Any one tried this????? 400 to 426 Question


16 replies to this topic
  • ready fredy

Posted June 14, 2008 - 07:17 PM

#1

Yes yes i have read many threads about changing the 400 rod or entire crank to the 426 but it usually includes a expensive cylinder work or complete change but has any one tried having the stock 400 piston pin bore enlarged by a machine shop keeping this upgrade less expensive. Personally i think 400 cc is plenty of power in the woods and some of the magazines are testing sleeving down 450,s to 400s. I just bought a 400 with a locked up engine as a fun project and am looking for the best and cheapest way to get good upgrades at a reasonable cost. Has any one tried this or will i be the ginney pig here??? Ill do it if it blows what the h#$% :thumbsup:

  • Birdy426

Posted June 14, 2008 - 07:54 PM

#2

I would be cooncerned that the pin boss will become too thin. There ain't much metal there to begin with, and I believe the 426 pin is a full 2mm bigger in diameter than the 400. Also, most conventional machine shops won't have the ability to cut the circlip groves, either...

  • ready fredy

Posted June 15, 2008 - 06:28 AM

#3

I actually havent got my hands on the piston yet to measure it yet but the circlips groove would be an easy job for a dremmel as it isnt a extreemly critical area and doesnt have to be machined to the 00001 its just a groove

  • Birdy426

Posted June 15, 2008 - 10:34 PM

#4

I actually havent got my hands on the piston yet to measure it yet but the circlips groove would be an easy job for a dremmel as it isnt a extreemly critical area and doesnt have to be machined to the 00001 its just a groove


Man, Fredy, you may want to reconsider that train of thought...The tolerance and geometry IS very critical to retention of the circlip, in terms of width, depth, and alignment. If the clip comes loose (and they do occasionally come loose even when everything is machined to .001 tolerance), it will really destroy the barrel and piston, and maybe even the bottom end...

  • ready fredy

Posted June 16, 2008 - 02:43 PM

#5

I know it sounds like im over simplifying this im really not quite that simple minded. What in asking is for actual data on caliper measurements of the lower pin boss areas to compare the 400 and 426 pistons. This area is supposed to be reinforced with steel under the aluminum that you cant see and the pin diameter difference is only 1mm total so thats .5mm on each side, actually not that much right? And for the pin clip groove im sure that in this day of technology that is a very small problem to over come. Come on guys think outside of the box for once!!!!!!!! Im open minded and love to try things that havent been done before, But for me the proof is in the calipers if the readings arent good than ill drop it.

  • Birdy426

Posted June 16, 2008 - 09:59 PM

#6

There is no steel in the piston. It is cast aluminum (stock) or forged aluminum (Wiseco or JE). As an aerospace engineer, I can tell you that when it comes to stength, especially fatigue strength, 1/2 mm (.02") IS significant. Remember, the reduction in strength goes as a square (for tension) or cube (for bending) function of the material you remove, and the pistons are designed to be as light as possible (meaning an absolute minimum margin of safety) to help the engine rev. Openig up the wrist pin bore (or, more accurately, line reaming the bore) really won't be that expensive...probably 50-75 bucks by the time your machinist develops a set up to hold the piston. Cutting the circlip groves will be somewhat more expensive. With machine shop time running upwards of a hundred bucks an hour for typical automotive machine shops and 150 bucks an hour for specialty shops (at least here in Cali), you don't have to burn too many hours to equal the cost of boring and replating your cylinder, or buying a new cylinder outright. (You can have your cylinder bored and replated by Eric Gorr, Millenium Technologies, or Luke's Racing for around 200 bucks.) I assume you are using a new piston in your rebuild, so the cost of a 400 vs 426 piston is really a non-player.

While I appreciate "out of the box" thinking as much as anyone ("Feed live tuna mayonaisse"...Billy Blaze from Night Shift), the reality is that most cases, as in this one, the cost of out of the box thinking is more that the cost of the conventional approach...

