stroke it! How do I stroke 300ex motor?

[dbc112]

So I have a ton of top end work done (port polish, valve job, heavy springs, and web cam), and really want to get the most our of my motor. Next step is to stroke the crank...

Sooo.. How much of a PIA is it to get at the crank on a 300ex? I tried watching youtube for videos etc, looks like the entire motor needs to come apart.. no thanks.

I am also ported +2mm.. could go another +2 but figured the stroke would make a larger diff..


Anyone who has stroked the 300ex motor? Whats the most we can get out of these?I have seen some 385 kits... Basically I want the most I can possibly get out of the motor!!! The goal is to beat 400 all day and stay with the 450's is it possible? or should I sell and just buy something else?

[honda250xrider]

yes you can beat many 450's and 400ex's with a highly built 300ex motor, i have seen up to 426cc out of a 300ex motor, i personally ran a 406cc stroker/big bore motor at one point.
it was a full race motor, and had to be treated like one. once you start running these engines this high and getting the power out of them the maintance is almost not worth the hassle of just getting a 450 and having a bigger base to build off of

[dbc112]

How did you get the motor to 406? WHat bore kit and stroke?

Was the 406 a maintenance nightmare? How would stoke and bore cause maintenance? Did things get out of sync? other parts that couldnt handle the power?


What would be safe? Just a stroke with the current +2mm bore I have?

[907Rider]

Originally posted by honda250xrider
yes you can beat many 450's and 400ex's with a highly built 300ex motor, i have seen up to 426cc out of a 300ex motor, i personally ran a 406cc stroker/big bore motor at one point.
it was a full race motor, and had to be treated like one. once you start running these engines this high and getting the power out of them the maintance is almost not worth the hassle of just getting a 450 and having a bigger base to build off of
Exeactly, you can get 370cc kits for mojaves, and their hella fast.
But buy the time you've made them that powerful, the maintance is almost not worth the hassle.
Now I not saying dont do it, and I'm not saying get a 450. just be prepared for alot of time a money to keep it running, If you realy want to.... well do it, be unique that want is all about!
just don't expect to blow away any modded 400,450ect.

[dbc112]

Actually reilaiblity is an issue for me... What is a safe mod? Just a stroke?

I already have heavier springs and valves plus port and Web Cam... and if the rings go on the piston, just opportunity to replace and bore +2 more!


What else could fail with the added power? Anything known to blow out?

The crank doesn't just "pull out"

You need to split the entire engine cases. Right down to the transmission. Basically assembling the whole thing from scratch when your done.

Honestly, I think you should go buy a 400ex or 450. A 460 stroker 400ex would be more reliable then a 400+ 300ex.

[dbc112]

Yeah... I am so far into the 300ex at this point... Maybe you are right.


Sooo.. Will a 400ex motor fit into a 250x frame? How much modification is needed? Besides wiring harness and electronics, and oil cooler?

[dbc112]

Found my own answer...

The 400EX engine is completely different from the 300EX - here are the differences that will make an exchange expensive and difficult:

1. 400EX is a dry sump engine - requires an external oil tank.
2. 400EX has twin exhaust ports - the two pipes wrap around the single downtube - the 300EX has a single exhaust port, and the headpipe goes through the split downtube.
3. 400EX cylinder and head are taller - meaning the carburetor has to be mounted about where you're rear end sits on the 300EX seat.
4. Head is dimensionally larger - requiring additional space between the frame tubes and below the gas tank.
5. Motor mount position is completely different.

So, by the time you convert - you will have a better engine in a poorer chassis (handling and ergos are better on the 400EX). It will be worth less than it was before the switch.

There is only one (relatively) easy conversion for the 300EX chassis - that's an ATC350X engine. The engine fits the 300EX chassis with no chassis mods - but does require a 350X wiring harness, and a special exhaust system (see what Powroll offers http://www.powroll.com/P_HONDA_CONVERSIO...

[elementryder]

the 300 motor is very relaible, and i wouldnt think twice about putting on over 400, i had a full national tc 300 motor, not one bit of difficulty with it

[dbc112]

SO in my situation, with the top end work already done.. Get me to 400cc...

Stroke and bigger bore? What about the piston?


I would have to pay someone to do the work, this is outside of my capabilities.

[cmaxx]

i had a 350x 300ex hybrid bike and it would beat a 400ex.never got to race a 450r but i would have been close.

[wilkin250r]

The 350X is a fairly easy swap, but at that point you would be basically starting over again with your engine. It would need all new porting, bigger bore, possibly a stroker.

Does your 300EX have oversized valves?




Oh, and I'm moving this to the appropriate section...

[dbc112]

I had a 350x motor for about 2 months. Was way more trouble than it was worth. Lots of smoke, kick start is a royal PIA.. It was more tourquey than my 300ex...

