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Discussion Starter #1
Just got a 07 400ex to rebuild. Piston was broke and slightly scored the cylinder so i was planning on getting a niche 87mm jug and weisco 10:1 piston kit with cometic gaskets and stage 1 cam and Didnt want to have to drill and tap for better studs. Will the 10:1 compression piston be good on stock studs?
If not then hows the je 10:8.1 piston compared to the weisco?
 

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Seeing how combustion pressures can be near 1000 psi, the stock studs are good for upwards of 15:1 compression ratios

And the J&E 10.8:1 is higher than the Wiseco 10.0:1, but you could also go for the Wiseco 11.0:1 and still run stock studs - when you go for the 465 stroker kit, then you might want the heavier studs.

Be sure to use the 89mm Cometic head gasket and not the stock Honda 85mm bore gasket
 

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Discussion Starter #3
Are niche cylinders any good? If they are i was going to get a new one already bored to 87mm and just keep my original for a spare.
 

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You are always better off running the Honda cylinder, even with a minor bore. Honda just makes good parts.

My personal machine has a niche cylinder with a 86MM (416) JE piston 10.8:1 ... I love it. Gobs of power yet not so high performance as to degrade reliability. I got it as a top end kit from AZQuadParts on ebay. I suggest giving them a call as they can tailor the parts build according to your needs including a stud kit etc etc. JE pistons are fairly expensive though.

But to answer your question, I'm running almost that exact build and no issues as of yet other than exhaust stud nuts keep loosening up (I finally figured out how to fix that issue once and for all). I went with 10.8:1 over +11:1 as I'm high altitude and didnt want to mess with always needing high octane gas). 91 octane ethanol free is problem free in it. I stuck with 86MM over a bigger piston as I didnt want to deal with overheating issues due to thin cylinder walls. If you dont race, I'd suggest staying with 86mm (416cc) vs going with something like a 440 kit.

I rebuilt a second machine with a complete top end kit, stock size and compression, cam etc... that one was on a tighter budget, but thus far its been great and reliable. It was a niche cylinder with a Namura 85MM piston. My son and wife fight over it.

I have 3rd 400ex completely stock... its a little tired but runs flawlessly... I keep waiting for an excuse to rebuild it... but it just runs too good to mess with it. So what if its a few seconds slower up the big mountain climbs.

-DallanC
 

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Discussion Starter #5
I can get the je 10:8:1 piston and ring kit cheaper then the wiseco 10:1 kit. I just read alot of things about high compression pistons with stock head studs especially with big bore kits.i was originally going with the je but wanted to keep compression down cause of that.
 

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I havent ordered the parts yet...on the description of the je piston it says the cylinder has to bored and replated. Whats replated?
 

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I havent ordered the parts yet...on the description of the je piston it says the cylinder has to bored and replated. Whats replated?
Covering several posts - Niche cylinders are as good as any Chinese POS counterfeit Honda part out there. If it were mine, I would have a heavy sleeve installed in the OEM Honda cylinder and then have it bored to 87mm - with the heavy sleeve, it leaves enough cylinder wall to bore all the way to 89mm if desired.

Stock head bolts will hold the compression with no problem even with a 13.0:1 compression ratio

Many novice engine engine builders want to increase the compression without thinking about what the end result is. Increasing the compression provides a boost to low end torque at the cost of upper end RPM - if the engine revs to 9000 RPM with the stock 9.1:1 CR, it may only rev to 8000 due to the higher compression slowing the piston as it pushes harder to compress the air.

Also take into consideration the fuel requirement - at 9.1:1 the recommended octane is 91 or better of non ethanol blended fuel - when using ethanol fuel the octane needs to be 93 or better - with a 10.0:1 compression ratio, the fuel requirement will increase to 93 octane non ethanol or higher - I use 94 octane VP Racing SEF in my race engine and have found that 100 octane is too high - the engine loses power above 96 octane - if I were to bump to 12:1 CR, then I might be able to use 100 or higher octane.

You are looking at the wrong J&E piston - the TRX450R uses a plated cylinder, but the 400EX uses a steel liner cylinder - no need to be concerned with plating the 400EX
 

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Remember octane requirements change with altitude... assuming your not running a turbo / blower. At my elevation 91 octane equals 93'ish (roughly anyway). My house is at 5000ft... dunes are at 5500, mountain rides can get upwards of 9500ft.

