All kinds of 300EX info II

[honda300EXtreme]

Im glad to see the original thread has helped people out. But I was reading through it the other day and it has started to get a little cluttered so i figured i will make another one that is a little bit more organized. This one will contain the same info but it will be a bit easier to use as a reference.

i apologize to those who have posted info. i cant take credit for alot of the info in that thread so if something usefull was posted by another there name will be underlined at the top of the post. (gotta give credit where credit is due)

as always if you have something usefull to post or have any questions fire away

thanks to every body who has helped.

[honda300EXtreme]

ok, here we go remember this all 300ex info, some corresponds to the 250x some doesn't.


stock valve lash =.004
Stock jetting = 122 main , 120 main (high alttitude), 38 pilot, stock needle position - 3rd groove
Wheel offsets - front = 4/144 rear =4/110
Stock gearing = 13 / 38
stock spark plug # - DR8ES-L

stock carb 32mm keihin with accelerator pump.

Ignition: CD with electronic advance
(300ex CDI will not work on 250x)

Ground Clearance : 4.6 in. (stock)

Will 400ex a-arms work?
yes, you will need a-arms, tie rods, and 400ex length shocks (16.25), and a shock relocator bracket, 400ex spindles are not neccessary but are an improvement with this set-up,and yes stock brakelines will stretch far enough.

will a 400ex steering stem work?
yes, stops on bottom need cut off beacuse there 180* off, and the little washer about 3/4 will need removed, it is roughly 1'' longer

will a 400ex carb work?
yes, i recomend it for engines that have atleast the basic mods, such as pipe. filter, ect.. stock boots will stretch, all you need to do is rejet, and i recomend a 42 pilot jet

Hardweld rockers are only necessary for a hard weld cam -
EX. web cams. billet cams such as hot cams do not require hard weld rockers, they will actually cause damage to your cam

What is max. compression piston on 93 octane. - 11:1
any thing over is pushing and detonation could result.

engine idle speed = 1,400 +/- 100 rpm
stock pilot screw setting = 2 1/4 out from closed

engine compression with stock piston - 171 - 200 PSI

engine oil capacity -
oil change only - 1.6 quarts
oil and filter change - 1.7 quarts
totally engine dissambly - 2.11 quarts

*if you run a oil cooler about 2 quarts even on basic oil and filter change*

Suspension
Front: Independent double-wishbone with dual hydraulic shocks, 5-position spring-preload adjustability; 7.1 in. travel
Rear: Swingarm with single shock, 5-position spring-preload adjustability; 7.9 in. travel

Fuel Capacity- 2.2 gallons, with a .5-gallon reserve

chain free play - 1 3/4 in. at most

heres a gearing calculator to show how variables such as rev-limit, tire size and gearing affect speed .Gearing calculator (http://home.earthlink.net/~gellett/mph.htm)


here is the link from the tech section on how to rig your reverse set-up, used when you use a aftermarket clutch lever & perch or if you are just tired of hurting yourself when you try to engage revers Reverse bypass (http://www.atvriders.com/articles/reverse300ex.html)


quad clicks when start botton is engaged -
its can usually be narrowed down to 2 things, assuming your battery has a proper charge, and it putting out correct voltage at (100% it should be reading about 13 volts)
now, its either your solenoid, or contact brushes in your starter

Common Rear end Swaps:
A 01 raptor rear shock will work but they are famous for blowing bladders on the 300ex. newer raptor shocks can be made to work. but because these shocks have a piggyback resivior the left tube that goes to the airbox will need to be cut out and the hole in the airbox will need to be sealed up.

a 450R swingarm will also work, how ever this set-up requires tabs to be welded or bolted to the frame to accept the linkage. You WILL have to use a 250R rear shock, linkage is up to you, the 250r or the 450r linkage will work, carrier and axle, and rear brakeline will also be needed. the swingarm is around 3 inches longer
the 350x rear end will also work
same as 250r
more info will be added by me constantly,, don't be shy feel free to add anything you think would be useful

QUAD BOGS WHEN IN WATER?
alot of times it is your carb vent tube. the one that hangs down behind the motor. the problem is this tube gets submerged, you can either trim the tube shorter, or put a T splittler on it and add a different length hose. other possibilites are an exposed wire.

