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Discussion Starter · #1 ·
I am building up a TRX 300 2WD engine for my Big Red 250es three wheeler. (Not the 'new' "big red" thing)

Can I use a full 300ex big bore kit? Looks like the bore is the same, and I know the ex uses 4 valves instead of 2, but what if I used the cylinder/head/valves and all? (Reason I ask is these Big Bore Kits seem easier to come by than TRX300 utility ones)

Also, anyone do any crank work on a TRX 300? Figured I'd have the cases apart might as well see if anyone did any mods to it like on other bikes.

Figured Big Bore Kit, good cam, port work, good exhaust, BR (ATC or new thing?) gear reduction, 30" tires all around, maybe a 350X or 400EX carb.

Thanks
 

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i dont know but let me know about the head if you find out!!!!! i wanna go the same route.

as far as the crank the only thing i think i know about that is i think it has more stroke than the 300ex. i have also heard the 400ex carb is a good upgrade.

let me know how things turn out or what you find, i wanna do the same thing pretty much, just have not been able to get started on it yet.
 

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Welcome to the forums.
 

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Welcome to the forums!
 

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Discussion Starter · #6 ·
Few updates:

Planning to run a TRX300 (1988) with big bore and maybe webcam or regrind on mine by these guys with the BBK:
Four Stroke Tech products for the Honda TRX300 (2 & 4 Wheel Drive).

Plan to run 30" tires all around, using a gear reduction either from the 300ex or the 250es Big Red 3 wheeler.

Going to cut and extend the swingarm and gearshaft by about 3", move forward/raise the rear shock mount a couple of inches, then cut and weld an extension to the forks.

Hopefully will be sitting almost 6" higher than stock due to tire size + fork and rear end work.

May drop on wheel spacers but I fear the strength of the rear axle will be tested with giant heavy 30" tires on there...may not use the spacers.
 

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Let us know how it turns out. I'm sure Blowfish will want to know as I think he is wanting to do about the same thing to his or something similar, anyway.
 

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heck yea im intrested.

how do you extend the driveshaft???

also what bbk are you going with??

i did some searching on the 300ex head on the fourtrax but it looks like a different bolt design so i dont think that works. i was really looking forward to that.

i dont think i would run the spacers. the foreman 350 rear end is about 2in wider tho than stock i think and with how its set up it would probably handle the stress of the big tires better.
 

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i did some searching on the 300ex head on the fourtrax but it looks like a different bolt design so i dont think that works. i was really looking forward to that.
I believe the guys over on the High Lifter forum said it would work, but they said you had to have a reverse grind cam. They may be wrong though, because I never saw where anyone had said that they had actually done it.
 

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i just looked up pictures and compared but from what i seen it was different bolt designs. ill look for some in a min to compare, see what you think.

heck i was thinking about filling in those holes and drilling and taping new holes. there is probably a good bit of power/flow to pick up by just swapping heads.

i never saw the results over there, ill have to look into it.
 

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i just looked up pictures and compared but from what i seen it was different bolt designs. ill look for some in a min to compare, see what you think.

heck i was thinking about filling in those holes and drilling and taping new holes. there is probably a good bit of power/flow to pick up by just swapping heads.

i never saw the results over there, ill have to look into it.
The cylinder and head look just like the cylinder and head on a Fourtrax 300, but the bolt pattern could be different.

That would be too much work trying to fill the holes and drill new ones.

Yeah, I think I was the one that asked the question about the 300EX head working on the Fourtrax 300, over on the High Lifter forums.
 

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Yeah, I just looked them up on Ebay and I believe you're right. They look different to me, too.
 

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ahhhh, from what there saying if you use the 300ex jug also it will bolt down to the fourtrax bottom end. so 300ex head and jug, they also said the cam does turn the other way.

seems like alot of work, for probably a 1/4th of the price i could just get a good cam for the fourtrax.
 

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ahhhh, from what there saying if you use the 300ex jug also it will bolt down to the fourtrax bottom end. so 300ex head and jug, they also said the cam does turn the other way.

seems like alot of work, for probably a 1/4th of the price i could just get a good cam for the fourtrax.
Yeah, you have to use the jug and the head. It appears that, that would work. Yeah, it would be alright to try if you already had the parts laying around or something. I just wonder what kind of an improvement the 4 valves of the EX head would be over the 2 valves.
 

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im a dummy, i was thinking you would need 2 cams, then the head and jug.

i too wonder the gains from it, from what i have seen nobody has went thru with it.
 

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im a dummy, i was thinking you would need 2 cams, then the head and jug.
No, just one cam. According to the guys on the High Lifter forums, a reverse grind cam.

i too wonder the gains from it, from what i have seen nobody has went thru with it.
Yeah, they just said it would work and nobody said that they had actually done it, so really, we don't know if it will work or not.
 

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Discussion Starter · #20 · (Edited)
the foreman 350 rear end

Ok here is some updates..........

Foreman 350 Rear End - May look into this, not sure if it's compatible
Looks like the ex swap is a little more complex due to the cam work needed, also the timing is a factor given there's now 4 valves as opposed to 2.

Found out about 3 BBK's
1. 380 Thumper - $400
2. High Lifter 355 - $??? - apparently eats rings quickly
3. FourstrokeTech.Net $300 and $400 (340cc and 380/390cc)

Cam regrinds at FST.Net = $165, Thumper said $200. Had to call as none is on their website.

I guess I will go with this setup:

Thumper BBK - Most Reliable
Some sort of cam, need to look into which is best or who mods stock best
Maybe Big Red timing chain, apparently it is thicker?
Extend the gearshaft and swingarm 3", raise rear shock mount a couple "s
Cut/weld front forks to add a few "
30" rear tires - their width may be enough, if not I may try the spacers

Seems like the 250ES has a great rear end, just want it longer so it won't have issues with the tires rubbing fenders

Here is what another guy did to extend his. Sure it may need paint, but if it functions, I'm happy with that.



Here is one with a 2" rear shock lift only, can't lift more due to driveshaft angle or something of the sort. Also I think you need angle drive from the 250es engine for the TRX300 to work.



EDIT: Supposedly people have seen this 300ex top end swap in person and dirtcrashers magazine, but I've yet to see pictures. Not worth it. I suppose 4 valves would allow more flow possibly? Port/polish your head, BBK, good exhaust/cam and you should be good to go. I'm going for torque to pull 30's, so I don't need the EX parts for that.

As far as a gear reduction, I guess the 300EX is the best way to go but needs some work done to fit. Custom ones get really expensive, $400-800+. I am trying to find the best/cheapest one, or hoping the EX one can spin 30s.
 
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