My current engine has a Tripple angle valve job, port and polish, and +2mm oversize higher compressoin (no idea what ratio is)

I am assuming oversized valves, but that may be off. I know GT thunder built it for naitionals, so i want to assume the best was done. How can I tell if they are oversized? Would a compression guage help?


I found a local guy who can remove my crank shaft and replace for $300-$400. This does not include the stroker work (another $229 from powroll) Is this the best I can get? What is the max stroke you can go? Powroll is 4mm.. I think FST has 4.5mm.

What do you think? Rip Off? He is not a dealer, just a guy on CraigsList... Has done a lot of work on 4 stroke in the past. And he offered to teach me as the build goes along. I actually sold it as a motor class to the wife! To funny...

Oh, and the 400 also incldes tunning in the engine, but I can do that myself.

What do you think price wise? What would you pay? And while you have the engine apart, what else would you do?

[honda250xrider]

they are a royal pain in the *** to get the jetting right as i found out, i had to go with if i remember right a 38mm or 40mm carb. I had to adjust the vavles every couple rides. I personally changed the oil just about after every ride, along with the filter. Changed the clutch plates about every month.

This is a high performance motor and needs to be treated like one, i inspected my piston and cyclinder walls on a regular basis and replaced the rings also on a regular basis.

I have heard of some reliable motors up in the high 300cc, but you have to remember that what your wanting is a high level engine. and you must treat it like one.

my motor consisted of +3 intake, +2 exhaust valves, decked head, full race port and polish, 12:1 compression with the stroke it raised it to 13:1 along with the decked head it raised it to a little around 13:5 to 14. reverse gear removed, custom cam from fst, reworked oil passages in the cases along through the cyclinder, vavle job, removed decompression so valves would never stick. there was a bunch of other little things but you get the picture.

There will be minor problems i will almost bet on that you will run into during this built and the price will go up, by the time you get the engine done you will have another 1000 or so at least into your motor i suspect. i have seen 450's go for as low as 2500 around these parts. i would take some time look for them as they are only going to get cheaper through the winter. they offer a much better ride along with the handling and power.

[dbc112]

I agree with you completly.. after heavy consideration, I am sticking with the work that is already done and focusing on tuning the bike in... I have dial a jet to help, as well as some better spark from hot wires, and nology non resistor plug.


After that, maybe help on the looks of the bike for resale. PC the frame and A-arms, hand guards and seat cover.. Maybe, paint the plastics with the father in laws professional sprayer (what paint?)


but $2500 for a 450? point me in that direction? and crap, what can I get for a 300ex with motor work and an older frame? Maybe $1500 if I am lucky....

[honda250xrider]

i can give you an idea of what i sold mine for awhile back i ended up selling the 250x that was basically stock for $1200.
mods it had was
ac bumper
ac nerfs
ac grab bar
renthal handlebars
pro design killswitch
douglas wheels
12:1 piston
webcam
exhaust
k@n filter

there were some others little things but pretty much it was mostly stock.

i ended up parting out all of the aftermarket things that i could.

i will list some prices that i got for some parts.

Big valve/port and polish head- $250
elka shocks fully adj-700
a-arms- 350
axle-150-200
sparks cdi box-50
stroker bottom end- 350
stablizer-50
another port and polish head with +1 valves- $150

this gives you an idea. i also gave the guy that bought my fourwheeler an offer of $200 and he could have a bunch of other extra's i couldnt sell. the box of extra's included 2 handlebars, 4 stators, wiring harnesses, valve covers, 2 cdi boxes, frame, axle, swingarm, 2 sets of a-arms, 2 sets of brakes, bumpers, grab bars, 12 13 14 15- 32 34 36 38 sprockets, 4 chains with several master links, pretty much another quad in parts.


I would recommend selling anything aftermarket on the quad seperate and put your quad back together as mostly stock as you can and sell it that way, i would guess you would be able to still get 1300 or 1500 for a 300ex.

heck i have had my 2007 ltr450 for sale for about 6 months now and still have no offers, blue book list's its value at 5500. i listed it locally for around 4100 i think and have told callers i will take 4000. and i have the following mods.

rath nerfs
tag t-2 handlebars
ac bumper
skid
black frame
holeshot tires
oury/renthal grips
pro design kill switch
have the cr style start button
cbrm chip
along with extra oil/filters/chain lube

lol the best offer i got so far was a trade for a bass boat.... its just a crappy time to sell anything in the economy but its a perfect time to buy

[honda250xrider]

as far as paint goes if you go that route i have had bad luck using car paint, its expensive and imo is not worth it. i would use the industrial tractor paint. i have used this several times and have worked wonder's.

i like powder coating but the fact is that i either still chip it away or i end up have a crack in the frame and have to sand down the area, instead with powder coat you have to then resend it back to have the whole thing redone, when i can go into the booth and shoot it with paint for far less and a much quicker turn around.