[honda300EXtreme]

MY FYN 79

sprocket combinations broken down into gear ratios.

12/38 - 3.17
12/37 - 3.08
12/36 - 3.00
13/38 - 2.92
13/37 - 2.84
13/36 - 2.76
14/38 - 2.71
14/37 - 2.64
13/34 - 2.62
14/36 - 2.57
14/35 - 2.50
14/34 - 2.43

[honda300EXtreme]

2muchquad debating the opinion of 11:1 compression piston as the maximum on 93 octane


engine set ups along with location are just a few of the variables to add to this.Did i mention cam as well?Valve overlap plays a huge factor in ACTUAL compression.Im at around 12 to 1 with my 385ex and i have never ran anything more than 93 oct.Thats almost $3.50 a gallon and that enough let alone paying for race gas.Of course the higher the compression the more strain it puts on the bottom end so i shoot for a happy medium

[honda300EXtreme]

If budget is not a concern and you are looking for serious gains here are some suggestions:

big bore. most common size being 330 cc's but there are people running as large as 390. 4 stroke tech has several options
as well as C&D racing (site sponsor) he did the head work and the machine work for my motor and i was very impressed.

next i would send my head out to a reputable builder and have them install larger valves +1 and +2 being the most common. all 4 oversized valves will allow alot more airflow to your engine, and show a nice increase across the board, and also have them port and polish your head for your riding style, then your gonna need HD valves springs if you plan on running any type of agressive cam. also remember to have them replace your valve seals because it added insurance and there cheap.,

also look into a 400ex carb because the stock will hold you back once you start going this far into it.

as far as exhaust, curtis sparks and hmf are both great pipes for the 300 and add great power, just remember to get a full system because 300ex headers are very restrictive.

as far as cams go,
personally i had a hot cam and wasn't impressed, so i would find something a bit more agrressive.

web cams are good, FST can make you a custom cam, curtis sparks sells them and there are many others, you will also need hardweld rockers.

alot of people ask why do you need hard weld rockers. the answer is simple. If you buy any type of agressive cam the process in which it is created makes the surface much harder than the stock or billet cam. A stock core will be taken and they will build the surface up and machine it to there specifications. the new surface will be harder than your stock rockers. if ran this way for an extended period of time you will destroy your new cam and the rocker arms. hardweld rockers go through a similar process as the cam.

[honda300EXtreme]

dabomb_350x

The Stock carb on a 300EX is as followed. '93 though '98 (49-states), Non emissions, is a 29mm Keihin '98(California) through current, emissions, is a 32mm Keihin. All stock 400EX have a 38mm Keihin.

Spark Plug gap is .024-.028.

[honda300EXtreme]

SET THE STAGE

+2 400 arms on a 300 would be about +3.25 (so about an extra 6 1/2" added).



the 300ex's front end is to say the least a weak point,
the shocks are terrible, and the front end is too narrow for any real kind of aggressive riding (IMO)

+2 400ex a-arms with stock offset wheels should put you somewhere in the 47-48 inch range i do believe

i personally ran +1 400ex a-arms and with stock offset wheels i measured in at 45''

[honda300EXtreme]

heres some random info that was thrown around

torque for the clutch basket nut 81 ft. lbs. and the bolts that hold the clutch springs in should only be snug. the spring tension will hold them in.

a 400ex bumper will work however a few spacers will most likely be requied to fill some space

stock speed - 54-55 MPH

stock horse power 15-17


will 450r a-arms work on a 300ex?
QuadCobbler

The mounting tabs on a 450 frame are wider than a 300ex. You would have to cut the tabs off and move them about 1". 250r and 400ex arms both fit the 300. The is some one on here that had a frame moded to fit 450 arms.


common shock swaps (if your using a relocator bracket) 400ex, 450r, yfz 450 they are a little shorter (15.75) and need ground down, z400 as well as others

[honda300EXtreme]

Uphill Rush 450

he asked: my 250x has a brand new wiseco piston, and recently new valve seals, but it still smokes untill warm is this normal?

