore and compression, why would you not use an OEM Yamaha piston?

If you are using the stock bore and compression, why would you not use an OEM Yamaha piston?

Probably should have but this one looked pretty good after a lot of use by me and who knows how much by the previous owner.

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