  • GCannon

Posted June 17, 2008 - 07:24 AM

#7

If you are really serious Just order a custom piston to what ever spec's you want.
http://www.jepistons.com/dept/order/
http://www.wiseco.com/ContactUs.aspx

Try these reputable companies this may take a little more time but should keep the cost down.

If you do it let us know what happens.

  • grayracer513

Posted June 17, 2008 - 08:54 AM

#8

I actually havent got my hands on the piston yet to measure it yet but the circlips groove would be an easy job for a dremmel as it isnt a extreemly critical area and doesnt have to be machined to the 00001 its just a groove

I can't believe I just read that. Wrist pin clips have failed to hold because the wrong clip was used (Tru-Arc used in place of wire, or vice-versa), or simply because the ends weren't placed right. Cutting clip grooves with a Dremmel is begging your engine to blow.

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  • ready fredy

Posted June 17, 2008 - 03:07 PM

#9

Well thanks guys, ill look into the price of a custom piston just for giggles. Ill explore all options before i make my decision on my approach. I understand the mistake in trying to save a dime but end up spending a dollar to do it!!!!!!!! Im always open to custom engine mods. Just look at all of the technology is at our fingertips. I thought the pin boss area should have steel in it because of my experience with automotive pistons it makes sense that motorcycle pistons wouldnt have this because of the weight considerations. Thanks for all of the input maybe it would be cheaper to go to the 426. Actually is it really necessary to do anything at all? Is the 400 a time bomb or is it reliable enough as it is? Im getting mixed vibes here!!!!!!!

  • ready fredy

Posted June 17, 2008 - 05:46 PM

#10

Do you think there would be any demand for the 400 piston with the 426 wrist pin hole diameter?????? I know wiesco makes pistons for some unusual cases like fir example the kdx 200 that comes with a nickel bore but they make pistons for over bore sizes also. Soo what do you think would any one buy these pistons or do you think everybody is sold on more CCs are better? Im an ex Ktm rider and ill never go back now that ive ridden jap bikes. But i read many times how riders claimed they were faster on their 400s than 450s and could just plain smoke their buddies on their 520s in the woods of course. As for me ill take suspension an handling over horse power any day of the week in the woods that is!!!

  • grayracer513

Posted June 17, 2008 - 07:46 PM

#11

More displacement, other things equal, IS better. By going to 426, which is by no means a huge jump, you have the opportunity, if you like, to put together a milder engine witha broader, more usable power curve at the same power level. Why wouldn't that be good?

  • Birdy426

Posted June 17, 2008 - 10:31 PM

#12

Actually is it really necessary to do anything at all? Is the 400 a time bomb or is it reliable enough as it is? Im getting mixed vibes here!!!!!!!


Fredy - I ride with a guy who works with a guy whose brother in law's nephews' ex-wifes' cousins' best friends' wife grenaded the small end on her 400, so the sky must be falling!

Seriously, 3 of the guys in our crew have 400s (2 WRs and 1 YZF), and so far, no one has lunched a small end bearing. You WILL find reports here of folks who have grenaded them, so I'm not implying that it doesn't happen, but if you are a typical weekend warrior and take good care of your equipment (are those non-sequiters?), the 400 should serve you well in stock trim. The factory did upsize on the 426, but I don't know if that was because the design was marginal for the loads a 400 put on it, or marginal for the loads a 426 puts on it. My guess is for the loads the extra piston mass of the 426 put on it. Either way, if you DO have to replace the connecting rod, the 426 conversion gets you more than just displacement and a bigger small end bearing for your money. The primary drive and balance shaft drive gears on the 426s were splined, not keyed as they are on a 400, so they are a lot more durable. Does that mean you'll have trouble with your 400? Likely at some point if you don't stay on top of the primary drive nut (keeping it tight), but it's a matter of addressing it before the keyway wears too much, and is just a matter of replacing the key and retorquing the primary drive nut.

