Got my first 300ex

[ridehonda400ex]

As you may know, I have a 400ex already but we went and picked up a 300ex. Its a 1998 and it smokes but the price was fair. Also needs some new plastics and a new exhaust. It has a full DG exhaust but the canister is junk. Could i still use the headpipe?, as its very nice. And my dad says he wants to re ring it and just use the old piston but i say get a new piston and rings. Hes also putting me in charge of the build:) Let me hear your input about ANYTHING since its my first build for a quad, im 15 also so bear with me lol. And if you have any 300ex parts please let me know

[dman66]

You need to check the piston to see if any damage to it, both top and sides. If piston looks good, check the piston to cylinder clearance. If all looks good, measure cylinder diameter in three or four areas to insure cylinsder is not oval shapped,and to get ring size you may need.If all looks ok, figure on new rings and a fresh honning of cylinder. Be more specific in what parts you need,people are more inclined to answer back if you are looking for specific parts. Ebay has plenty of good deals, and GDH Racing has real quality used parts on ebay.

[ridehonda400ex]

Thank you for the help. What should the piston to cylinder clearen

Parts we need: Plastics, Bumper, Something to change the ugly headlight.

There will probably be more later.

[dman66]

I mounted a 2001 400ex headlight up under the front hood of my fenders. I made a bracket up,welded it to the frame, and plastic epoxied the light to a metal bracket, to screw onto the light mount to the metel mount. The clearances, I'll get back to ya on that.

[smr]

Originally posted by ridehonda400ex
Thank you for the help. What should the piston to cylinder clearen

Parts we need: Plastics, Bumper, Something to change the ugly headlight.

There will probably be more later.

the way to test it is to put a new ring in your cylinder and see what the gap is. I am pretty sure .018 is max. Most of the time I will bore it anytime it's over .012

most likely you will need to bore yours.

[ridehonda400ex]

well took the plastics off and the air boot wasnt even connected to the carb! so it was sucking in tons of dirt so i imagine the cylinder will be scored and will probably need a bore. Also the air filter had a rip in it and was caked in mud so no clean air to that engine! Even with these problems im still having a blast working on it :)

[Tyler01]

Ha you just bought your first 300ex and i just sold my first 300ex

[ridehonda400ex]

Hey guys. I found out that my grandpa has a bore tool and can bore the cylinder for free!! How awesome is that!

[Tyler01]

ha thats rare finding one but i just sold mine yesterday for 800

[ridehonda400ex]

Could somebody tell me the bore sizes and what they will make the 300ex into. Thanks

[ridehonda400ex]

Another thing is-can I get valve lapping compound and reseat them like that? Or is it really that neccessary to send them off?

[400thacker]

this is what ya do...
take everything out of the head then put the valve in the head and put the stem in a cordless drill.

put valve grinding compound on the valve and spin the drill with the valve on the seat. that will clean everything up pretty good. no need to send them off

[ridehonda400ex]

Originally posted by 400thacker
this is what ya do...
take everything out of the head then put the valve in the head and put the stem in a cordless drill.

put valve grinding compound on the valve and spin the drill with the valve on the seat. that will clean everything up pretty good. no need to send them off


thats a good idea. could i do it the old fashion way too? with the suction cup? lol

[400thacker]

what do you mean by suction cup??

[ridehonda400ex]

In Ag Mechanics class we rebuilt Briggs push mower engines and to lap the valves we used lapping compound and a wood handle with a suction cup on the end and it sucks the valve head and rub the handle between your hands like a caveman would start a fire with a stick

[400thacker]

same principal different procedure. I like the sound of the drill a little better but the suction cup may be better

[smr]

Originally posted by ridehonda400ex
thats a good idea. could i do it the old fashion way too? with the suction cup? lol

either way will be fine. I usually use the suction cup. I just like the fill better than a drill.

[ridehonda400ex]

Thanks guys. Also, how many valves does the 300ex have? I read somewhere that it has 4-valves but the cam only has 2 lobes??

[smr]

it has 4. One lobe pushes both exhuast and one pushes both intake.

[ridehonda400ex]

Ahhh okay. I see. Thanks

[ridehonda400ex]

Help me out here guys. So today i got the motor apart and HOLY COW! it was not pretty....well at least the cylinder wasnt. The piston had room enough to wiggle and cylinder needs bored. And will probably need new valves. But my question is, that on Wiseco's website it says that for a bigger piston it says Cylinder sleeving required and boring. Okay i Know it needs bored but can i Just bore the stock sleeve?

[dman66]

This subject was brought up on another site recently, and states that you can bore your stock cylinder up to 76mm - 76mm will be the maximum bore you can go on a stock cylinder.

[ridehonda400ex]

I also forgot to mention earlier, that the oil drain plug in the bottom of the quad was stripped and pulled the threads out! So now we gotta tap the threads...anybody ever had to do this?

[dman66]

Yes, you can tap new threads and a plug for the oil plug. Just go to your local auto parts store, get a new oil plug the next size up from the oil plug you have now, get a new matching thread tap for the new plug, and take your time to get the tap as straight as you can with the oil drain hole. Heli coils, or perma coils work very good too. I put in a new oil plug with standard US threads,with a magnet on it. The closer you stay to the old thread size, will reflect on how hard it will be to retap a new plug in. The plug I put in has a main plug to screw into the engine, and within that plug, is a smaller drain plug with an o ring on it.This way you can easily use the smaller drain plug to drain oil, and when you reseal the plug, you have an o-ring to rely on or replace as needed.Make sure you put some grease on your drill bit,or your thread tap when your doing your work.Grease will help catch the fine aluminum pieces.

[ridehonda400ex]

Thanks dman. Does anybody know what size my 300ex will become with a 74.5mm piston? I got a wiseco 74.5mm piston on the way from dennis kirk.

[ridehonda400ex]

Will i need to put in a cam with 11:1 comp. ratio

[300ridr]

you shouldnt need a cam, unless yours is worn. it will make it a 286cc, as aposed to 282cc stock. but if you get a cam, you will want the higher comp piston.

[ridehonda400ex]

looks like its gunna be stock cam and 11:1 comp ratio. Hope my 11 yr old sis likes what shes getting;)