-DallanC
 

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Discussion Starter #9
Im at sea level. Not that it matters but i dont race or hill climb. Just ride with my 7yo on my property so hes not riding alone.
Just figured id hop it up a bit cause it needed to be rebuilt any way.
Ive ordered the 87mm wiseco 10:1 piston and rings, cometic big bore gaskets and niche cylinder... Not doing the cam or exhaust right now and if the niche cylinder dont work out then ill just have my jug bored.
 

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Octane combats pre-detonation or "pinging". You don't have to be racing or pushing the motor hard to get it... but when it happens, it is very destructive to the motor over time.

-DallanC
 

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Ill start off with 91 and once the motors broken in and jettings dialed then ill try to reduce octane but if it runs good ill just stick with 91..

Anyone have any break in tips?
 

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Octane combats pre-detonation or "pinging". You don't have to be racing or pushing the motor hard to get it... but when it happens, it is very destructive to the motor over time.

-DallanC
Very close description, but a little inaccurate

Octane is a measurement - it measures the speed at which a fuel burns - the higher octane number, the slower the burn and slow burning fuels are harder to ignite.

It's not pre-detonation, but pre-ignition - pre ignition is when the fuel/air mixture ignites before the ignition spark occurs at the tip of the plug. Pre-ignition may be initiated by compression, a lean fuel/air mixture, a glowing piece of carbon, tip of the spark plug too hot, the head gasket overhanging the cylinder, the top edge of a steel liner cylinder being too sharp after an oversize boring and honing without a de-burring procedure or a final honing with a ball hone (a ball hone will knock off the sharp edge as the hone enters and exits the cylinder).

On the other hand, detonation occurs at the bottom of the stroke primarily when too high of an octane fuel is used. Detonation is more damaging than pre-ignition. Uncontrolled pre-ignition usually results in a hole blasted into the top of the piston - detonation can bend rods and break pistons.

Detonation occurs when the piston moves away from the flame front of ignited mixture - if the fuel burns too slowly, the piston reaches BDC before the fuel/air mixture has finished burning - the piston starts up squeezing the unburned mixture between the piston and the pressure wave of burning mixture - the pressure increases to the point the remaining mixture is ignited by pressure and explodes violently. It does not take many cycles of detonation to destroy and engine.

So............. Too low of octane is bad and too high of octane is bad - you want the correct octane for the engine design.
 

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Nice, descriptions. I could see it.

I am sure there is a specific procedure for break in. Most 4 stroke singles are the same. I do not know, therefore I will not guess. I can tell you, the most stressful point in an engine cycle is "freespin". You open the throttle, gain rpm. Release the throttle... as the engine transitions from acceleration to deceleration there is a point in time where where there is no load. A free spin. That's what hurts. That's when things let go. Pistons are free to rock. Rod ends bounce. You can't avoid it, but you can minimize it very effectively.
All the right questions, shows you are thinking.
 

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Nice, descriptions. I could see it.

I am sure there is a specific procedure for break in. Most 4 stroke singles are the same. I do not know, therefore I will not guess. I can tell you, the most stressful point in an engine cycle is "freespin". You open the throttle, gain rpm. Release the throttle... as the engine transitions from acceleration to deceleration there is a point in time where where there is no load. A free spin. That's what hurts. That's when things let go. Pistons are free to rock. Rod ends bounce. You can't avoid it, but you can minimize it very effectively.
All the right questions, shows you are thinking.
The best break-in is under moderate load (what I refer to as pasture riding). You want the engine to propel the vehicle and then let the vehicle propel the engine - this creates pressure and load in both directions in an attempt make the parts seat (wear) evenly. Heating and cooling cycles are essential to a roper break-in. Ride for 20 to 30 minutes to heat the engine and then let cool for an hour. Ideally, the head and cylinder would be re-torqued prior to the next heat cycle, but while easily done on some designs, it is impractical on the TRX400EX.

During break-in, full throttle operation is not prohibited, just don't exceed 3/4 maximum RPM of the engine - accelerate, decelerate, ride up and down gently rolling terrain and in circles to the left and right. After about the 4th heat/cool cycle, change the oil and let er rip. Engines with plated cylinders do not require as much break-in time and if you are your own mechanic, you can forego break-in altogether as long as you are willing to accept the consequences of you actions and the related cost of repairs.

Side note, i double checked the kit I had ordered, it was with the 87mm JE Piston.

-DallanC
Good deal on the purchase.
 
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