If your motor is well worn and you have to replace the barrel, piston, and rod anyway, it's a small extra cost to upgrade to the 426 set up, but if your 400 is pretty low hours and well maintained, there's no real reason to blow the bucks if you're not really hard on equipment. One word of advice...when you are in there changing rings, pull that piston off and mic the bore of the small end...and replace the circlips. That way, you will know where you really are in terms of wear and durability.

  • GCannon

Posted June 18, 2008 - 10:39 AM

#13

Didn't the 400's come out in 1998?

If any dirtbike motor (4t 2t i don't care what brand) lasts 10 years then you are not ridding it enough!:thumbsup:

  • ready fredy

Posted June 18, 2008 - 03:27 PM

#14

Yes i have heard of 450s gernading also but we all know that is just the price of a mass produced high performance machine im stunned of how reliable these machines are for the money, not many other sports can u buy such performance so cheap. I gave up on muscle cars for this reason its just too expensive and bike are much more fun. Ok so if i do end up going to the 426 can i use a stock 03-04 wr 450 exaust cam i hear there is two different pins of some sort on the auto decompression between the yz and wr because of the electric start is it an issue or really a non issue i know the electric start doesnt usually work on the wr cold any way. I understand i can make smoother power with more CCs because i owned a 01 426 and an 04 450 and i noticed the 450 was smoother actually much smoother. And yes i di like the stock wr exaust cam better than the yz. i know the yz is more exciting to ride but for me i love the WRs motor just the way it is Its sooooooo SEXY!!!!! so if any one has stock cams out of an 03-04 Wr 450 in in the market!!!

  • grayracer513

Posted June 18, 2008 - 04:03 PM

#15

Ok so if i do end up going to the 426 can i use a stock 03-04 wr 450 exaust cam i hear there is two different pins of some sort on the auto decompression between the yz and wr because of the electric start is it an issue or really a non issue

The pins are two different lengths, but that is of no consequence unless you attempt to time either of the cams differently than their correct position.

The auto decomp works by extending a pin out of the cam near the lobe on the left side at speeds below 650-700 rpm. This pin is positioned so that it lifts the left exhaust valve off the seat just as the compression stroke starts. As the cam continues to rotate, the pin slides off the back of the lifter, allowing the valve to reseat about 50-60 degrees before TDC, so that there is enough of the compression stroke left that it will still be able to start.

Now, both the WR and the YZ450 used the same exhaust camshaft from '03-'05 (and in the '06 WR). The difference is that the WR has the sprocket pressed on so that it is more advanced than the YZ. This would cause the decomp pin to roll off of the lifter too soon, and not enough of the compression stroke would be relieved, making it nearly impossible to crank. The solution was simply to assemble the WR cams with a longer pin.

Using a WR450 cam in your engine will result in lower overall power and torque output and somewhat smoother overall operation at low engine speeds. That might be what you want.

  • ready fredy

Posted July 11, 2008 - 03:58 PM

#16

Well i got lucky!!!!!!!!!! Actually there was no engine problem at all, I guess a unskilled owner put in a vortex clutch basket and the bolts that hold the basket were hitting the case but it did require a total break down and cleaning. i had another idea on the rod situation What if a speed shop installed a bronze bushing in the small end of the 426 rod to accomodate the smaller 400 pin????? Actually i noticed the 400 doesnt have a bronze bushing in the small end isnt that a no no????? In the hot rod world this is definetly a no no and those engines only turn 7000 or so. Does the 450 and 426 have a bushing or not in the small end?? As We know same metal rubbing together can scuff and score so why is this????

  • grayracer513

Posted July 11, 2008 - 08:46 PM

#17

Does the 450 and 426 have a bushing or not in the small end?? As We know same metal rubbing together can scuff and score so why is this????

No, or perhaps, no-no, there is no bushing in the small end of any YZF. The pin and the rod are not the same metals or hardness, so it works.




 
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