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- New intake and exhaust cams
- Correct tappets / shims for cams
- ProFlo Adapter - K&N filter
- Keihin FCR 40mm Carb
- Aftermarket exhaust
- Buy a manual!

Note: Read the FCR carb article - that bigger 440 motor needs more juice, and the FCR is a perfect way to give it.
Do not attempt to duplicate this procedure unless you are well skilled in ATV engine maintenance.
*** We accept no responsibility if anything happens to your machine.

Give that BIG DOG some BITE!

Big Bore Z440 Project
Written by John Miller
Edited by ATVstore.com

The Suzuki Z400 is one of the most respected and loved sport quads of this new ATV era. Friendly handling, quality power, electric starting and lets not forget reverse - keep this quad in the same ball park as its high performance competition. Yet, to prevent being poodlized by the new dogs on the block, upgrading is required for more low down chomping power.

To get our Z closer in power to the new sport quads, such as Yamaha's YFZ450 and the new Honda TRX450r, we settled on pumping up the mighty Z to a 440cc engine displacement. Along with a new sleeve - we added a matched piston/rings, Hot Cam, and FCR 40mm carb. A fiery concoction the Z400 can use to maul anything in its path.

First things first:
In any engine surgery, cleaning your quad thoroughly is a must. Dirt is the Osama Bin Ladin of inner engine terrorism.

Lets break it down: Got that so far? Good, keep going!

Rap a towel around the crank and carefully remove the clip retaining the pin in the piston. (Using a knife I poked a nice size hole in my finger, then it finally came out - do not do this!) Pull the piston out, and that's the end of the tear down procedure.

We did that in about 1.5 hrs, and that was including the cool off time and a preferred beverage.

Clean, Resleeve, Regroup - Then Install:
Clean off the gasket mating surfaces and get the cylinder sleeve put in (by a reputable atv/mx bike mechanic).

New Piston and Rings Install:
Its really easy to install the rings (no, they don't come on it).

Check each ring gap a with feller gauge, they should be within spec. To check the gap, just put the ring in the newly sleeved cylinder and use the piston to square it up. Then using your feeler gauges if you get .04 for every inch of diameter of the bore, your are ok. (ex. 3" bore would be ok with .12" gap for 2nd and 1st rings)

Getting down to putting the rings on is easy, start with the oil ring on the bottom, then the spring, and then another oil ring. You do this so that your not fighting to get the 1st and 2nd rings on.

Put the 2nd ring on with the dimple up, near the gap. You'll know it when you see it. Then install the 1st ring, no dimple, so it can go in whatever way you need to.

Piston in:
When installing the piston be sure the arrow is pointing to the exhaust port, and if you don't see it, the deeper valve grooves are for the intake side.

Take a towel and put it around the rod. Install the piston and put the pin and clip in.

Put in the pin clip on the opposite side that you need to push the pin in on. (If your working on the left, put the clip in on the right side of the piston, so that when you install it - you can just put the pin in and worry about one side instead of both.)

We would reccomend getting some gasket spray, to create a better seal on the gaskets, doesn't hurt anyway. After your piston is in and your gasket is coated with sealant put the dowels in and put the gasket on.

Rebuild: Time To Get Dirty
Now is where an extra set of hands helps, but it can be done alone. Put tranny in gear. Apply some oil on the sliding surfaces (skirt) of the piston.

Pull the camchain up into the cyl and secure it to the frame/bars, whatever.
*** Make sure that the ring gaps are at:
1st ring - 6 O'clock
2nd ring - 10 O'clock
Oil rings - top at 10 O'clock and the bottom at 2 O'clock
All of the ring spacings are looking at the piston from the intake side.

Take the cyl and slide it over the 1st ring. Now hold down with the cyl and start pushing the ring into the piston, it will all wiggle in. (now you know why its in gear?) The second ring is the same, but the oil rings are a little tougher, be careful that you don't pinch the ring when your pressing down.

Once you have the cylinder on the hardest part is over. Install the camchain guide, then install the head gasket and head.

Check the shims under the tappets they look like watch batterys and they say the thickness on them. Pull the tappets off and the shim is in the center.

First you put your cam in (check TDC), then you measure your gap from lobe to tappet, and the service book has a chart to look in that says what shim you'll need, you just need to know the gap, and the shim you have. I had to get a .15 mm smaller shim for the intake. Check both intake and exhaust to be sure.


Time to torque all the stuff down: Dip the threads of the head bolts in oil and start the threads. (They are the bolts that are right beside the tappets.) Get your socket and snug them up, then get your torque wrench. Give a first torque of ??? 17 lbs ??? in a diagonal sequence. Then up to ??? 35 lbs ???. Don't quote me, these are off the top of my head.

Once you get this far - take it out of gear and double check TDC.

Put the chain around the exhaust cam, it has the lines on the gear and is even with the head. Make sure the chain is still tight, and put in the intake the same way. I think there are 15 pins on the chain between the top mark on the intake and exhaust.

Put on the cam journals, camchain guide and tensioner.

Check your clearances on the valves, and put on the cover. Make sure that you put a dab of gasket sealer on the cam caps on the camchain side.


Put the FCR carb on (be sure to rejet). Fire it up and begin the break in procedure... then away we go!!!

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