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400 to 420?
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Posted by: Hot4Teacher---------------------
I have a '99 YZ400. I have been thinking about going with the 420 kit. I am looking for feedback on; reliability, pros, cons, happy with the results, best price, and anything else I might have forgot to mention. Thanks for any help.
Posted by: Rich Rohrich---------------------
It's a great mod, in fact I think it's the BEST mod you can do to the 400 engine but the 94mm piston is heavier than the stocker so it's not a good idea to do it on an engine with a lot of hours. The connecting rod small ends are prone to failing in high hour engines that see high rpm, and a heavier piston just speeds this process up.
If you rebuild the crank with the 426 rod you eliminate the potential problems and you open up options for running a 95mm or 97mm piston with a 426 barrel.
Posted by: Hot4Teacher---------------------
As always, you be da man. Thank you. Where do you get all this information?
Posted by: Rich Rohrich---------------------
Quote:
Originally posted by Hot4Teacher
Thank you. Where do you get all this information?
|
It's easy, you take things apart, you put things together a little differently, you blow a few things apart when you push them too far and you talk to other guys doing the same thing. If you pay attention and take notes the whole time you end up learning a lot of useful stuff just like Gordon Jennings promised. :thumb:
Posted by: JasonJ---------------------
Rich, are you saying a 426 jug will bolt into a 400 tranny and head? Or are you talking about the liner?
Dont know why Im asking, I dont think I would mess with my 400 for a few cc's. Maybe if I ever toast the motor.
Is decking or shaving down the head advisable or is there a valve clearnace concern?
Posted by: Rich Rohrich---------------------
Yep the 426 barrel is what we use to build 426cc (95mm) and 444cc (97mm) motors on 400 bottom ends.
The 426 barrel is thicker in important areas and can handle being overbored and replated to 97mm. The 400cc barrels can only be safely bored 2mm to 417cc (94mm) and replated.
Posted by: john stu---------------------
i did a 426 kit on a 99yz400 back when it was almost new the kit was a bigger piston from wiseco with a stock 426 cyl and at the same time i had the head ported buy thumper racing and i must say it was great the bike had more power everywhere especially down low and it reved the same as stock if not more (but don't forget the head was ported)i loved it but...soon after the bike started making a ticking noise very slight every body that heard it said i am crazy and don't worrie about it but i took it apart anyway and everything looked great untill i disided to take the piston off to look at the wrist pin (witch i almost didn't do because everthing else look so good)and the wrist pin came out in four pieces it was i wiseco wrist pin that came with the piston anyway the rod was junk all scored from the pin so i ended up rebuilding the crank and at that time i put in a stock 426 rod on my crank because the 426 rod uses a much bigger and stronger wrist pin wiseco waranted the piston (after much effort)and they told me this was a common problem with the 426 piston on a 400 rod and they are working on making a stronger wrist pin for that application (who know if they did)after it was all back together it ran great for two years untill i sold it i highly recomend the big bore kit but i would pit the 426 rod in it to be safe, big deal it will cost you another $200 parts and labor it will be all apart anyway and then you will have nothing to worrie about because your bike will have a stock 426 motor .just think if it breaks you will be spending $2000 to fix it and it would suck more than you could amagine.just my advice think about it.still do it just spend a little more and do it right.
Posted by: john stu---------------------
the kit i did was called a 420 kit from thumper racing all it was was a stock 426 jug and a wiseco piston and gaskets you could make your owen you would be surprised how cheap the 426 jug is check your dealer its cheap it's not like a two stroke with all those ports
Posted by: JasonJ---------------------
So you replaced the whole block (jug) and not just the liner right?
So how much was the jug? Im curious. Maybe if I ever have to over haul the whole 400 motor Ill think about it, I definaltly wont risk the small end of the rod failing though. I would do the crank replacement too. I hope my WR power plant last the life of the bike in stock trim though, knock knock.
Posted by: john stu---------------------
yes it was a brand new 426 cyl. not a sleeve,as for the crank you don't need to buy the whole crank just bearings, seals,thrust washers,and of course the stock 426 rod and have a good bike shop rebuild it for you .i forget the price of the cyl but i remember being very surprised how cheap it was (i do get a good discount but even retail was much cheaper than i thought it would be)i think a paid under $150 for a brandnew stock yamaha 426 cyl. i might be wrong but i remember thinking gee thats way cheaper than buying a sleeve and paying labor to put it in and i could not figure out why people were sending there cyl's to be sleeved when its so cheap just to buy one from yamaha.
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