400EX engine rebuild: the most bang for the buck

[sideways]

Hey everyone. I am looking into rebuilding my 400ex and i was wondering what input anyone might have. Right now I am looking to get a hotcams stage 1 with a wiseco piston kit (11:1 compression) at standard bore. I was kinda trying to stay away from boring it out for money reasons only. (as in i dont have enough) I am hoping to get a few more HP out of the deal, i dont race, and do a lot of trail riding, stopping at sand pits along the way. anyway, has anyone done this type of work to their quad?? how about gains and downfalls?? feedback is great! yay

[SHADETREE101]

if your going to put a new piston and rings in, save yourself the heartache and bore it. just go to a 406 assuming your bore is stock. you'll do nothing but lose out if you don't broe and the cylinder is worn out. and going to the lighter piston and bigger compression will always make it more responsive.

[ridered86]

if your gonna mod your ex do it up with a 440, web cam and all the other stuff, its not the baddest quad out there any more. call up marcums motorsports at 1 386 325 6060, terry will fix you up and NOT ripp you off, he used to be the site sponsor back in the day

[nakomis0]

Sideways you sound like your on the right track for what you want. Theres only 1 thing I would change..... Instead of Weisco get a Ross 11:1 with the thinner gaskets.

I think C&D is having a group buy for Ross pistons right now so you might wanna call em up.

Ross should be a tad lighter than wiesco, other than that they are about the same.

Heres info on the group buy....

Groupbuy interest in Ross pistons
I would like to know if you people would be interested in a group buy on the ross piston kits. There would have to be a minimum of 20 pistons sold and the order would go in all at the same time.
This would only be on 400ex pistons from std to 89mm
The price would be $105 for the std,406,416,426 with out sleeve. That would include piston, rings, circlips, and piston pin. I am still working on the 440 kit price and the 426with sleeve price.

[sideways]

the ross piston group buy looks interesting. might have to go in on it... Alhough i am kinda looking to get this done within a week or 2. when does the group buy actually buy?? meaning when would i get the piston) And im not really interested in boring the cylinder, the machine doesnt have many hours on it so chances of the cylinder getting maimed is slim i think. what are the advantages of porting and polishing while im at it??

[SHANE03EX]

You should read the whole thread, I know I dont like to read that much either but some of the info you ask if already answered in the post. The pistons would be shipped in a could of weeks.

[Spikers400]

I am also in this same situation. I am going to send the money in for the groupbuy. I was planning on getting a std bore 10.5:1. Im considering gettting the 416 . But i dont know where to send the cylinder to have it bored... I live in connecticut, does anyone know where i could get it done, preferably locally. ALso, do you think its worth getting the 416 if i mostly ride trails?

[cals400ex]

Originally posted by Spikers400
I am also in this same situation. I am going to send the money in for the groupbuy. I was planning on getting a std bore 10.5:1. Im considering gettting the 416 . But i dont know where to send the cylinder to have it bored... I live in connecticut, does anyone know where i could get it done, preferably locally. ALso, do you think its worth getting the 416 if i mostly ride trails?



a local dealership should do that for you.

[EXDUNER127]

Hey sideways, you are on the right track and you do not need to get it bored, you may need to get it hone and that is only 10-15 bucks, because you want the piston to seat right. If you do alot of trails the stg 1 is perfect, and if you do port n polish it all depends who does it and how good of a job they do , my engine builder says he is going to get 10% increase in power. That is what i am in the process of doing and that is what he recommended for more power, cus he said there is very little difference from std. bore to a 406. good luck!

[sideways]

i came to the conclusion that i'm not going to bore it out. many people say that if i do the stage 1 and the 11:1 piston in standard bore, it'd only a few horsepower behind a 416. I havent tested the theory yet so once the work is done we'll see. thanks for the advice.

oh and with putting the new cam and piston in, am I going to have to rejet the carb again? I already have some white bro's jets in the carb, would they work with the mods??

[cals400ex]

Originally posted by sideways
i came to the conclusion that i'm not going to bore it out. many people say that if i do the stage 1 and the 11:1 piston in standard bore, it'd only a few horsepower behind a 416. I havent tested the theory yet so once the work is done we'll see. thanks for the advice.

oh and with putting the new cam and piston in, am I going to have to rejet the carb again? I already have some white bro's jets in the carb, would they work with the mods??


i only went up one size on the mainjet after my 406 10.8:1 with stage 2 hotcam. it probably depends on how well it is jetted right now.

[brif]

Originally posted by sideways
i came to the conclusion that i'm not going to bore it out. many people say that if i do the stage 1 and the 11:1 piston in standard bore, it'd only a few horsepower behind a 416. I havent tested the theory yet so once the work is done we'll see. thanks for the advice.

oh and with putting the new cam and piston in, am I going to have to rejet the carb again? I already have some white bro's jets in the carb, would they work with the mods?? Just get it bored out. Around here a good bore and hone runs about $30.

[sideways]

maybe i'm not looking in the right places, but every machine shop and atv store around here has given me prices upward of 200 bucks to bore out the cylinder and install new pistons and rings and whatever else. and thats the only reason im not boring it out and making it nasty...

[Billdog350]

How many people have actually checked their cylinder out of round (wear) when they do these piston kits? I live in CT also and my dealer (Vicious Cycle) over in Plainville where I work said that he rarely sees cylinders that need to be bored when he puts the aftermarket pistons in. He says he's done a few high compression kits and he hasn't had to bore one yet. I need to check my compression but as long as I'm still toward the high end of the spec, I don't see the need to bore and hone.....I would just hone if there isn't the cross hatch and slap the new piston back in there.....

[cals400ex]

Originally posted by Billdog350
How many people have actually checked their cylinder out of round (wear) when they do these piston kits? I live in CT also and my dealer (Vicious Cycle) over in Plainville where I work said that he rarely sees cylinders that need to be bored when he puts the aftermarket pistons in. He says he's done a few high compression kits and he hasn't had to bore one yet. I need to check my compression but as long as I'm still toward the high end of the spec, I don't see the need to bore and hone.....I would just hone if there isn't the cross hatch and slap the new piston back in there.....

it sounds pretty odd not having to bore when going with a piston one or several mm's larger than stock :huh

[cals400ex]

oh, are you referring to honeing the cylinder and not boring it out larger?? when using another 85mm piston,you won't need to bore it out. you should hone it in order for the rings to seat best.

[Billdog350]

you're not understanding me. A stock bore is 85mm. You can buy a high compression 85mm piston. However if you bore you need a bigger piston, and vice versa.

What I'm getting at is that everyone just blindly orders a bigger piston and has the jug bored accordingly. However does anyone check how worn the orig bore is? My dealer says that there is little or no wear...so a stock piston BORE (85mm) holds up fine with a new high comp piston. However this is in CT where we have no dunes and only put a few hundred miles on our machines a year....not like out west in the dunes where you probably do double or triple the amount of riding in high sand environments.

[cals400ex]

well of course you wouldn't bore when staying with the same sized piston. you would want to hone it out for the best ring seat though. also, your shop or builder should gap the rings and bore/hone the cylinder to match the pistons directions.

[skidaddyjr]

Dude if your going to buy a piston any,there is hardly any difference in the price of an overbore size.I would have it bored to 88mm at about $30 TO $40 leave the valvetrain stock spend that money on head porting you can have that done for 75.00 and up.Have the choke removed from the carb and it bored it works great. With a slip-on silencer this combo makes very smooth power and runs very well for the money.I run one of these motors in XC & Hare scrambles in TN it doesn't tire you out you can ride alot longer with a smooth power band than a (BEAT EM DOWN ROAD) MOTOR!