[What CC would a 300EX bored .120 over be?] - ATV Riders Forums - Honda, Yamaha, Suzuki, Kawasaki, Polaris, CanAm, Arctic Cat, Kymco ATVs

Pages:1

What CC would a 300EX bored .120 over be?
(Click here to view the original thread with full colors/images)

Posted by: Fast250EX

Saw a 300EX for sale that is supposedly bored .120 over and was wondering what displacement that would make it in cc's.

Also, could someone explain to me how a 330 big bore kit is more reliable than boring one to .120 over? I don't understand the difference. Do the big bore kits use an all new head or something?

I don't have any experience with boring a 300EX, so sorry if this is obvious stuff...

Posted by: xx3003xrdrxx

? im pretty damn sure .80 over is as big as you can go on the stock head ? thats what i have atleast . Mine is a true 300 with the .80 over.

Posted by: Fast250EX

Do you mean as big as you can reliably go, or as big as it is possible to do?

I haven't spoke with the person selling the bike, but other people are tellin me its bored .120 over, so I dunno. Maybe they made a mistake and its just .020 over.

Posted by: rm25x

quote:
Originally posted by xx3003xrdrxx
? im pretty damn sure .80 over is as big as you can go on the stock head ? thats what i have atleast . Mine is a true 300 with the .80 over.

You can get a 330 bore only kit.

Posted by: fasterblaster09

I beleive .80 is the highest you can go without a sleeve job.

Posted by: 660Grizz04

Yea .... I've never heard of .120 over before ..... IMO i think its .80 also ...

Posted by: Cody_300ex

No .120 over is the most you can go, and its a 305cc. .080 is the most you can go over and still be able to ride in the youth production MX class.

Posted by: Fast250EX

Thanks man, that's what I needed to know. It seems like it would be fine, it doesn't get any hotter than dad's 88 300 fourtrax does, so seems like it would be fine. I rode with it before for 5 hours (didnt know it was bored .120 over at the time, probably explains why i got my *** whooped bad in a drag race, lol) and it didnt have any problems. So i dunno...

Posted by: rm25x

quote:
Originally posted by fasterblaster09
I beleive .80 is the highest you can go without a sleeve job.

Do a search on ebay for 300ex big bore and you will see a 330 kit that is bore only, no sleeve required.

Posted by: Cody_300ex

quote:
Originally posted by rm25x
Do a search on ebay for 300ex big bore and you will see a 330 kit that is bore only, no sleeve required.

Theres no way, you HAVE to get a sleeve for a 330cc bore. I looked at it, even if you could do it youe sleeve would be about this thick | .

Posted by: rm25x

Ok this is from fourstroketech.net....

"330cc Big Bore Kit

Kit includes: piston, rings, pin & clips, sleeve, and head gasket. Price: $295"

They don't mention the need for a sleeve either.

Posted by: Cody_300ex

quote:
Originally posted by rm25x
Ok this is from fourstroketech.net....

"330cc Big Bore Kit

Kit includes: piston, rings, pin & clips, sleeve, and head gasket. Price: $295"

They don't mention the need for a sleeve either.

Posted by: rm25x

doh lol you caught me on that one. I read that several times and didn't notice that. Hmm thats a lot better kit to get then.

Posted by: Fast250EX

Just wondering, would the 330 kit with the new sleeve work on the motor that's already bored .120 over? I'd really rather have a 330EX, so I was making sure I could even do it on that motor with it being bored so big before i already made plans.

I have plenty of time to decide right now though. I was riding my friend's YZ125 for the first time yesterday in a wet field (dew was on the ground still) and ended up locking the front wheel up on accident (combo of STRONG brakes and being used to ATV's).

I laid it over going 45 or so (friend was ridin a 250EX right behind in upper 5th gear). Frame landed on my foot, drug me for a while, and then i caught traction and started rollin and gettin thrown around like a rag doll. Shattered my foot almost all the way across, so I can't ride or even drive (it was right foot) for 6-8 weeks. That YZ can flat out move though, lol...

Thanks for the help guys.

Posted by: ZeroLogic

well the problem with that is that it was a yamaha

my girlfriend was telling me a story about her cousins friends older brother

brakes craped out and he hit like a wire blocking off a road i geuss he didnt see it and he died from it the family sured yamaha and won

Posted by: hondardr4life

Ok, this is the honest to god truth. When I rebuilt my motor with the 330 kit. I was able to take the old stock sleeve and set it down INSIDE of the new 330 sleeve. So there is no possible way that you can go 330 without resleeving.

Posted by: Fast250EX

Just a question. Fourstoke tech's 330 kit, does it require any boring or do you just replace the stock sleeve with theirs and put it all together...

Just makin sure I got all this straight.

Posted by: rm25x

Well if the old sleeve fits inside of the new one, then you would have to machine it for the larger sleeve. I plan on getting the FST kit next month, can't wait.

Posted by: bwamos

quote:
Originally posted by Fast250EX
Just a question. Fourstoke tech's 330 kit, does it require any boring or do you just replace the stock sleeve with theirs and put it all together...

Just makin sure I got all this straight.

I beleive you have to bore out the aluminum cylinder so the sleeve will fit inside of it.

I just UPS'd the whole cylinder to him and he pulled out the lod sleeve.. bored the aluminum and pressed in the new sleeve.

Of course at the same time I had him do all the head work that should be done on a 330.

Posted by: rm25x

Cool post your feelings on the work done when you get it back and have a chance to ride it. Thats my winter project.

Posted by: chapmanmd

quote:
Originally posted by bwamos
I beleive you have to bore out the aluminum cylinder so the sleeve will fit inside of it.

I just UPS'd the whole cylinder to him and he pulled out the lod sleeve.. bored the aluminum and pressed in the new sleeve.

Of course at the same time I had him do all the head work that should be done on a 330.

How long did they say it would take?

Posted by: lumpy300

how would a 330 kit do on a stock cam with porting done to head, vs. a .080 overbore piston and porting with stock cam? there's no replacement for displacement, but not wanting to spend $$$$ on cam and rockers, trying to cheap out a little bit but with decent power

Posted by: allballs

.80 over is 397cc which is as high as u can go without resleevin

Posted by: Cody_300ex

quote:
Originally posted by allballs
.80 over is 397cc which is as high as u can go without resleevin

NO .120 over is. Its a 305cc bore. Do some research

Posted by: ZeroLogic

stop flaming the kid man he asked a simple qusion just give him a simple awnser....

Posted by: rm25x

who's flaming who?