yes this is normal, the rate at which aftermarket pistons expand differs from that of the stock pistons,

different metal types : (cast & forged) are the main factors in this


sparks427
how much more power do ya get w/ a 330 big bore, a stage 3 web cam, port and polished head, oversized valves, an oil cooler, sparks x-4 pipe, and k&N filter w/ 400ex carb. not sure if the hardened rockers and the HD valve springs figure into that but if they do how much more does that add

with that set up, anywhere from 28- 31 HP is respectable,
(stock 400 range)
the engine builder plays a huge factor into this though

[honda300EXtreme]

chargercalvin asked
can i put a 450r or 250r hood on my 300ex? it has stock front plastics

yes either hood can be made to work. the fender style and year will determine how much modification will have to be made. it will not just bolt on.

he also asked

what is this thing??? it is loose. i can pull it right out with ease. should i put a little liquid gasket on it?


that is a crank case breather and a think layer of silicone would not hurt.

[honda300EXtreme]

all these questions have been answered by SET THE STAGE

If I install houser +3 longtravel a-arms on a 300ex what will the wheel base be? I am trying to keep it 50" or a little less!

+3 for a 300 will be under 50 inches. no worries. a lot of people run +2 400ex arms which leaves you almost at 50


What about 400ex +3 long travel?

well i think even on a 400ex, +3 would be about 51 or so. +2 400ex arms on a 300 is pretty wide. it's what i run and i've had it on it's side wheels maybe twice. no worries.

We recently purchased a 2005 Honda 300 EX, I dont get to take it out everyweekend and from time to time forget to put it on the charger, its really easy to bomb start, but was wondering if you can get an aftermarket pull start kit, or kick start kit?

there are no kits per se, but you can convert the 300ex into a kickstart. the 1987-1992 trx250x had the same engine but a smaller stroke and it was kickstart. you would just have to find a good bottom end and swap some parts over. sadly, this involves cracking the cases to be done properly because one shaft that holds a gear is absent in our newer bottom ends.

[honda300EXtreme]

many people ask how to install a aftermarket oil cooler. here is a pic of the hoses routed into the stock oil line. its pretty self explanitory.

[racer36]

you wouldnt happen to know the torque specs and sequence for the clutch cover would you? and any tips on installing a new clutch would be great to

thanks

[Dylan227]

What class do you run with that 385 ex?

[IRISH-RACER-14]

Originally posted by Dylan227
What class do you run with that 385 ex?
u run it in the 300 class and shut ur mouth:devil: make it look like ur a really good rider:blah:

[IRISH-RACER-14]

oh and it was me who asked pappy to make this a sticky:devil:

[Dylan227]

hmm I hope this kids runs a neatv race on nationals.I wanna see how bad that"385"ex is ima whoops up on his a** haha I hope atva finds out his size haha

[honda300EXtreme]

Originally posted by racer36
you wouldnt happen to know the torque specs and sequence for the clutch cover would you? and any tips on installing a new clutch would be great to

thanks


as far as torque specs and sequence: get your case on just be very carefull that the gasket does not shift and start putting your bolts in. once all the bolts are in go over each one and snug them up DO NOT over torque these because the threads are aluminum and can and will strip. like i said just snug them with a ratchet. just dont make them super tight.

do you have any specific questions about installing a clutch so i can narrow in on what you need help with

dont be shy if you need more help

[IRISH-RACER-14]

i think this video will help to give people the idea of how to make the 250r swingarm linkage fit the 300ex.

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[racer36]

I got my clutch done now, but thanks for the help.

I just used a 1/4 inch drive socket so it wouldnt be as easy to over tighten them.

clutch works great so far, not really able to ride because of the dang snow

[honda300EXtreme]

heres a few more tips.

*if you run a gforce axle keep an eye on the axle castle nuts they have been known to back off due to the spacers being aluminum.
i personally used thread lock on them.

* a lonestar anti-vibe stem will not work with a IMS 4 gallon tank.

more to come

[firestarter7237]

The 400EX carb name code is a Keihin QB10A.

