This machine shop is the only one around, and i've been loking for about a week. This guy says that at high RPM's i am more prone to failures because something with the cam, and the cylinder wall is too thin...

He wonders why iw ent with 87mm piston and not 86...


What the HAIL? IS 87 A 416????? Am i trying to bore 1 450cc engine?? Is this guy a moron? He seemed to be very informative and know exactly what he was taliing about, seriously...

HELP
Someone help me out......

 

While the cylinder wall is getting thin at 87mm, it is OK, I have been turning mine very hard since the rebuild with no problems.... We did have to rechamfer the cylinder after boring - if he can't do this I would question his competence.

Yes, the 87mm calculates up to nearly 416cc.

Changing the bore will not affect the RPM range your engine likes to operate at

Yes, if you increase the maximum RPM that your engine operates at (with a camshaft change), and frequently make use of those RPMs, there will be increased wear and chance of failure (unless you upgrade parts), this is true for any engine - if you never turn your EX above 4000rpm, it would last longer than if you operated it at 9000 RPM all the time - it only makes sense. You will not be exceeding the design limits with an XR camshaft, that is a factory Honda grind for this engine.

If he tells you that you should have gotten a Wiseco instead of a JE, I would question his knowledge - JE is one of the most respected race piston manufactures there is..... Period.

There's a reason people building high dollar race car engines spend $100 or more per piston for JE when they could just as easily buy $10 a piece pistons out of Summit Racing.

If you're not confident in your machine shop's abilities, send your parts to an ATV race engine builder/machinist like GT Thunder - you will probably spend less, get a better job done, and straight answers.

 

ok... thx alot gabe..

1 more thing. is it a neccessity to get new head bolts before i install this thing? did you?


PS; should i have anything to worry about with a stock cam? becuase i rather sacrafise performace, for reliability, and "get back together to ride" time.


from what i understand, larger cam=more RPM's=less engine reliblilty

 

416's are known to be REALLY reliable....i meen come on man, that dude must not know what the hell hes talking about...i wouldnt leave my quad with him...and to get full potential of that piston etc, i would go ahead with the cam...the cam is'nt really going to make your ex unreliable...get your rocker arms sent off to be treated and heavy duty springs like mine, and even a rev kit to use those extra rpms, and man yours will fly....like the guy said above...just get those few lil extra parts to make it reliable...but dont put off getting a cam because this guy doesnt know what hes talkin about.... one more time, JUST GET THE ROCKER ARMS FIXED AND SPRINGS, then you have no worry in the world... .80 is not bad and is still going to very reiable, good luck
Jason

 

Now Hear THis....

the day that I wint he lottery, is the day i get my rockers hardened. I wanted a bore kit that i DIDn't have to get the rockers hardened. That is why i went with 416.. 200 bucks for what?? reliability? Sorry man, but you put mad money into your 416(PS: send me some pics, Chuck_D81@hotmail.com), i just don;t have it. I am only 16 ya know, lol

i am just double checking to make sure that it will be ok..


PS: do i have to get the stock sleeve removed, then bore the actual cylinder, then put a bigger sleeve in? or is that onyl on the 99's?

 

i totally understand the money thing...im just stating the topic on not getting a cam...but if you get the xr400 cam you have listed, you shouldnt need the rocker arms hardened anyway.. you will still have the reliable engine as before, just a drop im cam to waken it up a lil....good luck, and im trying to get some pics scanned...i really want my shocks first before i start posting picks cause this thing is soooo sweet,,,i never would have thought my quad would be this nice....

 

If bored correct, the 416 should be very reliable. I had a 87mm JE piston (the best brand out there) in the 400ex that I had and had no problems. One thing about the rings, mine had to be "filed to fit". Make sure and have a professional do this. Make sure the builder you choose knows what they are doing...even if you have to pay a little more.

 

In modest defense of the machinist:

Unknown parts, unknown procedure: Common sense and experience may lead him to turn down the job.

Consider: 87 mm piston. Not sure. What about an 88 mm? 89 mm? 90? and so on. At what point would a responsible machinist say, "Whoah!"?

Now, as to the mod. 87 mm give about 4-5 % more displacement, let's say; raising the compression ratio some also. How much performance increase from that modification alone could one expect? Worth it, considering at least some compromise in service life and reliability?

You decide.

Diogenes

 

416's aswell as the 426 have been know to run down 440s....it gives you allot better performance compared to stock, trust me....there is all the talk of 440 big bores, but in reality, the higher reving 16's and 26's might not have quite as much torque but through 3rd to 5th it pulls really hard and will run the 440 down and actually beat it in some races...with a good jump the big bore only holds the 416 off a bike....not bad considering you still have lots of reliability with this 416 compared to the service of a big bore (dont get me wrong the 440s are nice)

 

there is no replacement for displacement my friend. I am sure if you got a "Sik 440 kit" like 5 grand, you could smoke a 416, 426. But your right about the cheaper 440's. that's why i chose this kit.

PS: hook me up with some pics, don't worry about the suspension! I WANNA SEE THIS QUAD BAD!