400ex ring gap [Archive] - ATV Riders Forum

03-01-2002, 10:18 PM

hey, i just got a je 416 piston and i was wondering what i should set the ring gap at. i know it's gotta be way to tight the way it is. my friends says it should be aroung .040.. anyone know for sure

jcv400ex

03-01-2002, 10:25 PM

right out of the service manual:

Top : .008-.014
Second: .014-.020
Oil(side rail): .008-.028

I set the Top at .012, the second and the oil at .014

03-01-2002, 10:27 PM

nice. i don't have a service manual and i lost the owners manual. thanks

86atc250r

03-01-2002, 11:03 PM

.040" is WAY too much... The minimum should be .014" for an 87mm bore.

03-01-2002, 11:08 PM

thanks guys. i set my top at .009 cause i don't have another one in it's range. the 2nd at .017 and the oils were at around .017 so i didn't touch them

MIKE400EX

03-02-2002, 06:22 AM

.009 is TOO tight! Get a ring filer and grind to .014-.016".
Hint: Put the ring in the bore, and use the head of the piston (up side down) to push the ring down about half an inch. This will also straighten the ring in the bore - very important. Remove the piston & then you can check the ring end gap. Do that for each ring. Also, always grind the ring from outside to inside, and lightly deburr the ground edges. If in doubt take the rings/piston/cylinder to an auto/cycle machine shop, they can fit the rings in less than 5 minutes.

03-02-2002, 02:07 PM

while my .009 was lose in it so i know it's a larger gap. it's more aroun .011 at least.

MIKE400EX

03-02-2002, 03:07 PM

Get a whole set of feeler gages! If it gets hot and you seize it up from a tight ring you WILL be sorry!

beerock

03-02-2002, 04:19 PM

Lrd you cant estimate ring gaps, you have to be precise.

and you wonder why your R broke:rolleyes:

wise up man, other wise your gonna be bad mouthing the 400ex.

no offense, im not flaming here.

but you have to be precise with the gaps, you cant say oh I measured .009 but its more like .011.

if your stuck on doing it your self, best thing to do is get feeler gauges and a MICROMETER.

03-02-2002, 07:51 PM

The standard formula suggests that you should have .014 on the top and .012 on the second. Of course how you set it up can deviate the gaps slightly but for overall reliability these will be pretty close.