Sign in to follow this  
Followers 0
flats00

New top end, what piston?

21 posts in this topic

Hey there, putting in a new top end on my trusty 01 426. What would you suggest on the piston type? I am looking at the Vertex but the wiesco is less money. Need some help on this, Thanks

Share this post


Link to post
Share on other sites

I have a Wiseco , get the high compression if your looking for a little more punch. They are a little noisy, but all forged pistons are.

Share this post


Link to post
Share on other sites

Im using JE now,

read THIS POST for a description of why I think like I do.

also do yourself a favor and take the engine all the way out of the bike to do the top end, you will be glad you did even tho it can be done with the bottom end in the frame still.

Share this post


Link to post
Share on other sites

Cant go wrong with the O.E.M stuff. I had a 98 wr 400f and had a zillion hours on it. Rebuilt in in 02 and the guy that bought it from me is still riding it today. J.M.O. :thumbsup:

Share this post


Link to post
Share on other sites

Yeah without question OEM is the best stuff out there, but if you are going big bore, the there is no OEM choice.

You can go with an OEM piston and have the top of the cylinder shaved a bit to get you to the compression ratio you want.

Squeeze it a little bit harder.

Share this post


Link to post
Share on other sites

OEM =money

Wiseco is what I am using and I love it. I pulled the head back off after about 10 hours on the new top end and it is perfect. Love wiseco

Share this post


Link to post
Share on other sites

OEM pistons are pretty good but, the process in the way they are made after market pistons are much better with performance and reliability. Most stock pistons are very good but most of the time you can get a after market piston like PRO-X , WISECO , JE, VERTEX , CP that are much better and cheaper. Almost all stock pistons do not have the coatings and special proceeder's when making the pistons. I would go with a PRO-X, CP , OR WISECO when buying a piston kit. Just my 2 cents, Good luck

Share this post


Link to post
Share on other sites

For all of you who said OEM , please elaborate on why it's better than the aftermarket parts.

Truth is whether OEM or Aftermarket, they all make great motorcycle parts for the motorcyclist. Because of one hell of a salesman, we don't know any better.

Share this post


Link to post
Share on other sites

Ive always run Wiseco pistons in my bikes but in my opinion the OEMs are of better quality. They weigh more but are also very resistant to gouging and scuffing. When my bottom end went in my 125 the Wiseco that was in there was torn to pieces. Deep gouges and speckled all over the top of it. I dont belive this would have happened with an OEM piston as they seem to be made of a harder more durable material. Granted the lighter wieght aftermarket pistons do give better performance I think the reliability of the OEMs is unparralleled.

Share this post


Link to post
Share on other sites
Ive always run Wiseco pistons in my bikes but in my opinion the OEMs are of better quality. They weigh more but are also very resistant to gouging and scuffing. When my bottom end went in my 125 the Wiseco that was in there was torn to pieces. Deep gouges and speckled all over the top of it. I dont belive this would have happened with an OEM piston as they seem to be made of a harder more durable material. Granted the lighter wieght aftermarket pistons do give better performance I think the reliability of the OEMs is unparralleled.

The reason why your 125 chewed up the piston is because your bottom end went and that would have chewed up any piston you would have put in the bike. 95% of the time stock pistons in 2-strokes are cast pistons, which are not as strong as a forge piston like the wiseco piston that you put in the bike. I would never run wiseco pistons in a 2-stroke, always run a cast piston because it takes so much more time for the forge piston to heat up and expand in the cylinder ( much more material in forge piston to heat and expand ). With 4-stroke pistons all of them are forge pistons stock or after market, but the after market pistons are much higher quality, higher silicone content in them, moly or ti nitrile coatings, greater forging process then the stock pistons, usually less friction and better sealing which means longer life and better performance.

Share this post


Link to post
Share on other sites

A friend of mine worked at Yamaha as a Service Tech and has been a Yamaha mechanic for over 25 years. He receintly was the head R and D guy at Hot Cams , Hot Rods. He has nothing good to say about the JE Pistons. He told me that the shape of the dome on the high compression pistons is critical to the performance of the Yamaha four stroke motor. He said the JE Piston or (fake piston) as he said is not shaped right to allow the proper flow of intake and exhaust gasses from the combustion chamber. I can't argue with the results he has on his 426 motor. With stroker crank and big bore kit he has it making 62 HP at the tire.

I believe I have a JE piston in my most receint purchase, so if we end up changing it out, I will post pre and post replacement Dyno results.

The high compression piston will yield some extra HP, but may restrict you to running a better grade of fuel than the crap you can buy at the neighborhood Git and Go.

Later

Paul G

www.ciamr.com

Share this post


Link to post
Share on other sites
He told me that the shape of the dome on the high compression pistons is critical to the performance of the Yamaha four stroke motor.

Hmmm....

I am told that all of the current 4 stroke singles use a flat top piston?

The Wiseco 97mm high comp and the JE 97mm high comp pistons are flat tops with the deck height adjusted to increase the compression ratio.

The JE and the Wiseco are available off the shelf in 97mm right now, you will wait more than 5 weeks for a CP, and also CP still has not worked out the wrist pin breakage issue, they admit to it and defer to the fact that they do not make the wrist pins themselves, and that "they are working on it".

CP makes great pistons from what I am told, and if Yoshimura is using them then that says something for certain.

I have not heard of anyone breaking a JE (I am sure there is someone out there tho), but I have heard of CP and Wiseco failures.

both the 450 and 426 use(d) 95mm pistons so you have to go after market to do a big bore.

If all I was doing was trying to get a higher compression setup I would absolutely use an OEM piston and have the head and cylinder shaved, and the combustion chamber cc'd to arrive at my desired compression ratio.

Man I want to build a 62rwhp 426, will your buddy share some of his wisdom?

Share this post


Link to post
Share on other sites

jjjyz450f, Im in total agreement that any piston would have been wasted in that situation. But I dont belive the sides of the piston would have gotten gouged with a oem piston, I dont belive the pieces of metal would have made it past the crown at all. I dont think the OEMs forging dept. is lacking any. True they probably dont use as much silcon but the fit of the OEM is perfect whereas the Wiseco is too small. The less friction would come with coatings on the piston yes but what company offers coatings? And the rings do the sealing but even for a tight fit the Wisco does a poor job compaired to the OEM. So Im not sure I understand why the aftermarkets are definately better then the OEMs. I know a Yamaha mech who wont use anything but OEMs on any bike.

As for having to run race fuel with the 13.5:1 piston, you dont, my bike runs strong on 93.

TeamScream, the 450f piston I know has a small dish with releifs in it for the valves. On the Wiseco pistons at least the crown is not raised rather the dish is made a bit shallower to take up more space and ad compression. At least thats what I could gather holding the OEM and the Wiseco hi comp piston side by side.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0