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View Full Version : What CC would a 300EX bored .120 over be?


Fast250EX
10-13-2005, 03:10 PM
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...
xx3003xrdrxx
10-13-2005, 03:11 PM
? 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.
Fast250EX
10-13-2005, 03:31 PM
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.:confused:
rm25x
10-13-2005, 03:53 PM
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.
fasterblaster09
10-13-2005, 05:32 PM
I beleive .80 is the highest you can go without a sleeve job.
660Grizz04
10-13-2005, 06:06 PM
Yea .... I've never heard of .120 over before ..... IMO i think its .80 also ...
Cody_300ex
10-13-2005, 06:42 PM
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.
Fast250EX
10-13-2005, 08:27 PM
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...
rm25x
10-14-2005, 06:21 AM
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.
Cody_300ex
10-14-2005, 10:39 AM
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 | .
rm25x
10-14-2005, 02:07 PM
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.
Cody_300ex
10-14-2005, 02:10 PM
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.
rm25x
10-14-2005, 03:32 PM
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.
Fast250EX
10-16-2005, 12:54 PM
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... :D

Thanks for the help guys.
ZeroLogic
10-16-2005, 01:01 PM
well the problem with that is that it was a yamaha :o :p
my girlfriend was telling me a story about her cousins friends older brother:confused: 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
hondardr4life
10-16-2005, 02:22 PM
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.
Fast250EX
10-16-2005, 07:39 PM
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.;)
rm25x
10-17-2005, 05:36 AM
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. :cool:
bwamos
10-20-2005, 03:23 PM
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.
rm25x
10-20-2005, 05:53 PM
Cool post your feelings on the work done when you get it back and have a chance to ride it. Thats my winter project.
chapmanmd
10-24-2005, 09:46 AM
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?
lumpy300
10-24-2005, 09:21 PM
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
allballs
10-26-2005, 07:20 PM
.80 over is 397cc which is as high as u can go without resleevin
Cody_300ex
10-27-2005, 05:55 AM
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
ZeroLogic
10-27-2005, 02:08 PM
stop flaming the kid man he asked a simple qusion just give him a simple awnser....
rm25x
10-28-2005, 09:15 PM
who's flaming who?