[stevestauff]

you said the stock motor makes 15 to 17 hp.Do you have any clue as to about how much a built and reliable one makes?Still 300 cc .i have asked some people and no one has a round about idea.I know different builders will varry.thanks

[dawg]

i need some help on doing an extended swing arm on my 300ex.. right now it is stock but i want atleast 2 inches ..so my question is this ,, what swing arm should i go with and what shock should i go with and what dog bone ,,i have a trx 450er swing arm and rear shock and dog bone but i am not sure if it will mount up ..i want to do this swap with very minimum modifications .. please help me out ..

[QuadOwner]

all the carbs are a 29mm ventri. i have a 01-05 service manual to prove it. they call them 32mm carbs though in the specs anywhere else

[honda300EXtreme]

Originally posted by dawg
i need some help on doing an extended swing arm on my 300ex.. right now it is stock but i want atleast 2 inches ..so my question is this ,, what swing arm should i go with and what shock should i go with and what dog bone ,,i have a trx 450er swing arm and rear shock and dog bone but i am not sure if it will mount up ..i want to do this swap with very minimum modifications .. please help me out ..

idealy if budget allows you would want to get an extended aftermarket swingarm for the 300ex. as well as shock.
but if you want to use what you have the 450r swingarm will work. so will the linkage. the shock however will not. a 250r shock is what you will be needing.

dont forget you will have to weld brackets onto the frame to accept the added linkage of the new shock.

[dawg]

does anyone have pics and some more info on doing this with the 450 swinger?

[QuadOwner]

what are the stock rev limits on a 250x and 300ex?

[dawg]

Originally posted by dawg
does anyone have pics and some more info on doing this with the 450 swinger?

hello

[honda300EXtreme]

i dont have pics any more but what is it that you need clearification on?

[Eclipsemike]

i think he is basically wanting step by step intructions on how to make it work.

[dawg]

that would be really helpful if some one had that ,, or atleast were to weld the bracket for the shock (dog bone) (linkage )

[duke416ex]

How about all the basic torque specs from a manual or someone's memory? I need the head and cylinder bolts. I have found teh head is like 29ft lbs, but I was thinking the cylinder bolts were a little less????

[smr]

somebody may want to double check these but I believe they are as follows.

cap nuts are 28ft/lbs

allen head is 18ft/ibs

jug bolts (two little ones on the side) 8ft/lbs (these you can strip so be carefull)


Hey Ryan, you need any parts for that rebuild? I know were there is two setting I could get cheap.

[QuadOwner]

Originally posted by QuadOwner
what are the stock rev limits on a 250x and 300ex?

???

[QuadCobbler]

Originally posted by dawg
that would be really helpful if some one had that ,, or atleast were to weld the bracket for the shock (dog bone) (linkage )

The best thing to do is tack the bracket in place so it can be removed if need be. I would make a few brackets at different lenghts or one with 3 sets of holes just for trial and error. It took me a few months to get mine just right. I ended up making my own linkage. I also made it adjustable so I could lower the back down with out lossing shock travel. I used a 400ex swing arm which is basicly the same setup except the messurements are different. On my setup I had to use a sprocket as a spacer on the rear to shift the sprocket over a 1/4" to get the front and rear sprockets to line up. The 400 rear is wider than a 300 so something has to move. Alot of people were shimmin g the swing arm over at the pivot bolt. But I think that would make one side stick out further than the other. and as far as the shock goes you will want a 250r atv shock. a 250r atc shock will work but the hose to the rezi is shorter and you are left with many opitons for mounting locations for the rezi. Before you start tearing apart you bike I would find someone with a 450 and take messurements of the linkage and how far away the tab on the frame is from the center of the pivot point. This should be a good starting point for you but you will still need to make adjustments to your mounting location as the 300's frame is designed differnet and the uper shock mount will not be in the same position / angle. and if you havent already done so you will need a 450 axle. I was able to sell my stock axle and bearing carrier on ebay, that basicly payed for everything. with the help of some free parts to. Let me know if you want some pics. but Like I said mine is a 400 swinger

[IRISH-RACER-14]

mike kozuras old set up
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[QuadCobbler]

Wow, that is a nice setup, I never though about doing it that way. I welded my breacket to the frame so it wouldn't be legal to race but I just trail ride anyway, but that looks prety strong. and it's legal to race. There is another kid on here (born to ride) that has a bolt on bracket but I think it's aluminum.

