OEM Yamaha Replacement Piston.

I've been putting my Christmas list together of parts I need to freshen up my 01YZ426Fn and the part 5NG-11631-10-00 is the replacement part for the original Piston number 5JG-11631-10-00. Is this a standard 12.5:1 or 13.5:1 piston?

Thanks for the Help

The 5NG..10 is the standard, 12.something:1 piston for the '02 model YZ and WR426. 5JG...10 is still listed for the '01, but may change up when you order it.

If your looking for a little more low end and mid-range power, go for a 13.5:1 Wiseco. Its money well spent. :busted:

I'm mulling either Weisco or JE High Compression Piston vs OEM. I'm still up in the air right now. I've read posts saying Wiesco is Junk(Because of Piston Slap/Shrink) and JE is Junk(Or the Dome is misshaped). Others have said like yourself they are the best pistons ever purchased. I haven't had the top end apart since I bought the bike other than checking the valve clearances which is still within spec.

It has had some work done to it before I bough it I'm not sure what. Like the other stuff I've found I'm repairing/replacing it as the budget/wife allows.

I'm definitely going to do the 450 AutoDecom change out and I'm still figuring out the rest.

I'm may sell the bike next year, but I plan on racing it occasionally in the 2009 season. After that I plan on buying a Leftover 08/09 model. But Then again I may keep it since I will have it modified specifically for me. LOL so indecisive.

Thanks for the Replies.

Thrash- The forged pistons (like Wiseco ) make a little bit of slapping that you will hear. But, its not a big deal. I've ran them for years with no problems. (had 2 13.5:1 Wiseco's when my bike was a stock bore and now a 12.5:1 with the 444 kit). All of them have made noise, but none have gave me a moments trouble.

Don't forget to replace the timing chain while your in there. :busted:

If you decide on a high compression piston, the best available is the CP piston.

Myself, I would use the OEM parts, because they are less expensive, and the durability and fit is beyond question.

do you know if part # 2S2-11631-20-00 is oem piston replacment for the 06yz450f?

thanks

Gray - I want to freshen up one of my 400s that was bored out to 426 cc with a Wiseco 95 mm piston. Can I drop in an OEM 95 mm piston instead of going with another Wiseco 95 mm piston? My concern really revolves around the original cylinder to piston clearance which was set up for the expansion rate characteristics of a Wiseco piston. Would the clearance between an OEM piston and cylinder be too much if I did this? Any ill effects from running it like this? Thanks.

do you know if part # 2S2-11631-20-00 is oem piston replacment for the 06yz450f?

thanks

The 2S2...20 is the '08 piston. If that's what Yamaha sent you, it's because the older on was superseded.
Gray - I want to freshen up one of my 400s that was bored out to 426 cc with a Wiseco 95 mm piston. Can I drop in an OEM 95 mm piston instead of going with another Wiseco 95 mm piston? My concern really revolves around the original cylinder to piston clearance which was set up for the expansion rate characteristics of a Wiseco piston. Would the clearance between an OEM piston and cylinder be too much if I did this? Any ill effects from running it like this? Thanks.
You can't use an OEM 95mm piston in a 400 UNLESS you also use the connecting rod from a 426 (possibly a 2000 426 crank would work). The wrist pin diameter is larger on the 426/450. A 95 made for the 400 would take this into account. The con rod is a worthwhile upgrade, though, so you might want to go that way.

If you are going to run a hc piston you should replace the crank and bearings. How many hours on that oem crank?

If you are going to run a hc piston you should replace the crank and bearings. How many hours on that oem crank?

Thats a good question. I had about 500 hours on my 426 before I replaced the crank. It would have went further because it didn't appear to be hurt when I swapped it out.

High comp pistons have to be a little harder on the crank, but I don't think its mandatory to replace the mains and big end bearing when adding a high comp piston, unless you want to. I replaced mine because I have extra time in the winter for stuff like that, and breaking down during my limited riding season is not an option. (sometimes we travel 5 hours or so to go riding)

FWIW, my wifes bike had the same amount of time on it. Her big end bearing was shot. The rod had all kinds of play, but the bike ran fine..... I'm glad I replaced it when I did, because I think it wouldn't have made it through the next ride.

Oil changes and riding habits have a lot to do with how long a bottom end lasts. I'm sure some folks can't go 500 hours on a bottom end and then some can probably go 1000+ hours.....

You can't use an OEM 95mm piston in a 400 UNLESS you also use the connecting rod from a 426 (possibly a 2000 426 crank would work). The wrist pin diameter is larger on the 426/450. A 95 made for the 400 would take this into account. The con rod is a worthwhile upgrade, though, so you might want to go that way.

The crank upgrade was done when the engine was bored out to 426 cc and the current Wiseco piston has the larger diameter wrist pin. My question is can I replace the Wiseco 95 with an OEM 95 vis a vis the piston to cylinder clearance? Will it be too much?

The bores are more likely to all be the same size, and the additional clearance that Wiseco is so fond of would be built into the piston itself, so I see no reason you couldn't run either piston of your choosing.

Yup. I'm Bored on Vacation weather is crappy. :moon:

I'm just looking at doing some stuff to my bike I probably should have done a couple of years ago. I just ordered an 03YZ450 Cam and replacement Chain and will do that update first. www.servicehonda.com :busted: Then tackle the cylinder after the new year before the racing season starts. I'm just in trail riding/testing/practice/tuning mode right now. :p

im just going to open my 450 engine for the first time, top only. piston and timing.

i never did a 4t but i did a few smaller 2t.

do i need to get the whole engine out of the frame or can i do it without? theres enough space?

what do you guys think on this valves

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&_trksid=p3907.m32&_trkparms=tab%3DWatching&item=290265280019&viewitem=

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=360043884699&sspagename=STRK%3AMEWAX%3AIT&viewitem=

thanks

I put the new CP 13-75-1 piston in my bike and was great for low end boost.

CP +++++++++

I also ran it in 2 classes all year:thumbsup:

do i need to get the whole engine out of the frame or can i do it without? theres enough space?

what do you guys think on this valves?

On my son's bike, the left front and right rear head bolts had to be removed and put back in place along with the head, as there wasn't clearance to take them out until the head was tipped out of place. Otherwise, it's not bad.

The valves are Faction MX. They are OK, as far as I can tell from talikg with some people using them. You will have to use their springs, or another spring set made for stainless valves, though, as they are nearly twice the weight of titanium.

Pulling the motor is the best way to rebuild them, IMO. On the steel frame Yamaha 's you can pull them in less than 30 minutes.

Faction valves are good quality. I had them put in my wifes 290 last winter and they haven't moved in 50 hours. So far, so good. Wanted to put more hours on them before I started to recommend them, but we didn't ride half as much as usual this year.

Eddie Sisneros at OTD Cycles in Denver, the jetting expert here, has used them in customer engines, but when I last talked to him about it, he hadn't gotten any feedback yet.

On my son's bike, the left front and right rear head bolts had to be removed and put back in place along with the head, as there wasn't clearance to take them out until the head was tipped out of place. Otherwise, it's not bad.

The valves are Faction MX. They are OK, as far as I can tell from talikg with some people using them. You will have to use their springs, or another spring set made for stainless valves, though, as they are nearly twice the weight of titanium.

i heard light weight valve have better respond .

they are just so cheap compare to oem.

ill try geting it out and see how it goes.

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