[IRISH-RACER-14]

Originally posted by QuadCobbler
Wow, that is a nice setup, I never though about doing it that way. I welded my breacket to the frame so it wouldn't be legal to race but I just trail ride anyway, but that looks prety strong. and it's legal to race. There is another kid on here (born to ride) that has a bolt on bracket but I think it's aluminum.

yes thats him. i think ill try make my own mount as i work in a fab shop also.

[mxduner]

Have you guys done a computability chart for 250x- 300ex motor parts? how about chassis etc parts to other machines? I am thinking many people could benefit from that. I would help but i personally dont own an ex. just have a couple friends thou.

also a chart for other models chassis parts etc.

btw tanks to the thread starter for all the work you put into this.

[300exex]

does anyone know what the stock 2002 300 ex front and rear sprocket count is . ? and what is the best combo to make it take off fastest but still get go top speed .? thanks .

[QuadCobbler]

I think stock is 13 /38, most people run a 14 in the front for more top end.

[sm00th026]

Here's something useful that I haven't seen on here yet.

If you are running a dual row Aftermarket rear carrier an bearing..
You can get them at AutoZone:
Your bearing number is: 907257-RS
Just Tell them this bearing number: 907257 it cross's over as a GM Aircompressor bearing.But I do know it will work..

And for the rear carrier bearing seal's: (for stock and Aftermarket)
Go to Advance Auto Part's:
And Tell them this seal number: S-224820 I don't know what it cross's over with. But I do know it will work..

Maybe this will help someone..

[250xripper]

Can anybody tell me how many turns out the idle screw is stock?? i dont have any sort of tach to measure it so i was hoping somebody could get in a ball park range of where it should be

[theduke300]

alrite fellers. im on a low budget of about 300 bucks 400 tops. i was wantin to know what wuld be good to buy to give my 98 300ex the most power for my money. i done got a full system supertrapp,airfilter,bored out,thats about it. anyone got some ideas?

[250xripper]

Originally posted by theduke300
alrite fellers. im on a low budget of about 300 bucks 400 tops. i was wantin to know what wuld be good to buy to give my 98 300ex the most power for my money. i done got a full system supertrapp,airfilter,bored out,thats about it. anyone got some ideas?

400ex carb, maybe play with the gearing to set it up for your riding style and conditions, maybe port and polish and some other head work, but that might run you over your budget

[theduke300]

yea i was def. gunna get a 400 carb but anyone no how good a rev box wuld help it?

[JohnChilders]

Why do yall put on 400ex carbs? when is it ideal to put one on? after what mods?

[smr]

400ex carb works real good with a high flow air filter and exhuast. Do some dead work and it will really open things up.

[JohnChilders]

I have some type of aftermarket air filter, but no exhaust yet. If I put a pipe on it, will it need to be rejected if i put a 400ex carb on?

[Drfat400ex]

Originally posted by honda300EXtreme
ok, here we go remember this all 300ex info, some corresponds to the 250x some doesn't.


stock valve lash =.004
Stock jetting = 122 main , 120 main (high alttitude), 38 pilot, stock needle position - 3rd groove
Wheel offsets - front = 4/144 rear =4/110
Stock gearing = 13 / 38
stock spark plug # - DR8ES-L

stock carb 32mm keihin with accelerator pump.

Ignition: CD with electronic advance
(300ex CDI will not work on 250x)

Ground Clearance : 4.6 in. (stock)

Will 400ex a-arms work?
yes, you will need a-arms, tie rods, and 400ex length shocks (16.25), and a shock relocator bracket, 400ex spindles are not neccessary but are an improvement with this set-up,and yes stock brakelines will stretch far enough.

will a 400ex steering stem work?
yes, stops on bottom need cut off beacuse there 180* off, and the little washer about 3/4 will need removed, it is roughly 1'' longer

will a 400ex carb work?
yes, i recomend it for engines that have atleast the basic mods, such as pipe. filter, ect.. stock boots will stretch, all you need to do is rejet, and i recomend a 42 pilot jet

Hardweld rockers are only necessary for a hard weld cam -
EX. web cams. billet cams such as hot cams do not require hard weld rockers, they will actually cause damage to your cam

What is max. compression piston on 93 octane. - 11:1
any thing over is pushing and detonation could result.

engine idle speed = 1,400 +/- 100 rpm
stock pilot screw setting = 2 1/4 out from closed

engine compression with stock piston - 171 - 200 PSI

engine oil capacity -
oil change only - 1.6 quarts
oil and filter change - 1.7 quarts
totally engine dissambly - 2.11 quarts

*if you run a oil cooler about 2 quarts even on basic oil and filter change*

Suspension
Front: Independent double-wishbone with dual hydraulic shocks, 5-position spring-preload adjustability; 7.1 in. travel
Rear: Swingarm with single shock, 5-position spring-preload adjustability; 7.9 in. travel

Fuel Capacity- 2.2 gallons, with a .5-gallon reserve

chain free play - 1 3/4 in. at most

heres a gearing calculator to show how variables such as rev-limit, tire size and gearing affect speed .Gearing calculator (http://home.earthlink.net/~gellett/mph.htm)


here is the link from the tech section on how to rig your reverse set-up, used when you use a aftermarket clutch lever & perch or if you are just tired of hurting yourself when you try to engage revers Reverse bypass (http://www.atvriders.com/articles/reverse300ex.html)


quad clicks when start botton is engaged -
its can usually be narrowed down to 2 things, assuming your battery has a proper charge, and it putting out correct voltage at (100% it should be reading about 13 volts)
now, its either your solenoid, or contact brushes in your starter

Common Rear end Swaps:
A 01 raptor rear shock will work but they are famous for blowing bladders on the 300ex. newer raptor shocks can be made to work. but because these shocks have a piggyback resivior the left tube that goes to the airbox will need to be cut out and the hole in the airbox will need to be sealed up.

a 450R swingarm will also work, how ever this set-up requires tabs to be welded or bolted to the frame to accept the linkage. You WILL have to use a 250R rear shock, linkage is up to you, the 250r or the 450r linkage will work, carrier and axle, and rear brakeline will also be needed. the swingarm is around 3 inches longer
the 350x rear end will also work
same as 250r
more info will be added by me constantly,, don't be shy feel free to add anything you think would be useful

QUAD BOGS WHEN IN WATER?
alot of times it is your carb vent tube. the one that hangs down behind the motor. the problem is this tube gets submerged, you can either trim the tube shorter, or put a T splittler on it and add a different length hose. other possibilites are an exposed wire.


Thanks for that gearing calculator man that is gonna help me alot with my 400ex!

[Drfat400ex]

Originally posted by 300exex
does anyone know what the stock 2002 300 ex front and rear sprocket count is . ? and what is the best combo to make it take off fastest but still get go top speed .? thanks .

Stock is 13/39, before I had any mods at all on my 300ex, I ran 14/38, I found that you gain alot of speed and I personally didn't feel any power difference at all.

[qcitytile]

i am trying to put a 450r swinger with linkage in a 300ex. i made bracket to mount linkage to frame, but seems shock is binding have almost no movement at all?? Need some help

[trx350X1998]

how hard would it be to put an atc or trx 250r swing arm and axle on a 1987 trx250x chassis. are the trx and atc 250r swing arms and axles different? would the stock brakes work? and if the 2 are differnt what one would be better in this case?

[440monster]

will a 400ex swinger work on a 300? got a 330 just tryn to get a little info without spending another grand on an entire rear end set up

[TravisHicks]

hey guys my names Travis I was wondering will a Honda 300 EX fit on my 1987 Suzuki lt230 frame?

[boomer1745]

How difficult is it to replace the drive shaft(front sprocket shaft) on a 07 300ex? What should it cost to have it done? Do they make a after market shaft that is better then stock? The splines have broken off where the front sprocket sits on the shaft. Any help or advise you can provide would greatly help. Thanks in advance.